Perihelion: the point in Earth's orbit where it is closest to the Sun (in January)

Aphelion: the point in Earth's orbit where it is farthest from the Sun (in July)

Goldilocks Principle: "Venus is too hot, Mercury is too cold, and Earth is just right" for life to exist

Greenhouse Gases: Water vapor, carbon dioxide, methane, and nitrous oxide in the atmosphere that trap infrared radiation.

Greenhouse Effect: Heating of Earth's surface by certain atmospheric gases, which helps keep Earth's surface warm enough to sustain life.