AST 220 Midterm Exam Study Set With
Correct Solutions
Astronomical Unit (AU) - ANSWER Earth's average distance from the Sun, which is
about 150 million kilometers (93 million miles).
axis tilt - ANSWER The amount by which a planet's axis is tilted with respect to a line
perpendicular to the ecliptic plane.
big bang - ANSWER The beginning of the universe
cosmos - ANSWER The sum total of all matter and energy—that is, all galaxies and
everything between them.
ecliptic plane - ANSWER The Plane of Earth's orbit around the Sun.
galaxy - ANSWER A great island of stars in space, containing millions, billions, or even
trillions of stars, all held together by gravity and orbiting a common center.
galaxy cluster - ANSWER A collection of a few dozen or more galaxies bound together
by gravity; smaller collections of galaxies are simply called groups.
light year (ly) - ANSWER the distance that light can travel in 1 year, which is 9.46 trillion
km
local group - ANSWER the group of about 40 galaxies which the milky way galaxy
belongs to
nuclear fusion - ANSWER The process in which two (or more) smaller nuclei slam
together and make one larger nucleus.
observable universe - ANSWER The portion of the entire universe that can be seen from
Earth, at least in principle.
planet - ANSWER A large body in space that orbits a star and does not produce light of
its own
solar system - ANSWER A star (or sometimes more than one star) and all of the objects
that orbit it.
star - ANSWER A ball of hot gas, primarily hydrogen and helium, that undergoes nuclear
fusion.
superclusters - ANSWER The largest known structures in the universe, consisting of
many clusters of galaxies, groups of galaxies, and individual galaxies.
, universe - ANSWER the sum of all mater and energy
angular size - ANSWER a measure of the angle formed by extending imaginary lines
outward from our eyes to span an object
arcminute - ANSWER 1/60 of a degree
altitude - ANSWER (above horizon) the angular distance between the horizon and an
object in the sky
Azimuth - ANSWER A horizontal angle measured clockwise from north or south.
celestial equator - ANSWER The extension of Earth's equator onto the celestial sphere.
constellation - ANSWER A region of the sky; 88 official constellations cover the celestial
sphere.
crescent - ANSWER Moon phase in which less than half of the Moon appears to be
illuminated.
ecliptic - ANSWER The sun's apparent annual path among the constellations.
equinox - ANSWER Both the point in pisces on the celestial sphere where the ecliptic
crossed the celestial equator and the moment in time when the sun appears at that point
each year
gibbous - ANSWER Moon phase in which more than half of the Moon appears to be
illuminated.
horizon - ANSWER the line at which the sky and Earth appear to meet
latitude - ANSWER The angular north-south distance between Earth's equator and a
location on Earth's surface
longitude - ANSWER The angular east-west distance between the prime meridian (Which
passes through Greenwich, England) and a location on Earth's surface.
Lunar eclipse - ANSWER An event that occurs when the moon passes through Earth's
shadow, which can happen only at full moon. A lunar eclipse may be total, partial, or
penumbral.
meridian - ANSWER A half-circle extending from your horizon due south, through your
zenith, to your horizon due north.
Correct Solutions
Astronomical Unit (AU) - ANSWER Earth's average distance from the Sun, which is
about 150 million kilometers (93 million miles).
axis tilt - ANSWER The amount by which a planet's axis is tilted with respect to a line
perpendicular to the ecliptic plane.
big bang - ANSWER The beginning of the universe
cosmos - ANSWER The sum total of all matter and energy—that is, all galaxies and
everything between them.
ecliptic plane - ANSWER The Plane of Earth's orbit around the Sun.
galaxy - ANSWER A great island of stars in space, containing millions, billions, or even
trillions of stars, all held together by gravity and orbiting a common center.
galaxy cluster - ANSWER A collection of a few dozen or more galaxies bound together
by gravity; smaller collections of galaxies are simply called groups.
light year (ly) - ANSWER the distance that light can travel in 1 year, which is 9.46 trillion
km
local group - ANSWER the group of about 40 galaxies which the milky way galaxy
belongs to
nuclear fusion - ANSWER The process in which two (or more) smaller nuclei slam
together and make one larger nucleus.
observable universe - ANSWER The portion of the entire universe that can be seen from
Earth, at least in principle.
planet - ANSWER A large body in space that orbits a star and does not produce light of
its own
solar system - ANSWER A star (or sometimes more than one star) and all of the objects
that orbit it.
star - ANSWER A ball of hot gas, primarily hydrogen and helium, that undergoes nuclear
fusion.
superclusters - ANSWER The largest known structures in the universe, consisting of
many clusters of galaxies, groups of galaxies, and individual galaxies.
, universe - ANSWER the sum of all mater and energy
angular size - ANSWER a measure of the angle formed by extending imaginary lines
outward from our eyes to span an object
arcminute - ANSWER 1/60 of a degree
altitude - ANSWER (above horizon) the angular distance between the horizon and an
object in the sky
Azimuth - ANSWER A horizontal angle measured clockwise from north or south.
celestial equator - ANSWER The extension of Earth's equator onto the celestial sphere.
constellation - ANSWER A region of the sky; 88 official constellations cover the celestial
sphere.
crescent - ANSWER Moon phase in which less than half of the Moon appears to be
illuminated.
ecliptic - ANSWER The sun's apparent annual path among the constellations.
equinox - ANSWER Both the point in pisces on the celestial sphere where the ecliptic
crossed the celestial equator and the moment in time when the sun appears at that point
each year
gibbous - ANSWER Moon phase in which more than half of the Moon appears to be
illuminated.
horizon - ANSWER the line at which the sky and Earth appear to meet
latitude - ANSWER The angular north-south distance between Earth's equator and a
location on Earth's surface
longitude - ANSWER The angular east-west distance between the prime meridian (Which
passes through Greenwich, England) and a location on Earth's surface.
Lunar eclipse - ANSWER An event that occurs when the moon passes through Earth's
shadow, which can happen only at full moon. A lunar eclipse may be total, partial, or
penumbral.
meridian - ANSWER A half-circle extending from your horizon due south, through your
zenith, to your horizon due north.
