Concept
Apparent & Absolute Magnitude
How astronomers measure brightness.
A logarithmic scale where smaller (and negative) numbers mean brighter. A difference of 5 magnitudes = 100× in brightness.
See also
Right Ascension
Celestial longitude, measured eastward in hours.
Declination
Celestial latitude, measured in degrees.
Sidereal Time
Time measured by the stars rather than the Sun.
Solar Time
Time measured by the Sun's position.
The Big Bang
How everything began, 13.8 billion years ago.
Black Holes
Regions where gravity stops light itself.