Astronomy Chapter 1 Test
timeline of astronomy
Nicolaus Copernicus publishes De revolutionibus orbium coelestium containing his theory that Earth travels around the Sun. However, he complicates his theory by retaining Plato's perfect circular orbits of the planets. 1572 A brilliant supernova (SN 1572 - thought, at the time, to be a comet) is observed by Tycho Brahe, who proves that it is traveling beyond Earth's atmosphere and therefore provides the first evidence that the heavens can change. 1608 Dutch eyeglass maker Hans Lippershey tries to patent a refracting telescope (the first historical record of one). The invention spreads rapidly across Europe, as scientists make their own instruments. Their discoveries begin a revolution in astronomy. 1609 Johannes Kepler publishes his New Astronomy. In this and later works, he announces his three laws of planetary motion, replacing the circular orbits of Plato with elliptical ones. Almanacs based on his laws prove to be highly accurate. 1610 Galileo Galilei publishes Sidereus Nuncius describing the findings of his observations with the telescope he built. These include spots on the Sun, craters on the Moon, and four satellites of Jupiter. Proving that not everything orbits Earth, he promotes the Copernican view of a Sun-centered universe. 1655 As the power and the quality of the telescopes increase, Christiaan Huygens studies Saturn and discovers its largest satellite, Titan. He also explains Saturn's appearance, suggesting the planet is surrounded by a thin ring. 1663 Scottish astronomer James Gregory describes his "gregorian" reflecting telescope, using parabolic mirrors instead of lenses to reduce chromatic aberration and spherical aberration, but is unable to build one. 1668 Isaac Newton builds the first reflecting telescope, his Newtonian telescope. 1687 Isaac Newton publishes his first copy of the book Philosophiae Naturalis Principia Mathematica, establishing the theory of gravitation and laws of motion. The Principia explains Kepler's laws of planetary motion and allows astronomers to understand the forces acting between the Sun, the planets, and their moons. 1705 Edmond Halley calculates that the comets recorded at 76-year intervals from 1456 to 1682 are one and the same. He predicts that the comet will return again in 1758. When it reappears as expected, the comet is named in his honor. 1750 French astronomer Nicolas de Lacaille sails to southern oceans and begins work compiling a catalog of more than 10000 stars in the southern sky. Although Halley and others have observed from the Southern Hemisphere before, Lacaille's star catalog is the first comprehensive one of the southern sky. 1781 Amateur astronomer William Herschel discovers the planet Uranus, although he at first mistakes it for a comet. Uranus is the first planet to be discovered beyond Saturn, which was thought to be the most distant planet in ancient times. 1784 Charles Messier publishes his catalog of star clusters and nebulas. Messier draws up the list to prevent these objects from being identified as comets. However, it soon becomes a standard reference for the study of star clusters and nebulars and is still in use today. 1800 William Herschel splits sunlight through a prism and with a thermometer, measures the energy given out by different colours. He notices a sudden increase in energy beyond the red end of the spectrum, discovering invisible infrared and laying the foundations of spectroscopy. 1801 Italian astronomer Giuseppe Piazzi discovers what appears to be a new planet orbiting between Mars and Jupiter, and names it Ceres. William Herschel proves it is a very small object, calculating it to be only 320 km in diameter, and not a planet. He proposes the name asteroid, and soon other similar bodies are being found. We now know that Ceres is 932 km in diameter, and is now considered to be a dwarf planet.
3. What is a planet, a solar system, the Milky Way, a galaxy, the universe?
Our Solar System consists of our star, the Sun, and its orbiting planets (including Earth), along with numerous moons, asteroids, comet material, rocks, and dust. Our Sun is just one star among the hundreds of billions of stars in our Milky Way Galaxy.
How did Tycho Brahe and Johannes Kepler contribute to our understanding of how planets move around the Sun?
Tycho died the next year, Kepler stole the data, and worked with it for nine years. He reluctantly concluded that his geometric scheme was wrong. In its place, he found his three laws of planetary motion: I The planets move in elliptical orbits with the sun at a focus.
