How do you Use Reference Stars to Calibrate a Telescope?

C2A lets you define reference stars to make the calibration of a GOTO telescope easier. Just define a list of stars by their names (as used by C2A) in a file named Wap.vrs and put this file in the folder "C:\Users\<user name>\My Documents\C2aw" (under Windows 7) which is the folder that contains the user files. By default, C2A will look for the Wap.vrs file first in this folder, and if it is not found, it will look for it in the folder "C:\Users\<user name>\AppData\Local\C2aw" (under Windows 7) and then in the installation folder (by default "C:\Program Files\C2A", or "C:\Program Files (x86)\C2A").

An example of such a file is provided in the standard version of C2A in the installation directory of C2A.

Here is, for example, is a list of reference stars:

# List of reference stars
Achernar
Acrux
Alnair
Albireo
Aldebaran
Alphard
Alphecca
Alpheratz
Altair
Antares
Arcturus
Betelgeuse
Canopus
Capella
Deneb
Denobola
Deneb Kaitos
Dubhe
Fomalhaut
Hamal
Markab
Mirfak
Mizar
Nunki
Pollux
Procyon
Rasalhague
Regulus
Rigel
Rigel Kentaurus
Schedar
Sirius
Spica
Suhail Al Wazn
Vega

The # character at the beginning of the line means that the line is a commentary. You must ensure that the names of the stars are strictly identical to those used in the SAO catalogue in C2A.

These reference stars are displayed by using the command Reference points in the Telescope menu. A global view of the horizon is then displayed (with south at the bottom of the screen). Reference stars are enclosed in a coloured circle so that they are easy to recognise. Above 20 elevation the circles are green. Below 20 elevation the circles are yellow. Reference points are removed by using the Reference points command again.

The screenshot below shows what you get when you display reference points:

A second list of reference stars can be used with C2A. This is a list of stars around the pole (of the northern or southern hemispheres). These stars must be declared in a file named Wap.prs which must be placed in the folder "C:\Users\<user name>\My Documents\C2aw" (under Windows 7), which is the folder that contains the user files. By default, C2A will look for the Wap.prs file first in this folder, and if it is not found, it will look for it in the folder "C:\Users\<user name>\AppData\Local\C2aw" (under Windows 7) and then in the installation folder (by default "C:\Program Files\C2A", or "C:\Program Files (x86)\C2A"). An example of such a file is provided in the standard version of C2A in the installation directory.

the C2A installation directory. The list of reference stars to be used is selected in the Misc tab of the Telescope options dialogue box. Just select the All sky option (to display reference stars over the whole celestial sphere) or Polar alignment (to display stars around the pole). For reference points concerned with polar alignment, you can also specify in the Misc tab the symmetries to be applied to the field to reproduce the view that you could get in a polar scope. The screenshot below shows the polar field with the three reference stars defined by default in the Wap.prs file provided with C2A (Polaris, Yildun and SAO 1168 for the north celestial pole):

Note that C2A displays a view of Field type and that the correct symmetry and rotation of the field is applied to show it as it would appear in a polar scope for the current date and time of the map. You can use the $ key as a way to quickly update the polar view during an observation session. You can also capture in PDF file the appearance of the polar field at different times of the night to aid setting up in the field (see the section Polar clock).

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