Chapter 1 Flashcards
Ecliptic plane
the plane of Earth’s orbit around the SUn
Universe
the sum total of all matter and energy
Galaxy clusters
a collection of a few dozen or more galaxies bound together by gravity; smaller collections of galaxies are simply called groups
Local Group
the group of about 40 galaxies to which the Milky Way Galaxy belongs
Observable universe
the portion of the entire universe that, at least in principle, can be seen from Earth
Big Bang
the name given to the event thought to mark the birth of the universe
Superclusters
the largest known structures in the universe, consisting of many clusters of galaxies, groups of galaxies, and individual galaxies
Axis tilt
the amount by which a planet’s axis is tilted with respect to a line perpendicular to the ecliptic plane
Solar system
a star and all the objects that orbit it
Dark energy
name sometimes given to energy that could be causing the expansion of the universe to accelerate
Dark matter
matter that we infer to exist from its gravitational effects but from which we have not detected any light
Nuclear fusion
the process in which two smaller nuclei slam together and make one larger nucleus
Light-year (ly)
the distance that light can travel in 1 year, which is 9.46 trillion km
Rotation
the spinning of an object around its axis
Astronomical unit (AU)
the average distance of Earth from the Sun, which is about 150 million km