What is the approximate latitude of the observer in the diagram below?
50° N
A certain comet has a parallax 1/60 as large as the Moon's. How far away is it
60 the distance to the Moon
Declination
A measure of how far north or south an object is from the celestial equator
Why do we have seasons?
Earth has seasons because our planet's axis of rotation is tilted at an angle of 23.5 degrees relative to our orbital plane - the plane of Earth's orbit around the sun.
Celestial Meridian
The celestial meridian is the line on the celestial sphere joining the observer's zenith (i.e. the point directly overhead) with the north and south celestial poles.
circular velocity escape velocity
The orbital velocity needed to keep an object moving in a circular orbit. in physics, escape velocity is the minimum speed needed for a free object to escape from the gravitational influence of a massive body.
True or False: A space probe can be launched into an orbit around the Sun with an average distance from the Sun of 4 AU and an orbital period of 8 years? Use Kepler's third law (p^2=a^3)
True
universal law of gravitation
Newton's law of universal gravitation states that every particle attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Newton's universal law of gravitation says that the force acting upon (and therefore the acceleration of) an object toward Earth should be inversely proportional to the square of its distance from the center of Earth.
types of energy
Kinetic energy is the energy in moving objects or mass. Examples include mechanical energy, electrical energy etc. Potential energy is any form of energy that has stored potential that can be put to future use.
Mass vs. Weight
Mass is a measurement of the amount of matter something contains, while Weight is the measurement of the pull of gravity on an object. Mass is measured by using a balance comparing a known amount of matter to an unknown amount of matter. Weight is measured on a scale
The ___________ of an object is a measure of the amount of matter it contains. On the other hand _________ is a measure of the gravitational force on an object.
Mass, weight
Why do all objects fall at the same rate?
Newton's equations show that the acceleration of gravity is independent of the mass of a falling object, so all objects fall at the same rate.
An apparent westward motion of a planet in the sky compared to the background stars (as viewed from the Earth) when observed on successive nights is referred to as
retrograde motion
Altitude
the apparent height of a celestial object above the horizon, measured as an angle.
Summer/Winter Solstice
the longest and shortest days of the year
Can you state and explain Kepler's three laws of planetary motion?
(1) All planets move about the Sun in elliptical orbits, having the Sun as one of the foci. (2) A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time. (3) The squares of the sidereal periods (of revolution) of the planets are directly proportional to the cubes of their mean distances from the Sun.
What causes eclipses?
An eclipse occurs when the light from one celestial body is obscured by another as viewed from a given location. On Earth, eclipses are caused by the respective positions of the Sun and the Moon. There are two main types of eclipse. A solar eclipse (eclipse of the Sun) or a lunar eclipse (eclipse of the Moon).
What is the explanation for the Moon's phases?
As the Sun sets, the Moon rises with the side that faces Earth fully exposed to sunlight (5).The Moon has phases because it orbits Earth, which causes the portion we see illuminated to change. The Moon takes 27.3 days to orbit Earth, but the lunar phase cycle (from new Moon to new Moon) is 29.5 days.
How do the various celestial objects appear to move across the sky as the Earth rotates?
Because Earth rotates on its axis from west to east, the Moon and the Sun (and all other celestial objects) appear to move from east to west across the sky. Viewed from above, however, the Moon orbits Earth in the same direction as our planet rotates. So, the Moon actually moves from west to east through our sky, albeit so slowly that we almost never notice it.
How did Galileo contribute to our understanding of planetary motion?
Galileo first discovered that the Moon had mountains just like Earth. He also discovered 4 of Jupiter's moons. Using his telescope, Galileo made many observations of our Solar System. He came to believe that the idea that the Sun and other planets orbited around the Earth was not correct.
What are Newton's three laws?
I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. II. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector. III. For every action there is an equal and opposite reaction.
how do Right Ascension and Declination relate to latitude and longitude?
