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What is my Meridian Offset


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I am trying to figure out how to use my Vixen polar scope.

First problem is it is asking for my Merdian Offset. I can't figure out what this means though web sources are happy to tell me what I should put if I lived in Chicago or Austin....

FWIW I'm in Oxford UK, longitude 1.15.28 ......

any help appreciated.

Then I can start sweating over the next scale setting....

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The merdian offset is the differnce between GMT and your actual location. Its used on manual polarscope calculators where you would typically align the polarscope using a zero point of GMT - you would then apply an offset on the polarscopes date/time ring to get the correct position.

Its all kind of irrelevant if you use someting like polar finder to fix the position of Polaris. The offset ring/calculator on most polarscopes is a kind of hark back when you'd set the scope to GMT because thats what your celestial handbook would list its transit times as.

This is as qouted from the Skywatcher manual

Depending on where you live, "Zero" can be anyplace between the E and the W on longitude scale, so first you need to determine where zero is for your location.

Your Zero point is equal to the difference between your actual longitude and the longitude of the central meridian of your time zone. To calculate the longitude of your central meridian, multiply your time zone offset from Greenwich Mean Time (GMT) by 15. For example, in Waterloo, Ontario, Canada (Eastern Time) the time zone offset is -5 hours. Ignore the sign and simply multiply 5 x 15 = 75.The longitude of the central meridian for the Eastern time zone is 75 degrees west. The actual longitude at the viewing location in Waterloo is 80 degrees 30 minutes West. Ignore the 30 minutes and just use 80 in the equation. Now it's simple, 80 - 75 = 5. Since 80 is greater than 75 the result is positive 5. That means Waterloo, Ontario is west of its Central Meridian. In this case, the zero point is at the "5" mark on the W side of the scale. If the location was east of its central meridian the equation would yield a negative value. In that case the E side of the scale should be used.

As I say though if you use a program like Polarfinder you dont need to bother.

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having said that, why use polarfinder when using the circles on the mount is so easy ( after a bit of practice).

On the Vixen GP, the small E/W offsret allow you to program in the minutes offset E or W from the nearest time zone boundary. Use the local mean time and date on the polar finder to program in the rotation of the cross-hairs to the right angle and dial the mount in for polar alignment.

HTH

regards

Mike

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