Variable Stars

Variable stars are such stars that change their magnitude during a period of time. Each variable star looks like any other star in the sky. If you don’t know in advance that you are looking at one, you can’t tell the difference. To detect any variability you have to track the change of its magnitude during a period of time. Some change their brightness with a tenth of a magnitude, others even with ten magnitudes. Some have periods of hours, others months, or even years.


Before we continue, let me tell you why observing of variable stars is very important for any beginner amateur astronomer:

  • First and foremost, it forces you to look at the sky almost every night for around half an hour. I personally, didn’t know well enough the various constellations, their position and in which season they are visible, until I got into observing variables. I didn’t even know the order of the zodiacal constellations. Picking a few variable stars each season helped me tremendously, and from that moment on, I had no problem orienting on the sky. Star observing variable stars and soon enough you’ll know the sky as the back of you hand.
  • Second, there are many stars that have no specific periods or trend in magnitude change. Such observations are very valuable for the science!
  • Third, observing such stars does not require any equipment (a binocular maybe at some point), unless you get into it and want to observe very faint variables.

Every variable star is characterized by a few properties – type of the star, min and max magnitude and light curve. There are more of course (like spectral type, etc.. ), but as a beginners you won’t care about them.

Types of variable stars

There are several main types – eclipsing, Cepheids, and semi-regular/irregular. Some of these have sub types, which are named after the first discovered star in the class. Read more the types of variable stars here.

How to observe variable stars?

I will briefly describe a technique that I’ve used to observe variable stars. It was invented by Herschel, and refined by Argelander in the middle of XIX century. This is the technique used by the French Association of Variable Stars (AFOEV). Read more about how to observe variable stars here.

Which stars to observe?

There are plenty of bright variables suitable for beginners. I’m listing here just a few. I recommend observing with naked eyes first, and when you gain some experience and confidence with the technique, you could pick fainter stars and use a binocular. Read more about which stars to observe here.

What to do with the collected data?

First you need to collect the data for a given star over a few periods at least. After that you could make a graph of its light curve, and try to overlap a few periods for more accurate shape (in case it has constant period and shape). You could create a report for that star, and include it in your presentation, scientific report, etc.  No matter what you decide to do, I suggest you send the data to some International association, so that your observation will be included in their database, and help astronomers in their studies. For example, I’ve sent my data to AFOEV. Another organization is the American Association of Variable Star Observers (AAVSO).

Other ways of “observing”

At some point, if you have the desire and the equipment, you could use a photometer or a CCD camera. A photometer measures every light that enters the detector, no matter if one or two stars are in the field. With CCD (film plates in the past) you get an image and do a photometry (measure brightness) on the star of your choice. Nowadays, very few observers are using photometers. Photometric studies are what professional astronomers do. So, you’ll do exactly what the professional astronomers are doing, with one small difference – they use more expensive gadgets :).

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