Magnetic South and True Sout Please

[leon]

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

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:thumbsup:

[LewisM]

You move it in azimuth according to magnetic variation for the site, which for Warranambool is 10.8°E. 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)

[xelasnave]

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

[Outcast]

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

[leon]

Thank You Lewis, and Carlton, now I,m confused, (I know it doesn't take much at my age) :lol: so where do I go from here.:shrug:

Leon:thumbsup:

[Nikolas]

This should help mate
http://www.solaripedia.com/files/447
just work out the delineation in Warrnambool and go from there

[Outcast]

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.com/compass-variation-and-deviation-how-to-calculate-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

[leon]

Ok thanks guys, I am sure I will get it sorted.

Leon

[Outcast]

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.

[Dennis]

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

[multiweb]

Oooo... I like that mount. :thumbsup:

[LewisM]

Yes very true but remember we don’t point to MAGNETIC south in astronomy but to true south, so in this case, whatever the compass shows SUBTRACT mag var’n to get TRUE south

It’s the opposite of navigation where maps are in true and you use mag var’n to convert to magnetic to use in aircraft (in my case), ships etc

[LewisM]

This IIS article explains it too: https://www.iceinspace.com.au/63-498-0-0-1-0.html

[leon]

Excellent Lewis, thanks for the link plenty of reading there,

Leon :thumbsup:

[acropolite]

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/showthread.php?t=5690

[RB]

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.

:lol:

[leon]

Excellent idea RB, at least that is one way out of it. :lol::lol:

Leon :thumbsup:

[RB]

:lol: :thumbsup: :thumbsup:

[RB]

What a work of art is that mount Leon!!

:eyepop:

[Outcast]

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... :)

[Outcast]

Again, I'm sorry but, that article is wrong with respect to applying variation..

There just is no way round it... doesn't matter if it's astro, navigation or whatever.. variation is applied by adding an easterly variation to a compass bearing to obtain a true bearing... True South is 180* T... a true bearing...

Not trying (but, probably succeeding) to start an argument but, it just is what it is... C A D E T... & True South is 180T... :)

:):):):):):):):):):):)

[LewisM]

Carlton, yes 180 T is 180T, which equates in this case to magnetic south being 190.8. But compasses measure magnetic so to find true as we need to for Astro you SUBTRACT the variation to get an indicated compass bearing for True South.

We don’t use magnetic at all in Astronomy so we need to find TRUE. A compass shows 180 magnetic, do true is 10.8 degrees LESS in this example, being a compass bearing of 169.2

If you set up compass 180 plus variation you will be way off polar aligned.

On a map using a protractor you are measuring TRUE. The maps show lines of mag var’n which in the eastern states you add to the true to get the magnetic bearing.

Again we need to find true not magnetic. You reverse the nav procedure.

Or does this explain HMAS Melbourne’s grand misfortunes? ;)

[Outcast]

Sorry but, I'm not following your logic Lewis... When you take a compass bearing (magnetic) you add easterly variation to plot it as a true bearing... Eg: magnetic bearing of 080 becomes 090 (if variation is 10E) in order to plot it as a true bearing... To convert a true bearing to magnetic you subtract it from 090 to get a compass bearing of 080...

Okay... I see where you are going with this now... You're explaining to Leon what the bearing should read on his magnetic compass... I think... Penny may have just dropped... Please confirm...😁

[Outcast]

Sorry for the confusion Leon... If Lewis confirms where I think he's gone with this, then he is indeed correct.. I just had a little problem with his logic but, I get it now... I think...

[multiweb]

+1 Hey Leon, start a new thread in the DIY about that mount and tell us how it works. More pictures please. :thumbsup:

[xelasnave]

Leon to get a pretty good polar alignment place or mount your camera on your wonderful instrument such that it points exactly where your polar axis points..take time and in day light so you get the camera and polar axis in sync.. now at night... Importantly with your motor NOT running, you will be looking for star trails forming small arcs, point the polar axis at where you estimate the CSP is at..use a planetarium to eye ball it.. then take a long exposure probably minimum of 10 minutes maybe less at 100 iso .. look at what you have captured..you will see many semi circles or very small arcs..look at these and determine where the centre of these arcs will be found..that is your CSP ..at first it may be well out of the picture so don't worry...you then reposition to bring the polar axis closer to where you expect the center of the circle will be found..move the lot of course and dont let the camera move from your day time set up... and take another long exposure...re position again and continue until the centre of the circle is at the centre of your photo ( viewing screen) as the camera and your polar axis are aligned the polar axis and your camera now point at the CSP.

I hope you understand the idea..should not take more than an hour maybe much less...nefore I purchased pollemaster this is how I found CSP...
Good luck.
Alex

[RB]

Yes Leon, I'd love to see that too!!

