Variables of the Month:

Eta and S Carinae

I had already decided to offer Canopus these two stars as a double billing, when the January S&T came out with Eta Car as its cover story.

Eta and S Carinae are located in a spectacular part of the southern sky, midway between the Southern Cross and the False Cross. The naked eye cluster Theta is prominent, as are the third magnitude stars p and q. The whole region is a glorious mass of clusters and nebulae.

As you will see from the S&T article or Burnham's "Handbook", Eta is one of the most interesting objects in the sky. It is stellar history in the making, happening right in front of our eyes. In John Herschel's day it was one of the brightest stars in the sky but since then it has fallen on hard times and now sits at just beyond naked eye visibility.

It is located in the spectacular Keyhole Nebula and is worth a glance whenever you sweep the southern skies with binoculars or a telescope. Its present brightness is around 6th magnitude but every now and then it seems to brighten a little before re lapsing. Astronomers do not really know what is going on inside the melting pot which is Eta and expect something dramatic to happen, in the next few days or the next million years. So keep watching. If you are uncertain of its identity, you should contact me or another experienced observer.

S Carinae on the other hand, is a staid Mira long period variable. It has a satisfyingly shortish period of around 150 days and can be observed with binoculars during most of its cycle. At maximum, it sometimes reaches naked eye visibility. Its minima vary in brightness from cycle to cycle. It is very suitable for new observers because it is easily located and the sequence of comparison stars is user friendly - the magnitude numbers really seem to relate to the brightness of the stars. Another plus is it's high Southern declination. This means that it can be observed the year round.

Enjoy these two jewels in our Southern skies.

Danie Overbeek.