a single object in space large enough be held together by its own gravity
examples are moons, asteroids, planets, dwarf planets, stars.
a scientist who's main focus is on the space and more specifically celestial bodies
when an object circles another object in space due to the second object's gravitational pull.
for example the Earth revolves around the sun on an annual basis
when an object spins on an axis within itself.
for example the earth spins on a axis, that is why we have night and day because the Earth rotates at a speed that exposes a location on the earth to the sun for half of the day and exposes the other half of the earth to the sun while it is night where you are