Wrong Ascension

[ZarTheEducator]

Greetings All:

I have an equatorial mount with setting circles. The declination circle seems to read accurately, but the RA is giving me fits.

Before we go on, I am technologically savvy. I understand what RA is, that the numbers increase to the east, and that the circle has to be reset to stay in synch with the sky. I also understand that there are two scales, one for the northern, the other for the southern hemispheres.

So far, so good, except that NEITHER is giving me anything at all like rational results! If I aim at Arcturus (14h 15m 19n) and set the top numbers (ascending to the LEFT as you look at the mount) on the hour circle, I wind up with the scope pointing into empty sky when I change to Vega (18h 35m 38n). A similar result seems to happen when I use the lower set of numbers (ascending to the RIGHT). The polar axis is aligned to north, and the mount is levelled beforehand.

Any advice is appreciated.

JTC

[clop]

Well I'm not sure if it's relevant or not, but somebody once sent me this set of instructions for using RA:

One thing that people find difficult (and for good reason) is figuring out how to set the East/West offset on the Polar Alignment time circle. The world is supposed to be divided into 24 equal time zones each 15 degress of longitude wide. Local political considerations may make a given time zone wider or narrower. The sky does not care about local politics. The offset dial on the mount is there to adjust your local time to the reality of the sky.

To determine your particular mount's offset degrees and direction, you must know your local longitude and your local civil time GMT offset. Divide your longitude by 15. Subtract your local civil time GMT offset from this value. If the value is plus you will use the West offset. If the value is minus you will use the East offset. Mulitply the results of the subtraction to give the number of degrees offset.

For example, if I am at 122 degrees longitude. Dividing 122 by 15 gives 8.1333. My local GMT offset is 8. Subtracting 8 from 8.1333 gives 0.1333. The value is positive, so I use the West offset. Mulitplying 0.1333 by 15 gives 2.00. I set my mount offset to 2 degrees West.

Chicago is at 80 degrees longitude. Dividing 80 by 15 gives 5.333. Chicago's GMT offset is 6. Subtracting 6 from 5.333 gives -0.666. The value is negative, so someone in Chicago should use an East offset. Multiplying 0.6666 by 15 gives 10. Someone in Chicago should set thier their SP offset to 10 degrees East.

Note: The signs and directions are for the Western Hemisphere. If you live East of GMT, change them.



Does this help?

clop

[hhEb09'1]

So far, so good, except that NEITHER is giving me anything at all like rational results! If I aim at Arcturus (14h 15m 19n) and set the top numbers (ascending to the LEFT as you look at the mount) on the hour circle, I wind up with the scope pointing into empty sky when I change to Vega (18h 35m 38n). A similar result seems to happen when I use the lower set of numbers (ascending to the RIGHT). The polar axis is aligned to north, and the mount is levelled beforehand.That's a swing in RA of 20m 19s. I just looked up Arcturus, and it is listed as 14h 15m 57.22s in SkyMap, and Vega as 18h 37m 10.17s, which would be a swing of 1m 12.95s farther, only about a quarter of a degree.

Declination also has to be reset as I'm sure you know but you don't mention it in your post, so I'll include them too: Arcturus is listed as 19 8' 56.5", and Vega as 38 47' 33.4"