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Reading the Setting Circles

Both the RA and Dec setting circles are equipped with verniers. With care, the practiced observer can set the telescope to 10 in RA and and 5' in declination. Examples of how to read the verniers are given in Figs. 2 and 3.

 
Figure 2:   The RA vernier is read by obtaining the hours and minutes from the ``0" mark (16:00 here) and reading the number of seconds based upon where the marks on the two scales line up from the top scale (30 sec in this example). Thus the telescope is pointing to an RA of 16 00 30, if the circle was set to the correct LST at the start of the evening.

 
Figure 3:   The dec vernier is read by first obtaining the nearest 15 arcmin from the ``0" mark ( in this example) and adding the appropriate number of 5' intervals based upon where the marks line up with the upper scale: 5' here. Thus the telescope is pointing to in this example. For negative decs the left side of the scale would have been used.


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kessel@noao.edu
Mon Apr 3 09:15:22 MST 1995