Astronomy

1. Describe the differences among primitive, igneous, sedimentary, and metamorphic rock, and relate these differences to their origins.

1. Primitive- Any rock not under great heat or pressure and therefore remaining representative of the original condensed materials from the solar nebula. 2. A. Igneous- Any rock that is produced by colling from a molten state. 3. Sedimentary- Any rock formed by the deposition and cementing of fine grains of materials. 4. Metamorphic- Any rock produced by physical and chemical alteration under high temperature and pressure.

Imagine you are a travel agent in the next century. An eccentric billionaire asks you to arrange a "Guinness Book of Solar System Records" kind of tour. Where would you direct him to find the following (use this chapter and Appendix F and Appendix G):

1. The least dense planet- Saturn 2. The densest planet- Earth 3. The largest moon in the solar system- Ganymede 4. Excluding the jovian planets, the planet where you would weight the most on its surface is directly proportional to surface gravity- Earth 5. The smallest planet- Mercury 6. The planet that takes the longest time to rotate- Venus 7. The planet that takes the shortest time to rotate- Jupiter 8. The moon with the thickest atmosphere- Titan 9. The densest moon- Io 10. The most massive moon- Ganymede

1. State Kepler's three laws in your own words.

A. (The Law of Ellipses) All the planets of our universe have an orbit that is an ellipse while the Sun is at a focus. The planets orbit the Sun. B. (The Law of Equal Areas) There are lines that join the Sun and a planet that sweep out into equal areas within equal intervals of time. C. (The Law of Harmonies) The ratio of the squares of a planet's orbit is the same proportions of the planet's distance from the Sun.

What is a charge-coupled device (CCD), and how is it used in astronomy?

A. A CCD is a modern detector similar to the detectors used in video camcorders. High pixel cameras record brightness and color of image and computers. They sort info to create photos.

When astronomers discuss the apertures of their telescopes, they say bigger is better. Explain why.

A. A bigger aperture allows you to use more magnification and produce image with higher resolution. The bigger apertures of a telescope also collect light, making for a sharper image and can detect fainter sources than a smaller one.

What is the difference between a differentiated body and an undifferentiated body, and how might that influence a body's ability to retain heat for the age of the solar system?

A. A differentiated body is heated to the point where it's liquid, and heavier, denser materials sink to the center of the planet, and the lighted elements rise to the out layer. The concentration of materials help retain heat in the interior of a planet. Undifferentiated bodies were never heated enough for the elements to separate. They cool quickly and are typically smaller in size.

1. The gas pedal, the brakes, and the steering wheel all have the ability to accelerate a car—how?

A. A gas pedal is used to accelerate the car, as it is designed to increase the speed of a car. Brakes within a car are used to decelerate the car, as it is designed to decrease the speed of a car. A steering wheel are used to change direction of a car, as it is designed to give direction of a car.

Explain how high-speed impacts form circular craters. How can this explanation account for the various characteristic features of impact craters?

A. A high-speed projectile will penetrate somewhat into the surface of the larger body before stopping. This abrupt loss of energy is transferred into a shock wave and heat that fractures and vaporizes some of the rock. It is this rapid heating and explosion that throws debris out of the impact site. The explosion tends to send energy in all directions, generating a circular crater. There is a rebound effect from the shock wave that will fill in the crater a little and flatten the floor, sometimes creating a central peak. Some of the debris ejected during the explosion will also fall back into the crater, the rest will be distributed outward from the impact site and make the ringed mountains that surround each crater. These are the characteristics features of impact craters.

Why don't lunar eclipses happen during every full moon?

A. A lunar eclipse occurs when the moon enters the Earth's shadow. They do not happen every month, because the Earth's orbit around the sun is not the same as the Moon's orbit around the Earth.

How do the planets discovered so far around other stars differ from those in our own solar system? List at least two ways.

A. A much greater variety of planets has been found around other stars than exists in our solar system. Large Jupiter-sized planets have been found orbiting close to their stars, which challenges our simple view of planetary system formation. There are also super-Earths and mini-Neptunes, planets intermediate in size between the terrestrial and Jovian planets in our solar system. A number of exoplanets have eccentric orbits, unlike the planets of the solar system.

What is meant by "reflecting" and "refracting" telescopes?

A. A reflecting telescopes uses a mirror rather than a lens to form an image. A refracting telescope uses a long tube with a large glass lends at one end and uses that lens as its main optical element to form an image.

What are the three basic components of a modern astronomical instrument? Describe each in one to two sentences.A. A telescope for collecting visible light, an instrument that sorts the incoming radiation by wavelength, and a detector that senses the radiation in the wavelength regions selected. Then it records the observations.

A. A telescope for collecting visible light, an instrument that sorts the incoming radiation by wavelength, and a detector that senses the radiation in the wavelength regions selected. Then it records the observations.

Describe three ways in which the presence of life has affected the composition of Earth's atmosphere.

A. A. The sophistication of life cause for an increase in plant population, increasing the amount of oxygen being produced- this accumulation of oxygen was the reason for the creation of the ozone layer. B. The ozone layer filters out UV rays that was only able to be done by living in the depths of water, so when the ozone layer was created animals were able to adapt and live on land, breathing oxygen. C. Living things have removed most of the carbon dioxide from the atmosphere.

What was the problem with the Hubble Space Telescope and how was it solved?

A. After it was launched, scientists discovered that the primary mirror had a slight error in its shape. Scientists installed a corrector plate which improved the camera before releasing it back into orbit.

1. Why did Pythagoras believe that Earth should be spherical?

A. After observing the Earth's moon, he stated that it was spherical by observing the terminator line of the Earth's moon. Because of this, he deduced that the shape of the Earth would also be spherical.

1. Outline the main events in the Moon's geological history.

A. After the formation, more than four billion years ago, the low-density silicates cooled first and made up the initial crust. This surface was exposed to heavy meteor cratering early in the Moon's history. About 3.8 to 3.3 billion years ago, extensive volcanism released large amounts of lava that flowed over the surface, filling in the lowest parts of the large impact basins and forming the darker maria we see today. Both the highlands and the maria continue to be battered by additional impacts ever since.

Why do meteors in a meteor shower appear to come from just one point in the sky?

A. All the meteors in a meteor shower typically come from the same comet, which is in a periodic orbit around the Sun. The loosened dust from the comet follows the path of the parent body. As Earth intersects the debris along the comet's orbit, it plows into this material. Since the dust particles are all moving together in space before they encounter Earth, if you trace back the streak of each meteor, its path will appear to diverge from one place in the sky called the radiant.

1. Which has more mass: an armful of feathers or an armful of lead? Which has more volume: a kilogram of feathers or a kilogram of lead? Which has higher density: a kilogram of feathers or a kilogram of lead?

A. An armful of lead has more mass as mass is related to weight. A kg of feathers has more volume as it is less dense than lead. Lead has a higher density.

1. What is an asterism? Can you name an example?

A. An asterism is a small, easily recognizable group of stars within a larger constellation. Some examples are like the Little Dipper inside Ursa Minor and the Big Dipper inside Ursa Major.

What is the origin of the terms "a.m." and "p.m." in our timekeeping?

A. Ante meridiem- before the sun reaches meridiem (before midday) and post meridiem- after the sun reaches local meridiem (after noon).

1. How did Aristotle deduce that the Sun is farther away from Earth than the Moon?

A. Aristotle noticed during solar eclipses that the Earth's moon passes in front of the Sun, and the opposite case never happens.

1. What are two ways in which Aristotle deduced that Earth is spherical?

A. Aristotle noticed that the shadow of the Earth when being casted on the moon during a lunar eclipse is always circular, which is only possible if a spherical body casts the shadow. Aristotle also noted that as travelers go farther south, fewer stars are circumpolar and more stars are visible to them overall.

1. The features of Mercury are named in honor of famous people in which fields of endeavor?

A. Artists, writers, composers, and other contributors to the arts and humanities.

Explain how a rocket can propel itself using Newton's third law.

