Compass directions on sketches?

[Ursa Major]

I have seen on some sketches in the sketching section of the forum that the artist/observer has put compass directions on the disk at the edge of the sketch. How do you know where to put these compass points?

(I have attached this picture to show you what I mean.)

Thank you.

[Andrew*]

It's surprisingly easy to do, actually. If you have a non-motorised mount, just watch the direction that the stars/object drift across the field of view - this is west. To find north, slowly move the telescope towards Polaris (this will usually be up) so you know the orientation in the eyepiece. This will be towards north and will be 90 degrees from the East-West line.

If you have a motorised mount which is polar aligned, press the Dec+ (usually up) button to move the telescope northwards, and RA- (usually left) to move the telescope Eastwards

Hope that helps

Andrew

[Ursa Major]

Thanks Andrew.

I have been on Stellarium to see if I could find the compass points of some objects. I noticed that you can only have the compass points going from north to west, to south to east in a clockwise direction? Whereas in the image first provided its goes from north to east, to south to west in a clockwise direction. Are the compass points on this first image wrong?

(This is an image of the points the other way round so you can see what I mean.)

[Andrew*]

That's down to telescopes which reverse the images. I usually get this wrong, but I think refractors the image is left-right reversed, and in newtonians it's left-right and up-down reversed. That's why orientation on maps will differ from views, and why it's particularly important to label correctly.

[Ursa Major]

OK, that makes sense.

So, to sum it up, for reflectors the east and west are the wrong way round, and for reflectors they are the right way round.

Now I need to do some sketches to put the compass points on!

[Andrew*]

In maps we are looking down and have W on the left and E on the right, but in the sky, looking up, as a general rule, E is left and W is right, especially when looking south. (there is an exception to this, when looking N between zenith and the north pole, where W is left).

So in refractors, using a mirror diagonal, the compass points will be in the same order as on maps.

Andrew

[keef_uk]

OK silly question, but wont looking at a compass yield the same results? I have one attached to my tripod is this not accurated?

[Andrew*]

Well, looking in the eypiece is different to ground directions. Eyepieces can be at any angle, and compases don't work vertically!

It works for naked eye astronomy, but not for determining directions in the eyepiece.

Andrew