All of the stars we can see in the night skies of Connemara with the naked eye are part of our Galaxy, the Milky Way.  Some are single stars, like our Sun, but the majority are multiple stars,  having one or more companions.  These multiple star systems all orbit a common centre of mass.  Some stars look like they are very close to one another in the night sky simply because they lie along the same line of sight from Earth.  These may be referred to as “optical” double stars as opposed to the real thing.

 The nearest stars to Earth are the small Proxima Centauri (which orbits the others from a distance) and the very close binary stars Alpha Centauri A and Alpha Centauri B.  Alpha Centauri A, also known as Rigil Kentaurus, is the principal member, or primary, of the binary system. It is a Sun-like star with a similar yellowish colour and it is slightly larger and more luminous than the Sun.  Alpha Centauri A is about 10 percent more massive than the Sun, with a radius about 22 percent larger.  Alpha Centauri B has around 90 percent the mass of the Sun and a 14 percent smaller diameter.  Although it has a lower luminosity than A, Alpha Centauri B emits more energy in the x-ray band.  Alpha Centauri B has an apparent magnitude of +1.35.  

Study of our near neighbours in the night sky other than in a telescope will take a great leap in our technology over the next several thousand years.   Any Earth-based astronauts who could take advantage of light speed or near light speed would take over 4 years to get to the Alpha Centauri system.

Mercury is lost in the Sun’s glare this month, and won’t be visible to us for several weeks.  Look for Mercury again in the evening sky after September 23rd.

Venus passed through superior conjunction on the far side of the Sun on the 14th August so will not become visible again in the evening twilight until late autumn.

Like the other neighbouring planets, Mars, which passes behind the Sun (superior conjunction) on September 2nd, lies too close to the Sun to be visible.   We will have to wait until November to spot it in the pre-dawn sky at the start of its next apparition.

Jupiter, which began on the 1st of August at magnitude -2.41 and falling to -2.21 during the month, can be seen in the south as darkness falls.   Its angular size drops slightly from 42.6 to 39.9 arc seconds as the month progresses.   Jupiter ended its retrograde motion in the 11th of August so will begin to move away from Antares in Scorpius initially lying some 7 degrees up and to its left.  

Saturn, is highest in the sky at around 11:30 p.m. as August concludes. Then, its disk is about 18.2 arc seconds across and its rings – which are still nicely tilted from the line of sight – span some 42.5 arc seconds across.   It will be best seen at around 9:30 p.m. when lying due south.   During the month its brightness falls from magnitude +0.16 to +0.33 whilst its angular size falls to 17.6 arc seconds.  

Now that the evenings are drawing in, the night sky gets darker earlier, thus encouraging one to go out to observe.

High over head towards the north lies Ursa Major. As one moves southwards one first crosses the constellation Hercules with its magnificent globular cluster, M13.  To the right of Hercules is found the arc of stars making up Corona Borealis and then Bootes with its bright star Arcturus. Rising in the east is the beautiful region of the Milky Way containing both Cygnus and Lyra. Below is the constellation of Aquilla, the Eagle. The three bright stars Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila) make up the “Summer Triangle”.

Gerrit Nuckton