Peterborough Astronomical Society is not meeting just now (for obvious reasons) but that doesn't stop our members from stargazing in their gardens - and we do. I'll let you know when we are getting back together and how to find out more about the society in a future article.
For now, for those folks who have an interest in the night sky but aren’t sure what to look out for, here's a brief guide for August.
We are now a few weeks further on from the Summer Solstice (June 20), so the nights are beginning to lengthen. By the middle of the month, we will be getting just over 4 hours of true darkness, from 11pm to just after 3am - but it will be reasonably dark for an hour either side of that, so from 10pm onwards.
Mercury is now past the furthest point in its orbit and is beginning to swing around the far side of the Sun. Its rising time each morning will become later and later, until it eventually disappears into the glare of the Sun. At the beginning of August though, it is brighter than the brightest stars, so it will still be visible as day breaks and the sky lightens.
Venus is starting to move away from us but, rising about 3 hours before the Sun and at magnitude -4.5, it will still be a very bright object indeed.
Magnitude is a measure of the brightness of a star or planet. The lower the number, the brighter the object appears to be. The brightest stars are magnitude zero, so Mercury is just a little brighter than the brightest star. Venus, on the other hand, is very bright and, at this point in its orbit, it's known as the Morning Star - although, of course, it isn't a star at all.
Mars will make its closest approach to Earth in October, so through August and September, it will appear to get bigger, brighter and redder. Because Mars will be directly opposite the Sun in October, astronomers call this 'opposition'. Happening every two years, this will be the best opposition we have enjoyed for a long time, with Mars at its closest to the Earth and at its highest in the night sky.
Currently it is at magnitude –1 and is rising just after 11pm, but by the end of the month it will brighten to magnitude -1.8 and rise at 9.30pm. Through binoculars or a small telescope, we will begin to see its surface features. At its closest, Mars will be only 62 million kilometres (39 million miles) away.
The gas giants, Jupiter and Saturn are also about just now. They are best seen around midnight, low down (elevation 15°) to the south-south-west. With the naked eye, both planets will appear as bright stars but with binoculars or a small telescope, you should be able to see Jupiter's Great Red Spot and Saturn's Rings.
For those with binoculars or telescopes, the ice giants, Uranus and Neptune are with us too this month.
Uranus is slightly to the left of Mars and at magnitude +5.8 may just be visible with the naked eye, although it will be difficult to pick out because it's in busy part of the night sky. Through a telescope though, it will be clearly visible as a blue/green disk, rather than a point of light, so it will be much easier to identify.
Neptune is to the right of Mars, in the South-East. At magnitude +7.8, you will definitely need a telescope to pick it out but, once again, it will be easy to identify, appearing as a blue disk.
With the dark skies arriving so late in the evening, there is little for the casual observer to see at this time of year. If, however, you have a telescope, you might like to try finding one of the most beautiful sights there is.
Begin by facing south. Look up into the night sky, immediately above your head. You should be able to see three bright stars, which make up an asterism called the Summer Triangle. (An asterism is a shape, drawn out by the stars, that isn't a formal constellation).
The three stars are Deneb, Vega and Altair, the brightest stars in the constellations Signus (the Swan), Lyra (the Lyre) and Aquila (the Eagle) respectively. In fact, Vega is the second brightest star in the night sky and is used as the zero point for the magnitude scale.
You should be able to make out a cross shape at the top of the triangle, with Deneb at the tail of the Swan. The crossbar is the wings and the long upright of the cross is the neck of the Swan. The second brightest star in Cygnus, at the head of the Swan, is called Albireo.
If you can find this in your telescope and you have sufficient magnification you should be able to see that Albireo is in fact two stars. The smaller one is a piercing, bright blue; the other is larger and bright orange.
The astronomical jury is out at the moment about whether Albireo is a double star or a binary. A double star is two stars that appear as one to the naked eye but which can be resolved as two stars with a telescope. These stars are not necessarily close together but are along the same line of sight when viewed from Earth.
A binary is similar but the two stars are in close proximity, in the same system and in orbit around each other. Either way, Albireo is a beautiful sight and well worth a long look.
As well as viewing these stars, if you are in a dark location, you may be able to make out the Milky Way running down the left-hand side of the triangle, through Deneb and Altair.
Perseid Meteor Shower
In mid-August, we have the Perseids meteor shower. The peak is on the night of August 11 into the morning of August 12, at about 100 meteors per hour, although meteors will be visible for several days either side of that.
The Moon will be in its last quarter, rising just after midnight, so the meteors should be best visible just after dusk. Get out your sun lounger, a blanket and, with a flask of your favourite hot drink, you can lie back to watch the streaks of light passing over. They can appear anywhere in the sky but if you trace their path back, you should find they all appear to come from the same spot, near the constellation Perseus, low down in the north-eastern sky – hence the name of this shower.
To learn more about the night sky or just see it during the daytime, you can use a planetarium app such as Stellarium. This is free to download on PCs and on Macs and it's also available on Apple and Android devices.
You can also use an app called Star Walk 2 (for Apple and Android) when you are out at night. By holding your device up to the sky, the app will give you a dynamic map of the stars you are viewing. It also has pages showing information about the planets, so you can predict when they will be up and about.
That's it for August, but we'll have more next month.