North-south meridian line

[teleskopjo]

A simple question, what's the procedure to draw a north-south meridian line, using a declination-corrected magnetic compass?

You cannot simply put the compass on the ground, mark the north end, do the same thing at another location and join the two points as they have to be collinear.. How is this best done? (ignore the solar noon shadow option).

[bobmoss]

Are you using a compass with flat sides (like a walking compass?) If so, simply line your compass up and then get something which is dead straight (like a long spirit level) , butt that up against the side of the compass and use that to draw your line.

[teleskopjo]

I was going to use an app in my phone which has no flat sides.. So guess the most reliable method is to mark a shadow before and after local noon and then bisect the angle.

[michael8554]

A marching compass has a mirrored lid with a vertical slot in it.

You tilt the mirror so that you can see the needle and also see your intended destination through the  slot.

I your case you put up a pole in your telescope's intended position, then sight the pole from the north and then from the south, marking each position,

Then join up the three positions to get a magnetic NS line.

Sun's shadow at local "noon" is a better way to do it.

Michael

[astrofox]

I used a vertical pole at our local noon. By far the most simple way.