by Dr David Weldrake
August gives us the best view for the year of our Galaxy, the Milky Way, with the centre being directly overhead. Our galaxy spans the sky all night during August, with a huge amount of detail visible. Made up of hundreds of billions of distant stars, they are so far away that they look like giant clouds in our skies.
Dark patches in the Milky Way are giant clouds of molecular hydrogen, which block out the light from the stars behind. It is from this material that future generations of stars will be born.
Can you see these ‘starclouds’ and ‘dustclouds’? Our rural skies give us an advantage, these details are very hard to see from the light polluted skies of a city.
As well as the Milky Way, bright stars visible during August include orange Arcturus low in the north west, white Vega low in the north, white Altair in the north east, orange Antares high overhead, yellow Alpha Centauri towards the south west and white Fomalhaut, low in the east.
Fomalhaut is known to astronomers as a young star with a large disk of material around it. The disk is fairly thick with a hole in the middle, a bit like a giant doughnut.
One day, this disk will collapse down and settle out to form planets. It was in this exact same way that, four and a half billion years ago when the Sun was young, the Earth and the rest of the Solar System was formed.
The planets in August: Mars, Saturn and Neptune
There are three planets in our evening skies this August, although only two of them are visible with the unaided eye. High in the north west shine the bright planets Mars and Saturn, both of which have been visible to us for a few months now and will continue to be visible for a few months hence before they move behind the Sun as seen from Earth.
During August Mars and Saturn appear to be very close to each other in the sky, which helps when trying to see them and identify them for yourself. They lie in the constrellation Libra and can be seen as a pair of fairly bright ‘stars’, one reddish-orange and one yellow.
Can you spot them and see the colour difference between them? The colours give away which is which, Mars is famous for its reddish colour.
Mars and Saturn appear to be close together as seen from Earth due to a chance alignment which happens fairly regularly. They are in fact still more than a billion kilometers away from eachother.
The third planet visible this month is Neptune, although it is so far away and faint you would need a telescope to even see it. It is not marked on the map for this month for that reason.
Neptune lies at the frozen outer edges of the Solar System, and is in fact the furthest planet from the Sun, a full thirty times further away from the Sun than the Earth is. From Neptune, the Sun would look like a very bright star in the sky.
Neptune is a little under four times the diameter of the Earth, and is not a solid planet, but rather a collection of gases, mainly hydrogen and helium but also with ammonia and methane, which help give Neptune a deep blue colour. Neptune takes 165 years to orbit the Sun once, and was discovered in 1846. It has 14 known moons.
Through a telescope Neptune looks like a tiny blueish disk. It is very difficult to see it as a planet at all due to its distance and tiny size. Neptune has been visited once, by the Voyager 2 probe in 1989. Due to the length of time it takes for a spacecraft to get there (it took Voyager 22 years), there are currently no further plans to go back.
The Moon is first quarter (half) phase on the 4 August, full on the 11 August, at third quarter phase on the 18 and new on the 26.