A. As a rocket is propelled, the fuel inside of the rocket burn, creating exhaust gases that are released into the atmosphere. These exhaust gases are directed towards the ground, creating a large reaction of force. This is in line with Newton's third law. As the exhaust gases touch the ground, it creates a reaction force that lifts the rocket in the air.

1. Why is it difficult to drop a probe like Galileo? How did engineers solve this problem?

A. Aside from having to engineer the craft to survive the magnetosphere of Jupiter, the high speeds involved would guarantee that the probe would burn up on entering the atmosphere. The problem was solved using a heat shield in front of the spacecraft to absorb the heat. After the probe had slowed down, the heat shield was jettisoned and the parachute was deployed, further slowing the probe.

How do asteroids and comets differ?

A. Asteroids are composed primarily of rock and metal and reside in the inner part of the solar system. Comets are typically icy objects that come from the outer part of the solar system. Asteroids have greater densities than comets.

1. How did our exploration of the Moon differ from that of Mercury (and the other planets)?

A. Because of its proximity to Earth, we have been able to send manned missions to the Moon and return lunar material to Earth for study. Robotic missions have also been used to explore the lunar surface. All other solar system objects, planets, asteroids, and comets have been studied only by telescope and/or robotic missions. No human have visited them.

Why is it difficult to construct a practical calendar based on the Moon's cycle of phases?

A. Because the period required by the moon to complete its cycle of phases is 29.5306 days

Briefly describe NASA's Spaceguard Survey. How many objects have been found in this survey?

A. Beginning in 1998, the Spaceguard Survey is designed to discover all near-Earth asteroids that are greater than 1 km in diameter. It is objects of this size that could cause globally significant damage, should one strike Earth. To date, close to 1,000 objects of this size have been found.

1. With no wind or water erosion of rocks, what is the mechanism for the creation of the lunar "soil?"

A. Billions of years of impacts breaking up the rocks and scattering the debris over the surface have created lunar "soil." Enough impacts have occurred to cover much of the surface with sand and dust sized particles.

How are Triton and Pluto similar?

A. Both Trion and Pluto are very cold worlds in the outer reaches of the solar system. They are similar in size and similar in density, and thus similar in the proportion of rock and ice that makes them up. Both have a thin atmosphere of nitrogen, which freezes and sublimates depending on the temperature. Both have irregular or unusual orbits, with Triton moving in a retrograde orbit and Pluto in a tilted, high elliptical orbit. Astronomers think that Triton may be a captured moon from the realm of trans-Neptunian dwarf planets like Pluto.

1. What two factors made it difficult, at first, for astronomers to choose between the Copernican heliocentric model and the Ptolemaic geocentric model?

A. Both gave inaccurate predictions of planetary positions and motions from complicated models. In those days, little weight was given to observational experimental methods of validating one model or the other.

Explain how tidal forces are causing Earth to slow down.

A. By gradually transferring rotational energy to the sun and moon.

Compare the geology of Callisto, Ganymede, and Titan.

A. Callisto is an ice-covered moon whose inner materials have never fully differentiated into different density layers. It has no inner or outer activity and is basically geologically dead. Ganymede has a central rocky core and shows signs of tectonic activity, including regions of young surface terrain and long cracks in the crust. Titan has similar mass, size, and composition to Callisto and Ganymede, but has an active geology of liquid hydrocarbons on the surface, evaporation into the atmosphere, and rain back onto the surface.

Detail some of the anthropogenic changes to Earth's climate and their potential impact on life.

A. Climate is the change in the atmosphere over time, which has been gradually warming. This could be harmful for the health of all living things on the planet.

What is the composition of clouds on Mars?

A. Clouds on Mars are of three types: dust clouds; water-ice, like those on Earth; and clouds of frozen carbon dioxide crystals.

Describe the nucleus of a typical comet and compare it with an asteroid of similar size.

A. Cometary nuclei are quite small, on the order of a few kilometers in diameter, and are composed of ices, volatile organic compounds, silicate grains, and dust. Asteroids of similar size are denser and contain stonier and/or metallic materials. Comets react strongly to solar heating, releasing gases and dust, sometimes forming long tails that point away from the Sun.

Describe the origin and eventual fate of the comets we see from Earth.

A. Comets that fall into the inner solar system were once located either in the Oort cloud about 50,000 AU from the Sun or the Kuiper belt. The Oort cloud is far enough away that the gravitational influence of passing stars can perturb a comet's orbit. Some perturbations can send a comet out into interstellar space never to return. But others can send the comet nucleus inward toward the Sun; it is these comets that occasionally dazzle us here on our planet. Kuiper belt chunks can be perturbed by interactions with Neptune. A comet headed toward the inner solar system could hit the Sun or impact a planet. Or it could be caught by an interaction with one of the giant planets to become a really short-period comet. A comet trapped in the inner solar system will have a lifespan of just a few thousand orbits before it collides with a planet or all the volatiles escape, making it a dead comet.

What is comparative planetology and why is it useful to astronomers?

A. Comparative planetology is the study of how planets work and evolve by comparing them and the process that have influences their development. This method allows us to learn about the origin and evolution of the entire solar system, instead of each planet as a discrete object in space.

1. Why did Copernicus want to develop a completely new system for predicting planetary positions? Provide two reasons.

A. Copernicus wanted to improve upon the predictions of planetary positions because the geocentric model often gave inaccurate results. He also thought his system was simpler and more elegant. Copernicus thought that the existing system was needlessly and implausibly complicated.

1. Discuss how latitude and longitude on Earth are similar to declination and right ascension in the sky.

A. Declination is similar to latitude and right ascension is similar to longitude. Declination is the angular north-south distance between the celestial equator and a location on the celestial plane. Right ascension is the angular east-west distance between the spring equinox and a location on the celestial sphere.

13. What was the great insight Newton had regarding Earth's gravity that allowed him to develop the universal law of gravitation?

A. During Newton's era, gravity was thought to be related to Earth and no other planets. Newton's insight was that Earth's gravity interacted with other planets, with the Sun, and the Moon. He thought that the motion of celestial bodies around other celestial bodies had to be due to gravity. He believed that all celestial bodies in the universe attract every other matter or object through gravity.

The term solstice translates as "Sun stop." Explain why this translation makes sense from an astronomical point of view.

A. During a solstice, the sky goes completely dark during the middle of the day, making it seems almost as if the sun has stopped.

Venus rotates backward and Uranus and Pluto spin about an axis tipped nearly on its side. Based on what you learned about the motion of small bodies in the solar system and the surfaces of the planets, what might be the cause of these strange rotations?

A. During the early solar system, collisions between celestial bodies were frequent. This could be the cause for the rotations.

What are the two ways that the tilt of Earth's axis causes the summers in the United States to be warmer than the winters?

A. During the summer, the Northern Hemisphere is tilted towards the sun. The sun stays above the horizon longer, allowing it to heat things up longer than in the winter when days are shorter.

If Earth was to be hit by an extraterrestrial object, where in the solar system could it come from and how would we know its source region?

A. Earth could be hit by any of the small bodies in the solar system, most likely a comet or a near-earth asteroid. We can tell the difference based on the orbit of its approach to Earth and by its composition-whether it is primarily rocky or icy.

Why are there so many craters on the Moon and so few on Earth?

A. Earth is geologically active while the moon is geologically dead.

Compare the current atmospheres of Earth, Venus, and Mars in terms of composition, thickness (and pressure at the surface), and the greenhouse effect.

A. Earth's atmosphere is about 4/5 nitrogen and 1/5 oxygen; Venus' atmosphere is mostly carbon dioxide, with a pressure about 90 times higher than Earth; Mars' atmosphere is also mostly carbon dioxide, with a pressure only about one hundredth that of Earth. Venus has had an ongoing runaway greenhouse effect, leading to extraordinarily high surface temperatures. Earth is presently seeing the greenhouse effect increase with higher levels of carbon dioxide in the atmosphere. Mars has had a "runaway refrigerator" effect leading to a thinner atmosphere and colder temperatures over time.

How and why is Earth's Moon different from the larger moons of the giant planets?

