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Transcript
Astronomy and Space articles
by Martin George of the Launceston Planetarium
1 February 2014
The First Star at Night
I was asked recently which star is the first one to be visible at night. It is a question I hear
often, and it is a quite interesting one because together with the question is usually
another: 'is that the one called the evening star?'
There is some confusion surrounding this topic. Indeed, I recall that when I was growing
up, my grandmother would sometimes spot the first point of light in the sky that she could
find, and call it the 'evening star'.
The term evening star is actually a misnomer, because that is the description applied not
to a star, but, in times gone by, to the planet Venus when it is visible in the western
evening sky after sunset.
Similarly, Venus was called the 'morning star' when it was on the western side of the sun,
and therefore visible in the eastern morning sky before sunrise, as is the case at the
moment.
The names Hesperus and Phosphorus, amongst others, were given by the ancient
Greeks to these appearances of Venus. Of course, it must be remembered that long
ago, it was not clear that the two were the same object, although eventually it was
realised that this was indeed the case.
The main point, however, as I have mentioned, is that Venus is not a star.
So, having digressed somewhat, what is the first star visible in the evenings?
Currently, and unsurprisingly, it is Sirius, the brightest star in the night sky. Sirius is also
known as Alpha Canis Majoris, being the brightest star in the constellation of Canis
Major, The Great Dog. As the twilight begins in early February, Sirius becomes visible
high in the north eastern sky, becoming the first star to be visible while the sky is still a
quite bright blue.
At some times of the year, however, Sirius is not visible in the evenings from here at all,
being either too closely in line with the direction of the Sun, or being first visible quite late
at night or in the early morning sky.
When Sirius does not have that honour, it usually falls to Canopus, the second brightest
star in the night sky.
Astronomy and Space articles
by Martin George of the Launceston Planetarium
1 February 2014
Canopus is the second brightest star in the night sky, so given that it is always above our
horizon from here in Tasmania, one might expect that without Sirius in the sky, Canopus
would always be the first star visible.
However, it is rather more complicated than that. Even though we can always see
Canopus at night - unless, of course, there are obstacles like hills or trees in the way Canopus can be quite low down in the sky, and appear less bright than usual because of
the increased amount of air through which its light is passing. For example, on October
evenings, Canopus is very low in our southern sky, and is dimmed considerably. Under
those conditions, the third brightest night time star, Alpha Centauri (the brighter of the two
'pointer' stars that help us to identify the Southern Cross), would be the first one to be
noticed.
So the question is a little complex, but it's always fun to go out just after sunset, gaze all
over the sky, and try to spot the first stars that become visible!
Article by Martin George, Launceston Planetarium, QVMAG.
Reproduced with permission of the Mercury newspaper.