Chapter 1: A Modern View of the Universe Flashcards
a star and all objects that orbit it
star system
a great island of stars in space
galaxy
the group of about 40 galaxies to which the Milky Way belongs
Local Group
a collection of a few dozen or more galaxies bound together by gravity
galaxy clusters
the largest known structures in the universe, consisting of many clusters of galaxies and individual galaxies
supercluster
the sum total of all matter and energy
universe
Earth’s average distance from the Sun; about 150 million kilometers
astronomical unit
the distance that light can travel in one year; about 10 trillion kilometers
light-year
the portion of the universe that can be seen from Earth
observable universe
a large, glowing ball of gas that generates heat and light through nuclear fusion in its core
star
a moderately large object that orbits a star and shines primarily by reflecting light from its star; must orbit its star, be large enough for its own gravity to make it round, and have cleared most other objects from its orbital path
planet
an object that orbits its star and is massive enough for its gravity to have made it round, but has not cleared most objects from its orbital path
dwarf planet
an object that orbits a planet
moon
a relatively small and rocky object that orbits a star
asteroid
a relatively small and ice-rich object that orbits a star
comet
an asteroid, comet, or other object that orbits a star but is too small to qualify as a planet or dwarf planet
small solar system body
the Sun and all the material that orbits it
solar system
the spinning of an object around its axis
rotation
the motion of one object around another due to gravity
orbit
the increase in the average distance between galaxies as time progresses
expansion (of the universe)
the event thought to mark the beginning of the universe
Big Bang
the process in which lightweight atomic nuclei smash together and fuse to make heavier nuclei
nuclear fusion
the plane of Earth’s orbit around the Sun
ecliptic plane
the amount by which a planet’s axis is tilted with respect to a line perpendicular to the ecliptic plane
axis tilt
