Atomic Digital Clocks, Master Clocks, System Clocks, Accurate Time, UTC, ZULU and 24 Hour Clocks.

BRG Sidereal Time

All BRG Tiger Series time displays are capable of displaying Universal and Local Sidereal Time. Time zone displays may be configured to display Sidereal Time on one of the zones, or a single display may be configured to alternate between multiple time zones, including Sidereal Time. The Sidereal Time displayed is calculated from the clock's internal UTC time. Therefore, if the clock obtains its' time from an atomic clock (using GPS, Ethernet, IRIG-B, PC, or other methods), then the Sidereal Time displayed will be highly accurate and will not deviate over time. An ultra-high precision oscillator option is also available when connecting to an outside time source is impractical.

What is sidereal Time?

The time most people use in their everyday lives is Solar Time. The fundamental unit of Solar Time is a Day; the time it takes the Sun to travel 360 degrees around the sky, due to the rotation of the Earth. However, the Earth doesn't actually spin around 360 degrees in one Solar Day. The Earth is in orbit around the Sun, and over the course of one day, it moves about one Degree along its orbit (360 degrees/365.25 Days for a full orbit = about one Degree per Day). So, in 24 hours, the direction toward the Sun changes by about a Degree. Therefore, the Earth has to spin 361 degrees to make the Sun look like it has traveled 360 degrees around the Sky.

Astronomers are concerned with how long it takes the Earth to spin with respect to the "fixed" stars, not the Sun. So, they need a time scale that removes the complication of Earth's orbit around the Sun, and just focuses on how long it takes the Earth to spin 360 degrees with respect to the stars. This rotational period is called a Sidereal Day. On average, it is 4 minutes shorter than a Solar Day, because of the extra 1 degree the Earth spins in a Solar Day.

Sidereal Time (literally means "star time") is useful for determining where the stars are at any given time. Sidereal Time divides one full spin of the Earth into 24 Sidereal Hours; similarly, the map of the sky is divided into 24 Hours of Right Ascension. This is no coincidence; Local Sidereal Time (LST) indicates the Right Ascension on the sky that is currently crossing the Local Meridian. So, if a star has a Right Ascension of 05h 32m 24s, it will be on your meridian at LST=05:32:24. More generally, the difference between an object's RA and the Local Sidereal Time tells you how far from the Meridian the object is. For example, the same object at LST=06:32:24 (one Sidereal Hour later), will be one Hour of Right Ascension west of your meridian, which is 15 degrees.

Therefore, Local Sidereal Time is the most useful form of Sidereal Time since it gives the right ascension of a transiting celestial object at a given location.

Of course, BRG offers clocks that display both Universal and Local Sidereal Time.