Aligning mount to True North

[gkec]

I have a compass and a smartphone app and I know the angle between true north and magnetic north (magnetic declination not to be confused with the other declination!).

However the mount has residual magnetism so I can plonk the compass on the mount and align it like that.

At the moment I just stand away from the mount and peer down the North heading on the compass but it is not terribly easy. I have thought of drawing a line on the ground and aligning the tripod feet with that. But I wondered if anyone else had better methods.

I did think about demagnetising the mount but the diy methods I found that involved heating the mount or hitting it with a hammer. The thought of positing a thread here starting with "I have just melted my mount", or "I have beaten my mount with a hammer and now it is broken" wouldn't do my reputation here any good let alone my chances of observing anything.

Any ideas?

Thanks

Graham

[Grotemobile]

I do what you do, & draw a line on

the ground. I have now drilled holes

in the patio,so it goes back to the

same place every time.My mount is the

CG5, so i just put it in hibernate mode,

when i have finished.All ready to go

for next time.

Steve

[astrofox]

I went back to basic. I stuck a rod vertical in the ground and at 12:04 (my local noon) marked where the shadow fell. Now I have a permant meridian mark on the ground.

[Mondlicht13]

What I did was to find the exact times for solar noon at my location from this site www.solar-noon.com .

You can print out times for the whole year. Then I simply set up a perpendicular line, waited for the exact time and then marked a line which is true North-South.

Now I can line up the mount and be sure I'm almost spot on for alignment.

Of course this does require the sun actually being out. :clouds1:

Cheers

[Tinker1947]

The indents in the patio slabs work for me, there well over a year old now and don't show up as the holes have tarnished.......

[chiltonstar]

For an alt-az mount I have, I have put a white splodge of paint on the patio where I stand the mount, and a white mark on a fence at true north (found by aligning the mount to the Pole and moving the alt back from 52 degrees to horizontal).

Chris

[Carbon Brush]

To demagnetise anything, without a hammer is reasonably easy, but not many people have the gear.

Basically you need an alternating magnetic field that gradually reduces in intensity.

End of technical jargon.

Electronics repair people used to have these 'degaussing wands' for removing residual magnetism from tape recorder heads, metalwork arount cathode ray tubes, etc. If you can get hold of one and spend a few minutes waving it around the steel parts of your mount, it should do the trick.

The same goes for any steelwork in proximity to a mobile phone that includes magnetic field sensors.

[AstroTux]

Electronics repair people used to have these 'degaussing wands' for removing residual magnetism from tape recorder heads, metalwork arount cathode ray tubes, etc. If you can get hold of one and spend a few minutes waving it around the steel parts of your mount, it should do the trick.

Nice idea, but unfortunately you would have to demagnetize the entire mount in one fell swoop and a demagnetizing wand is just not big enough to do this. Any residual magnetism in one part of the mount could re-magnetize any other parts that had just been done, although to a lesser degree. I think demagnetizing the entire mount this way could take a very long time.

[Carbon Brush]

Demagnetising could be done gradually without too much problem. I used this technique some years back on large objects.

Another alternative is to heat above curie point. Success here depends on the type of steel and paint finish.

It would be interesting to hear about the mount type. Usually there is a mix of aluminium alloy and steel. So not everything will be magnetised.

[skir]

I guess using magnetic north to roughly align the mount for observational work only is not good enough then? This site http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp gives my deviation from magnetic to polar north as 1 degree 33'.

[gkec]

Thank you very much for all the replies, I think the vertical stick/marking the leg positions sounds useful (note to self find out how to do hibernate mode). I did get in touch with a local company that does industrial degaussing wands half hoping they might just say bring it in and we'll do it for £20. Anyway they sent me a quote for £220 for the wand and £2000 for the magnetic shield, whatever that is for!

[Grotemobile]

How to do Hibernate Mode.Start off with the

MENU-Go down untill you see UTILITIES.

