Moonrise Moment

Orbit glossary

What is sidereal month?

Sidereal Month is the roughly 27.3-day interval the Moon takes to complete one orbit relative to the background stars.

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

What it means

Sidereal Month 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 Equinox

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

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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