Imagine the lines of latitude and longitude ballooning outward from the Earth and printing themselves on the inside of the sky sphere, as shown at right. They are now called, respectively, declination and right ascension.
On what is our modern calendar based? What is a leap year and how are they determined in our current calendar system?
In 1582, when Pope Gregory XIII introduced his Gregorian calendar, Europe adhered to the Julian calendar, first implemented by Julius Caesar in 46 B.C. Since the Roman emperor's system miscalculated the length of the solar year by 11 minutes, the calendar had since fallen out of sync with the seasons(Julian Calendar) Leap year. ... A leap year (also known as an intercalary year or bissextile year) is a calendar year containing one additional day (or, in the case of lunisolar calendars, a month) added to keep the calendar year synchronized with the astronomical or seasonal year.
Horizon
In astronomy, boundary where the sky seems to meet the ground or sea. (In astronomy it is defined as the intersection on the celestial sphere of a plane perpendicular to a plumb line.)
What is Newton's law of inertia?
Inertia is the tendency of an object to remain at rest or in motion. Newton's First Law of Motion states that an object will remain at rest or move at a constant speed in a straight line unless it is acted on by an unbalanced force.
Tycho Brahe's greatest contribution to astronomy was
his 20 years of careful observations of the planets.
Planetary period
how long a planet takes to revolve around the sun
A third quarter moon is visible
in the southern sky at sunrise.
Motion
In physics, motion is the change in position of an object with respect to its surroundings in a given interval of time.
A solar eclipse that occurs when the moon's umbra does not reach Earth's surface is called
an annular solar eclipse.
Newton concluded that some force had to act on the moon because
a force is needed to pull the moon away from straight-line motion.
Why do objects move at constant velocity if no force acts on them? What keeps a planet rotating and orbiting the Sun?
Objects continue at constant velocity because of conservation if momentum. Newton realized that the reason the planets orbit the Sun is related to why objects fall to Earth when we drop them. The Sun's gravity pulls on the planets, just as Earth's gravity pulls down anything that is not held up by some other force and keeps you and me on the ground.
What are the Sun's celestial coordinates at the equinoxes and solstices?
On June 21, the Sun reaches its most northerly extent (as seen in the right-hand "Earth" in the illustration), at a declination of 23.5 degrees north at the Summer Solstice, to begin northern- hemisphere summer (southern hemisphere winter). It then rises as far north of east and sets as far north of west as possible.
How does the length of daylight depend on our latitude?
Our amount of daylight hours depends on our latitude and how Earth orbits the sun. Earth's axis of rotation is tilted from its orbital plane and always points in the same direction — toward the North Star. ... Similarly, the sun's energy spreads out over differing geographic areas when it reaches Earth's surface
Explain what determines the strength of gravity
Planets have measurable properties, such as size, mass, density, and composition. A planet's size and mass determines its gravitational pull. A planet's mass and size determines how strong its gravitational pull is. The strength of the gravitational force between two objects depends on two factors, mass and distance. the force of gravity the masses exert on each other. If one of the masses is doubled, the force of gravity between the objects is doubled.
How much of the sky can you see from a given latitude?
