Back to: Astronomy & the Cosmos
The sky is a machine of interlocking cycles, and once you understand three of them, most of what you see makes sense. The daily cycle: Earth rotates once every 24 hours, so the entire sky appears to wheel around Polaris, with stars rising in the east and setting in the west just like the Sun. The stars aren’t moving; you are.
The yearly cycle: Earth orbits the Sun, so our nighttime window faces a different direction each season, which is why Orion rules winter evenings and Scorpius rules summer. Seasons themselves come not from distance to the Sun but from Earth’s 23.5-degree axial tilt, which changes how directly sunlight strikes each hemisphere. (Earth is actually closest to the Sun in early January, during the Northern Hemisphere’s winter.)
The monthly cycle: the Moon orbits Earth in about a month, and its phases are simply our changing view of its sunlit half. A crescent, half, or full Moon is not Earth’s shadow; it’s geometry. One elegant consequence you can verify yourself: a full Moon always rises around sunset, because it must sit opposite the Sun in the sky to appear fully lit. Track the Moon for two weeks, noting its shape and rise time, and you’ll feel the machinery click into place.