Last modified on 29th June 2004.
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Airmass calculator

Latest version (Linux): 1.0 Date: 10/01/2002
Latest version (Windows): 1.0 Date: 20/01/2002


Once too often someone was wondering what might be the airmass for the object he was observing. This information is often included in the header of an image file at the telescope, but what about when you are planning and selecting which object to observe and when. Well, now you can download my simple (but exact) airmass calculator for that purpose.

The calculator uses the Earth radius and height of atmosphere to extract an as exact as possible airmass for any given zenith distance. If you don't like the standard Earth radius = 6378.14 km and atmospheric thickness = 60.0 km you can modify the Airmass.ini file (Linux version) or give new value for atmosphere in the program (Linux and Windows version).

In the program you can give either zenith distance or altitude of your object and the corresponding airmass is calculated accordingly. The program gives results in four/five decimal places, but I have noticed that the way different computers and systems handle real numbers and trigonometric functions produces slight errors on the last digit.


Download Windows98/NT/2000 executable (v. 1.0) from here:
To get the program just unload and unzip the file into any folder. To run the program place it on your desktop and doubleclick on it or doubleclick on it in Windows Explorer. The program will warn you if you try to enter incorrect values. You can change any of the values (zenith distance, altitude, airmass, Earth radius, or height of atmosphere) and the program will immediately and automatically update the other values to match the one you typed in.

Download Linux executable (v. 1.0) from here:
To get the program just download, untar, and unzip the file into any folder (tar xvzf Airmass.tgz). If the command in the parentheses does not work try to give the following two commands (gunzip Airmass.tgz and tar xvf Airmass.tar). If even that does not work, try just command (tar xvf Airmass.tgz).

To run the program just type Airmass (and press enter). If the current folder is not in the path you probably need to give command ./Airmass to run the proram. You can give either zenith distance or altitude of your object and the corresponding airmass is calculated accordingly. Airmass.ini is pure ASCII so you can use any editor to change values therein.

If you find a bug in the program, don't be afraid to send me an email about it so I can fix the program.

Created by Rami T. F. Rekola
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