Using the setting circles
(The following applies to telescopes using a single index on the R.A. circle)
The easiest way to use setting circles is to off- set from a known position. Set the telescope on an object whose position is known (i.e. a bright star in a recognisable constellation - such as listed in the appendix). Unclamp and turn the R.A. circle so that the its pointer indexes the observed object's positional hour and minute. E.g. In figure 6 , the R.A. circle has been set to indicate that the initial object has a listed position of 5 hours 40 minutes. (The declination circle should read the object's declination correctly if the polar axis alignment has been maintained.) It is now only necessary to move the telescope in both axes until the R.A. and Declination pointers index the new object's position.
E.g. In figure 7 , the telescope has been moved to a new object having an R.A. of 7 hours 30 minutes. If the 'target' is not visible, delicate 'sweeping' with a low power eyepiece should bring it into view.
Figure 6
Figure 7
Appendix
Most good star atlases will list the R.A. and Dec.
Constellation | Star | Right Ascension | Declination | |
Spring | Arcturus (α Boötis) |
|
|
|
Bootes | 14h 13.4m | +19˚ | 27' | |
Virgo | Spica (α Virginis) | 13h 22.6m | - 10˚ 54' | |
Leo | Regulus (α Leonis) | 10h 05.7m | +12˚ 13' | |
Summer | Altair (α Aquilae) |
|
|
|
Aquila | 19h 48.3m | +8˚ | 44' | |
Cygnus | Deneb (α Cygni) | 20h 39.7m | +45˚ 06' | |
Lyra | Vega (α Lyrae) | 18h 35.2m | +38˚ 44' | |
Autumn | Algenib (α Persei) |
|
|
|
Perseus | 3h 20.7m | +49˚ 41' | ||
Cassiopea | Schedir (α Cassiopeiae) | 0h 37.7m | +56˚ 16' | |
Pegasus | Markab (α Pegasi) | 23h 02.3m | +14˚ 56' | |
Winter | Sirius (α Canis Majoris) |
|
|
|
Canis Major | 6h 42.9m | - 16˚ | 39' | |
Orion | Betelguese (α Orionis) | 5h 52.5m | +7˚ | 24' |
Auriga | Capella (α Aurigae) | 5h 13.0m | +45˚ 57' | |
Taurus | Aldebaren (α Tauri) | 4h 33.0m | +16˚ | 25' |
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