A. Earth's moon is not geologically active compared to the other moons and it is close to the sun, making it rocky.

Explain briefly how the following phenomena happen on Earth, relating your answers to the theory of plate tectonics

A. Earthquakes- Tectonic plates crash together, pull apart, burrow under one another, slide alongside each other, jam together, causing part of Earth's crust to move and quake. B. Continental drift- Tectonic plates can slowly separate the crust, which could cause a continent to be detached from it's parent body of land. C. Mountain building- Tectonic plates jam against another, forcing the crust upwards along with deep rock being pushed above the surface. The great pressure from the plates essentially causes the Earth to buckle. D. Volcanic eruptions- Volcanoes are found at mid ocean ridges (mountain ranges formed at Earth's mantle at plate boundaries) and along subduction zones. E. Creation of the Hawaiian island chain- Hawaiian Island chains came from hot spots where heat is rising from the mantle. These hot spots fed volcanoes and as plates shifted, a chain of volcanoes formed.

1. Is the ecliptic the same thing as the celestial equator? Explain.

A. Ecliptic is the Sun's apparent annual path in the sky and the celestial equator is the projection of Earth's equator onto the sky.

Who first calculated the orbits of comets based on historical records dating back to antiquity?

A. Edmund Halley presented the calculations for 24 cometary orbits in 1705. One of these he predicted to return to the vicinity of Earth in 1758. That comet, which did indeed return as predicted, is now known as Halley's Comet.

Why are some planets and moons more geologically active than others?

A. First of all, a world needs to be solid to have geological activity. Among the terrestrial planets, geological activity depends to a large degree on the size of the planet and resulting internal heat; larger planets are better able to retain their primordial heat or to keep the heat from the decay of radioactive materials inside them. The Moon and Mercury, being small, are now geologically dead. Mars, Earth, and Venus all exhibit volcanism, but less for Mars as it has cooled more due to its smaller size. Some of the moons of the outer planets are geologically active due to heat caused by structural flexing in the large gravitational fields of the giant planets. How this internal activity manifests on the surface also depends on the composition of the object.

What are the main atmospheric heat sources of each of the giant planets?

A. For Jupiter, Saturn, and Neptune, both sunlight and internal sources provide energy to the atmosphere. The source of this energy is the separation of helium from hydrogen in Saturn's interior. Uranus has no or very little internal heat, so it gets its energy from the Sun.

Compare the atmospheric circulation (weather) of the four giant planets.

A. For both Jupiter and Saturn, convection from their internal heat sources mixes the atmosphere and promotes cloud formation. Their rapid rotation spreads out these cloud features into parallel bands that circle the planets at all latitudes. For Uranus, the circulation is also equatorial, and the wind speeds are high. Since there is no convection to mix the gases and create many clouds, Uranus' atmosphere is smeared out and rather featureless. Neptune's wind speeds are much higher than its rotational speed, so the atmosphere smears out into parallel bands like Jupiter and Saturn.

1. Frozen water exists on the lunar surface primarily in which location? Why?

A. Frozen water exists primarily in deep craters on the Moon's south pole. Parts of these craters are permanently in shadow and therefore do not receive enough energy from the Sun to evaporate the ice and escape into space.

Which type of planets have the most moons? Where did these moons likely originate?

A. Giant planets have the most moons. Jupiter and Saturn having the most. Many of them are thought to have been captured from small-body population during the formation of the solar system.

What fraction of the Moon's visible face is illuminated during first quarter phase? Why is this phase called first quarter?

A. Half of the visible face of the Moon is illuminated. The phase is called first quarter because the Moon at this time has completed the first quarter of its phase cycle.

13. Why is Tycho Brahe often called "the greatest naked-eye astronomer" of all time?

A. He extended observation without the use of a telescope.

1. Why was Brahe reluctant to provide Kepler with all his data at one time?

A. He feared that Kepler would take all credit for a universal theory for himself.

1. What differences did Grove K. Gilbert note between volcanic craters on Earth and lunar craters?

A. He found that Earth volcanoes have small, deep craters on mountaintops, whereas lunar craters are larger, have different shapes than volcanic craters and are mountain-rimmed and circular with floors generally below the level of the surrounding plains.

1. How did Hipparchus discover the wobble of Earth's axis, known as precession?

A. Hipparchus compared his careful observations of the stars with those of earlier observers and noticed that the positions of the fixed stars had changed slightly and systematically over the course of 150 years, consistent with the direction of the celestial pole changing relative to the stars.

Although he did not present a mechanism, what were the key points of Alfred Wegener's proposal for the concept of continental drift?

A. His key points were that South America and Africa were joined together in one land mass called Pangea, they became separated. Similar fossils were found on both continents suggesting that they were together, along with their matching borders.

In which domain of living things do you find humankind?

A. Humankind is under the Eukarya domain/

What evidence do we have that there was running (liquid) water on Mars in the past? What evidence is there for water coming out of the ground even today?

A. Images from orbiting spacecraft of runoff channels and outflow channels all show evidence of formation by running water. Several dry basins contain minerals that only form with water and indicate extensive lakes in the past. In 2015, some dark streaks that got longer over the course of several days showed spectra of hydrated salts, and may be evidence of saltwater on Mars today.

Explain the role of impacts in planetary evolution, including both giant impacts and more modest ones.

A. Impacts in early planet formation led to heating of the protoplanets, allowing for differentiation of materials and outgassing of lighter elements. Later, larger impacts probably led to some of the unusual characteristics of planets, such as formation of the Moon around Earth, Mercury's consisting of mostly core material and not as large a mantle or crust as the other planets, and the slow, retrograde rotation of Venus. Later impacts led to craters on all the solid worlds and to the deposition of volatile substances on worlds in the inner solar system that lacked them. Such impacts contributed to changes in the early planetary atmospheres.

1. The Sun was once thought to be a planet. Explain why.

A. In the geocentric system, all objects moving in the sky were considered "wanderers", so the Sun was considered a planet.

1. Explain how Kepler was able to find a relationship (his third law) between the orbital periods and distances of the planets that did not depend on the masses of the planets or the Sun.

A. In the year 1619, Kepler introduced the relation of orbit of a planet and their distances from the Sun. The mathematical relation is P^2=a^3. P represents the period in which the planet orbits, while A represents the distance from the Sun. This relations is known as Kepler's third law of planetary motion.

Explain the energy source that powers the volcanoes of Io.

A. Io is close enough to Jupiter to experience significant tidal heating, where the moon alternately stretches and relaxes in its elliptical orbit about the planet. This generates enough heat to produce molten silicate lava that erupts as volcanoes.

List, in order of decreasing altitude, the principle layers of Earth's atmosphere.

A. Ionosphere, Mesosphere, Ozone Layer, Stratosphere, Troposphere.

Why is it difficult to observe at infrared wavelengths? What do astronomers do to address this difficulty?

A. It is difficult to distinguish between the amount of heat radiation that reaches Earth from other stars and galaxies, and the greater heat radiated by the telescope itself and our planet's atmosphere. To solve this problem, astronomers must protect the infrared detector by cooling and also by storing the detector in space or mountains.

1. Why do we say that Neptune was the first planet to be discovered through the use of mathematics?

A. John Couch Adams and Urbain Jean Joseph Leverrier used mathematics in order to predict that gravity from a planet beyond Uranus was affecting the orbit of Uranus. This planet was Neptune. They determined that Uranus was being pulled slightly out of its orbit by Neptune using mathematics. They also determined how much mass it had.

Explain the origin of the leap year. Why is it necessary?

A. Julius Caesar created the leap year in 45 BC. The Romans had a 355-day calendar and to keep festivals occurring around the same season each year, a 22 or 23 day month was created every second year. Julius Caesar decided to simplify this by adding days to different months of the year to create the 365-day calendar. Leap years are necessary, because the actual length of a year is 365.242 days, not 365 days.

1. Which planet has the strongest magnetic field, and hence the largest magnetosphere? What is its source?

A. Jupiter has the largest magnetosphere. The large, rapidly spinning, liquid-metallic hydrogen above the core is the source of its magnetic field.

