Full Moon

The Moon doesn't make light — it reflects the Sun's. As it orbits Earth (about every 29.5 days), the angle between Sun, Earth, and Moon changes, so we see different fractions of its sunlit hemisphere.

The dividing line between lit and unlit on the Moon's surface is called the terminator. From Earth, the terminator's projected shape is a half-ellipse, which is why the bright portion looks curved at every phase except full and new.

A synodic month (29.53 days, the cycle of phases) is slightly longer than a sidereal month (27.32 days, the time to orbit Earth once relative to the stars) — because Earth itself moves around the Sun during the orbit, so the Moon has to "catch up" to align with the Sun again.

New Moon

Moon between Earth and Sun; sunlit side faces away. Disc is dark.

Waxing Crescent

Lit fraction growing from 0 toward 50%, terminator on the right side (Northern Hemisphere).

First Quarter

Half lit; right hemisphere bright, left dark. Rises around midday.

Waxing Gibbous

More than half lit, growing toward full. Sets after midnight.

Full Moon

Earth between Sun and Moon; entire near side lit. Rises at sunset, sets at sunrise.

Waning Gibbous

More than half lit, shrinking from full. Rises after sunset.

Last Quarter

Half lit; left hemisphere bright, right dark. Rises around midnight.

Waning Crescent

Lit fraction below 50%, shrinking to 0; rises before sunrise.

The Moon's gravity tugs on Earth's oceans, lifting a bulge of water on the side facing the Moon. A second bulge forms on the opposite side because Earth itself is being pulled toward the Moon, leaving the far ocean slightly behind.

Earth rotates through both bulges roughly every 24 hours, which is why most coasts see two high tides and two low tides per day. The Sun adds about a third of the Moon's tidal pull — when both align (new and full moons), tides are extra strong (spring tides); when they're at right angles (quarters), tides are gentler (neap tides).

For coastal trail riders and beach haulers, this means the timing of safe ride windows shifts about 50 minutes later each day, tracking the Moon's transit.

Mares foal more on full moons

Mostly false. Several large studies of equine birth records found no statistically significant correlation between lunar phase and foaling rate. Daylight, temperature, and individual mare patterns drive timing far more than the moon.

More colics on full moons

No good evidence. Vet practice records consistently show no lunar pattern. The myth probably persists because vets remember the late-night calls — and full moons make for vivid memories.

Bright moonlight makes horses spookier at night

Plausible and partly supported. Bright moonlight casts crisp moving shadows that can trigger flight responses, especially in less-trail-experienced horses. The countervailing effect: better visibility means horses can identify what they're seeing, which often calms them.

Predators are more active under bright moons

Mixed by species. Some predators (coyotes, mountain lions) actually hunt less during bright moons because prey is more cautious. Pasture risk to horses on full-moon nights isn't elevated by predator behavior alone.