polar alignment

[sejanus]

i thought I'd make a new thread rather than cluttering my old one.

so this is what I do right? :help:

make tripod dead level with spirit level

1) point mount exactly dead south according to magnetic compass
2) adjust elevation of scope to 34 degrees
3) manually position the south celestial pole or at least position octans in the viewfinder or polar finder of the eq6.
4) turn eq6 on and run the telescope alignment process

missing anything?

cheers

[h0ughy]

offset the scope to point 10 degrees to the east of due south for a start

[sheeny]

Not sure...

It depends how accurate you want your alignment to be. If you are just visual observing, then what you are doing may be close enough.

But first, presumably you are correcting for magnetic declination at your location when pointing your scope "dead" south (meaning true south I assume)? Magnetic declination adjustment is what HOughy is referring to. For me in Oberon it's about -12 degrees i.e. when the compass is set to 168 degrees magnetic it is pointing to true south (180 degrees true).

So if you have your magdec right, then what you are doing above is probably OK for most visual observing. If you want to do any real accurate GOTO work or astrometry or imaging (particularly long exposure) then you might need to go the next step and drift align.

There are quite a number of threads in this forum covering drift alignment - try a search if you need more information, and then if you still have questions - don't hesitate to ask! Drift alignment is a skill well worth having, developing and maintaining!

Al.

[Dennis]

As the wise Mr. H0ughy said; you actually want the polar axis pointing to the “geographic” South Celestial Pole (SCP) rather than the “magnetic” S Pole. The SCP is the point on the imaginary celestial sphere around which the stars appear to revolve. It essentially defines the axis of rotation of the Earth as it spins on its axis once every 24 hours.

This “geographic” axis of rotation and the “magnetic” axis defined by a compass do not line up, and their offset varies quite markedly world wide. For me in Brisbane, when the magnetic compass is pointing to magnetic South, the "true" SCP, or axis of rotation, lies 11 degrees to the East.

Just another trap for newcomers to the black art of polar alignment...

Cheers

Dennis

Edit: ...and the wise Mr. Sheeny, I didn't see his very nice explanation before posting...

[sejanus]

thanks heaps guys

[sejanus]

btw I'm just wanting to get the basic polar alignment going so I can use the GOTO stuff, then once I'm nice and comfy with it thats when the camera and the more precise polar alignment/drift will come out.

cheers & thanks again

[sheeny]

No problem. If you find your GOTO isn't as accurate as you'd like, then I would suggest you start playing with drift aligning because 1) it will help with accuracy of the GOTO, and 2) it also will help to get a head start on drift aligning for when you do get the camera etc - just the spread the learning curve a bit and get a leg up on the frustration factor when you want to make the most of the camera!:P

What GOTO mount are you using?

Al.

[sejanus]

hey sheeny,

it's a eq6. going to give it another crack tonight, hope the sky stays clear!

[OneOfOne]

My procedures are similar, except I am pretty used to estimating the 12 degrees deviation where I am so I just put the mount on the ground, no compass. Pointing directly at the back fence is due magnetic south, so I just turn it to the left "a bit". I don't generally bother to level the tripod if I only expect to be outside for an hour or so. Usually the alignment is a bit out by then but I am going inside anyway. Mine is an EQ5.

[Omaroo]

Hey sejanus :)

Where abouts are you in the southern suburbs? Maybe you'd like to come out to "Stargard" at the Oaks one night with the MAS guys.:hi:

[sejanus]

i couldn't try last night as i left it until 11pm to try and then the clouds rolled in :(

omaroo I'm at helensburgh near wollongong - I'd love to come out - how far are you guys? not sure where the oaks is?

cheers

[I.C.D]

Hey sejanus
I have been using a hand held GPS to find true South by changing the setting on the GPS from Mag South to true south so no matter were you go you will fine SCP with the correct offset

[sejanus]

hi ian

thats a neat idea. I only have a crappy little $15 compass it drives me nuts.

[Lee]

This may help people work out your approximate magnetic declination for polar aligning purposes.... you can also look in your local street directory too....
Sorry the quality is low, I downloaded it as a 2.5MB bmp..... (forgotten where from....).... jpg compression surprisingly hard....

[Omaroo]

It's about 15 minutes from Camden. Not far! All you have to do is come back up to Appin Road & go right. Hang a left on Narellan Rd to the Camden bypass - turn left for Camden and take the second right into Burragorang Road. That road will take you to The Oaks in about 15 minutes. Go through the town (about 3 streets - it isn't big) and take the first left out of town into McIntosh St. At the end of that street and through the gate is the Dudley Chesham Oval. We are on a road that skirts right around to the left hand side and then over a little bridge. It's out of the way but nice and dark. According to the club mag, the next session will be on 25/11/06.

Cheers
Chris

[sejanus]

Camden is fairly close yeah I've been there a few times. Is there a website or something with joining details or similar?

[Omaroo]

Here's the address: http://www.macastro.org.au/

Maybe we'll see you there one night! :)

[sejanus]

hey guys just an update as last night was the first night i had a real chance to try it after kulnurra (work/clouds kept interfering)

With the 80mm I had an incredibly accurate alignment, so much so that I had canopus centered in the viewfinder and then had to go inside for a hour so i left it there, and when I came back it was still in the exact same position!!! Wish I had set the camera up :) Doing a goto on any object placed it dead centre and kept it there. Go the eq6 :)

With the sct it was nowhere near as accurate and with the sct i was having probs finding the alignment stars, but had to pack it up as i had to get up early this morning for work. But at least I'm getting there.

[ving]

aint it great when you get the alignment spot on! :D

i only do a rough alignment as i am mostly a visual person with the occasional slor/lunar/planet shot.

hey, this monday mas are having a meeting (not for viewing) at uws (7:30)... if you want to come along just PM me, oomaroo or astronut and we'll give you teh details

[sejanus]

hey ving would love to but i have a work related thing on tonight :(

[FNQ_View]

I have read this thread with some interest. I recently discovered that the published declination for my area is very different to the actual declination. Since perfforming the following excercise I find that my previously questionable goto scope actually locates quite well when it's setup correctly. I had been introducing an error of at least seven degrees due to some local irregularities.

If you are using your 'scope at the same location regularly, I would suggest you try the following exercise.

To find celestial North or South, you need need a long stick and two small sticks or tent pegs - even two similar size rocks will do.

At approx. 11.00 am on a sunny day go to the spot you usually set up your telescope. Drive one end of the long stick into the ground so it stands up vertically.

Drive a tent peg into the ground at the western end of the stick's shadow.

Return every 15 to 30 minutes to monitor the movement of the shadow.

When the shadow length to the East is the same as it was to the west, drive the second tent peg in to the ground at the end of the shadow.

Remove the long stick from the ground and align it against the tent pegs.

Stand with the sun to your right and your toes touching the long stick. you are now looking towards the SCP. :D. ( Have the sun to your left if you want North ) Look for a marker that you can use to align your telescope against or make a mark at the furthest point that you can reasonably gain access to ( the further away your mark - the more accurate your alignment.