Putting aside the curvature of the Earth and refraction and terrain and so forth, we can say that at any moment, half the sky is available to view. Over the course of 24 hours, the percentage of the entire celestial sphere that's available to view varies from 50% (at the poles) to 100% (at the equator)
Compare the orbital characteristics of the planets and other objects in the solar system
Recall that the path of an object under the influence of gravity through space is called its orbit, whether that object is a spacecraft, planet, star, or galaxy. An orbit, once determined, allows the future positions of the object to be calculated. Two points in any orbit in our solar system have been given special names. The place where the planet is closest to the Sun (helios in Greek) and moves the fastest is called the perihelion of its orbit, and the place where it is farthest away and moves the most slowly is the aphelion. For the Moon or a satellite orbiting Earth (gee in Greek), the corresponding terms are perigee and apogee. (In this book, we use the word moon for a natural object that goes around a planet and the word satellite to mean a human-made object that revolves around a planet.) According to Kepler's laws, Mercury must have the shortest orbital period (88 Earth-days); thus, it has the highest orbital speed, averaging 48 kilometers per second. At the opposite extreme, Neptune has a period of 165 years and an average orbital speed of just 5 kilometers per second. All the planets have orbits of rather low eccentricity. The most eccentric orbit is that of Mercury (0.21); the rest have eccentricities smaller than 0.1. It is fortunate that among the rest, Mars has an eccentricity greater than that of many of the other planets. Otherwise the pre-telescopic observations of Brahe would not have been sufficient for Kepler to deduce that its orbit had the shape of an ellipse rather than a circle. The planetary orbits are also confined close to a common plane, which is near the plane of Earth's orbit (called the ecliptic). The strange orbit of the dwarf planet Pluto is inclined about 17° to the ecliptic, and that of the dwarf planet Eris (orbiting even farther away from the Sun than Pluto) by 44°, but all the major planets lie within 10° of the common plane of the solar system. orbit all the planets except Mercury and Venus. In addition, there are two classes of smaller objects in heliocentric orbits: asteroids and comets. Both asteroids and comets are believed to be small chunks of material left over from the formation process of the solar system. In general, asteroids have orbits with smaller semimajor axes than do comets (Figure 1). The majority of them lie between 2.2 and 3.3 AU, in the region known as the asteroid belt (see Comets and Asteroids: Debris of the Solar System). As you can see in Table 1, the asteroid belt (represented by its largest member, Ceres) is in the middle of a gap between the orbits of Mars and Jupiter. It is because these two planets are so far apart that stable orbits of small bodies can exist in the region between them.
Right ascension
Right ascension is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the point above the earth in question.
What is the nature of science? Define hypothesis and theory? How does the process of science work?
Science consists of a body of knowledge and the process by which that knowledge is developed. The core of the process of science is generating testable explanations, and the methods and approaches to generating knowledge are shared publicly so that they can be evaluated by the community of scientists. A supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation.
Standard Time& Time Zones
Standard time is the synchronization of clocks within a geographical area or region to a single time standard, rather than using solar time or a locally chosen meridian to establish a local mean time standard. Time zones give specific areas on the earth a time of day that is earlier or later than the neighboring time zones. ... Greenwich Mean Time is now called UTC (Coordinated Universal Time). UTC is the time standard of the world. All other parts of the world are offset (plus or minus) according to their longitude.
How do we measure the distance to the Moon
Start with the few knowns. We know, as did the Ancient Greeks, that the Moon travels around the Earth at a constant speed - about 29 days per revolution. The diameter of the Earth is also known to be about 12,875 km or 8,000 miles.By tracking the movement of the Earth's shadow across the Moon, Greek astronomers found that the Earth's shadow was roughly 2.5 times the apparent size of the Moon and lasted roughly three hours from the first to last signs of the shadow. From these measurements, it was simple geometry that allowed Aristarchus (c. 270 BC) to determined that the Moon was round 60 Earth radii away (about 386,243 km or 240,000 miles). This is quite close to the currently accepted figure of 60.3 radii.
An observer in the Northern Hemisphere takes a time exposure photograph of the night sky. If the illustration to the right depicts the photograph taken by the observer, which direction was the camera pointing?
Straight north
How did the ancient astronomers describe the universe?
The Ptolemaic Model. By the time of Ptolemy Greek astronomers had proposed adding circles on the circular orbits of the wandering stars (the planets, the moon and the sun) to explain their motion. ... With the eccentric circle the center of the planets orbit would not be Earth but would instead be some other
How did the Greeks explain planetary motion?
The Ptolemaic Model. By the time of Ptolemy Greek astronomers had proposed adding circles on the circular orbits of the wandering stars (the planets, the moon and the sun) to explain their motion. These circles on circles are called epicycles.
The sun is on the celestial equator at the times of the
autumnal equinox and the vernal equinox.
