Download FRIENDS OF THE PLANETARIUM NEWSLETTER April2002

FRIENDS OF THE PLANETARIUM NEWSLETTER – APRIL 2002
Well the first quarter of the year is now history and our favourite constellation (Orion) is
only just with us being low in the evening western sky. Soon it will no longer with us until
it appears in our dawn eastern sky in about three months time. Scorpio is now appearing in
the southeastern part of the sky with a reminder that winter is approaching and that it is
time for another newsletter. Having just mentioned the constellation Orion, no doubt you
have had no trouble recognising the usually ruby red star in the shoulder of Orion. This is
the red super giant star Betelgeuse. The casual observer may not realise that this star fades
in brightness from time to time by as much as one-third of its maximum brilliance. It is a
variable star. The length and intensity of its variable cycle cannot be predicted. Its
diameter at any time can be somewhere between 550 to 920 times that of the sun making
Betelgeuse the largest star known. It emits energy at a rate equivalent to 14000 suns at its
maximum brilliance and 7600 at its minimum, yet the star only emits around 13% of its
energy in visible light. Betelgeuse’s red colour is related to its surface temperature, which
is around 3000 degrees Celsius. This is cold for a star. Just as a piece of iron changes
colour as it is heated, so too does the colour of a star change with temperature. Initially the
iron glows a dull red. Then as it is heated it glows orange and finally a brilliant white at its
hottest. Stars are the same; with the hot 30,000 degree stars being a bluish white in colour
and the cold stars like Betelgeuse being red. Our yellow sun lies in between with a surface
temperature of around 6000 degrees. Despite its size of at least 160 million suns, its mass
is only equivalent to some 20 suns. This means that its density is very low, less than one
ten-thousandth that of a normal star. In fact, this has led to Betelgeuse jokingly being
called not really a star, but rather a red-hot vacuum. It is about 310 light years distant.
(These notes are based on information from the Carter Observatory).
COMING EVENTS
INTERNATIONAL ASTRONOMY DAY Saturday April 20
3pm. to 8pm.
To celebrate International Astronomy Day and to help promote the planetarium to schools
and the Hawke’s Bay community, the Hawke’s Bay Astronomical Society has organised
an open day at the planetarium on Saturday April 20 from 3pm. to 8pm. There will be
slide presentations and planetarium shows taking place throughout the day. Astronomy
Society members will have (weather permitting) telescopes and binoculars set up for solar
and planetary observing. Please help us out by mentioning this day to all of your friends.
CARTER MEMORIAL LECTURE
Wednesday May 22
7:30pm.
Once again we have been fortunate to be selected to be a host for the Carter Memorial
Lecturer. This year’s lecturer is Dr. Robin Catchpole who is the Senior Astronomer at the
Royal Observatory, Greenwich. His subject is “The Universe Unveiled with the Hubble
Space Telescope”. Starting in our Solar System, Robin will take us out into our Galaxy
and beyond. This lecture will presented at the Holt Planetarium located on the Grounds of
Napier Boys High School (Chambers Street entrance). The cost is $10 per person. Seating
is limited and “Friends” are being offered this opportunity to make a booking before seats
are offered to the general public. To make a reservation, please ring the Planetarium on
8344345 as soon as possible. If you make a booking and find that you will be unable to
attend, please let us know as soon as possible.
SUBSCRIPTIONS
Subscriptions to “Friends of the Planetarium” for the year 2002 are now due. Your
continuing support will be very much appreciated.