The document defines key terms used in astronomy: - An astronomical unit (AU) is the distance from the sun to Earth, which is used to measure distances inside the solar system. 1 AU equals 92,955,807 miles. - A light year is used to measure distances outside the solar system, which is how far light travels in one year or 5,878,499,810,000 miles. - Rotation is when an object spins on its axis, causing day and night on Earth which rotates every 24 hours. Revolution is when an object goes around another object, causing seasons as Earth revolves around the sun every 365.25 days.

1. Astronomy
• The study of planets, stars and other objects
in outer space

2. Astronomical Unit
(AU)
The unit of measure equal to the
distance from the SUN to the
EARTH. AU’s are used to measure
distances INSIDE the solar system
Distance from
the Earth to the
Sun = 1 AU
92,955,807 miles

3. Light Year
Light years are used to measure
distances outside of our solar system
Distance light travels in
one year.
1 light year=
5,878,499,810,000
miles

4. Rotation
• An object spins on its axis; It causes day and
night. Earth rotates once every 24 hours.

5. Revolution
• An object goes around another object; It
causes seasons. Earth revolves once every
year (365.25 days).

6. Orbit
• It is the curved path the planets follow around
the Sun.