Newsletter 3                         October 1998

AIG Takes Part In REAL Astronomy

On Thursday 29^th October at approximately 8:30 pm, a fairly unusual celestial phenomenon took place - and the Astronomy Interest Group was there to help gather scientific data as part of a national project.

A DISAPPEARING STAR
Tethys, one of the moons of planet Saturn, was scheduled to pass in front of (occult) a fairly bright star in the background sky. This means that from certain parts of the earth the target star would be seen to disappear for a few seconds as Tethys moved in front of it.

An occultation such as this can reveal much information about both the moon and the star involved. For example, it is not known whether Tethys has an atmosphere or not. If it has, then some observers (those not in the direct shadow band) would see the star dimming (as the moon’s atmosphere passed in front of it) instead of disappearing completely.

Of course, in science even negative observations are as important as the positive ones. That is, if observers did not get to see an occultation (either partial or complete), then that fact would still be useful in helping determine the thickness of the moon’s atmosphere, if any.

LOCATION AND TIMING
To make sense of all the data collected, the national co-ordinator of this project would obviously need to know EXACTLY where each observer was positioned, and EXACTLY at what time the occultation was observed. So participants were encouraged to set up their telescopes in as many different places as possible. The Astronomy Interest Group team observed from Mr Andrew Carter’s (Museum graphic artist & entertainer) vacant plot in Hilltop Rd, Hillcrest. It turned out to be a really nice, dark (and safe) viewing spot, and we hope to use it again in the future.

CLASSICAL MUSIC TIME
Determining the EXACT TIME that various observers see an event is far more difficult than determining their exact location. Yet, there is a simple and ingenious way to do this.

Observers were asked to take along a radio and a separate tape recorder. With the recorder running and the radio tuned to SA-FM, at the moment of occultation the observer was to shout GONE!, and then BACK! when the star reappeared. This way, the background radio programme (in this case a live performance of Brahms) would be used to determine the exact moment of the various observations.

NOTHING HAPPENED
Well, the Astronomy Interest Group viewed and recorded the expected occultation, and showed that it was not visible from Durban. Apparently it was only observed from a few locations in the Western Cape.

All in all, our contribution was useful to the project, as were all the other negative results obtained from around the country.

It was an exciting experience for the seven of us who took part in the observation. We also enjoyed looking at the Moon, Jupiter (and its four Galilean moons) and a globular star cluster 16 000 light years away. And it was great having Brahms playing in the background.

Look out for many more such stimulating outings in the weeks to come!

Mario Di Maggio

General enquiries: Mario Di Maggio Tel: 3006228 (w)
Enquiries about viewing evenings at Marist Brothers : Raymond Field   Tel: 3094126 (w) 4657188 (h)