As the name implies " Cataclysmic " variable stars (CVs) are those which vary in brightness both dramatically and quickly. This includes Novae, Dwarf Novae (DNe) and the so called 'anti-dwarf novae' (more properly called 'VY Scl' types).
Most people have heard of Novae and confuse them with Supernovae. They do look pretty much the same in the telescope (in both cases there are suddenly bright stars where there were none before) but what is actually happening to cause the light we see is fundamentally different between the two different cases. Supernovae are much more luminous than novae, but generally also much more distant.
If an object is seen to erupt once (and it is confirmed as being an 'outburst' of the right type) the object is called a "Nova". If a "nova" erupts more than once it is called a "Recurrent Nova".
Objects which undergo frequent 'outbursts' are called "Dwarf Novae". As a general rule the more frequently an object undergoes an 'outburst' (i.e. a sudden explosion in brightness) the less bright the outbursts will be. There are all sorts of 'classes' of dwarf novae, (the major purpose for which seems to be to give the professionals something to fight over - which star belongs in which class, and what behaviour separates one class from another).
There is much more to be said about CVs, but I'll leave that just for now. If you want to know more about CV's then you need CV Fanatic-in-Chief Gary Poyner, check out this link to his site which is just full of information and links on CV related topics.
The cataclysmic variables I observe I've collected from quite a wide range of sources. The majority are part of the Recurrent Objects Program (ROP), which is run by the British Astronomical Association Variable Star Section (BAAVSS). The ROP includes quite a number of objects which have only been seen once or twice, and the true nature of which has yet to be identified. Most are cataclysmic objects with recurrence rates of a year to tens of years.
In recent years the observation of pulsating stars has been increasingly neglected by amateurs, which I think is a real shame. There are still a great many pulsating stars about which very little is known. I never fail to be astonished by just how many of the pulsating stars, which have already been identified and supposedly classified, show very different character once they are systematically observed over a period of time.
For this group I try to follow those objects which aren't observed by others, and those which are faint. I try to leave the brighter ones for those with smaller instruments (there are plenty to go around so why fall over each other's feet?). I do tend to change the list of objects of this type (and in particular the 'Mira' type stars) which I follow every year. I'll follow a particular Mira for long enough to get information on two or three complete cycles (from faint to bright and back again) then drop it from my program and add another unwatched object. By doing that on a sort of rolling basis I can get data on a larger number of objects over time. In due course the original object will return to my program again in future.
There are quite a number of Mike Collins (see below) discoveries, or recoveries, which are of this type which tend to get first priority on my program, as least is generally known about them.
I observe a small number of objects which are on the BAAVSS Active Galaxy Program.
These objects include quasars and the hearts of extremely active, but very distant galaxies.
Not as exciting as CV's but much more mind blowing in the contemplation. Some of the objects I follow are a significant fraction of the distance to the edge of the observable universe. Being that distant means that light has taken at least hundreds of millions of years to reach us. The light that strikes my eye left these objects when the universe was young and has been travelling ever since.
It's seriously scary stuff when you think about it.
A phenomenally diligent and dedicated man by the name of Mike Collins has been photographing the sky with a pair of camera's and telephoto lenses for more than ten years now. His primary objective is the discovery of Novae his solitary success to date being with the discovery of V1548 Aquila (Nova Aquila 2001).
In the course of these photographic 'patrols' Mike has recovered a great many variable stars and discovered even more new ones. The current list on The Astronomer's web site shows something over 160 discoveries and recoveries(*), although as I sit and type this in December 2005 his actual total tally is probably well over 400.
(* - I should explain that a recovery is where an object has been previously discovered by somebody else, but because, for example, proper positional data was not taken, or a decent chart was not made, the object could not subsequently be found.)
Of Mike's recoveries and discoveries, just a hand full have been observed well enough for their type and period to be determined. The majority have not been observed by visual observers at all and have less then 20 data points spread over the 10 or so years of Mike's patrol photographs.
This strikes me as an absolute gold mine for the amateur astronomer. Many of Mike's objects are bright enough to be observed with really very small instruments. There are so few people observing them that there is no real competition, and there is the opportunity to discover something entirely new.
The discovery might only be the type of the star, its range in brightness and the period of its varying (all easily found just by watching the star over a period of time). This information is still very valuable and is, at the very least, something which had not been known before - a true "discovery".
Mike isnít the only one doing this (although he is by far the most successful and least recognised in my humble opinion). A golden age of discovery of variables is now starting for amateurs thanks to the various automated sky surveys. These objects also seem to attract shockingly little attention beyond their initial identification.