Variable-Star Observing Programs
General Information for all Instruments
To find a variable star in the night sky you will need a good star map where you can plot its location using the Right Ascension and Declination coordinates provided by an observing guide, such as the RASC Observer's Handbook, or from a variable-star database. A good knowledge of the night sky should be the goal of every serious observer, and variable-star observing is an excellent way to develop these skills. The best approach is to start with variables that are relatively easy to find, then, as your skills develop, you can move on to more difficult objects. For those who have Go-To telescopes, this will be less of a problem, but they will still have to identify the star field and the exact location of the variable star they are looking for. For this reason, we encourage all observers to develop good star-hopping skills, and to become familiar with using star charts of various scales. You will also need to understand the size of the fields of view through various eyepieces in your collection, and how that relates to the star charts. You should also become proficient at using a good finder scope – as many experienced observers know, it can speed up your navigation of the sky tremendously, and very often the star you are looking for will be visible right in the finder. Today there are computer programs available that can print charts suitable for various types of telescopes, since instrument designs present the sky in various configurations.
Choosing Variable Stars to Observe
The first thing you need to determine before choosing a variable star to observe is the limiting magnitude of the instrument you are using, as well as the limiting magnitude of that instrument in the location where you are going to observe. This can be done fairly easily by using a chart with the visual magnitudes of the stars clearly indicated on it. Here is a general guideline for various instruments.
- Binoculars and small telescopes: There is a good variety of variable stars bright enough to be seen through small instruments. Generally, but with some exceptions, binoculars can see to 8th or 9th magnitude and small telescopes to 11th or 12th magnitude. The RASC Observer's Handbook is a good source of information about long-period variable stars that will be magnitude 8.0 or brighter at maximum each year, and that are located north of -20 degrees declination.
- Medium-sized telescopes: Observers with medium-sized telescopes can seek out fainter objects in the 12th- to 14th-magnitude range using data available from the American Association of Variable Star Observers situated in Cambridge, Massachusetts. The RASC also has a list of variable stars as part of our observing program in cooperation with the AAVSO. These stars have been chosen with northern Canadian latitudes in mind to help the AAVSO cover parts of the sky not easily seen from other parts of the world.
- Large-sized Telescopes: For those who have access to large telescopes, a great many variable stars can be observed. There is, in fact, a great need for observers with large-aperture telescopes within the variable-star observing community. Many faint variables go unchecked because they are too difficult to observe through average-sized telescopes. Since observing variables at the limit of a telescope's magnitude range is a good thing, large telescopes are excellent for measuring stars 15th magnitude or fainter.
Sample Charts Available
For all instruments, sample charts are available by clicking on the sample charts links in this section. You are welcome to print and use these charts to get started in the fascinating world of variable-star observation and discovery.
Manual for Visual Observing of Variable Stars (AAVSO)
The AAVSO Manual for Visual Observing of Variable Stars is the standard reference work for all RASC members who wish to observe variable stars and contribute observations to their international database. They also have an Observing Page that you can go to for more information.
Variable Star Observing Tutorial
Dr. Bob Nelson of the Prince George Centre, British Columbia, has written an outstanding tutorial titled How to Observe Variable Stars that we highly recommend you read. Dr. Nelson covers all of the basics, using easy-to-understand language that will provide you with the knowledge you will need to go out variable-star observing on the next clear night.