Distant Suns in our Neighbourhood

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Newsletter 6 January 1999

Distant Suns in our Neighbourhood

The spiral galaxy we are a part of, the Milky Way, contains an estimated 400 thousand million stars. The star nearest to us, the sun, is just one of these billions of stars, situated somewhere near the outer fringes of the galaxy .

Yet even under the most ideal viewing conditions, only about 10 000 of our galaxy’s stars are visible with the naked eye - all of them distant suns in our neighbourhood.

OUR NEAREST NEIGHBOUR
After the sun, the star nearest to us is Proxima Centauri, part a double star system - ie. it is one of two stars moving around each other. Interestingly, up to half of all the stars we can see at night are in fact double or triple star systems! If you attend the AIG viewing outings you can see this for yourself through the telescope.

Proxima Centauri is 4a light-years away - this means that the light from the star that we are seeing now, actually left the star 52 months ago. So, although it is the star closest to us, it still very far away! If we had to compare the sun to say, a basketball in Durban, then Proxima Centauri would need to be a basketball in Singapore.

STARS ON A MERRI-GO-ROUND
Because the earth rotates on its axis, when we look at the stars over a period of a few hours it seems to us that they are revolving around a central point in the sky.

This unique point is called the South Celestial Pole. It is extremely useful to know where the South Celestial Pole is, as directly below it is due south. Also, telescopes with tracking motors need to be aligned towards this Pole to function properly.

As the diagram shows, it is relatively easy to find the South Celestial Pole. One just needs to extend two imaginary lines from the prominent stars of the Southern Cross constellation - and where these lines meet is the South Celestial Pole.

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THE BRIGHTEST STARS
The stars which appear the brightest to us are not necessarily the largest or the nearest - a star can be large and far away, or small and nearby. For example Sirius, the brightest star visible from earth, is fairly near-by (only 8.6 light-years away) and yet it is also 26 times brighter than the sun. Right now in the evening sky we can see 8 of the 10 brightest stars. Come to the viewing outings and have fun learning to identify them!

BEAUTIFUL COLOURS
Stars may all look white to the naked eye, but closer observation reveals their true colour. For example, Sirius is a wonderful
bright blue colour and Betelgeuse (10^th brightest star) an outstanding orange. We may only be able to see relatively few of our galaxy’s billions of stars, yet these distant suns in our neighbour hood are enough to keep us fascinated many life-times over.
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Mario Di Maggio

AIG Event Horizon

All enquiries: Mario Di Maggio
Tel: 3006228 (w) or 082 829 7645

Enquiries about viewing evenings at Marist Brothers:
Raymond Field Tel: 3094126 (w) or 4657188 (h)

	AIG viewing evenings (at Marist Brothers College)*	Special Events	Astronomy Meetings (at Marist Brothers College)*
Feb 1999	First clear night of either: Fri 12^th or Sat 13^th or Fri 19^th or Sat 20^th at 19h00.	An Annular Eclipse of the sun occurs on the morning of the 16th. From the best viewing location, in the Indian Ocean southwest of Australia, the Moon will cover 99% of the sun, leaving only a slender ring of light encircling the Moon's black disk ("annular" comes from the Latin word anulus, meaning "ring"). We are quite far from the best vantage point, so from Durban we’ll see 54% of the Sun darken at 6:50AM	Wednesday 10^th February, 7:00pm: Simulated Planetarium presentation by Mario Di Maggio *NOTE - this meeting will be at the Natural Science Museum*
Mar 1999	First clear night of either: Fri 12^th or Sat 13^th or Fri 19^th or Sat 20^th at 19h00.	Many bright stars are visible on March evenings. The brightest of all stars Sirius, is easily visible, as is the second brightest of all stars Canopus, together with Alpha Centauri (3^rd), Rigel (7^th), Achernar (9^th) and Betelgeuse (10^th). Attend the monthly viewing evenings and not only learn to identify these beautiful celestial jewels, but also get to see their distinct colours through the telescope.	Wednesday 10^th March, 7:30pm: "On The Geology Of Mars" - illustrated up-to-the-minute talk by Professor Watkeys
Apr 1999	First clear night of either: Fri 16^th or Sat 17^th or Fri 23^rd or Sat 24^th at 18h30.	BLUE MOON PARTY! For the second time this year a full moon occurs twice in the same month: on April 1 & April 30 (the latter one being called a Blue Moon). We’re celebrating this most unusual event with a Blue Moon Party on Friday evening, April 30^th, at Marist Brothers Observatory. You will need to dress in blue, bring something blue to eat/drink (eg blueberry cheesecake, bluecheese dip, drinks in blue bottles, etc). Also bring blues music or "moon" songs if you can. Telescopes will be on hand for close observation of the moon’s surface.	Wednesday 14^th April, 7:30pm: Speaker to be announced
*Directions to Marist Brothers College: travel south along Ridge Road from Tollgate towards Entabeni Hospital. Just after the hospital turn right into Glenwood Drive, which is an L-shaped road. At the end of the road you will see Marist Brothers College in front of you. Turn left into the school car park.