Sidereal Clock

The Sidereal Clock is an Android based astronomical clock. It displays sidereal times and several other time standards.

In digital mode it has 3 time displays and you can choose what time to show in each of them. In analog mode it shows a nice 24 hours analog clock that displays Local Mean Sidereal Time or Local Apparent Solar Time.

All the displayed times are computed from the Sidereal Clock's own timebase which is synchronized to an external NTP time server, a networked precision time reference. You may expect a precision within +/- 200ms or better if you have a stable data connection.

Local times, such as Local Mean Solar Time and Local Sidereal Time, are computed based on your true geographic longitude, obtained via GPS, if available, or via Network Location otherwise.

Available Time Standards

Local Standard Time
The local standard time is your watch time, which is defined for your time-zone.
Local Mean Solar Time
While the standard time is the same in any place inside your time zone, the solar time is computed for your particular longitude. It is your true local time.
Local Apparent Solar Time
The length of a solar day is actually not constant. It varies throughout the year, and the effect of these variations produces seasonal deviations of up to 16 minutes from the mean solar day, which is exactly 24 hours. The apparent solar time scale takes in account these variations, applying the daily deviations (known as equation of time) to the solar mean time, to get the true local position of the Sun. This is the time you would read on a sundial.
Local Mean Sidereal Time
The sidereal time is based on the apparent motion of the distant stars instead of the Sun. One sidereal day is approximately 23 hours, 56 minutes, 4.091 seconds.
By definition, the right ascension of any object currently crossing the meridian is equal to the current local sidereal time, and that's why it is widely used by astronomers.
UTC Coordinated Universal Time
UTC is the universal time reference. It is the mean solar time at the Royal Observatory in Greenwich (GMT) and consequently the standard time at time-zone zero (GMT+0).
Greenwich Mean Sidereal Time
The sidereal time at longitude zero, which corresponds to the Royal Observatory in Greenwich.
Julian Day
The Julian Day or Julian Date is the interval of time in days and fractions of a day since January 1, 4713 BC Greenwich noon. Julian Day Number is the integral part of the Julian Date.
Modified Julian Date
The Modified Julian Date is found by rounding downward the Julian Date, by subtracting the value 2400000.5. The MJD was introduced by the Smithsonian Astrophysical Observatory in 1957 to record the orbit of Sputnik via an IBM 704 (36-bit machine) and using only 18 bits until August 7, 2576.
Equation of Time
The equation of time is the difference between apparent solar time and mean solar time for each day of the year. It varies between (approx) -14m06s and +16m30s through the year.

There are two versions of Sidereal Clock:

Get it on Google Play
Sidereal Clock is free and supported by ads.
Get it on Google Play
Sidereal Clock Pro is paid and shows no ads.