Sidereal Wall Clock

What is Sidereal Time

So what use is a sidereal clock? It is a clock that is linked to the stars rather than the sun and reports the Right Ascension at your local zenith. It can be used to tell which stars are in the sky at any particular time.

 Move yourself out from the earth and orient yourself according to the nearby stars. From that vantage point, from noon one day to noon the next the earth rotates a full 360 degrees plus another small amount corresponding to the angle the earth has moved in its orbit around the sun – almost one degree, about 1/365th of a circle. In one year, the earth revolves one complete revolution more than the number of days reckoned from the position of the sun in the sky. The sidereal day – the time it takes for the “fixed stars” to return to the same position in the sky – is a few minutes shorter than the solar day, about 23 hours and 56 minutes. The ratio of the length of the sidereal day to the solar day is approximately 1/1.00273791.

 A sidereal clock measures time by a scale that has 24 sidereal hours in a sidereal day, so the sidereal hours, minutes and seconds are all slightly shorter than their conventional equivalents. There are no time zones using sidereal time. Sidereal time is not used to organise peoples affairs so there is no motivation to standardise the time between nearby places and every different longitude has its own local sidereal time. Local sidereal time for any location can be obtained from the internet from sites such as or

The sidereal clock is built by replacing the electronics and the face in a normal clock and calibrating the rate with a computer linked to time references using the network time protocol (NTP). The calibration is designed to be accurate to about 1 part per million, or about half a minute per year, although variation in the crystal frequency over time will probably degrade this to about 1 part in 100,000 or about 1 second per day.

Production and Ordering

Comments - Suggestions - Questions:

If you have any comments, suggestions or questions please email me. This is a new product and I am very interested in your suggests and questions. This helps me get the product right and make the web page information as useful as possible.


You can order the clock from my normal order page. Select clock from the left menu under Shopping.


I will be trying to keep a number of the clocks built and on the shelf. In stock clocks are indicated on the order pages. I have developed a production process that cycles weekly through any clock orders which are not in stock. So your clock will be produced in a week if it isn't on the shelf. Shipping takes between 4 and 14 days to arrive. On average allow about two to three weeks before your adapter will arrive.


Prices available on the order page in various currencies

Return to TOP