Observing variable stars

This article isn't meant to be a complete guide to observing variable stars, but more of an introduction to this fascinating branch of amateur astronomy. I must admit I have something of a passion for variables, it always amazes me that by studying a particular stars brightness over a period of several months that I am actually witnessing an event that is happening in (or near) a stars atmosphere, that is maybe thousands of light years away. It really brings home the fact that the stars are not static points of light, but are dynamic, evolving objects.

From the point of view of the amateur, the basic observation in the study of variable stars, is the estimation of a star's brightness (magnitude) at a particular time. The variable is compared with stars of known magnitude whose brightness is invariable, and the deduced magnitude is plotted as a graph against time to form a lightcurve

The simplest method, and the best for beginners is, to make a direct comparison between the variable and at least two other stars of known magnitude, e.g. the variable (V) is much brighter than star A(10.6mag) but only slightly dimmer than star B(9.8mag), therefore, assuming an accurate estimate, V=10.1 (+/- 0.1mag). There are more complicated ways of obtaining an estimate, but whether or not they are any more accurate is a matter for deabte. For the beginner the above method should be more than adequate and with practice an accuracy of 1/10 of a magnitude can achieved.

When making an estimate it is essential to record just how accurate the observation is. The traditional way is to use a class code. A class1 estimate is very reliable (+/- 0.1 magnitude) observation. Class 3 is a poor observation made with the Moon closeby, or through thick haze, and is just about worth recording. A class 2 estimate has a +/- 0.2 magnitude accuracy

When recording your observations you should record the date, time, the variables designation or name, your estimate, and the accuracy of your estimate, along with details of the instrument used and any other notes. If a variable is not visible it may have faded beyond your scopes/binoculars limiting magnitude. Record your estimate as the magnitude of the faintest star visible followed by a plus sign, e.g. 12.5+

Note: If using a scope never make an observation of a star until the instrument has had time to cool down and reach thermal equilibrium. The resulting estimate is very likely to be way out!

10 Easy Binocular Variables.(suggested frequency of observation)

Omicron Ceti	2.0mag - 10.1mag 332days (monthly)
R Leo	5.8 - 10.2 313days (monthly)
X Hercules	6.3 - 7.4 100days (7-10days)
RR Coronae Borealis	7.2-8.4 57days (2-3 days)
R Coronae Borealis	5.8 - 14.8+ : A special star that stays at maximum for indefinate periods, then plunges down for a while to it's minimum. (nightly)
V Bootes	7.0 - 11.3 258days (fortnightly)
Chi Cygnus	5.2 - 13.4 407days (monthly)
T Ursa Major	7.7 - 12.9 257days (monthly)
R Lyra	3.9 - 5.0 46days (2-3days): Can be difficult due to deep red colour
U Orionis	4.8 - 12.6 372days (monthly)

Variable stars come in several different flavours such as, Mira type stars, semi-regular, cepheid, cataclysmic, eclipsing and many, many more. Each with it's own unique characteristics. There isn't room to detail them all here so I will save a description of these for a future article.

Modern astronomical software such as "Skymap Pro" and "Redshift" can very easily produce detailed finder charts, alternatively you can try the AAVSO website.