Is this Sidereal Time Calculator free to use?

Yes, Sidereal Time Calculator is 100% free to use online with no installation or account required.

How do I use the Sidereal Time Calculator?

Simply enter your values into the required input fields and click calculate to view the results instantly.

Yes, the calculator is fully responsive and compatible with Android, iOS, Windows, macOS, and Linux web browsers.

Sidereal Time Calculator — Free Online Tool

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Calculate Greenwich and Local Sidereal Time for stargazing and celestial tracking

Astronomy Formula: $\text{LST} = \text{GMST} + \text{Longitude (in hours)}$. Enter your observation date, UTC time, and observer longitude below.

Observation Parameters Input

Observation Date (UTC)

Universal Time - UTC (HH:MM)

Observer Longitude (Degrees East +)

⚠️ Sidereal time is measured relative to the stars rather than the Sun, making a sidereal day roughly 4 minutes shorter than a solar day.

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