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The celestial sphere - An imaginary sphere surrounding Earth to which the stars are attached. Ancient astronomers believed the sky was a great sphere surrounding Earth with the stars stuck on the inside like thumbtacks. Modern astronomers know that the stars are scattered through space at differ...

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  • August 28, 2024
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ASTR 102 exam 2024| Questions with
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The celestial sphere - ✔✔An imaginary sphere surrounding Earth to which the stars are attached.
Ancient astronomers believed the sky was a great sphere surrounding Earth with the stars stuck on
the inside like thumbtacks. Modern astronomers know that the stars are scattered through space at
different distances, but it is still convenient to think of the sky as a great starry sphere enclosing Earth.



celestial sphere - ✔✔the eastward rotation of Earth causes the Sun, Moon, planets, and stars to
move westward in the sky as if the celestial sphere were rotating westward around Earth.is a scientific
model of the sky, to which the stars appear to be attached. Because Earth rotates eastward, the
celestial sphere appears to rotate westward on its axis.



the celestial sphere - ✔✔Stars seem to be on the inner surface of a sphere

surrounding the Earth They aren't, but can use two

dimensional spherical coordinates (similar to

latitude and longitude) to locate sky objects



precession. - ✔✔In addition to causing the obvious daily motion of the sky, Earth's rotation is
connected with a very slow celestial motion that can be detected only over centuries rotation of Earth's
axis itself; makes

one complete circle in about 26,000 years



Hipparchus - ✔✔More than 2000 years ago, Hipparchus compared positions of some stars with
their positions recorded nearly two centuries earlier and realized that the celestial poles and equator
were slowly moving across the sky. (Precession)

,seasons - ✔✔Rather, the seasons arise because Earth's axis is not perpendicular to its
orbit.Because Earth's axis of rotation is inclined 23.4 degrees, the Sun moves into the northern sky in
the spring and into the southern sky in the fall.



Planets - ✔✔The planets of our Solar System produce no visible light of their own; they are
visible only by reflected sunlight. appear to move generally eastward along the ecliptic



Planets - ✔✔All of the planets of our Solar System, including Earth, move in nearly circular orbits
around the Sun. If you were looking down on the Solar System from the north celestial pole, you
would see the planets moving in the same counterclockwise direction around their orbits, with the
planets farthest from the Sun moving the slowest.



Flux - ✔✔is a measure of light energy striking one square meter per second. The magnitude of a
star is related directly to the flux of light received on Earth from that star.



The rotation of Earth on its axis - ✔✔produces the daily cycle of day and night, and the revolution of
Earth around the Sun produces the annual cycle of the seasons.



Because Earth orbits the Sun - ✔✔the Sun appears to move eastward along the ecliptic because
the ecliptic is tipped 23.4 degrees to the celestial equator



The seasons are caused by - ✔✔the angle of sunlight and how long the Sun is in the sky at
different times of year.



Why are most of the constellations that were invented in modern times composed of faint stars or
located in the southern sky? - ✔✔Faint stars or stars in the southern sky were not visible to
early astronomers observing from northern latitudes



How does the Greek letter designation of a star give you clues both to its location and its
apparent brightness? - ✔✔The brightest star in a constellation is usually designated as Alpha,
the second brightest as Beta, and so on. The star's approximate location is described by the name
of the constellation.

,From your knowledge of star names and constellations, which of the following stars is
probably brighter? Explain your answers.

Alpha Ursae Majoris; Epsilon Ursae Majoris - ✔✔Alpha Ursae Majoris is brighter because it has
a Greek letter designation that suggests that it is the brightest star in the constellation of Ursa
Major



How did the magnitude system originate in a classification of stars by apparent brightness? - ✔✔The
stars were divided into six classes: the brightest were called first magnitude and the faintest were called
sixth magnitude



What does the word apparent mean in apparent visual magnitude - ✔✔How bright the star
appears to us, observing from Earth



What does the word visual mean in apparent visual magnitude? - ✔✔The magnitude includes
only light that is visible to the human eye.



Do the apparent visual magnitude numbers of two stars tell us which one is farther from Earth? Explain
your answer. - ✔✔No. A faint, nearby star could appear brighter to human eyes than a faraway,
bright star



Do the apparent visual magnitude numbers of two stars tell us which one is bigger? Explain your answer.
- ✔✔No. A small, nearby star could appear brighter than a faraway, large star



In what ways is the celestial sphere a scientific model? - ✔✔It describes what we see as the
sky appears to turn above us, and enables us to predict the positions of the stars.



Where would you need to go on Earth to see the celestial equator very near your horizon? - ✔✔To
Earth's North or South Pole.



Where would you go on Earth if you wanted to be able to see both the north celestial pole and
the south celestial pole at the same time? - ✔✔To Earth's equator

, Why does the number of circumpolar constellations depend on the latitude of the observer? -
✔✔Because from a latitude close to a celestial pole, there are more circumpolar stars than at
a latitude closer to the equator



It is the first day of summer. Will the days start getting longer tomorrow, start getting shorter tomorrow,
or will the Sun stay up in the sky tomorrow for as long as it did today? - ✔✔The days will start getting
shorter



How much flux from the Sun does the Northern Hemisphere of Earth receive compared to the Southern
Hemisphere on the first day of fall at noon? - ✔✔Both hemispheres receive the same amount of flux



The motion of the Moon around Earth. - ✔✔Moon takes about 29.5 days to go through cycle of
phases synodic month time to make full 360°rotation around Earth, sidereal month, is about 2
days shorter due to motion around sun



synodic month - ✔✔about 29.5 days



sidereal month - ✔✔is about 2 days shorter due to motion around sun



eclipses - ✔✔occur when Earth, Moon, and Sun form a straight line



Lunar eclipse - ✔✔Lunar eclipse: •Earth is between Moon and Sun •Partial when only part of Moon is
in shadow•Total when it all is in shadow



Solar eclipse - ✔✔Moon is between Earth and Sun •Partial when only part of Sun is blocked •Total
when it all is blocked•Annular when Moon is too far from Earth for total



Motions of the Moon - ✔✔eclipses don't occur every month because Earth's

and Moon's orbits are not in the same plane



Precession is caused by - ✔✔the gravitational pull of the Moon and Sun.

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