Quote:
Originally Posted by alistairsam
thanks. as the position of the objects in the equatorial co-ordinate system don't change significantly (we're rotating and not the stars), do we use the Hour angle to find an object?
eg, position of sirius from stellarium at 0011hrs at Melbourne is
RA/DE(j2000): 6h 4m 8.8s / -16d 43' 1.1"
HA/DE : 17h 56m 22s / -16d 43' 44"
and at 0311hrs is
RA/DE(j2000): 6h 4m 8.8s / -16d 43' 1.1"
HA/DE : 21h 56m 22s / -16d 43' 44"
so if I were to have a list of objects with their RA/DE values and I use just the gradations on my equatorial mount, after polar aligning, how do i find out what the RA angle would be or where the object would be?
I'm guessing it would be based on an offset of the RA angle from the observing time and position
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I have never used the hour angle just the RA and DEC.
Yes you are correct. You set the RA by offsetting against a known RA.
Even for a goto scope it has to be originally aligned to a known point but the computer will then compensate for the rotation of the sky with time.
If you start at a known star and set the RA setting circle on your scope it will only be correct at that time without tracking. If the scope tracks then the RA will remain correct until you turn off the scope.