With the nights of late summer upon us, and the constellation Cygnus the swan flying high overhead, it is a good time to become acquainted with one of the most fascinating stars in the sky. This star is normally a faint, nondescript point of light about 12th magnitude (easily within reach of a 4-inch telescope)-literally one among hundreds in a medium powered field. However, every now and then, on a somewhat regular schedule of about 52 days, it brightens suddenly in the course of a night by about 40 times (4 magnitudes). It stays bright for several nights, then begins it decline back to quiescence. For the next 20-50 days or so, it remains there, perhaps flickering slightly. Then all of a sudden it explodes again-becoming one of the brightest stars in the field. This star is one of my favorites, and it has captivated me on many summer nights. This star is non other than the famous prototype of the cataclysmic variables — SS Cygni.
SS Cygni is a binary star; however, both components are much too close to be resolved from earth in any telescope. In fact, they have one of the quickest rotation periods known-just 6.5 HOURS! This means the stars must be nearly in contact. It is this binary nature that accounts for this stars unusual behavior. According to theory, one component is a solar type star and the other a white dwarf. The gravitational field of the white dwarf pulls material off the outer atmosphere of the larger star. This material spirals down onto the surface of the white dwarf, and when certain conditions of temperature and pressure are met- BANG-the star explodes. Here on earth we see the star brighten suddenly. There are two general types of maxima-one lasting about 8 days and the other about 18 days. These two types usually alternate, but sometimes similar maxima types can reoccur.
SS Cygni is located in northern Cygnus at RA 21h41m Dec +43.3 degrees There is a quaint asterism of about 10-12 stars arranged in a multisided figure with a small triangle attached that catches the eye 20 arc-minutes to the northeast of SS Cygni. This group has always reminded me of a duck floating on some celestial sea, and I never fail to give it a look when making magnitude estimates of SS. If you are interested in observing this star, and have trouble finding it, just track me down at a future star party and I would be happy to show you where it is. If we get some magnitude estimates from club members, I will forward them to the AAVSO, which is always interested in your observations of variable stars!
Contributed by Myron Wasiuta