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Overview of Reduction Packages

Digital images of a star field contain all the information needed to determine an accurate magnitude of the target star. Obtaining this magnitude is accomplished in a two-phase process. The tutorial refers to phase one as “Starting Analysis” and phase two as “Finishing Analysis”.


Starting Analysis: In this step of the tutorial we will use one of three software packages to obtain raw instrument magnitudes (a measure of the brightness of the stars that is camera-dependent) from our images.


Finishing Analysis: Step two employs an Excel Spreadsheet to calibrate the instrument magnitudes and produce an accurate V-magnitude.

There is currently one options available in Finishing Analysis. The Basic Procedure provides color calibration only and does not include corrections for variations in atmospheric attenuation whereas the Intermediate Procedure (to be completed soon) adds in a correction for atmospheric extinction. We have also planned for an Expert Procedure which will present you with the theory behind the reduction and let you develop your own routines for reducing data.



Image Processing Software

In order to extract magnitude from your photos, you will need a photometric reduction package. Below we have highlighted three of the most used photometric analysis packages. One is entirely free, whereas the others are commercial.  Once you have selected your analysis package you can start analyzing your data.


Iris is a general purpose astronomical image processing software suite by Christian Buil with both English and French translations that runs on Windows, and under WINE in Linux. It is full featured, updated frequently, and has a modest number of "how to" articles written for it. The program is free to download and use.

Where to get it:
The download and installation instructions can be found on Christian's AstroSurf webpage.


AIP4WIN comes as software bundled with the book The Handbook of Astronomical Image Processing written by Richard Berry and James Burnell. It is a very thorough book that discusses image analysis, astrometry, photometry and spectroscopy. The bundle sells for $100.00

Where to get it:
The book and software bundle may be purchased from Willmann-Bell Inc. (the publisher) or through other book sellers.


MaximDL is a full camera control suite with complete observatory integration. There are several versions available, depending on your needs. This software is commercial, and the lowest priced version that includes photometric analysis is $300.00

Where to get it:
The software may be purchased in either boxed or downloadable form from Cyanogen Imaging Products.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484