Do you know the differences between the Ptolemaic, Copernican, and Tychonic theories of planetary motion?
The Ptolemaic Model. By the time of Ptolemy Greek astronomers had proposed adding circles on the circular orbits of the wandering stars (the planets, the moon and the sun) to explain their motion. These circles on circles are called epicycles. Copernican heliocentrism is the name given to the astronomical model developed by Nicolaus Copernicus and published in 1543. It positioned the Sun near the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths modified by epicycles and at uniform speeds. Brahe proposed a model of the solar system to explain Galileo's observation that Venus has phases without making it necessary for Earth to be moving. His model had all the planets (except Earth) orbiting around the Sun, but then the Sun orbited around the Earth.
What are the special latitudes - Arctic and Antarctic circles, Tropic of Cancer, and Tropic of Capricorn.
The Tropic of Cancer is the circle marking the latitude 23.5 degrees north, where the sun is directly overhead at noon on June 21, the beginning of summer in the northern hemisphere. The Tropic of Capricorn is the circle marking the latitude 23.5 degrees south where the sun is directly overhead at noon on December 21, the beginning of winter in the northern hemisphere. When the lines were named 2000 years ago, the Sun was in the constellation of Capricorn during the winter solstice and Cancer during the summer solstice (hence the names). Now due to the precession of the equinoxes the Sun is no longer in these constellations during these times, but the names remain. The equator is the circle where the Sun is directly overhead at noon on the equinoxes. The Arctic and Antarctic Circles are located at ±66.5 degrees latitude. Note that 66.5 + 23.5 equals 90 degrees. This means that on December 21, when the Sun is directly over the Tropic of Capricorn at noon, it will not be visible from the Arctic Circle. So above the Arctic Circle, there is a period during the winter when the sun remains below the horizon. The same is true of the Antarctic Circle during Southern Hemisphere winter. On June 21st, when the sun is directly over the Tropic of Cancer at noon, it is not visible from below the Antarctic Circle.
16. Parallaxes of stars were not observed by ancient astronomers. How can this fact be reconciled with the heliocentric hypothesis?
The parallax is the shift of an object in the sky when seen from two separated vantage points. It depends inversely on the distance to the object. Stars are so far away, compared to the size of Earth's orbit, that their parallax angle could not be measured to the necessary precision attainable at the time.
Why do the polar regions experience a "'midnight sun" in summer?
The polar regions are called the "lands of the midnight sun" because in the summer, the sun never sets. ... As the Earth orbits around the Sun, that tilt makes the North Pole face towards the sun in summer (keeping it in sunlight even as the Earth spins) and away from it in winter (keeping it dark).
What is the Moon's rotation period? What is its period of revolution?
The sidereal month is the time it takes to make one complete orbit around Earth with respect to the fixed stars. It is about 27.32 days. The synodic month is the time it takes the Moon to reach the same visual phase. This varies notably throughout the year, but averages around 29.53 days.
Why are there more hours of daylight in summer than in winter?
Tilted Earth at summer, spring, fall, and winter positions around the Sun, clearly showing polar regions in daylight and dark at winter/summer positions. ... Other planets also experience these changes in day and night length because they too are tilted on their axes. Each planet's axis is tilted at a different angle.
How do gravity and energy allow us to understand orbits?
Total orbital energy (gravitational + kinetic) stays constant if there is no external force. Orbits cannot change spontaneously. Change in total energy is needed to change orbit Add enough energy (escape velocity) and object leaves.
Which of the following people did not accept a heliocentric model for the universe?
Tycho
What is our place in the universe?
Well, Earth is located in the universe in the Virgo Supercluster of galaxies. A supercluster is a group of galaxies held together by gravity. Within this supercluster we are in a smaller group of galaxies called the Local Group. Earth is in the second largest galaxy of the Local Group - a galaxy called the Milky Way.
Given the orbital period of a planet in years and its distance from the Sun in astronomical units, can you tell whether this planet could be a member of our Solar System?
