||Sun Angle ?
Each month, we identify the best constellations to be seen from the UK between 9pm and 10pm.
This month we'll be looking for the summer constellations of Lyra, and
which can be found towards the south in the August night sky.
Lyra - is named after the Latin word for 'Lyre', which is a type of
harp that was used by the ancient Greeks. Whilst it is a relatively small constellation,
being only 52nd largest of the 88 modern constellations, its main star, Vega,
is the fifth brightest star in whole the night sky. This makes the locating of Lyra
a fairly easy task, especially given its position within the Summer Triangle
- see below. Vega has been extensively studied by astronomers, and was the first star,
other than the Sun, to have its photograph taken and the first to have its
spectrum photographed. Due to the precession
of the Earth (its rotation axis changing direction - a bit like a spinning top), Vega
was once the northern pole star at about 12,000 BC and will be so again around 14,000 AD.
Lyra is a rapidly rotating star (once every 12.5 hours) that is just over twice the
mass and radius of the Sun, and pumps out around
50 times as much energy. It is white-ish coloured star that appears bright to us
because it is just 25.3 light years away.
Scutum - is named after the Latin word for 'shield' and is one of the few
constellations that owes its name to a historical figure, rather than a mythological being
of object. It was so named back in 1683 after the Polish King, John III Sobieski, following
a famous victory at the battle of Vienna. It is a very small constellation, at just 84th largest
of the 88 modern constellations, and contains no bright stars. This makes is somewhat difficult to
identify, and requires knowledge of the Summer Triangle to start off from, followed by
a good deal of patience. Scutum contains several
open clusters, as well as a globular cluster
and a planetary nebula. The most notable object in Scutum is M11, the Wild Duck
Cluster, which is a dense open cluster containing around 2900 stars.
Summer Triangle - is not actually a constellation, but is three bright
stars called Vega, Altair and Deneb, which make up a triangular shape
during the summer months and can help us to identify less obvious constellations in the
vicinity. Because the stars all look about the same brightness, it's easy to think that
they are about the same distance away. However, Deneb is actually 100 times more distant
than Altair, which is only 17 light years away. For
Deneb to appear almost as bright as Altair in our sky means that Deneb must be far brighter
than Altair in terms of true light output. In fact astronomers estimate that it pumps out
around 60,000 times more light than our Sun, while Altair outshines the Sun by just 13 times.
Vega, by comparison, is 25 light-years away and some 50 times brighter than the Sun. The reason
Deneb is so bright is because it's a type of star known as blue supergiant, whose size is around
200 times larger than the Sun. Because supergiants are in the last stages of their lives, it's
likely that Deneb will become a supernova in the next couple
of million years - which could cause significant problems for us still stuck on Earth when it goes off.