1. Why did Kepler need Tycho Brahe's data to formulate his laws?

A. Kepler wanted to deduce a universal theory of the motion of planets. Kepler needed data to do this and that data needed to support the heliocentric model. Brahe had records which deviated from the Ptolemic model and Kepler believed in Brahe.

How do impacts by comets and asteroids influence Earth's geology, its atmosphere, and the evolution of life?

A. Large enough comets can cause extinction in certain species, changing then how new species will evolve.

Explain why the year 1800 was not a leap year, even though years divisible by four are normally considered to be leap years.

A. Leap years are divisible by four. Though 1800 is divisible by four, there is an additional rule for century years. The century year must be divisible by 100 and 400.

Briefly describe the greenhouse effect.

A. Light penetrates our atmosphere and the heat is absorbed by the ground, the heat at Earth's surface is reemitted as infrared or heat radiation. However, the molecules in our atmosphere that lets visible light through absorbs the infrared waves, trapping the heat in our atmosphere.

3. Explain the runaway refrigerator effect and the role it may have played in the evolution of Mars.

A. Martian gravity is not strong enough to hold a gaseous atmosphere over a long period of time, so the atmosphere would have gotten thinner as gas escaped. This would lead to lower temperatures, and more gas would have frozen and deposited out of the atmosphere, lowering temperatures still further. The thinner atmosphere and colder temperatures would lead to the loss of most water from the planet, except for water ice, permafrost ground deposits, and perhaps underground saltwater.

Look back at Figure 6.18 of Cygnus A and read its caption again. The material in the giant lobes at the edges of the image had to have been ejected from the center at least how many years ago?

A. Material was ejected at least 160,000 years ago.

1. Describe the basic internal structure of Mercury.

A. Mercury is one of the densest of the planets, at 5.4 g/cm^3. It has an enormous iron-nickel core nearly 3500 km in diameter, which is encased in rocky/silicate crust about 700 km deep. The metallic core, representing nearly 60% of the planet's total mass, produces a weak magnetic field.

1. What is the main consequence of Mercury's orbit being so highly eccentric?

A. Mercury's distance from the Sun varies hugely, ranging from 4.6 million km at perihelion to 70 million km at aphelion.

1. What is the relationship between Mercury's rotational period and orbital period?

A. Mercury's rotation is 59 Earth-days long, while the year is 88 Earth-days long. That is a ratio of 3 to 2. Thus, three Mercury days equals two Mercury years.

In what ways are meteorites different from meteors? What is the probable origin of each?

A. Meteorites are large enough to withstand the violent passage through Earth's atmosphere, whereas meteors burn up from the heat of friction. Meteors typically come from comets that have passed through the solar system; their solid material is freed when the ice is vaporized by the heat of the Sun. Most meteorites, on the other hand, are from asteroids or from debris kicked up on the Moon or Mars during an impact

What is the difference between a meteor and a meteorite?

A. Meteoroids that collide with Earth's atmosphere are called meteors. If the object makes it through Earth's atmosphere and lands on the surface of Earth, then it is called a meteorite.

A friend of yours who has not taken astronomy sees a meteor shower (she calls it a bunch of shooting stars). The next day she confides in you that she was concerned that the stars in the Big Dipper (her favorite star pattern) might be the next ones to go. How would you put her mind at ease?

A. Meteors do not come from stars, but from pieces of comets or asteroids that have broken off or been set free, and that enter Earth's atmosphere. Meteors are small solid objects of stone or metal, whereas stars are huge balls of hot gas and are trillions of miles away. You could also point out that meteor showers like the one she saw occur annually and yet no one has reported stars missing after any of them. The constellations (star patters) have been observed since humans have had written history, with no reports of any disappearing.

How are comets related to meteor showers?

A. Most meteor showers originate with particular comets that pass through the inner solar system and lose some of their solid material, which then goes into orbit along the comet's path. Showers happen whenever Earth in its orbit passes through the path of the comet and its debris.

1. Which of the gas giants has the largest icy/rocky core compared to its overall size?

A. Neptune has the largest core, extending out to about 20,000 km from the center of the planet.

Make a list of each main phase of the Moon, describing roughly when the Moon rises and sets for each phase. During which phase can you see the Moon in the middle of the morning? In the middle of the afternoon?

A. New moon rises at sunrise and sets at sunset. Waxing crescent rises mid-morning and sets between sunset and midnight. First quarter rises at noon and sets at midnight. Waxing gibbous rises mid-afternoon and sets between midnight and sunrise. Full moon rises at sunset and sets at sunrise. Waning gibbous rises between sunset and midnight and sets mid-morning. Third quarter rises at midnight and sets at noon. Waning crescent rises between midnight and sunrise and sets mid-afternoon. You can see the moon mid-morning during third quarter and waning crescent. You can see the moon mid-afternoon during waxing crescent and first quarter.

1. Write out Newton's three laws of motion in terms of what happens with the momentum of objects.

A. Newton's three laws define the mass of the moving object and the velocity of which it is moving. There are three factors within the three laws. They are speed, the objects mass, and the direction the object is moving.

What is, by far, the most abundant component of Earth's atmosphere?

A. Nitrogen (78%).

On a globe or world map, find the nearest marked latitude line to your location. Is this an example of a great circle? Explain.

A. No, the only great circle is the Equator as it is the longest circle of latitude.

Do all planetary systems look the same as our own?

A. No. There is thousands of other planetary systems. Of the ones we observed so far, systems continually evolve along different evolutionary paths. Some examples are that of giant gas planets that are much closer to the sun.

How was the Mars Odyssey spacecraft able to detect water on Mars without landing on it?

A. Odyssey used a gamma-ray spectrometer to detect hydrogen below the Martian surface. Analysis of the signals indicated that the hydrogen was probably from water molecules in ice frozen below the surface.

The term equinox translates as "equal night." Explain why this translation makes sense from an astronomical point of view.

A. On the date of the equinox, everyone on Earth experiences an equal-length day and equal-length night of roughly 12 hours each.

1. Why is the shape of the magnetosphere not spherical like the shape of Earth?

A. Our magnetosphere extends farther away from the sun, because solar wind is blowing charge particles toward Earth, basically blowing the magnetosphere in that direction, because more charged particles are flowing that way.

What evidence do we have for the existence of the Kuiper belt? What kind of objects are found there?

A. Over a thousand members of the Kuiper belt have been found directly in recent years, including dwarf planets Pluto and Eris. The size and numbers of these icy objects suggest that many additional smaller bodies must also exist in the same region, in a disk extending out to about 50 AU from the sun.

Why do the giant planets and their moons have compositions different from those of the terrestrial planets?

A. Planets formed initially through the accretion of solid materials in the solar nebula. Due to the temperature in the interior of the solar system, the only substances capable of condensing there were rocks and metals. Any volatile materials could not condense so close to the heat of the early Sun. In the out solar system, rock, metal, and hydrogen compounds were all solids and, as a result, there was much more material to form planets. The protoplanets that formed were large enough to also capture H and He gas and grow much, much larger and become the giant planets.

Compare the eye, photographic film, and CCDs as detectors for light. What are the advantages and disadvantages of each?

A. Planets, stars, and galaxies send more light to Earth than any human eye can catch. Though, eyes are the most inexpensive method. Photographic films create permanent records that can be used for detailed and quantitative studies. The disadvantages of photographic films is that only 1% of the light that actually falls on the film contributes to the chemical change that makes the image. CCDs can detect much fainter objects than photographic film, making it better and more accurate.

List at least three major differences between Pluto and the terrestrial planets.

A. Pluto is much smaller than all the terrestrial planets. Its composition is ice and rock as opposed to the composition of rock and metal of the terrestrial planets. Pluto's orbit is highly elliptical and inclined to the plane of the ecliptic as opposed to the circular orbits near the plane of the ecliptic for the terrestrial planets. Pluto has a thin and variable atmosphere of nitrogen, while three of the terrestrial planets have much thicker and warmer permanent atmospheres. Pluto is but one object of many in the Kuiper Belt, whereas each of the terrestrial planets dominates the mass in their respective orbits.