Yes
Given the orbital period of a planet in years or its distance from the Sun in astronomical units, can you calculate the other?
Yes p^2=a^3
The ________ is the point on the celestial sphere directly above any observer.
Zenith
Define mass, volume, and density and how they differ
a coherent, typically large body of matter with no definite shape. the amount of space that a substance or object occupies, or that is enclosed within a container, especially when great. degree of consistency measured by the quantity of mass per unit volume. Mass and volume are two units used to measure objects. Mass is the amount of matter an object contains, while volume is how much space it takes up orbit all the planets except Mercury and Venus. In addition, there are two classes of smaller objects in heliocentric orbits: asteroids and comets. Both asteroids and comets are believed to be small chunks of material left over from the formation process of the solar system.
Ecliptic
a great circle on the celestial sphere representing the sun's apparent path during the year, so called because lunar and solar eclipses can occur only when the moon crosses it.
synodic month(lunar month)
a month measured between successive new moons (roughly 29 1/2 days). (in general use) a period of four weeks.
Kepler's second law implies that
a planet should move at its greatest speed when it is closest to the sun.
Can you define the Astronomical Unit? A Light-Year?
a unit of measurement equal to 149.6 million kilometers, the mean distance from the center of the earth to the center of the sun. a unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 1012 km (nearly 6 trillion miles).
Acceleration
acceleration is the rate of change of velocity of an object with respect to time.
sidereal year &tropical year
the orbital period of the earth around the sun, taking the stars as a reference frame, being 20 minutes longer than the tropical year because of precession A tropical year is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice
Momentum
the quantity of motion of a moving body, measured as a product of its mass and velocity.
angular momentum
the quantity of rotation of a body, which is the product of its moment of inertia and its angular velocity.
velocity
the speed of an object in a particular direction
Astrology
the study of the movements and relative positions of celestial bodies interpreted as having an influence on human affairs and the natural world. Astronomy is the study of the universe and its contents outside of Earth's atmosphere.
Explain how an object can be put into orbit around Earth or escape from orbit.
the term orbit refers to the path of an object whose motion through space is controlled by the gravitational pull of another object. The Moon orbits the Earth, and the Earth, in turn, orbits the Sun. Spacecraft can also orbit the Earth. If an object gains enough speed to attain escape velocity, its orbit becomes an open curve called a parabola. If it continues moving faster than escape velocity, its orbit is a flattened curve called a hyperbola. A spacecraft that leaves its orbit around the Earth on a journey toward another planet travels in a hyperbolic orbit These forces of inertia and gravity have to be perfectly balanced for an orbit to happen. If the forward movement (inertia) of one object is too strong, the object will speed past the other one and not enter orbit. If inertia or momentum is much weaker than the pull of gravity, the object will be pulled into the other one completely and crash.
Solar Day
the time between successive meridian transits of the sun at a particular place.
Sidereal day
the time between two consecutive transits of the First Point of Aries. It represents the time taken by the earth to rotate on its axis relative to the stars, and is almost four minutes shorter than the solar day because of the earth's orbital motion.
sidereal month
the time it takes the moon to orbit once around the earth with respect to the stars (approximately 27 1/4 days).
Apparent solar time mean solar time
time as calculated by the motion of the apparent (true) sun. The time indicated by a sundial corresponds to apparent solar time. time as calculated by the motion of the mean sun. The time shown by an ordinary clock corresponds to mean solar time.
Vernal and autumnal equinoxes
vernal-the equinox in spring, on about March 20 in the northern hemisphere and September 22 in the southern hemisphere. autumnal-the equinox in autumn, on about September 22 in the northern hemisphere and March 20 in the southern hemisphere.
Given the period (in years) and the distance (in AU) of a satellite revolving around its planet, or of one member of a double star system revolving around the other, can you find the total mass of the two bodies (in solar masses)?
yes p^2=a^3
The two members of a double star system are seen to be 2 AU apart. Their orbital period is 4 years. Remembering that m1 + m2 = a3/P2, the total mass of the system is
½ solar mass