Moonrise Moment

Orbit glossary

What is an equinox?

Equinox is either of two yearly moments when the Sun crosses Earth's celestial equator and day and night are roughly equal in length.

Earth and the Moon shown at two points along an elliptical lunar orbit.
A visual guide to equinox. Original Moonrise Moment illustration.

What it means

Equinox describes part of the Moon's motion or position in space. The Moon follows a slightly elliptical, tilted orbit, so its distance, apparent path, rise time, and alignment with the Sun change continuously. These orbital relationships explain many patterns that observers notice from night to night.

Keep exploring

Orbit Apogee

The point in the Moon's orbit where it is farthest from Earth.

 Orbit Declination

A celestial coordinate comparable to latitude on Earth. It measures angular distance north or south of the celestial equator.

 Orbit Ecliptic

The Sun's apparent yearly path across Earth's sky. The Moon and planets remain near this path because their orbits have relatively small tilts.

 Orbit Libration

The Moon's apparent nodding and rolling motion, which lets observers on Earth see slightly more than half of its surface over time.

Sources and further reading

This definition was written in plain language and checked against these science references.

Moonrise Moment showing the live direction and countdown screen.

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