altitude
distance in degrees from the horizon to the object
aphelion
the point in the planet's orbit that it is the farthest from the sun
axis of rotation
imaginary straight line through the Earth between the North and South
Pole, on which the Earth rotates
celestial body
natural or man-made object found in the celestial sphere
celestial sphere
imaginary sphere encircling the Earth
circumpolar constellations
constellations that are visible all year
constellation
group of stars that take the appearance of animals, humans, or objects
geocentric
the Earth is the center of the solar system
heliocentric
the Sun is the center of the solar system
horizon
where the Earth meets the sky
orbit
the path an object takes as it revolves around another object
perihelion
the point in the planet's orbit that is the closest to the Sun
retrograde
when a planet appears to be orbiting backwards, but it actually is
just slowing down
revolution
when one object moves around another object
rotation
spinning of an object on its axis
solar noon
time of day when the sun is at its highest altitude
zenith
object that is directly overhead (90 0)