Sidereal Time Estimator
Free sidereal time calculator. Calculate local sidereal time for astronomical observations. Essential for telescope pointing and star tracking.
Calculate the local sidereal time for any location and date. Sidereal time tracks Earth's rotation relative to distant stars, essential for astronomical observations and telescope alignment.
Common use cases
- Amateur astronomers planning observations
- Telescope pointing calculations
- Satellite tracking coordination
- Astrophotography planning
- Observatory scheduling
How to use
- Enter your longitude or select a location
- View the current local sidereal time
- See Greenwich Sidereal Time
- Calculate for any date and time
- Convert between solar and sidereal time
FAQ
What is sidereal time?
It's time measured by Earth's rotation relative to distant stars, not the Sun. A sidereal day is about 4 minutes shorter than a solar day.
Why do astronomers use it?
Stars return to the same position in the sky at the same sidereal time each night, making observation planning easier.
How is it different from regular time?
Regular time tracks the Sun; sidereal time tracks the stars. They drift apart by about 4 minutes per day.