How was Pluto discovered? Why did it take so long to find it?

A. Pluto was discovered at Lowell Observatory by a young, relatively untrained Clyde Tombaugh, from comparisons of photographs taken several days apart that showed the relative motion of Pluto against a background of stars. Pluto was difficult to find because of its small size and great distance from Earth. Although Percival Lowell had suggested that Pluto could be found by its effects on the orbits of other outer planets such as Uranus and Neptune, in fact a planet with so little mass could not be pinpointed by its gravitational effects. It was just luck that Pluto was found where Tombaugh had been told to search.

13. Pluto's orbit is more eccentric than any of the major planets. What does that mean?

A. Pluto's orbit is less circular than other planets.

What do we mean by primitive material? How can we tell if a meteorite is primitive?

A. Primitive material was formed in the early stage of the solar system, before planets cooled off enough to differentiate elements of different density. It was not subject to great heat or pressure after it formed. We can identify primitive meteorites by their composition; primitive meteorites are usually undifferentiated stones, with some metallic grains mixed in. Some primitive meteorites are darker, carbonaceous stones.

1. Why did Ptolemy have to introduce multiple circles of motion for the planets instead of a single, simple circle to represent the planet's motion around the Sun?

A. Ptolemy had to account for the observed occasional retrograde motion of planets.

Radio and radar observations are often made with the same antenna, but otherwise they are very different techniques. Compare and contrast radio and radar astronomy in terms of the equipment needed, the methods used, and the kind of results obtained.

A. Radio observations use a dish reflector, a spectrometer and a detector. The dish acts like the mirror of a reflecting telescope. It collects and focuses radiation. It can detect objects from far away. With radar astronomy, a radio dish is used as a radar telescope only if it is equipped with a powerful transmitter & receiver.

Describe how we use radioactive elements and their decay products to find the age of a rock sample. Is this necessarily the age of the entire world from which the sample comes? Explain.

A. Radioactive elements decay in a systematic way. The half-life measures the amount of time it takes half of a sample to decay. The world melts and this time is only for the last time it was melted.

1. Describe the main differences between C-type and S-type asteroids.

A. S-types are stony or silicate-based bodies with few carbon compounds and are more reflective. The C-types are rich in carbon compounds and are less reflective. The C-types are considered primitive and are little changed since their formation.

Describe and compare the rings of Saturn and Uranus, including their possible origins.

A. Saturn's rings form a wide and complex system consisting mostly of particles and pieces of ice and are highly visible. They may have formed from one or more moons that broke up due to a collision or are left over from early debris that never coalesced into a moon. The rings of Uranus are thin and hard to see, consisting mostly of chunks of carbon and hydrocarbons with very little reflectivity. They may also have formed from the breakup of a small moon due to collision. They may be kept thin by the presence of shepherd moons.

1. In the context of the giant planets and the conditions in their interiors, what is meant by "rock" and "ice"?

A. Scientists describe materials in these environments that are composed primarily of iron, silicon, and oxygen as rock. Similarly, those composed of carbon, nitrogen, and oxygen in combination with hydrogen are described as ice. The layers described in this way don't necessarily resemble rocks and ice sheets on Earth.

What is the composition of the polar caps on Mars?

A. Seasonal ice caps are made up of dry ice, or crystals of frozen carbon dioxide; the northern residual cap is water ice, whereas the southern permanent ice cap is made predominantly of water ice with a covering of carbon dioxide ice.

1. What are the seasons like on Jupiter?

A. Since Jupiter's spin axis is only tilted about 3 degrees from the perpendicular, it does not experience seasons at all.

1. Why are asteroids and comets important to our understanding of solar system history?

A. Since comets and most asteroids are small, they have not undergone chemical differentiation as have large planet-size bodies. As such, they retain the structure and composition they acquired upon formation. These objects provide evidence for the conditions that existed in the solar nebula and early solar system.

Where would you look for some "original" planetesimals left over from the formation of our solar system?

A. Small asteroids, Kuiper belt objects, small moons that haven't been heated. These things have not been altered much since the creation of the solar system, so they can tell us about the structure of the past.

Explain our ideas about why the terrestrial planets are rocky and have less gas than the giant planets.

A. Terrestrial planets and gas planets are thought to have formed under different conditions. Inner planets are made of elements that can survive the heat of the sun and gases would have evaporated. The giant planets are far enough away that gases could accumulate around the planet cores and remain there for the age of the solar system.

How do terrestrial and giant planets differ? List as many ways as you can think of.

A. Terrestrial planets are closer to the sun, they are smaller, they have higher densities, they have silicates and metals. Giant planets are farther from the sun, they are larger, have lower densities, they have no solid surface, and they have more moons.

Why is the warmest day of the year in the United States (or in the Northern Hemisphere temperate zone) usually in August rather than on the day of the summer solstice, in late June?

A. The Earth has the property of retaining the temperature of the atmosphere of the Earth. When the Sun's rays hit the Earth, the temperature of the Earth increases with time. When the maximum light or energy of the sun hits the ground, it doesn't represent the hottest part of the day. The hottest day will come when maximum light hits the Earth. This property of the Earth is called thermal inertia.

1. How many degrees does the Moon move per day relative to the fixed stars? How many days does it take for the Moon to return to its original location relative to the fixed stars?

A. The Earth's moon moves 12 degrees per day and it takes 30 days to return to its original location.

Describe one visible-light or infrared telescope that astronomers are planning to launch into space in the future.

A. The James Webb Telescope is schedule for a launch by NASA on October 31, 2021.

Explain why the Gregorian calendar modified the nature of the leap year from its original definition in the Julian calendar.

A. The Julian calendar has its average year differing from the true year by about 11 minutes, so the Gregorian calendar dropped ten days and then made the average length of the leap year more closely approximate to the tropical year.

The Hooker telescope at Palomar Observatory has a diameter of 5 m, and the Keck I telescope has a diameter of 10 m. How much more light can the Keck telescope collect than the Hooker telescope in the same amount of time?

A. The Keck telescope can collect four times than the Hooker Telescope.

Give brief descriptions of both the Kuiper belt and the Oort cloud.

A. The Kuiper belt is a disk-shaped region of space beyond the orbit of Neptune that is dynamically stable. It is the source of short-period comets. The Oort cloud is much farther out than the Kuiper belt. It is a spherical region surrounding the Sun out to near 50,000 AU. This is the source of newly discovered long-period comets.

1. In addition to the ones mentioned in Exercise 13.3, what is the third, rarer class of asteroids?

A. The M-types, or metallic asteroids.

Describe the current atmosphere on Mars. What evidence suggests that it must have been different in the past?

A. The Martian atmosphere consists mostly of carbon dioxide, but is very thin, less than 1% of Earth's atmosphere. However, the strong evidence of water on Mars in the past that our missions have found means that the atmosphere must have been thicker and warmer, or water would have evaporated away very quickly.

1. What is the composition of the Moon, and how does it compare to the composition of Earth? Of Mercury?

A. The Moon is principally composed of silicate rocks, whereas Earth has more metals and volatile compounds. Earth has an iron core, but the Moon does not. Earth has liquid water in its surface layer, but the Moon does not. Mercury contains substantially more metals than the Moon, with a significant iron-nickel core.

1. Why does the Moon not have an atmosphere?

A. The Moon's mass, and therefore its gravitational force, is not large enough to retain gases and volatile compounds. Therefore, any gases released on the Moon quickly escape into space.

1. How many degrees does the Sun move per day relative to the fixed stars? How many days does it take for the Sun to return to its original location relative to the fixed stars?

A. The Sun moves about 1 degree per day. It takes about 360 days, exactly 365.25 days, for the sun to return to its original location.

What are advantages and disadvantages of apparent solar time? How is the situation improved by introducing mean solar time and standard time?

A. The advantage of apparent solar time is that it is very simple. The disadvantage of apparent solar time is that it is inconvenient because the apparent solar day varies slightly during the year and because the Earth's axis of rotation is not perpendicular to the plane of its revolution, so it does not advance at a uniform rate. The situation is improved by introducing mean solar time and standard time, because is it based on the average value of the solar day over the course of the year, so it progresses at a uniform rate.

