The earth, moon, and sun are not capitalized unless in a list of celestial objects or part of another name.
Correct: I was born on the earth.
Correct: The first three planets from the Sun are Mercury, Venus, and Earth.
(In a list)
Seasons are not capitalized unless part of another name.
Correct: This summer was very hot.
When discussing mythological deities, the word god or goddess is not capitalized. Their names are capitalized.
Correct: The Romans were careful not to offend any god.
Correct: The Egyptians considered their pharaoh a god, an incarnation of the god Osiris.
(Osiris, the name, is capitalized.)