Astronomy 101 Midterm Exam
What were the major observations made by Galileo that were used to advance astronomy of the time?
1609 he built his first telescope and began making observations. The following year he published his first results, where he described the highlands and "seas" of the Moon, four of Jupiter's largest moons, and many newly discovered stars. He also discovered the phases of Venus and sunspots, thereby confirming that the Sun rotates, and that the planets orbit around the Sun, not around the Earth. He thought that most planetary orbits are circular in shape, when in fact they are elliptical, as shown by Johannes Kepler.
Suppose you have a 100-watt light bulb that you leave turned on for one minute. How much energy does it use?
6,000 joules.
You observe a full moon rising at sunset. What will you see at midnight?
A full moon high in the sky.
Which of the following correctly describes the meridian in your local sky?
A half-circle extending from your horizon due north, through your zenith, to your horizon due south.
What is true about Scientific Theory?
A scientific theory cannot be accepted until it has been proven true beyond all doubt.
Which of the following scenarios involves energy that we would typically calculate with Einstein's formula E=mc2?
A small amount of the hydrogen in of a nuclear bomb becomes energy as fusion converts the hydrogen to helium.
Suppose the planet Uranus were much brighter in the sky, so that it was as easily visible to the naked eye as Jupiter or Saturn. What would most likely be true in that case?
A week would have eight days instead of seven.
Eratosthenes
Accurately estimated the size of Earth in about 240 B.C. He did it by comparing the altitude of the Sun on the summer solstice.
Libration
Allows us to see a total of about 59% of the Moon's surface over the course of a month, even though we see only 50% of the Moon at any single time.
Constellation
An easily recognized group of stars that appear to be located close together in the sky and that form a picture if lines connecting them are imagined.
Venus has a higher average surface temperature than Mercury. Why?
Because its surface is heated by an extreme greenhouse effect.
In what way is Venus most similar to Earth?
Both planets are nearly the same size.
Explain how we describe a location on Earth's surface.
By stating its latitude and longitude.
Tropic of Capricorn
Circle of latitude that contains the direct overhead point on the December solstice. Southernmost latitude where the Sun can be directly overhead.
Tropic of Cancer
Circle of latitude that contains the direct overhead point on the June solstice. Northernmost latitude where the Sun can be directly overhead.
Solar System
Collection of eight planets and their moons in orbit around the sun, together with smaller bodies in the form of asteroids, meteoroids, and comets.
Copernicus
Discovered simple geometric relationships that allowed him to calculate each planet's orbital period around the Sun and its relative distance from the Sun in terms of the Earth-Sun distance. The model's success in providing a geometric layout for the solar system convinced him that the Sun-centered idea must be correct.
Which of the following represents a case in which you are not accelerating?
Driving in a straight line at 60 miles per hour.
What facts can be used with Newton's version of Kepler's third law to determine the mass of the Sun?
Earth is 150 million km from the Sun and orbits the Sun in one year.
For most of history, the lack of observable stellar parallax was interpreted to mean that _________.
Earth is stationary at the center of the universe
Explain an eclipse of the moon and sun occur.
Eclipses occur only when the Moon is at both a node (passing through the pond surface) and a phase of either new moon (for a solar eclipse) or full moon (for a lunar eclipse) a. The phase of the Moon must be full (for a lunar eclipse) or new (for a solar eclipse). b. The new or full moon must occur during one of the periods when the nodes of the Moon's orbit are aligned with the Sun and Earth.
True or False: An observer on Earth can see the entire surface of the moon over 365 day period.
FALSE. The fact that we always see the same face of the Moon means that the Moon must rotate once in the same amount of time it takes to orbit Earth once.
How are galaxies important to our existence?
Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist.
Why are radio telescopes generally much larger in size than telescopes designed to collect visible light?
Getting an image of the same angular resolution requires a much larger telescope for radio waves than for visible light.
Newton
He quantified the laws of motion and gravity, conducted crucial experiments regarding the nature of light, built the first reflecting telescopes, and invented the mathematics of calculus.
Ptolemy
His greatest accomplishment was to adapt and synthesize earlier ideas into a single system that agreed quite well with the astronomical observations available at the time. In the end, he created and published a model that could correctly forecast future planetary positions to within a few degrees of arc, which is about the angular size of your hand held at arm's length against the sky. "the greatest compilation."
What is not an advantage of the Hubble Space Telescope over ground-based telescopes?
It is closer to the stars.
Suppose you are in an elevator that is traveling upward at constant speed. How does your weight compare to your normal weight on the ground?