To calculate the angular momentum of an object, which properties of an object do you need to know?

A. The angular momentum of an object depends upon the mass of the rotating object, the velocity of the rotating object, the radius of path in which the object moves, and the angle subtended by the path.

1. Give a brief description of the asteroid belt.

A. The asteroid belt is a region of space between the orbits of Mars and Jupiter containing a few large minor planets and thousands of smaller bodies. These all have orbital periods ranging from 3.3 to 6 years.

The Hubble Space Telescope images of Pluto in 2002 showed a bright spot and some darker areas around it. Now that we have the close-up New Horizons images, what did the large bright region on Pluto turn out to be?

A. The bright spot turned out to be what has been nicknamed Sputnik Planum. It appears to be a bowl or sea of frozen and perhaps liquid nitrogen, much brighter and younger than the darker highlands of Pluto.

1. According to Kepler's second law, where in a planet's orbit would it be moving fastest? Where would it be moving slowest?

A. The closer a planet is to the Sun, the faster it moves. The farther a planet is to the Sun, the slower it moves.

What are the visible clouds on the four giant planets composed of, and why are they different from each other?

A. The clouds of Jupiter and Saturn are primarily crystals of frozen ammonia. On Uranus and Neptune, the clouds are composed of methane. The temperatures of these worlds dictate the cloud composition. For Jupiter and Saturn, the temperatures keep methane in a gaseous state, while on Uranus and Neptune, the colder temperatures allow the methane to freeze and condense into clouds.

How do storms on Jupiter differ from storm systems on Earth?

A. The cyclonic storm features on Jupiter are regions of high pressure, whereas storms on Earth, such as hurricanes, are low-pressure areas.

1. What are the principal features of the Moon observable with the unaided eye?

A. The dark maria, the lighter highlands, and a few large craters such as Tycho are visible. The contrast between the light and dark of these features is sometimes called "the man in the Moon."

Why does the Moon create tidal bulges on both sides of Earth instead of only on the side of Earth closest to the Moon?

A. The differential force of gravity exerted by the moon has the effect of stretching Earth out along a line connecting Earth and the moon, so both sides of Earth bulge out.

1. Summarize the four main hypotheses for the origin of the Moon.

A. The fission hypothesis suggests that the Moon was once part of Earth but separated early in their history. The sister hypothesis proposes that the Moon formed together with, but independent of, Earth. In the capture hypothesis, the Moon formed elsewhere in the solar system and was later captured by Earth. The newer giant impact hypothesis suggests that a Mars-sized object grazed Earth, ejecting material from both Earth and itself, material that condenses to form the Moon.

Why do the upper levels of Neptune's atmosphere appear blue?

A. The gaseous molecules in Neptune's atmosphere scatter blue light, giving Neptune its color. The same process makes Earth's sky appear blue.

1. Describe the interior heat source of Saturn.

A. The heavier helium is sinking, displacing the lighter hydrogen, which then rises. The falling of the helium releases gravitational energy, which heats the interior

Why do the heights of the tides change over the course of a month?

A. The heights of the tides change every month, because changes in the positions of earth, the moon, and the sun affect the height of the tides during the month.

List the largest-aperture single telescope currently in use in each of the following bands of the electromagnetic spectrum: radio, X-ray, gamma ray.

A. The largest radio telescope is 305m located in Arecibo, Puerto Rico. The X-ray telescope Chandra currently orbiting in space. The Fermi Gammy Ray telescope currently orbiting in space.

What is the latitude of the North Pole? The South Pole? Why does longitude have no meaning at the North and South Poles?

A. The latitude of the north pole is 90 degrees north, and the south pole is 90 degrees south. Longitude is pointless since there is no east-west direction at the poles.

1. The mountains on the Moon were formed by what process?

A. The long, semi-circular mountain ranges that border the maria are debris ejected from the massive impacts that formed these basins, piled up at the edge of the bowl dug out by the explosion that resulted from the impact. The central peak mountains in large craters are due to rebound from the sudden removal of overlying rock.

1. What are the main challenges involved in sending probes to the giant planets?

A. The main challenges involved in sending proves to the Giant planets is that the Giant planets are solely made up of gas, hence there is no surface to land the probes on. Also, because of the crazy atmosphere on these planets, the probes would most likely get destroyed once they hit the atmosphere of the planets. It is also very costly to send probes to the Giants.

1. What are Earth's core and mantle made of? Explain how we know.

A. The mantle is made of rock, which we know from chemical analysis of samples from the upper mantle material that is ejected occasionally from volcanoes. The structure, density and size of the core can be determined by analyzing the seismic waves traveling through Earth's interior. Based on our understanding of planetary formation, internal differentiation, the calculated density of the core, and the relative abundances of chemicals in the solar system, scientists conclude that the core consists of heavy elements. The elements residing in the core are primarily, but not limited to, iron and nickel.

1. What is the thickest interior layer of Earth? The thinnest?

A. The mantle is the thickest region at about 2,900 km. The crust is the thinnest, ranging from about 6 to 70 km deep.

1. What are the maria composed of? Is this material found elsewhere in the solar system?

A. The maria are composed chiefly of basalt. Basalts are also found on Earth, Venus, Mars, and to a much lesser extent, Mercury.

1. A certain material has a mass of 565 g while occupying 50 cm3 of space. What is this material? (Hint: Use Table 3.1.)

A. The material is lead. This is found by finding the density, then using the periodic table to find the element that has a matching density.

What are the moons of the outer planets made of, and how is their composition different from that of our Moon?

A. The moons of the outer planets consist of a mixture of ice and rock, whereas our Moon is just rock.

1. What is the source of Earth's magnetic field?

A. The movement of Earth's liquid metallic core.

Explain three lines of evidence that indicate that the seasons in North America are not caused by the changing Earth-Sun distance as a result of Earth's elliptical orbit around the Sun.

A. The orbit of Earth is elliptical by only a few percent, not enough of a distance difference to cause significant difference in temperature as we experience due to season shifts. Our closest approach to the sun occurs in January, one of the coldest months in the northern hemisphere. The northern and southern hemisphere experience opposite seasons simultaneously, which is not possible if changing distance to the Sun is the cause. If it were, both hemispheres would experience the same seasons at the same time.

What is the phase of the Moon during a total solar eclipse? During a total lunar eclipse?

A. The phase of the moon during a total solar eclipse is a new moon. The phase of the moon during a total lunar eclipse is a full moon.

List some reasons that the study of the planets has progressed more in the past few decades than any other branch of astronomy.

A. The planets are relatively close to Earth, and technology has been developed that has allow us to send spacecraft to all of the major planets and many other small worlds. Space missions to these bodies will allow us to make close observations that we cannot obtain from Earth's surface, or from telescopes in orbit around Earth. Spacecraft that land on other planets allow us to make measurements of rocks and the lower atmosphere, and spacecraft that orbit other planets allow us to study surface geology.

1. At the pressures in Jupiter's interior, describe the physical state of the hydrogen found there.

A. The pressure is so high that the hydrogen, normally a gas, has been compressed into a liquid-metallic form not seen on earth.

1. What is the primary source of Jupiter's internal heat?

A. The primary source of Jupiter's internal heat is from the material that fell inside their core when the planet was formed which is called primordial heat.

Why are the largest visible-light telescopes in the world made with mirrors rather than lenses?

A. The reason the largest visible-light telescopes use a mirror is because the use of a small secondary mirror allows more light to get through the system and to see the image clearer.

Why were the rings of Uranus not observed directly from telescopes on the ground on Earth? How were they discovered?

A. The rings of Uranus consist of dark, coal-like particles in narrow bands, making them almost impossible to see from Earth. They were discovered using a flying infrared telescope during the occultation of a star as Uranus passed in front of it. The light from the star dimmed several times before it was blocked by the disk of Uranus and afterward, indicating the presence of several distinct rings.

What do our current ideas about the origins of the Moon and Mercury have in common? How do they differ?

