Polar Alighning

[George]

How do you find local magnetic offset from true north? I want to polar align my obsevatory to maximise the southern view

On a footnote when I have found it , how far is that off polar north?

[GordonCopestake]

Most polar scopes have the offset engraved on the reticule, if you havn't got a polar scope you can use drift alignment

[barkis]

Hi. Upgrader,

If you are merely wishing to centralize your observatory viewing aperture on due south, find out what time a particular star crosses your local meridian.

For example the star Aldebaran in the Hyades will transit the meridian at something like 2200 hours. That is not the exact time, just an example.

If you want to know a particular objects transit time across your local meridian, I would need to know your exact coordinates. You can get that from a Ordnance survey map, or a GPS device. you can email me if you want to use this method. Once you know the transit time on a particular night, all you need do is move your Observatory opening so that the object in question is central. Then mark where your equatorial head needs to be positioned. on your North / South line. Or, place a line on your observatory floor indicating your local meridian. Which never changes. At least not for a very long time. Of course after you have done that, your telescope mount has to have its polar axis parallel to the earths axis, and pointing at the celestial pole, which for observational activity could be Polaris. For any long exposure photography of course more accurate pole alignment is required, as Polaris is almost a degree away from the true pole. The full moon subtends an angle of half a degree.

So if you can imagine the circle polaris would draw on the sky in 24 hours, you would be able to fit a few moons inside it.

Sorry to be a bit long winded over this, but I am sure more help is available on the forum from other guys too.

Good luck Barkis.

[Astroman]

There are a couple of ways to determine your local magnetic offset. One is to consult aeronautical charts for the nearest airport. They usually have it noted. Another is to go ahead and polar align your scope. Basically, just setting it at 90º Dec and pointing it straight at Polaris will work well enough. Then, cget a good compass and compare where your scope is pointed and where the compass points north. A good compass will have an adjustable dial used for charting that you can then preset to your local offset. In the field, you can plunk down your tripod, wiggle it to match the compass setting, set the scope at 90º Dec and finagle it to Polaris. This will get you close enough for long visual sessions, and is a good starting point for drift alignment. This is the exact procedure I use DAILY at the Grand Canyon Star Party and it works very well, indeed.

BTW, my magnetic offset is 12º to the west, so it's considerable.

[George]

There are a couple of ways to determine your local magnetic offset. One is to consult aeronautical charts for the nearest airport. They usually have it noted. Another is to go ahead and polar align your scope. Basically, just setting it at 90º Dec and pointing it straight at Polaris will work well enough. Then, cget a good compass and compare where your scope is pointed and where the compass points north. A good compass will have an adjustable dial used for charting that you can then preset to your local offset. In the field, you can plunk down your tripod, wiggle it to match the compass setting, set the scope at 90º Dec and finagle it to Polaris. This will get you close enough for long visual sessions, and is a good starting point for drift alignment. This is the exact procedure I use DAILY at the Grand Canyon Star Party and it works very well, indeed.

BTW, my magnetic offset is 12º to the west, so it's considerable.

Found the info I was looking for

Localisation

Area Code EUR

Country ICAO Code EG

FIR ICAO Code EGTT

Latitude N53° 21' 13.48''

Longitude W002° 16' 29.82''

Geodetic Datum

Magnetic Variation 003.0W <---------

Aerodrome Elevation 257 Ft

Thanks guys