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Old 09-10-2021, 05:33 AM
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Magnetic South and True Sout Please

Hi Guys, I have redesigned my Curved Bolt Astro Photography tracking device, which worked very well sometime ago.

It is now in a different location and on a very sturdy flat surface.

I understand that Magnetic South and True South is different, so when I have this thing pointed Magnetic South, how many degrees do i move it either East or West in my location of Warranambool.

It is at the Latitude of Warranambool of 38.4 and dead flat I just need to move it either East or West, or Left or Right at the correct degrees difference, which ever suits.

Thank You.

Leon
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Old 09-10-2021, 05:42 AM
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You move it in azimuth according to magnetic variation for the site, which for Warranambool is 10.8E. Therefore, you SUBTRACT 10.8 from 180, which is 169.2 for TRUE South (where you point).


The latitude of 38.4 is to set the altitude of the mount (the equatorial angle)
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Old 09-10-2021, 07:02 AM
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Leon this is the first time I have seen your tracker and no doubt missed a thread that I expect you started re this most interesting approach.
I expect with a little thought you should be able to use software that most all use to find CSP...it only requires you are able to rotate you device thru about 90 degrees on the polar axis in the case of Polemaster, but look at the other software as I expect with a spot on polar alignment your device would track very well.
It looks great...matey still has not sent our stuff so I sent him $100 using a money order that he has to cash at the post office with instruction to use most of the money to send our stuff...
Alex
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Old 09-10-2021, 08:41 AM
Outcast (Carlton)
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Quote:
Originally Posted by LewisM View Post
You move it in azimuth according to magnetic variation for the site, which for Warranambool is 10.8E. Therefore, you SUBTRACT 10.8 from 180, which is 169.2 for TRUE South (where you point).


The latitude of 38.4 is to set the altitude of the mount (the equatorial angle)
Sorry but, that is incorrect. East is a positive, west is a negative. Variation is always added no matter where you are... Thus a variation of 10.8E is added to 180 resulting in a bearing of 190.8.

28yrs Navy, navigation specialist: Nmeumonic drummed into our heads is C A D E T = Compass ADd East True

Cheers

Last edited by Outcast; 09-10-2021 at 09:42 AM.
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Old 09-10-2021, 11:43 AM
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Thank You Lewis, and Carlton, now I,m confused, (I know it doesn't take much at my age) so where do I go from here.

Leon
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Old 09-10-2021, 11:53 AM
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This should help mate
http://www.solaripedia.com/files/447
just work out the delineation in Warrnambool and go from there
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Old 09-10-2021, 11:55 AM
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Hey Leon,

I acknowledge this is wikeedia but, I can provide more references if you would like.

https://en.m.wikipedia.org/wiki/Magnetic_declination

Have a read, specifically under the heading ' using declination' specifically with respect to the non adjustable compass

Magnetic declination & variation are one & the same. A magnetic compass is reference to the north magnetic pole (red tip always points magnetic north) so it's irrelevant whether you are in the northern or southern hemisphere. Variation is applied uniformly in relation to magnetic north irrespective of where you are. Easterly variation is added to the compass bearing, westerly variation is subtracted.

This link explains the CADET Nmeumonic Compass to True & reverse for true to magnetic.

https://www.getlostpowerboattraining...alculate-them/

Ignore the reference to deviation, this refers to the magnetic field around a fixed compass generated by steel fittings of a ship for example. This is measurable & is corrected out using magnets undertaking a process known as a compass swing.

Hope this helps
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Old 09-10-2021, 12:01 PM
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Ok thanks guys, I am sure I will get it sorted.

Leon
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Old 09-10-2021, 12:06 PM
Outcast (Carlton)
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If you've ever wondered why those plastic bushwalking compasses have a rotating bezel, this would be why...

So you can correct for magnetic variation/declination by moving the bearing bezel the appropriate amount left or right as appropriate for the variation in your area & then once applied you can read off the true bearing without having to do any calculations.

Note, variation 'varies' dependant upon your geographic location... there is an area in WA where the variation is zero... Variation also can vary for the same reason over time, it usually progresses in the same direction... ie: if say it was 5* east, it will precess in an easterly direction... so a few years on it may become 6* east & so on...

This is one (among many) very good reason that nautical charts are updated very regularly.. in addition to applying any newly discovered features that may be hazardous to navigation, it also updates magnetic variation to be applied to the area that chart covers. Survey maps are the same... when used professionally, updates are released regularly (nautical charts via monthly Notice to Mariners), don't recall the publication used for survey (land) maps.
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Old 09-10-2021, 12:40 PM
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This is how I do it for Brisbane (11.152E) Leon, in the daytime and then fine adjust when it begins to get dark to dial in the accuracy.

Cheers

Dennis
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Old 09-10-2021, 12:50 PM
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Oooo... I like that mount.
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Old 09-10-2021, 12:54 PM
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Quote:
Originally Posted by Outcast View Post
Sorry but, that is incorrect. East is a positive, west is a negative. Variation is always added no matter where you are... Thus a variation of 10.8E is added to 180 resulting in a bearing of 190.8.

28yrs Navy, navigation specialist: Nmeumonic drummed into our heads is C A D E T = Compass ADd East True

Cheers
Yes very true but remember we dont point to MAGNETIC south in astronomy but to true south, so in this case, whatever the compass shows SUBTRACT mag varn to get TRUE south

Its the opposite of navigation where maps are in true and you use mag varn to convert to magnetic to use in aircraft (in my case), ships etc
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Old 09-10-2021, 12:57 PM
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This IIS article explains it too: https://www.iceinspace.com.au/63-498-0-0-1-0.html
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Old 09-10-2021, 01:44 PM
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Excellent Lewis, thanks for the link plenty of reading there,

Leon
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Old 09-10-2021, 03:50 PM
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Leon, forget the compass, they’re rarely accurate and affected by nearby metal. Use the Solar noon method described here. https://www.iceinspace.com.au/forum/...ead.php?t=5690
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Old 09-10-2021, 03:54 PM
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Leon, mine is the best way but it takes just over a year.
Rotate the mount by one degree each night until the trailing stops.

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Old 09-10-2021, 04:00 PM
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Excellent idea RB, at least that is one way out of it.

Leon
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Old 09-10-2021, 04:11 PM
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Excellent idea RB, at least that is one way out of it.

Leon
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Old 09-10-2021, 04:13 PM
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What a work of art is that mount Leon!!

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Old 09-10-2021, 04:49 PM
Outcast (Carlton)
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Quote:
Originally Posted by LewisM View Post
Yes very true but remember we dont point to MAGNETIC south in astronomy but to true south, so in this case, whatever the compass shows SUBTRACT mag varn to get TRUE south

Its the opposite of navigation where maps are in true and you use mag varn to convert to magnetic to use in aircraft (in my case), ships etc
I'm sorry Lewis but, that is still not correct... I know we use True South but, a magnetic compass will indicate Magnetic South by virtue of the opposite pointer of the red one that's pointing to magnetic North. You still have to add the easterly variation to convert it to a true bearing, doesn't matter whether you are navigating, trying to find true south or whatever application... easterly variation still has to be added to the magnetic bearing to obtain a true bearing... in this case True South or 180* True...

Other than Martin's Solar method, the other way round this is to use a phone compass with GPS & set it to read true rather than compass... that works too...
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