Chapter 1 Flashcards
Star
a large, glowing ball of gas that generates heat and light through nuclear fusion in its core
Planet
A moderately large object that orbits a star and shines primarily by reflecting light from its star
Moon (satellite)
an object that orbits a planet; the term satellite can refer to any object orbiting another object
Asteroid
relatively small and rocky object that orbits a star
comet
relatively small and ice rich object that orbits a star
solar system
the sun and all the materials that orbit it, including the planets, dwarf planets, and small solar system bodies
star system
a star (sometimes more than one star) and any planets and other materials that orbit it\
galaxy
A great island of stars in space, containing from a few hundred million to a trillion or more stars, all held together by gravity and orbiting a common center
Cluster of galaxies
A collection of galaxies bound together by gravity. Small collections are generally called groups, while larger collections are called clusters
Supercluster
A gigantic region of space where many individual galaxies are packed more closely together than elsewhere in the universe
Universe (or cosmos)
The sum total of all matter and energy- that is, all galaxies and everything between them
Observable universe
The portion of the entire universe that can be seen from Earth, at least in principle. The observable universe is probably only a tiny portion of the entire universe
Astronomical unit (AU)
The average distance between earth and the sun, which is about 150 million kilometers. More technically, 1 AU is the length of the semimajor axis of Earth’s orbit
light-year
The distance that light can travel in 1 year, which is about 9.46 trillion kilometers
rotation
the spinning of an object around its axis. For example, earth rotates once each day around its axis, which is an imaginary line connecting the North pole to the South Pole
