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Dundee Astronomical Society
The Sky in August 2014
Sky at 10pm on 15th August 2014
[Chart courtesy of www.heavens-above.com]
Darkness starts to return to the night sky in August after the long midsummer days. By mid
August the fainter stars of the constellations can be seen after about 10pm and by that time
the shapes of the well known constellations Cygnus, the Swan, and Hercules can be seen
dominating the southern sky with Pegasus following towards the east.
Last month I mentioned Vega, the brightest star of the constellation Lyra, and of the Summer
Triangle. The Triangle can be easily seen high in the south during August and moving left of
Vega we come to the brightest star of Cygnus, Deneb. Deneb is a totally different type of
star to Vega as it is a blue-white supergiant which is estimated to be about 200,000 times
more luminous that our Sun. Although it appears less bright than Vega in the sky, it is
actually at a distance of 1,550 light years while Vega is only 25 light years away. Supergiant
is a good description for Deneb as it is about 150 times the diameter of the Sun and twenty
times the Sun’s mass making our Sun look very small indeed by comparison. The large
mass of Deneb and its temperature mean that it will have a relatively short lifespan and will
become a supernova, blowing itself to bits in only a few million years while our Sun will
continue to shine for at least another four billion years.
Below both Vega and Deneb is the third star of the Triangle, Altair, the brightest star of the
constellation Aquila, the Eagle. Aquila is much more like Vega and our own Sun than
supergiant Deneb. It is even closer to us at only 16.7 light years and a mere 11 times the
luminosity and 1.8 times the mass of the Sun. These three stars stand out because of their
brightness and form the familiar triangle which can help us locate constellations and other
objects in the night sky.
August is the month of one of the best meteor showers of the year, the Perseids. This
reliable shower should produce about 80 meteors per hour at its maximum which, this year,
is on the 13th August at midnight. Perseid meteors can be seen in good numbers for quite a
few nights, especially before the maximum, but this year the light of a nearly full moon (17
day old) will interfere and hide the fainter ones.
Perseid radiant
Remember that Andy Heenan’s Perseid barbeque will be held on Saturday 9th August
to which all DAS members are invited. Please phone Andy if you will be there on the
night at 07873 154718.
Being either quite close to the Sun or low in the sky, none of the planets is particularly well
placed and easy to see during August.
Mercury will be close to the Sun during August, moving westwards later in the month but still
not readily visible.
Venus is quite close to the Sun but may be seen low towards the north-east before sunrise.
Mars sets about two hours after the Sun in mid August and will be very low towards the
south-west.
Jupiter gradually moves away from the Sun during the month and appears to approach
Venus, being only 0.2 degrees south of Venus on the 18th of August. This will be an
interesting sight in the morning sky before sunrise.
Saturn, in Libra, appears to close on Mars during the month and will be about three degrees
north of Mars on the 25th August. This approach will not be easily seen as the planets will
only be about ten degrees above the horizon.
Uranus is in Pisces and Neptune is in Aquarius and can be seen throughout the evenings in
August although both are low in the sky.
The Moon is at first quarter on the 4th, full on the 10th, at last quarter on the 17th and new on
the 25th.
A talk entitled ‘Great Moments in Astronomy’ will be given by Ken Kennedy of Dundee
Astronomical Society on Sunday, 10th August at 1.30pm at Mills Observatory. The talk will
be a personal selection of events and people who have brought our understanding of our
Universe to that which science accepts today. Visitors to Mills are welcome to attend this
talk for which there is no charge.
A family drop-in afternoon will be held on Saturday 23rd August between 2pm and 4pm when
there will be a range of activities. Any member who would like to come along and help out or
chat to the Mills visitors is welcome. We will also use the solar telescope if conditions
permit.
Ken Kennedy
Director of Observations