Sidereal Time - CosmoWerx
$0.99 £0.59 0.79€


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

  • Local Apparent Sidereal Time (LAST) based on longitude. Perfect to set your setting circles on the telescope!
  • Rough estimate of LAST based on Time Zone.
  • Greenwich Mean Sidereal Time.
  • 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.