Data Reduction

After collecting your observational data, the first step that you must take in analyzing variable-star data is to organize it. When organizing variable-star data, the date/time of the observation, the estimated magnitude of the variable star and the star with which it is being compared and perhaps a remark regarding special conditions are necessary. In some cases, more information is recorded but for basic analysis of variable-star data, we will use the date/time and magnitude of the star being measured. Try to configure your database so that your entries match your analysis needs. By considering this, you can use copy and paste operations to move blocks of data quickly.

Here is an example of a journal entry made by a variable-star observer:


Clear with moon Clear with moon Clear with moon Cloudy with moon

As you can see, something simple is all that is really needed. Here the observer records the star's name, the date and time of the observation, the estimated magnitude and the charts/comparison stars used. Try this simple method first. You may not need any more information that this. Don't allow record keeping to become a burden so that it interferes with your observing.

After a night of observing you should have a record of your work. You're next effort will probably be in reducing your data. Reducing your data is simple converting it into a form that allows proper analysis. In most cases, you'll not be required to do much with your estimates before you begin to conduct a proper analysis of your data. However, in situations where you are using instruments, you're reduction procedures can be a bit time-consuming. It would be impossible to describe all of the procedures within this book. It really requires a more in-depth description, so I recommend a couple of books specifically written for CCD and PEP

Variable Star Journal

Date Star Time Est. Mag.

Sep 27, 2001R Vir 9:30 PM 10.1

Chart xxxx, comparison stars 10.5 and 9.8 Sep 27, 2001R Per 9:33PM 12.1

Chart xxxx, comparison stars 12 . 5 and 11.5 Sep 27, 2001R Psc 9:37 PM 9.2

Chart xxxx, comparison stars 9.7 and 8.8 Sep 27, 2001R Ari 9:41PM 11.4 Chart xxxx, comparison stars 11.9 and 10.9

observers. Two good books are Photoelectric Photometry, by A. Henden and R. Kaitchuck and Photoelectric Photometry of Variable Stars, by D. Hall and R. Genet, both published by Willmann-Bell. Both provide excellent descriptions of data reduction for CCD and PEP users.

If you're going to simply report your data and conduct no analysis yourself, all that is required is to put your observations into the proper format. Each reporting organization, such as VSNET, AAVSO or BAA VSS, has their own format. Visit their Web site and see what their wishes are in regards to reporting format.

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