Sidereal Time 4+


Designed for iPhone

    • 2.9 • 9 Ratings
    • $0.99

iPhone Screenshots


Sidereal Time at any location on Earth.

The Sidereal Time App gives the user a simple and quick way to determine:

- Local Apparent Sidereal Time (LAST) based on longitude
- Rough estimate of LAST based on Time Zone
- Greenwich Apparent Sidereal Time (GAST)
- Select one of 30 Stratum-1 NTP servers or add your own to synchronize the clock against the primary network time standard

The App uses core location (GPS, cellular triangulation and/or Skyhook Wireless's Wi-Fi system) to determine the users present position and hence his LAST. The user may also manually select the longitude coordinate to determine LAST or make a rough estimate by selecting a Time Zone.

A running clock with the Coordinated Universal Time is presented in parallel with the Sidereal Time clock.

Local Apparent Sidereal Time at any location differs from the Greenwich Sidereal Time value of the same moment, by an amount that depends on the longitude of the location. When one moves eastward 15° in longitude, sidereal time is larger by one hour and hence wraps around at 24 hours. Unlike computing local solar time, differences in longitude and time are counted here to the accuracy of measurement, not just in whole hours.

What’s New

Version 1.7

This app has been updated by Apple to display the Apple Watch app icon.

Updated for iOS 11.0.
Minor bug corrections.

Ratings and Reviews

2.9 out of 5
9 Ratings

9 Ratings

PaplooTheLearned ,

Accurate calculation, but no night mode

Straight-forward app for displaying times useful for astronomers, such as UTC and LAST, and does so correctly to better than 1 second accuracy!

Unfortunately, this suffers from a major problem: I cannot find a setting to display as a night-vision safe dim red, making this useless as a visual astronomy observation clock.

luciusg ,

Nice app

Needs an alarm to alert when is your own sidereal time.

The Soul Rider ,

Nice App

This seems to be a nice app. Simple, pleasing design, nice colors. But needs an alarm clock for sidereal time and a countdown clock without an alarm.

App Privacy

The developer, CosmoWerx, has not provided details about its privacy practices and handling of data to Apple.

No Details Provided

The developer will be required to provide privacy details when they submit their next app update.


  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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