Newsletter
10
May 1999
A New Star
Unveiled!
ON SATURDAY MAY 22nd
THIS YEAR A ‘NEW’ STAR APPEARED IN THE SKY.
Astronomers in Australia and New Zealand independently noticed a faint new star just to
the right of the Southern Cross constellation. This was an unusual and exciting event as
the last time a ‘new’ star visible to the naked eye appeared in the southern sky
was in 1925 (and was then first spotted by a South African).
A “NEW” STAR?
Well, not exactly. Brand
new stars take thousands of years to form, and are born out of huge clouds of hydrogen
gas. What we saw in the sky this year was in fact a massive explosion on the surface of a
very old star - an event known as a NOVA (meaning “new” in Latin, as it
appears to be a new star in the sky). An aging star can undergo a number of such surface
explosions in its lifetime. Seeing as the nova occurred in the Vela (The Veil)
constellation, it was named NOVA VELA 1999. Why though, do some old stars
explode in this way?
A DOUBLE STAR
You probably know by now
that about half of all the stars in the sky are in fact multiple stars ie. two (or
more) stars in close proximity. With time, all stars age, run out of hydrogen, and begin
to die. On reaching old age, average-sized stars like our Sun begin to expand slowly,
eventually releasing the last of their hydrogen supply into space (and such events
regularly result in beautiful gas spheres called Planetary Nebulae). What is left behind
is the very dense core of the star (containing about 90% of its original mass), yet much
smaller in size (eg. the Sun will shrink to the size of the Earth!). Such a
‘burned-out’ and extremely compact star has an intense gravity field and is
known as a white dwarf.
DEVOUR THY NEIGHBOUR
Depending on the distance between the stars in a double star system, the white
dwarf’s intense gravity can begin pulling at its companion star’s hydrogen
material. This material gradually accumulates on the white dwarf’s surface, where the
intense gravitational and magnetic forces eventually cause it to explode, resulting in a nova.
| Stellar
material collects on the surface of a white dwarf (left) as it gradually devours its
binary companion star (right). Intense forces on the surface of the white dwarf repeatedly
cause the accumulated material to be blasted away in violent nova explosions - like
the one observed from Durban in May this year. |
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NOVA VELA 1999
Before we spotted Nova
Vela 1999 , we could see no star in that part of the sky, even through moderate-sized
telescopes. This clearly means that the double star involved in Nova Vela 1999 is
very far away and the explosion was a truly massive one!
SEEN FROM DURBAN
From
Durban the nova was clearly visible with the naked eye from Saturday 22nd to
Tuesday 25th May - after which it gradually faded and was only visible through
binoculars or a telescope. AIG members with e-mail addresses received news of the nova on
the evening of Monday 24th, and
the nova was pointed out to those who attended the astronomy course on Tuesday 25th.
After being mentioned on the radio (on 5fm on Monday evening and heard by ±900 000
people), the Museum received numerous calls from people wanting to know more - many
complaining about the fact that Durban does not have a real Planetarium!
Mario Di Maggio
All enquiries:
Mario Di Maggio Tel: 300 6228 (w)
or 082 829 7645 or Mario Di Maggio
Viewing evening enquiries: Raymond Field Tel: 309 4126 (w) or
465 7188 (h)
|
Viewing Evenings
at Marist Bros. College* |
Special Events |
Meetings - 7:00PM
at
University of Natal* |
June
1999 |
First clear night of either:
Fri 11th or
Sat 12th or
Fri 18th or
Sat 19th at 18h30 |
High up in the south we have the Southern
Cross with the two bright stars Alpha and Beta Centauri to the
left. In parts of southern Africa this bright group of stars is known as the Giraffes - dithuthlwa in Sotho, or ‘rising
above the trees’. The Southern Cross is an ideal constellation to get to know well.
Once one becomes familiar with it, it is easy to slowly increase one’s knowledge of
the sky by discovering the other constellations around it. |
No meetings due to University exams |
July
1999 |
First clear night of either:
Fri 9th or
Sat 10th or
Fri 16th or
Sat 17th at 18h30 |
7:00PM, Wednesday 14th
July, at the Durban Natural Science Museum:
“Astronomy in Southern African Rock
Art” -
illustrated presentation by Natural
Science Museum Research Associate
Mr Bert Woodhouse.
Admittance FREE. All welcome. |
No meetings due to University vacation |
Aug
1999 |
First clear night of either:
Fri 6th or
Sat 7th or
Fri 13th or
Sat 14th at 18h30 |
There should be good meteor viewing
during the middle of August, with the North Delta Aquarids (peaking on the 12th) and the
North Iota Aquarids (peaking on the 20th) causing enhanced meteor rates for more than a
week.
On Wednesday August 11 a major total eclipse of the Sun will take place over
Europe, the Mideast, and southwest Asia. It will not be visible from southern Africa, and
will be the last total solar eclipse of this Millennium. |
Thursday 19th August:
Solar Eclipses - including a
report back from individuals who saw the total eclipse in Turkey and Europe. |
*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. |
*Directions to lecture room
S4, Science Block, University of Natal: travel to the top of Francois Road, turn right
into the University private road. Directly after boom gate turn left and the Science Block
is on the right.
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