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Post by oopfan » Thu Mar 29, 2018 12:54 pm


Another labor saver, even greater than "OBJCTRA and OBJCTDEC" described in my feature suggestion here:


is a key/value pair named AIRMASS which is a measure of the amount of atmosphere between you and the star.

The first approximation of AIRMASS is the secant of the zenith distance:

AIRMASS = SEC(Z), where Z = 90 - Altitude

I think that SharpCap has enough information to calculate zenith distance. What is needed is the observer's latitude and longitude, Universal Time, and the coordinates of the center of the image (i.e. OBJCTRA and OBJCTDEC).

As you can see AIRMASS is constantly changing as time marches forward.

As an example of how much of a time saver this can be, a few weeks ago I measured the light curve of the short period variable star named 'YZ Boo'. I captured a total of 100 frames over a period of 3 hours. Each frame was captured with a 100 second exposure. As you can see AIRMASS changed dramatically over the entire sequence, and even from frame to frame. In order to obtain the best quality photometry I had to obtain the timestamp from each frame and calculate the zenith distance in a spreadsheet, and then use F4W2HDU to write AIRMASS to the associated FITS file. Very time consuming and prone to error.


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