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BRG Precision 6 Digit 4" Sidereal Clock With GPS Receiver

BRG Precision 6 Digit 4'' Sidereal Clock With GPS Receiver
 BRG Precision 6 Digit 4'' Sidereal Clock With GPS ReceiverBRG Precision 6 Digit 4'' Sidereal Clock With GPS Receiver 
Price:  £629.00(Inc. 20% VAT)Earn 629 Loyalty Points

Model:  SD640
Brand:  BRG Precision



Generally In Stock, Please Confirm Before Ordering

2 Year Warranty On All New Items
(Excluding Batteries & Globes)

High quality 4" 6 digit sidereal clock by BRG Precision. One of the leadest manufacturers of sidereal and other precision clocks. Also comes with the mains power supply.

All BRG 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. The addition of the optional GPS Atomic Time Receiver allows the display to obtain the local latitude and longitude for use in the internal calculations. This option is highly recommended. Manual input of the required information involves a set of control buttons on the back of the unit with a numeric menu system.

These clocks come in either 2.5" or 4 LEDs in a plastic enclosure with a a TCXO Oscillator and auto-brightness included. Options for the single position displays will be –OCXO, -EN, -AFS, and –AFS-GP. The last option will include auto-brightness as well.

What is Sidereal Time?

The time most people use in their everyday life is Solar Time. The fundamental unit of Solar Time is a Day; the time i 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 it's orbit (360 degrees/265.25 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 traveled360 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.

Side Time (literally means "star time") is useful for determining where the stars are 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 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.

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Some items that are showing as in stock are in stock at our holding warehouses, not at the shop. To double check the stock levels at the shop, please contact us on 01909774369 or

The delivery times for most items is 1 - 2 days but again, please double check stock levels on important orders before placing an order via the website.

The delivery costs for courier next day are for mainland UK only. If you live in the Scottish Highlands/Islands, Channel Islands or Northern Ireland, then a shipping surchage will apply. please contact us for prices. Smaller items can still go 1st class via Royal Mail.

Please note that if you are wanting to take advantage of our Saturday and Sunday timed services or next day pre 12 or pre 10:30 services, you MUST check that the stock is here at the shop before placing orders. Also, orders using the Saturday and Sunday services must be placed before 1pm the previous working day. Also, please remember to check that the stock is here at the shop before placing orders. If the stock is not at the shop, we won't be able to ship on any of the timed services. 

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Rother Valley Optics now have a loyalty point scheme active on the website. As you can see from the products, every item has a point value. Each pound you spend with us, you will receive 1 loyalty point. 1 point is worth 1p. You can accumulate these points as you shop with us, then when you are over £5, you can spend them on the website! Easy as that.

Even if you collect most of your items from our shop, you can still order via the website and select the "shop collection" delivery option. Then you can come to our shop, collect your item and still get your points!

Please note this scheme is online only. Customers who order via the telephone can still be added to the scheme manually. Please ask for more details on this. Before placing orders online, please make sure you are registered with us first otherwise your points won't be allocated.

So happy shopping and if you have any questions about the scheme or any other queries, please get in touch.

Rother Valley Optics


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Please note some items are NOT eligible for finance. Please contact us for eligibility first. 

Please get in touch with us today to find out if you're applicable.

You must be over 18 years to apply, live in the UK, have a valid UK bank account and not be bankrupt. Your credit file will be searched on application to see if you are eligible.

Rother Valley Optics Ltd is registered in England and Wales 04762707. Registered Office: 21 Station Road, Kiveton Park, Rotherham, S26 6QP. Rother Valley Optics Ltd acts as a credit broker only. Rother Valley Optics Ltd are authorised and regulated by the Financial Conducts Authority. Credit provided subject to age and status..

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- - - Rother Valley Optics Ltd

01909 774 369