Celestron 91510 instruction manual Using the R.A. Vernier Scale

6.Hold the telescope and release the R.A. clamp.

7.Move the telescope in R.A. until the indicator points to the correct coordinate.

8.Lock the R.A. clamp to prevent the telescope from slipping in R.A. The telescope will track in R.A. as long as the motor drive is operating.

9.Look through the finderscope to see if you have located the object.

10.Center the object in the finder.

11.Look in the main optics and the object should be there. For some of the fainter objects, you may not be able to see them in the finder. When this happens, it is a good idea to have a star chart of the area so that you can “star hop” through the field to your target.

This process can be repeated for each object throughout any given night.

Using the R.A. Vernier Scale

To increase the accuracy of the R.A. setting circle, the mount comes with a vernier. This device allows you to get more precise readings down to one minute of right ascension.

Before we go into the specifics on how to use the vernier, let’s take a look at the scale and learn how to read it. First, the zero (0) mark on the vernier is the R.A. indicator and will hereafter be referred to as such. It is on the extreme right end of the vernier scale with the other numbers increasing as you move toward the left.

If the R.A. indicator is right on one of the marks of the R.A. setting circle, then that is the coordinate the telescope is pointing at. The problem arises when the R.A. indicator (zero mark) is in between two of the marks on the R.A. setting circle. If this is the case you will notice that along the vernier scale, one of the marks will line up with one of the marks on the setting circle. This mark indicates the number of minutes that should be added to the R.A. reading of the indicator. Since the indicator is between two R.A. marks, add the minutes to the lower value that the R.A. indicator falls between.

For example, let’s say the R.A. indicator (zero mark on the vernier) is just left of the 5h 40m mark. This would place it between the 5h 40m mark and the 5h 50m mark. If you look down the vernier scale, you will see that the “4” is the only mark to line up with any of the marks on the R.A. setting circle (see figure 8).

This means that you are 4 minutes to the left of the 5h and 40m mark or more simply at 5h and 44m.

Figure 8

Here’s how to use the vernier:

1.Look up the coordinates of the object you want to observe. For our example we will use the Ring Nebula (M57) which is at 18h 53m right ascension.

2.Release the R.A. clamp and rotate the telescope until the R.A. indicator is between the 18h 50m mark and the 19h 00m mark on the R.A. setting circle.

3.Lock the R.A. clamp to hold the telescope in place.

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