A. The similarities are mainly those of appearance: both suffered frequent and sometimes massive impacts early in their histories, with heavily cratered surfaces visible on each body. Mercury has much more iron than the Moon, so early on, Mercury must have lost most of its rocky mantle, probably due to impacts. At some point, probably due to internal cooling, Mercury shrank enough to create long "wrinkles" and scarps in the crust; such scarps are not seen on the Moon.

What was the solar nebula like? Why did the Sun form at its center?

A. The solar nebula was a huge cloud of material made up of gas and dust. The sun formed at the center due to gravitational forces, causing that material to stick together. Once the mass and density increased sufficiently, nuclear fusion caused a star to form, that star being the sun.

Describe the solar nebula, and outline the sequence of events within the nebula that gave rise to the planetesimals.

A. The solar nebula was initially a cloud of dust and gas that began to rotate around its center due to conservation of angular momentum as it contracted by gravitational attraction. The central region of the nebula became a star, while the outer regions flattened and made a rotating disk. Things near the center remained hot, while farther out in the disk things cooled off. Grains or droplets of material condensed could survive only father out. Closer in, particles began to cool and form compounds, including rock and metal grains that grew larger by gravitational impacts and mergers. Farther out, the droplets and icy pieces were able to grow. Accretion of these larger pieced formed planetesimals.

What is the evidence for a liquid water ocean on Europa, and why is this interesting to scientists searching for extraterrestrial life?

A. The surface of Europa features jagged blocks of ice that seem to have rotated and collided with one another, which would not likely happen on a solid moon. Long, straight cracks in the crust are also more likely to happen over a liquid subsurface layer than a solid one. Also, a weak magnetic field implies the presence of a liquid layer below the surface. This is interesting for searchers of extraterrestrial life because liquid water is essential for life as we knew it, and life seems to exist in most place on Earther where liquid water is found. For example, life is found near vents on the deep ocean floor where chemical energy from hot springs can serve as a source of energy.

Why are there so many impact craters on our neighbor world, the Moon, and so few on Earth?

A. The tectonic plates on Earth are constantly rebuilding the crust, so when an impact happens the crater is covered by new crust being formed via the movement of the tectonic plates. Earth is the only planet with these plates, so on the moon when there's an impact there's no way for the crater to be covered.

Explain why there are two high tides and two low tides each day. Strictly speaking, should the period during which there are two high tides be 24 hours? If not, what should the interval be?

A. The tidal force of the moon creates bulges on both the near and far sides of Earth, so there are two high tide bulges. As Earth rotates, a person would be carried through both of these bulges during any given 24-hour period.

Describe the two types of comet tails and how each are formed.

A. The two different types of tails are the dust tails and the ion tails. Dust particles create the dust tail, and it generally points back along the comets path. The ion tail is created by the ions that come from the nucleus. Due to the sun's magnetic field, the ion tail always faces directly away from the sun.

Name the two spectral windows through which electromagnetic radiation easily reaches the surface of Earth and describe the largest-aperture telescope currently in use for each window.

A. The two spectral windows are visible light and radio waves. The largest radio telescope at 305m which is located in Arecibo, Puerto Rico and the Visible Light telescope at is the Gran Telescopio Canarias at 10.4m located in the Canary Islands of Spain.

What characteristics do the worlds in our solar system have in common that lead astronomers to believe that they all formed from the same "mother cloud" (solar nebula)?

A. Their orbits lie roughly in the same plane. They generally revolve and rotate in the same direction. The chemical makeup of the giant planets is similar to the Sun.

1. Explain the evidence for a period of heavy bombardment on the Moon about 4 billion years ago.

A. There are about 10 times more craters on the highlands than on similar area of maria. The radioactive dating of highland samples shows that they are only slightly older than the maria, about 4.2 billion years versus 3.8 billion years. If the impact rate was constant over the Moon's history, the highlands would be least 10 times older than the maria, or about 38 billion years old. That's older than the age of the universe. Thus, the impact rate must not have been constant, and been at a much higher rate earlier than 3.8 billion years ago.

Why do astronomers place telescopes in Earth's orbit? What are the advantages for the different regions of the spectrum?

A. There are distorting effects of the atmosphere that can affect the use of a telescope. Getting above said distorting effects is an advantage at visible and infrared wavelength. Bypassing Earth's disadvantages like clouds, storms, and moisture, having a telescope in space eliminates that.

1. What are the difficulties with the capture hypothesis of the Moon's origin?

A. There does not seem to be any way that Earth could have captured a large satellite from elsewhere. One object approaching another cannot go into orbit around it without losing large amounts of energy. Also, the new satellite would go into a very eccentric orbit rather than the nearly circular orbit the Moon has now. Finally, there are too many compositional similarities between Earth and the Moon to warrant an independent origin.

How might Venus' atmosphere have evolved to its present state through a runaway greenhouse effect?

A. There may have been carbon dioxide in the Venus atmosphere to begin with. But however large that initial supply was, heat from the Sun could have evaporated water from the surface of Venus, releasing carbon dioxide absorbed in the water. The carbon dioxide in the atmosphere prevented infrared radiation from escaping the planet, leading to a rise in temperatures and further loss of water and release of carbon dioxide. Sunlight would break up water vapor molecules higher in the atmosphere into hydrogen, which escaped the planet, and oxygen, which combined with surface rocks. The loss of water reduces the planet's ability to absorb carbon dioxide.

Summarize the origin and evolution of the atmospheres of Venus, Earth, and Mars.

A. These atmospheres were produced by gas escaping from the interior of the planet, and the deposit of volatile materials by the impacts of chunks from farther out in the solar system. How well a planet retained its atmosphere depends on its mass; since Mars has lower mass than Venus and Earth, it lost more of its atmosphere over time. We think all three planets started with similar atmospheres of carbon dioxide, ammonia, and methane. The reducing molecules were broken up by ultraviolet radiation from the Sun, with hydrogen escaping into space. On Venus, large amounts of carbon dioxide produced a runaway greenhouse effect, leading to the thick, hot atmosphere observed today. On Mars, temperatures fell as more of the atmosphere was lost and the greenhouse effect of the carbon dioxide could no longer keep the warmth in; cold temperatures froze water on the surface and out of the atmosphere, leading to the present thin atmosphere of mostly carbon dioxide. On Earth, a mild greenhouse effect and the presence of liquid water that could absorb carbon dioxide led to an atmosphere of mostly nitrogen and to conditions that could lead to the development of life. Free oxygen was added to Earth's atmosphere when plants evolved and gave off oxygen as a byproduct of photosynthesis.

What classification is given to objects such as Pluto and Eris, which are large enough to be round, and whose orbits lie beyond that of Neptune?

A. These objects are called dwarf planets, and given their location, are also called trans-Neptunian objects.

What kind of visible-light and infrared telescopes on the ground are astronomers planning for the future? Why are they building them on the ground and not in space?

A. They are planning a large synoptic survey telescope, an 8.4 meter telescope. It should be fully built by 2021. They are building it on the ground, because it is too costly to put it into space, and too heavy.

List the possible interactions between Earth's crustal plates that can occur at their boundaries.

A. They can create subduction/rift zones, fault zones/mountains, and volcanoes.

1. What is the consequence of Uranus' spin axis being 98 degrees away from perpendicular to its orbital plane?

A. This essentially means that Uranus is on its side, with the poles alternately facing toward and away from the Sun. Each pole experiences long periods of light and darkness. The season alternate between half the planet being in the light and half in darkness for one season, to the planet's axis being sideways to the Sun and its rotation causing regular alternation of light and ark for the next season.

Explain how tidal forces are causing the Moon to slowly recede from Earth.

A. Tidal friction takes energy out of the earth and puts it into the moons orbit.

Compare the properties of Titan's atmosphere with those of Earth's atmosphere.

A. Titan's atmosphere is four times denser than Earth's atmosphere at the surface, even though both atmospheres are mostly nitrogen. However, 20% of Earth's atmosphere is oxygen; Titan's atmosphere is 98% nitrogen, with no free oxygen in it. Methane makes up 1.5% of the atmosphere, and it also has small amounts of various other organic gases, including ethane, carbon monoxide, and hydrogen cyanide. Both atmospheres have a weather cycle of evaporation form surface liquid, formation of clouds, and precipitation back onto the surface, but Earth's cycle is water-based, and Titan's cycle is hydrocarbon based.

