The weather hasn't been particularly favourable recently but at least we can look forward to earlier sunsets and the chance to see some stars in the evening skies again. Let's hope there are clear skies as well.
The following charts represent the night sky at 11.59BST on the 8th of August and at 10.59pm on the 23rd of August. To use the chart, face south at the appropriate time with the bottom of the chart towards the southern horizon and you will see the stars in the chart.
Having described the Summer Triangle last month we shall use that as our starting point for navigating the skies. Locate Altair at the bottom of the Summer Triangle and continuing on a line from the two small constellations we introduced last month, Sagitta- The Arrow and Delphinius- The Dolphin, we find the smallest constellation in the northern hemisphere night sky Equuleus- The Little Horse or Foal. It is supposed to represent the head of a young horse. Its brightest star, Kitalpha, is only of magnitude 4 and because it is so small this constellation is easily overlooked.
Between Equuleus and the horizon is the zodiacal constellation Capricornus- The Sea Goat. It is relatively small with stars dimmer than magnitude 4 so it doesn't offer much to the unaided eye. Similarly to the left of Capricornus is another zodiacal constellation Aquarius- The Water Carrier and it is equally faint and indistinct. However this month they are the region of the sky in which we find the two planets Jupiter and Saturn of magnitudes -2.8 and 0.2 respectively and these two will outshine any nearby stars and there are more details about them in the final section.
Now let's go to the other end of the Summer Triangle, locate Vega and Deneb and look at some circumpolar constellations.
Facing Deneb, look above your zenith and find Polaris- the Pole star. To avoid neck strain best to use a deckchair! Between Deneb and Polaris is a group of not very bright stars forming a shape similar to the gable end of a house. This is the constellation Cepheus- King Cepheus of Ethiopia in ancient mythology. To the east of Cepheus is the welcome sight of the constellation Cassiopeia- wife of King Cepheus, its familiar 'W' shape now standing on its end. This is a sight you can enjoy more and more in the coming months as it rises higher in the sky until it is at your zenith in the winter months.
To the west of Cepheus is the large constellation Draco- The Dragon, which wraps otself around Ursa Minor. Unfortunately Draco has no stars brighter than magnitude 2 but it does contain the star Thuban which 5,000 years ago was the pole star in the northern hemisphere. Due to the precession of the Earth's axis, the position of the celestial pole traces out a circle, over a period of about 26,000 years, on the celestial sphere and over the last 5.000 years it has moved from Thuban to Polaris. This is rather fortunate for us because at magnitude 2 Polaris is considerably brighter than Thuban at magnitude 3.7.
Finally between Cassiopeia and Cygnus and straddling the Milky Way is the small and obscure constellation Lacerta- The Lizard. Because of its small size it contains few objects of interest but it is the site of 'Nova' explosions, the subject of Hugh's recent talk
Something to look out for
I think we can allow ourselves to get a little excited becuase this month has the potential for some good observation. The planets Saturn and Jupiter are at opposition on the 2nd August and 20th August respectively so they are on the opposite side of the Earth from the Sun and at their closest approach to the Earth. This means that they appear larger and brighter and compared with last year higher in the sky. They rise as the Sun sets and set as the Sun rises so are visible all night being their highest about midnight. Of course they will continue to be visible for some time to come with Saturn having a close approach with the Moon on the 21st August when the 12 day old Moon will pass 7 Moon diameters to the south of Saturn. Similarly there will be a close approach of the Moon and Jupiter on the 22nd August.
Equally exciting is the prospect of an impressive Perseid meteor shower which, although active from 17th July to the 24th August, will peak on the 12th August. What we call a meteor or 'shooting star' is a grain of dust burning up in the Earth's atmosphere. In the case of the Perseids the grains of dust were left by the comet Swift-Tuttle and each year the Earth passes through that dust trail as it orbits the Sun. The meteors appear to radiate from a point in the sky called the 'radiant' in the constellation Perseus, hence the name, but you don't have to be looking at the radiant to observe the meteors. More important is that you can lie back on a lounger, allow your eyes to become accustomed to the dark and avoid light pollution as much as possible. a blanket and warm drink will help to keep you comfortable. If you are watching with a group then a real party atmosphere as I recall when the group had a meeting in Cheddar a few years back and Ben Sutlieff was recording the meteors indoors with his radio equipment. Let's hope for a return to such times soon. Clear skies.