EQ mount and celestial sphere

ColHut (Colin) · #1 17-01-2009, 03:19 PM

Dear all,
A couple of questions.

Suppose my eq mount is in the home position - aligned with the pole and pointing at celestial south. Further suppose that the local line of RA passing perpendicular to the ground is 6 o'clock. i.e. Orion is just east of N/S. Now if I swing the scope clockwise without altering the RA (i.e in declination only) through Tucana I am on RA 0. If left past corvus then RA is 12. Is this right? This seems possible because we only use +90 t0 -90 for declination but use a full 24 hors for RA.

cheers

rogerco (Roger) · #2 17-01-2009, 06:52 PM

Not really as what you suggest is that one horizon is 0 and the other 12 which it isn't. There is twelve hours of RA between them but that is not the same. You are correct in assuming the two directions are twelve apart but you haven't swung the telescope though twelve hours of RA. In fact you wouldn't move the telescope in the way you suggest if following a celestial object.

As I understand it your starting point "pointing at the south pole" would be with the DA axis horizontal that is with the telescope on one side of the mount and the counterweight sticking out the opposite side. The telescope can then swing south to north in declination and can cover half the sky in RA.

Again as I understand it with an German Equitorial mount such as an EQ5 a problem is that the telescope has to swing round if you want to follow an object past the meridian otherwise the back of the scope bumps into the mount support.

I hope I am not leading you astray.
Roger

ColHut (Colin) · #3 17-01-2009, 10:12 PM

Thanks for that. I mean the telescope is aligned N-S with the mount, and the telescope was free to move in dec only through 180 degrees on each side (360 in total) . I understand that I would have to rotate the scope in RA 6hrs east or west to be able to move in dec "straight up".

Not really as what you suggest is that one horizon is 0 and the other 12 which it isn't.

For the sake of this example 6 is "straight up"

thanks

Sionnagh (Mick) · #4 17-01-2009, 10:35 PM

I think I see what you're getting at. If the RA 6h00 line passes straight overhead between the poles (the meridian) then to aim the telescope at something along that line you'd have to rotate the RA axis 90deg to either the east or west to be able to see your target. Yes? On a German equatorial a line drawn from the counterweights through the RA axis to scope is always at right angles to the angle of right ascension.

;-)
Mick