In which atmospheric layer are almost all water-based clouds formed?

A. Troposphere.

1. Describe the seasons on the planet Uranus.

A. Uranus is on its side. Each pole experiences a 21-year sunlit summer and later a 21-year dark winter. For the other half of the Uranus year, the equator receives the light of the Sun and each hemisphere experiences what we would call a normal day. In all, each pole experiences 42 years of light and 42 years of dark during its 84-year long orbit

Describe two anomalous features of the rotation of Venus and what might account for them.

A. Venus has retrograde rotation about its axis, opposite to the direction of spin of most other planets; also, its rotational period is longer than any other planet's. It is in fact longer than its orbital period, so its day is longer than its year. Astronomers think Venus suffered a collision with another large body during the formation period of the solar system, changing its rotational motion in both these ways.

1. What phases would Venus show if the geocentric model were correct?

A. Venus would only show crescent phases because the illuminated side would only ever partially be visible from Earth.

1. List several ways that Venus, Earth, and Mars are similar, and several ways they are different.

A. Venus, Earth, and Mars are similar in that they consist of rock and metal for the most part; they are terrestrial planets, closer in to the Sun than the Jovian planets; all have atmospheres; all have volcanic activity on their surfaces; and all have or have had some kind of greenhouse effect change their surface temperatures. The three planets are different in many ways, among them: their size; their atmospheres, the presence or absence of liquid water on their surfaces today; the major way that their surfaces undergo large-scale changes.

Vesta is unusual as it contains what mineral on its surface? What does the presence of this material indicate?

A. Vesta's surface is partially covered with basalt. Basalt indicates volcanic activity at some point in Vesta's distant past, and thus that Vesta must be a differentiated world.

Saturn's E ring is broad and thin, and far from Saturn. It requires fresh particles to sustain itself. What is the source of new E-ring particles?

A. We now know from investigations with the Cassini mission that the new particles in the E ring are produced by the geysers on Saturn's moon Enceladus, which blasts considerable amounts of salt water, ice vapor, and crystals into space from the "tiger stripe" features on the Moon's surface.

Explain why visual observation of the gas giants is not sufficient to determine their rotation periods, and what evidence was used to deduce the correct periods.

A. What is seen visually on each of these worlds is the upper atmosphere, with winds and storms that do not necessarily move at the same rate as the planet as a whole. Radio observations revealed the existence of magnetic fields originating in the cores of these planets. The rotations periods are determined from the fact that the magnetic fields rotate at the same velocity as the interiors.

What changed in our understanding of the Moon and Moon-Earth system as a result of humans landing on the Moon's surface?

A. When landing on the surface of the moon, we were able to collect surface samples and then use radiocarbon dating techniques to determine the age of the moon. We were able to conclude that the moon is dead geologically.

Compare asteroids of the asteroid belt with Earth-approaching asteroids. What is the main difference between the two groups?

A. While compositionally similar, the asteroid belt objects have fairly stable orbits. Earth approaching asteroids have rapidly changing orbits and could potentially collide with our planet. Such a collision could produce relatively minor to catastrophic damage.

What evidence is there that Venus was volcanically active about 300-600 million years ago?

A. While small impactors burn up in Venus' thick atmosphere, larger chunks from space make craters on Venus' surface, as they do on other worlds. Do counts of larger craters on Venus can be compared to counts of such craters elsewhere in the solar system. Such crater counts on Venus show that its surface is about 300-600 million years old. Nothing older appears on the Venusian surface. The implication is that the surface consists of lava flows from that time that covered older surface features, showing only more recent ones.

Why is Mars red?

A. Winds on Mars are strong enough to blow surface dust all over the planet. This dust contains iron oxide, which gives it the rusty red color.

1. How was the rotation rate of Mercury determined?

A. With the use of radar. Radar beams were directed to Mercury and the reflected beams showed the tell-tale signs of Doppler broadening. The measured degree of this frequency broadening provided an exact value for the rotation rate of Mercury.

1. Explain how the zodiacal constellations are different from the other constellations.

A. Zodiacal constellations intersect with the elliptical. From Earth, the Sun seems to move through the zodiacal constellations, but not the others. Zodiacal constellations are the constellations which give the zodiac signs to people.

What does a planet need in order to retain an atmosphere? How does an atmosphere affect the surface of a planet and the ability of life to exist?

A. n order to determine whether a planet can retain an atmosphere, there must be gravity. Mars' atmosphere is shallow compared to Earth's atmosphere, but it is only 1/3 the size of Earth. Earth and Venus are about the same size and they both have atmospheres. A dense atmosphere insulates the surface of a planet in order to retain more heat. However, an atmosphere's composition is also important. Certain gases lead to greenhouse effect, allowing a planet to be warmer than you would expect the planet to be from its position from the sun.

Ursa Minor contains the pole star, Polaris, and the asterism known as the Little Dipper. From most locations in the Northern Hemisphere, all of the stars in Ursa Minor are circumpolar. Does that mean these stars are also above the horizon during the day? Explain.

Circumpolar stars are located above the horizon during the day and can always be seen because they always orbit the north pole star.

Explain, according to both geocentric and heliocentric cosmologies, why we see retrograde motion of the planets.

For geocentric, the planets move on epicycles that are closest to Earth on their own deferent and move in a direction opposite to that of their larger motion on the deferent, which makes them appear to move backwards. For Heliocentric, the Earth moves faster than the outer planets, so it overtakes and passes these other planets and makes them appear to go backward in their orbits.

13. Which of these properties of an object best quantifies its inertia: velocity, acceleration, volume, mass, or temperature?

Mass

Which major planet has the highest average orbital speed around the sun?

Mercury has the highest average orbital speed around the sun.

Which major planet has the highest eccentricity?

Mercury has the highest eccentricity.

Which major planet has the highest orbital period around the sun?

Neptune has the highest orbital period around the sun.

1. Which major planet has the largest semimajor axis?

Neptune has the largest semi major axis.

Describe the techniques radio astronomers use to obtain a resolution comparable to what astronomers working with visible light can achieve.

Radio Astronomers use an interferometer to sharpen their images by linking two or more radio telescopes together electronically. Astronomers combine a large number of radio dishes into an interferometer array.

Explain the origin of the magnitude designation for determining the brightness of stars. Why does it seem to go backward, with smaller numbers indicating brighter stars?

The Greek astronomer, Hipparchus, created one of the first star maps where he ranked his starts by calling the brightest "of the first magnitude" and those less bright "of the second magnitude/" The faintest he referred to as "of the sixth magnitude." This is why it seems to go backward, with smaller numbers indicated brighter stars.

What were four of Galileo's discoveries that were important to astronomy?

The discovery of Jupiter's Moons, Io, Ganymede, Europa and Callisto. The features on the surface of the Earth's moon, being craters and mountains. The discovery that the Milky Way is simply a mass of unresolved stars.

13. To calculate the momentum of an object, which properties of an object do you need to know?

The momentum of an object depends upon the mass of the object and the velocity of the object.

Give four ways to demonstrate that Earth is spherical.

The shadow that is casted on the moon is always round in shape. When ships sail away on an ocean, they appear to sink because of the curvature of Earth's surface. When orbiting satellites take photographs of the Earth, the photos show that the Earth is round on every direction. Because of different longitudes, the sun is at different altitudes in the sky.

In what ways did the work of Copernicus and Galileo differ from the views of the ancient Greeks and of their contemporaries?

They both believed that Earth spins on its axis and revolves around the Sun as one of the planets. This belief went against the belief that the Earth is motionless at the center of the solar system. Galileo thought that the best way to understand nature is through experiments, and Greeks believed pure thought was the best way.

1From where on Earth could you observe all of the stars during the course of the year? What fraction of the sky can be seen from the North Pole?

You can observe all of the stars from the equator. Only half of the sky can be observed from the North Pole.