Set Reference Magnitude - Meade Autostar Software Manual

Autostar IP

Set Reference Magnitude

To calculate the magnitude of any object in the current image, you must first select an object whose
magnitude is already known. Draw a selection box around the object. Then select the Set Reference
Magnitude function. The following dialog will appear.
All magnitude calculations in Meade Autostar IP are based on a technique called Aperture Photometry.
This method comparing the total energy inside a measurement radius around a target object with that
within the aperature of the reference object. Total energy is defined to be the sum of all pixels the
aperature less the average sky brightness times the number of pixels in the aperture. The sky
brighteness in determined by measuring the sky background in an annulus about the object. This dialog
allows you to select the size of the aperature and annulus for measurements.
Additionally, the aperture is centered on your target before the measure measurements are made. The
size of the box used to centroid your object for centering is also configurable in this dialog. Finally, if you
check the Auto Log Magnitudes box, all measurements are automatically written to the log file for export
to spread sheets or other analysis programs.
Determining Magnitude
To perform photometry, draw a box around the area that you wish to determine by moving the cursor to
the upper left corner of the region, depress and hold the left mouse button, then drag the opposite corner
of the box to the other side of the object. Release the button when you are satisfied with the appearance
of the photometry region cursor.
The Photometry region cursor has three main components: the Magnitude/Centroid area, the Pixel list
area, and the Profile line. The Magnitude/Centroid rectangle bounds the entire area used in the
magnitude and/or centroid calculations. This area can be as large as the entire image if desired. Finally,
the Profile line delineates the pixels that will be displayed when the Draw Profile function is selected.
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