This really good resume by Guy Hurst editor of The Astronomer ( a great monthly magazine for the more serious astronomer) and former President of The BAA, about Variable Stars was for a recent BAA workshop.
Worthy of the posts title I think.
VARIABLE STARS Guy Hurst
The important thing to remember about all observing is that it should be fun. This
applies to both beginners and those experienced amateurs who undertake observations in
co-operation with professionals.
Variable stars have been a long-standing passion of mine since I began observing in
1970. What appealed to me was that I could start playing my part in this fascinating branch
of astronomy using only binoculars or even just observing with the naked eye.
Why should variable stars be important? Well, some binary stars (physically related
doubles) eclipse each other and provide a challenge in timing such events. However other
stars physically change in brightness and the British Astronomical Association (BAA)
has collected observations of all of these from its members ever since 1891! This is one of
the longest runs of information held by any group in the world and we must now play our
part in keeping this going!
The real reason for the importance of these observations, though, is the link between
variation in brightness and the evolution of stars. Some become unstable even before
they enter the main part of their lives (which we call the ‘main sequence’) and again after
they begin to run out of hydrogen. Some undergo major ‘hiccups’ (novae) and others
explode and destroy themselves in a blaze of brightness (supernovae). It is amazing that
amateurs can contribute to our understanding of these life stages of a star by studying
brightness fluctuations in what is called the ‘magnitude scale’.
This ‘brightness system’ was developed by Hipparchus around 129BC and showed
magnitude +1 (brightest) to +6 (faintest). Each magnitude is about 2.5x different to its
neighbour and magnitude +6 is about 100X fainter than magnitude +1.
Some stars, such as Sirius and also planets, the Moon and Sun, are brighter still and so
minus values were introduced. Sirius is mag –1.4 and the Sun a staggering mag –26!
However for your estimates of variable stars with binoculars most will be ‘plus’
magnitudes. Although magnitude 6 is the faintest most see to the naked eye even in very
dark sites, your binocular lenses allow you to see fainter, possibly to about magnitude 8-9.
This allows observation of so many variable stars and there are already over 120 in the
BAA VSS Sections’ binocular programme to choose from.
The website at:
http://www.britastro.org/vss/chartcat_binoc.htmdescribes the different types of variables and lists the stars on the target list. The section
can also supply charts, which not only act as ‘finders’ but also give suitable comparison
stars with accurately measured magnitudes from which estimates can be made.
These comments do not mean telescopes are excluded. On the contrary the extra
aperture of most scopes allows you to see fainter and include many other variables on
your programme. Details can be found at:
http://www.britastro.org/vss/chartcat_telescopic.htmRegards