It is the same.
What is not true of the recently-discovered object Eris?
It is thought to be the first example of a new class of object.
How much time is takes to go between each phase?
It takes 29.5 days for the moon to rotate around the Earth once. Each phase lasts about 3.69 days
Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. What can you infer from its red color?
Its surface is cooler than the surface of the Sun.
Can you apply an understanding of Kepler's Laws to astronomical principles stated in your textbook and illustrated in the Mastering Astronomy assignments?
Kepler showed that an elliptical orbit did match the data for Mars!
Kepler
Kepler's key discovery was that planetary orbits are not circles but instead are a special type of oval called an ellipse. Once he abandoned perfect circles in favor of ellipses, Kepler soon came up with a model that could predict planetary positions with far greater accuracy than Ptolemy's Earth-centered model. Kepler's model withstood the test of time and became accepted not only as a model of nature but also as a deep, underlying truth about planetary motion.
Observatory X consists of a single 50-meter telescope. Observatory Y is an interferometer consisting of five 10-meter telescopes, spread out over a region 100 meters across.
Observatory X can detect dimmer stars and Observatory Y reveals more detail in images.
Last Quarter
One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.
First Quarter
One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
Relative to the age of the universe, how old is our solar system? How old is the Earth?
Our solar system & the Earth are about 4 ½ billion years old.
Which of the following is not consistent with the major hallmarks of science?
Science consists of proven theories that are understood to be true explanations of reality.
If you could count stars at a rate of about one per second, how long would it take to count all the stars in the Milky Way Galaxy?
Several thousand years.
Which of the following is not a major reason why astronomers would like an observatory on the far side of the Moon?
Telescopes on the Moon could see objects in all parts of the sky equally well, whereas telescopes on Earth can see only portions of the sky that depend on their latitude.
Why do astronomers infer that the universe is expanding?
Telescopic observations of distant galaxies show that the entire universe is expanding, meaning that average distances between galaxies are increasing with time. The universe as a whole has continued to expand ever since the Big Bang, but on smaller size scales the force of gravity has drawn matter together.
How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?
The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.
When did humans learn that the Earth is not the center of the universe and what evidence supported this revelation of thought?
The Copernican revolution, which showed us that Earth is not the center of the universe but rather just one planet orbiting the Sun.
Which of the following telescopes would benefit most from adaptive optics?
The Keck I telescope on Mauna Kea.
Waning Gibbous
The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.
Waxing Gibbous
The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
Waning Crescent
The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.
Waxing Crescent
The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
Which of the following best explains why the Moon's orbital period and rotation period are the same?
The Moon once rotated faster, but tidal friction slowed the rotation period until it matched the orbital period.
Full Moon
The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.
New Moon
The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse).
Why are astronauts weightless in the Space Station?
The Space Station is constantly in free-fall around the Earth.
Suppose you kick a soccer ball straight up to a height of 10 meters. Which of the following is true about the gravitational potential energy of the ball during its flight?
The ball's gravitational potential energy is greatest at the instant when the ball is at its highest point.
Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?
The cloud is cool and lies between you and a hot star.
Local Group
The group of more than 20 galaxies to which the Milky Way Galaxy belongs.
Kepler's Second law
The line joining the Sun and a planet sweeps through equal areas in an equal amount of time. A planet is moving faster near perihelion and slower near aphelion. The orbits of most planets are almost circular, with eccentricities near 0. In this case, the changes in their speed are not too large over the course of their orbit.
Why do we have phases of the moon?
The moon has phases with distinct appearances because it is constantly rotating around the Earth and being illuminated by the sun at different angles.
What is not true about motion in the universe?
The mysterious dark matter is the fastest-moving material in the universe.
Suppose you have two small photographs of the Moon. Although both look the same at small size, when you blow them up to poster size one of them still looks sharp while the other one becomes fuzzy (grainy) looking. Which of the following statements is true?
The one that still looks sharp at large size has better (smaller) angular resolution than the one that looks fuzzy.
Which of the following best describes why we say that light is an electromagnetic wave?
The passage of a light wave can cause electrically charged particles to move up and down.
The angular separation of two stars is 0.1 arcseconds and you photograph them with a telescope that has an angular resolution of 1 arcsecond. What will you see?
The photo will seem to show only one star rather than two.
Imagine another solar system, with a star more massive than the Sun. Suppose a planet with the same mass as Earth orbits at a distance of 1 AU from the star. How would the planet's year (orbital period) compare to Earth's year?