Press enter & you will find it half way

down.Then just follow what the hand set tells

you.When you swith back on,just follow the

instructions on the hand set once again.

Steve.

[Scooot]

I've been experimenting with ways of placing my Equatorial Platform in line with true north on a repeatable basis. The feet are hidden below the base so marking the ground isn't very easy or practical. Also I use it on my drive so I can't use a permanent marker on it. So I've done the following which is working quite well.

I've placed a brick on the edge of the drive with cable ties wrapped around it to form a cross. Then I place the platform roughly in the correct place on the drive. I then rest a laser pen against a straight edge on the platform and aim the laser at the cross on the brick. I then adjust the position of the platform until its spot on the cross. It takes a couple of minutes and is proving very accurate. I need it to be accurate for my object locating system to work accurately whilst using the platform.

i don't know if the method could be adapted for an EQ mount though but it might be food for thought.

[Carbon Brush]

Thank you very much for all the replies, I think the vertical stick/marking the leg positions sounds useful (note to self find out how to do hibernate mode). I did get in touch with a local company that does industrial degaussing wands half hoping they might just say bring it in and we'll do it for £20. Anyway they sent me a quote for £220 for the wand and £2000 for the magnetic shield, whatever that is for!

I think the company didn't really understand the problem and offered you rather more than is required. I did a quick (not exhaustive) look for a degaussing wand. these seem to be available in the USA for $20. But in the UK, only professional kit, with a higher price tag, came up. It might help if you know a retired TV repair man, or someone who is into amateur radio. These wands are the sort of kit that gets left in the back of a drawer and forgotten.

Hope this helps, David..

[Din]

I must admit I've never heard of demagnitising any metal objects. Compasses are always affected by local metal. When fitted to ships there is a complex system of magnets in place to correct out errors.

I would have thought the simplest solution would be to put a wooden stake or a stone where you intend to place your scope. Use your compass to take a bearing from that object, applying local variation to get a true north bearing. Ensure there are no metal objects about your person that will induce an error. Look for an object, or place something on that bearing line, then place the mount on the first marker, pointing at the second marker.

Ed

[Guest]

It's not just metal objects that cause errors. I wanted to scribe a true north line on my patio so I laid the compass on the patio with a long wooden ruler beside it. After scribing the line I picked up the compass and noticed that it was now pointing in a different direction, the slabs on the patio were slightly magnetic - enough to create an error of about 4 degrees.

[Alfven]

It's not just metal objects that cause errors. I wanted to scribe a true north line on my patio so I laid the compass on the patio with a long wooden ruler beside it. After scribing the line I picked up the compass and noticed that it was now pointing in a different direction, the slabs on the patio were slightly magnetic - enough to create an error of about 4 degrees.

You picked up on a very interesting point there about your "magnetic" slabs. Most aggregates quarried in the UK contain quite large amounts of magnetite, as do those "pink gravel" mixes for drive ways.

[gkec]

Done! Sun shone at solar noon (12:19 you learn something every day!) so I draw a line to align to.

[JimD]

I tried hanging a plumb line up to cast a shadow accross the patio yesterday. The sun was out in the morning when I tested it out, then conveniently went behind clouds for an hour or so, covering the period of solar noon (12.20 here). Then it came out again in the afternoon.

I'll try again today!

[brantuk]

I peg out a line on the ground using string and two tent pegs pointing magnetic north using a compass. Then I set the the front leg on the line and the two rearward legs equidistant either side of it. Then I use the altitude and azimuth bolts to point the polar scope at polaris (refine using "polar finder" free to d/l software). A spirit level is then put in the mount shoe to get RA vertical, and a laser pen to point Dec at the pole star putting the axes it in the home position. No magnetism involved (except the compass bit). Hth

[gkec]

Thanks for all the suggestions. The Sun came out briefly at Solar noon on Saturday so I took the opportunity to draw a line which I then use in a similar manner to brantuk. Pointing was bang on each time not so sure about tracking though.