---
title: "Earth's Rotation & Star Tracking"
canonical: https://stackingstarlight.com/start-here/earths-rotation
description: "Earth rotates once per sidereal day, so stars drift. Equatorial mounts cancel that motion for sharp long exposures."
---

# Earth's Rotation & Star Tracking

> Earth rotates once per sidereal day, so stars drift. Equatorial mounts cancel that motion for sharp long exposures.

Earth spins once every 23h 56m (a sidereal day), making stars appear to drift east-to-west. Any exposure longer than a few seconds shows star trails unless the camera tracks. An **equatorial mount** aligns one axis (the RA axis) with Earth's rotation axis and turns it at exactly the sidereal rate, so the sky appears frozen. This is what makes minutes-long exposures of faint objects possible.

---

Source: [https://stackingstarlight.com/start-here/earths-rotation](https://stackingstarlight.com/start-here/earths-rotation) · Part of [Stacking Starlight](https://stackingstarlight.com) by Michael Kalika.

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