The planet's year would be shorter than Earth's.
How did the Ptolemaic model explain the apparent retrograde motion of the planets?
The planets moved along small circles that moved on larger circles around the Earth.
Kepler's First Law
The planets orbit the Sun in ellipses with the Sun at one focus (the other focus is empty). The distance between a planet and the Sun changes as the planet moves along its orbit. The Sun is offset from the center of the planet's orbit.
Aphelion
The point in the orbit of a planet, asteroid, or comet at which it is furthest from the sun.
Suppose you are listening to a radio station that broadcasts at a frequency of 97 Mhz (megahertz).
The radio waves from the radio station are causing electrons in your radio's antenna to move up and down 97 million times each second.
Kepler's Third Law
The square of the period of a planet's orbit (P) is directly proportional to the cube of the semimajor axis (a) of its elliptical path. P2∝a3
Why are telescopes built on mountaintops that are relatively far from cities and are in regions with dry climates?
The thin air on mountaintops makes the glass in telescope mirrors less susceptible to warping.
What is not true when studying a spectrum from a star.
The total amount of light in the spectrum tells us the star's radius.
The planet Neptune is blue in color. How would you expect the spectrum of visible light from Neptune to be different from the visible-light spectrum of the Sun?
The two spectra would have similar shapes, except Neptune's spectrum would be missing a big chunk of the red light that is present in the Sun's spectrum.
Why do the ancient Greeks get a lot of attention for their contributions to science?
They were the first people known to try to explain nature with models based on reason and mathematics, without resort to the supernatural
What best describes the origin of ocean tides on Earth?
Tides are caused by the difference in the force of gravity exerted by the Moon across the sphere of the Earth.
Equinox
Two times a year, when the sun crosses the celestial equator, when day & night are of equal length. (Vernal & Autumnal)
Solstice
Two times a year, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days. (Summer & Winter)
Brahe
Tycho's fame grew after he observed what he called a nova, meaning "new star," in 1572. By measuring its parallax and comparing it to the parallax of the Moon, he proved that the nova was much farther away than the Moon. (Today, we know that Tycho saw a supernova—the explosion of a distant star.
Which planet has the most extreme seasons?
Uranus
The Andromeda Galaxy is faintly visible to the naked eye in the constellation Andromeda. Suppose instead it were located in the same direction in space as the center of the Milky Way Galaxy (but still at its current distance). How would it appear to the eye in that case?
We could not see it at all.
Which of the following have the greatest frequency of occurrence: lunar eclipse or solar eclipse?
You see lunar eclipses more often than solar eclipses, even though both types occur about equally often.
Which of the following has your "cosmic address" in the correct order?
You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe.
Super Cluster
a cluster of galaxies which themselves occur as clusters.
Longitude
angular distance east or west on the earth's surface, measured by the angle contained between the meridian of a particular place and some prime meridian (Greenwich, England) and expressed either in degrees or by some corresponding difference in time.
When we look at an object that is 1,000 light-years away we see it _________.
as it was 1,000 years ago
When traveling north from the United States into Canada, you'll see the North Star (Polaris) getting _________.
higher in the sky
"We are star stuff"
in the sense that the elements of our bodies were produced by nuclear fusion inside stars.
Astronomy
is the science which investigates all matter-energy in the universe. It is based upon the scientific method, which states that theories must be grounded upon observational facts and endure repeated testing as new observational information is acquired.
Suppose you use the Southern Cross to determine that the south celestial pole appears 40 degrees above your horizon. Then you must be located at _________.
latitude 40 degrees south
A net force acting on an object will always cause a change in the object's _________.
momentum
Zenith point
on the celestial sphere directly above an observer on the Earth.
Declination
one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle.
Mars has two moons that are most similar in character to:
small asteroids
Galaxy
system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
Latitude
the angle between the plane of the earth's equator and the plumb line (direction of gravity) at a given point on the earth's surface
Ecliptic
the apparent path of the Sun on the celestial sphere
Zodiac
the constellations that the Sun passes through in its apparent path across Earth's sky.
Meridian
the great circle passing through the celestial poles, the zenith, and the nadir of a particular location.
Perihelion
the point in the orbit of a planet, asteroid, or comet at which it is closest to the sun
Cosmos
the universe seen as a well-ordered whole.
The stars in our sky twinkle in brightness and color because of ______.
turbulence in the Earth's atmosphere
Gamma rays have a very small ______.
wavelength
Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case ________.
we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2