:thumbsup:

[Startrek]

I started off this hobby trying to find my True South line using an expensive Silva compass with magnetic declination at both my Sydney location and South Coast NSW location and found that my polar alignment after the initial or first iteration was way off , up to 4 degrees.Every time I used it there were significantly different readings. I noticed the closer the compass was to the ground the deviations were worse and on the ground were all over the place ( obviously picking up iron sources somewhere.For every set up I was meticulous in setting up the tripod , levelling , orientation, latitude settings and so on , even using right angled set squares etc.... and so on

I thought there’s gotta be a more consistent reliable method to find True South and permanently score a line on the ground for repeated use at both sites.
The penny dropped from my scouting days , Solar Noon Shadow method
So set up a 1.2m high 12mm dia rod ( painted black ) at 90 degrees with guy strings anchored NSEW for fine adjustin. Waited for exact Solar Noon time and marked the centre of the shadow as precise as possible with a thin indelible marker.
Set up my tripod meticulously aligned to the new Solar Noon True South line. Performed my polar alignment routine and after the first iteration ended up only 5 or 6 arc minutes away.Both locations ended up with really accurate initial PA and usually only require another couple of iterations to get below an arc minute
So sold the Silva compass and now I have my extremely accurate permanent True South lines at both sites thanks to the good old Sun.
Nothing wrong using the compass but I found it had poor reliability ( not always the same line )
NB: Also at both sites the ground is laid pavers not concrete but fairly level ( if your out in the bush with uneven ground you would need a flat bit of plywood to use to mark your line.
My experience.........

Cheers
Martin

[leon]

Well guys this is an energetic discussion indeed and some very useful and varied opinions loved reading all the responses, thank you.

RB I will see what I can put together sometime up the track, Alex was also very impressed and I did give him some DIY information, in a PM.

Thank you for your interest.:thumbsup:

Leon :thumbsup:

[LewisM]

I dunno, been using a bog-standard Silva for years (I am ALWAYS portable - nothing permanent). I use the iPhone compass occasionally too. I then polar align with SharpCap, and always have it in the "Excellent" range within 5 minutes without any problem.

I stand about a metre behind the mount, eyeballing it along the RA axis. I don't go to close to the mount at all, and always have the mount OFF and no EM sources around whilst doing this rough setup.

[xelasnave]

Actually Leon to start with just out your camera on a run if the mill tripod and do some start trail circles..you will get where South is very easily.. you will even get a good idea where CSP is from your star circle photos..plus they are fun...see how long you can expose for..tip cover half the lens.
Alex

[mura_gadi]

"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... :)"

-------------

I'd be abandoning the compass pretty much, movement of the magnetic pole is stupid atm. Anywhere from 55-80km's+ a year... you'd have to keep track of the current position for non-permanent setups.

Martin's option or the phone would prove a better future proof option imo to use.

Your probably doing better than 1 degree of movement every three years using magnetic north. So, you would need the latest co-ords closest to the day you set the mount up.

I like the camera and a long exposure idea myself as well. Just mount the camera using the same rack(same position) as the telescope if possible.

[xelasnave]

Up my way, out on the back ridge we were lucky to get back before dark the first time we took a compass ..so far out ..but apparently there is a lot of iron stone out there which I was told caused the problem..but I dont know ..lucky we picked up the one and only fence line and followed it back to the road and walked down the road to get home ..added about five k but better than wandering around lost all night...as soon as the Sun sets that bush is like another world, even in familiar tracks you feel lost...thats why we took a compass..
Alex

[Dennis]

Sounds like pretty much what I do Lewis, but I sit the compass on a non-magnetic wooden beam.:)

I then used to touch up the PA via the Tak PA Scope when it got dark and found this method to surprisingly accurate.:)

I now use the QHY PoleMaster when I set up in our back garden.

Cheers

Dennis

[leon]

I am bound to get it pointing in the right direction with all this enthusiastic debate, thanks to all.:)

And I will try and write up an explanation of how i put this device together, the equation the curved thread follows, and the angles and motor to run it all.

It can be easily build if you are a bit DIY in the shed, so to speak :thumbsup:

Leon :thumbsup:

[RB]

.... and then tell us also which method you used to find True South.
I bet you choose my method!! :thumbsup:

:lol:

[leon]

Andrew,

I have chosen which i see as the best, and I also have a version of my own, that might just beat all of them, :shrug: but I do not wish to disclose this on open forum in case I start a war. :P :lol:
Watch this space in the near future

Leon :thumbsup:

[RB]

:lol: :thumbsup:

... yeah but my method is so easy... it just takes a year...

:rofl:

[LewisM]

Leon mightn’t have that much time left RB… ;) :)

[RB]

Leon's a legend Lewis, young at heart and strong as a bull.
I'd be more worried about you, my little souvlaki...

:lol:

[LewisM]

I don't taste like chicken, so buzz of buzzard breath

[leon]

Such confidence Andrew, hope I'm up to the task, however when this project is up and running, which will be soon i hope you will all be treated to a front row seat.;)

Stay well fellow IIS'S

Leon:thumbsup: