Where's the meridian?

bloodhound31 · #1 06-05-2007, 05:54 PM

My telescope is telling me to use the RA drive to point the tube at the meridian. I am at 35 degrees south (in canberra)

Is this telling me to point the telescope in the general direction of that imaginary line between north and south? Or is it asking me to point at a particular location (IE an exact position in the centre of the eyepiece?)

I have no idea what to point at. I can draw a line straight overhead from north to south, but that line would not be deadly accurate of course.

so, where is this fabled meridian?

BAz.

matt · #2 06-05-2007, 06:10 PM

An imaginary line which runs from north to south, passing through the zenith.

bloodhound31 · #3 06-05-2007, 06:59 PM

Yes Matt, that much I have known for years....

But is it an exact point? Is there a position..ie RA and DECL, where you can point the scope for a perfect alignment on the meridian?

Better still, is there a named star ON the meridian?

Baz.

Astroman (Andrew Wall) · #4 06-05-2007, 07:04 PM

No Baz the meridian doesn't move with the stars. It is not a defined point in space and has no RA/DEC. What is the mount you are using? I only know of mounts pointing at the pole or Due north/South for Alt/Az mounts. If its at the pole the scope is pointed at the pole with counterweights pointing at the ground.

Astroman (Andrew Wall) · #5 06-05-2007, 07:06 PM

I better add its a fixed line, running from true south directly overhead (zenith) to true north. So as the stars move it does not. Also the RA on that line is also the sediral time

bloodhound31 · #6 06-05-2007, 07:26 PM

So we are talking north south earth coordinates then? True north as a pose to grid north or magnetic north?

I have the telescope set up on a wedge at my correct lattitude.

As part of the alignment process, the telescopes software tells me to point the tube, using the RA motor, at the meridian.

So I rotate the tube to point straight up as best as I can by eye. A line that goes from north to south straight overhead, must be straight up!!

No?

Baz.

matt · #7 06-05-2007, 07:35 PM

Baz.

Aim for as close to 0 Dec as possible. You want to find a star along the equator, close to the meridian

I'm assuming you are polar aligning?

bloodhound31 · #8 06-05-2007, 08:04 PM

Quote:

Originally Posted by matt

Baz.

Aim for as close to 0 Dec as possible. You want to find a star along the equator, close to the meridian

I'm assuming you are polar aligning?

Yes mate I am. Are there any star maps or charts that show this position?

matt · #9 06-05-2007, 08:07 PM

Do you have any planetarium software?

If not, you can download Stellarium for free.

Just google it... download it... away you go.

solissydney (Ken) · #10 10-05-2007, 05:19 PM

With the scope pointed North, and the counter-weight shaft horizontal, pointed East, you then raise the tube and point it at the Meridian.
Ken

solissydney (Ken) · #11 10-05-2007, 05:40 PM

To polar align you point the tube towards North, with the counter-weight shaft horizontal, pointed East. Then you raise the tube and point it towards the Meridian. Select the closest star, it varies, dependent on the season. With an illuminated recticle turn the eyepiece so that the star stays within one line of the crosshairs. Then, if the star drifts up-wards, move the tube a bit towards East. If the star drifts downwards, move the tube West-ward.
To really get to understand what happens. turn the tube a fair bit until the star drifts in the opposite direction.
Ken