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Astronomy compass...?

emadmoussa

By emadmoussa
in The Astro Lounge

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emadmoussa

emadmoussa

Posted
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OK, I usually use my android compass which depends on GPS to determine the correct direction. For some reason it doesn't seem dead accurate these days...For practicality I want to fit a compass on the mount. I can't think of a proper one that doesn't get affected by close contact with metal... :Envy:

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EBXL5

EBXL5

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Every compass is affected by the introduction of material ferrous or not as the magnetic field will be altered in some way, all be it far stronger with ferrous materials.

I think the solution to you problem would be to set up a cross on the ground or simple pointer even that you have derived from your unaffected compass readings and then set up your scope afterwards.

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emadmoussa

emadmoussa

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Every compass is affected by the introduction of material ferrous or not as the magnetic field will be altered in some way, all be it far stronger with ferrous materials.

I think the solution to you problem would be to set up a cross on the ground or simple pointer even that you have derived from your unaffected compass readings and then set up your scope afterwards.

Yep, good idea - I was thinking about that. Something like points or indents on the floor...

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Andy_E

Andy_E

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Every compass is affected by the introduction of material ferrous or not as the magnetic field will be altered in some way, all be it far stronger with ferrous materials.

I think the solution to you problem would be to set up a cross on the ground or simple pointer even that you have derived from your unaffected compass readings and then set up your scope afterwards.

I've got a sundial that after some careful (if not obsessive compulsive!) tweaking now faces as accurately to N as I can get it. Plus the missus doesn't mind having it in the garden!

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The Sailor

The Sailor

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What we done when using a compass close to metal as in armoured vehicles was to move away from the vehicle get north and mark it, move back to the vehicle check the error and allow for the difference, never a problem, bombs dropped in the correct place :D.

Jim

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emadmoussa

emadmoussa

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What we done when using a compass close to metal as in armoured vehicles was to move away from the vehicle get north and mark it, move back to the vehicle check the error and allow for the difference, never a problem, bombs dropped in the correct place :D.

Jim

Now, this is fantastic. Locking on target for some Eurofighter to hit. :D

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EBXL5

EBXL5

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Not sure what the technique is called but; have two thin pegs in the ground, make sure that they are both aligned to north, and then using a laser collimating tool or even mk1 eyeball make sure the scope and both pegs are in line with each other voila MAGNETIC north, obviously you would need to take any variation etc out to derive TRUE north which I guess is what you're after.

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Spikey

Spikey

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What we done when using a compass close to metal as in armoured vehicles was to move away from the vehicle get north and mark it, move back to the vehicle check the error and allow for the difference, never a problem, bombs dropped in the correct place :D.

Jim

Used to do the same with aircraft to get a deviation map that we could get typed out and stick next to the magnetic compass. Called it a compass swinging exercise, just shows up the error that is used in your mental calcs when navigating by compass.

In answer to the OP's question, just hold a compass near to the leading leg and get it as near to magnetic North as you can get. That will get you in the general vicinity assuming your mount elevaion is accurate. You'll have to do the rest with the polar scope, again assuming you've calibrated it correctly.

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The Sailor

The Sailor

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I don't even use a compass, I have a rough idea of north, plonk the tripod down keeping the mount pin to north, on with the mount and use the alignment wheels to get on polaris, if really out just move the tripod slightly. Once you have Polaris mark the ground and thats that.

Jim

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EBXL5

EBXL5

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Used to do the same with aircraft to get a deviation map that we could get typed out and stick next to the magnetic compass. Called it a compass swinging exercise, just shows up the error that is used in your mental calcs when navigating by compass.

Ah the joys of a compass swing, "it's too windy" or "it's due to rain chief"!

Double mustard sandwich on the Watts Datum compass, good times!

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Spikey

Spikey

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Ah the joys of a compass swing, "it's too windy" or "it's due to rain chief"!

Double mustard sandwich on the Watts Datum compass, good times!

I used to keep the props running at past tickover, kept me dry at the tail end :) Don't touch those chocks Ginger, theres a good fellow, we don't like that shade of red :)

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