Noth/South, East/West scketch references advice please

[Scosmico]

Hi

Can you please give me an advice to locate North/ South, East/West in my sketches?

I have my own ideas how to do that. But I am not confident that I got it right.

I know that I need to consider my scope West/East inversion.

How do you do it?

[Mike73]

Good question..Its something that I guess I should do but haven't.

[Qualia]

Just seen this and I apologise for not replying sooner. Whenever it is necessary to measure angles, separations or do a rough sketch, I do the following.

Polar align your mount and switch off any tracking motors.

Skew your scope to a relatively bright star away from Polaris. For the sake of brevity, I usually go for something like Epsilon Cassiopeiae.

Place this or any other star - other than Polaris - in the centre of your EP's field of view and let it drift. Where it exits is by definition your west, resting at 270º.

Now, looking through your eyepiece (you may need the finderscope to help a little), nudge or move your mount's axis towards Polaris.

Your EP's north is where that star enters your EP field-of-view, and is by definition at 0º. To make sure you've got it right, the angle distance from north to west on your sketch pad should look like 90º.

If you are using a reflector type set up, your north is counter clockwise from your west. If I've got the mental picture right - stars will drift toward the left.

If you're using a refractor, then west will be clockwise from your north. That is, stars will drift toward the right.

Now that west (270º) and north (0º) are known, east (90º) and south (180º) should be easy to work out.

For sketches, two cardinal points ought to be included, so that others can appreciate your art-work observation relative to their own position.

Hope that helps

(In my own case, Tal supplied a nice cross-hair screw-in type recticle which is useful for this kind of thing).

[rory]

when i sketch through the reflector i usually mark west where the stars drift away, is that correct ? close enough without being over critical ?

[Qualia]

That sounds good, Rory. If you wanted to get a little more precise, after marking your 270º, just pan the scope to Polaris and where it enters the EP is 0º. Mark this on your sketch and see if the west point (270º) and the north point (0º) on yur sketch make that rough angle distance of 90º.

Tal owners should find this easier to do because I think most of their OTAs are equipped with a thread-on crosshair recticle. If they let the star drift parallel to one of the crosshairs where it exits will be west.