Well the autumn equinox is past now and we should begin to enjoy some dark skies again. Remember the clocks go back on the 31st of this month. The Harvest Moon on the 21st September looked quite spectacular as I caught it rising in the east and just fitting between two nearby houses.
The following chart represents the night sky at 11.00pm BST on the 8th of October and at 10.00pm BST on the 23rd October. 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. If you are observing a little earlier in the evening then the view is shifted 15 degrees eastwards for every hour before the specified time.
The chart this month should look familiar because facing south and just above your zenith will be the magnitude 2.3 star ,Caph, a member of five bright stars forming the readily recognisable ‘W’ shaped asterism in the constellation Cassiopeia. Being circumpolar it is visible all year round and six months ago it was low over the northern horizon but now we have a chance to admire it high in the sky.
Below Cassiopeia and to the right is the Great Square of Pegasus which we looked at last month. However, our focus this month is on the constellation Andromeda- the princess and daughter of the mythological Queen Cassiopeia and King Cepheus. Remember that the brightest of the stars in the Great Square of Pegasus, Alpheratz, is actually in the constellation Andromeda so we shall start from there. The main features of Andromeda are two curved strings of relatively faint stars starting at Alpheratz and lying above it and to the left, below Cassiopeia. The bright stars Algol and Mirphak in the constellation Perseus to the east can also help with navigation. The lower string of stars is fairly easily followed by star hopping from Alpheratz: delta Andromeda, Mirach and Almach have magnitudes of 3.3, 2.1 and 2.2 so no problem. The higher string of stars is fainter and poor viewing conditions and light pollution will make them difficult to see with the unaided eye as they are typically of magnitude 3.5 to 4.5. The constellation Andromeda is home to one of the most famous objects in the night sky- the Andromeda galaxy also known as M31 and shown on the chart by a red cross. The Andromeda galaxy is the nearest large galaxy to Earth and is similar in many ways to our Milky Way galaxy and is the only one visible to the unaided eye in the northern hemisphere. To locate it for observing, (your eyesight needs to be pretty good as its magnitude is 3.4), start at Alpheratz and by star hopping, jump to the second pair of stars along the curved strings and extend a line from Mirach through the second star and the Andromeda galaxy will be at a distance approximately equal to the distance between the two stars. Now some mind boggling statistics- the distance to the Andromeda galaxy is about two and a half million light years which means that the light entering your eyes from Andromeda set out two and a half million years ago. Andromeda is the most distant object you can see with the unaided eye but you will need a dark site with no light pollution and clear skies. Don’t expect to see something like the images shown in the gallery of the WMA website, you will have to settle for something which might be described as a smudge or fuzzy star but that doesn’t detract from the sense of achievement. Perhaps we will be able to do it together when we meet at Oakhill on the 9th October. Let’s hope for clear skies.
Only two stars in the constellation Pisces- The Fishes, are brighter than magnitude 4 so it offers little to the unaided eye. The constellation, Triangulum- The Triangle, is equally insignificant but because of its compact size, and a shape matching its name, it is relatively easy to spot.
We’ll finish this month with another zodiacal constellation Aries- The Ram. In Greek mythology it represents the golden ram whose fleece was sought after by Jason and the Argonauts. I can see no resemblance to a ram but its brightest star, Hamal, shines brightly at magnitude 2.0 and can be readily picked out.
Something to look out for
There will be a close approach of the Moon with Saturn and Jupiter on the 14th October and 15th October respectively. Perhaps I should explain that the chart in this blog is selected because it gives the view of the stars shown as they are crossing our meridian and therefore at their highest in the sky and as far away as possible from atmospheric disturbance closer to the horizon. However it is good to take a wider view from time to time and if you look west you can see the Summer Triangle with Altair getting closer to the horizon before it disappears from view later on. Similarly if you look towards your eastern horizon you will catch the beautiful star cluster known as the Pleiades or Seven Sisters. And don’t forget to cross from Cassiopeia through the pole star, Polaris, to The Plough which is currently close to the northern horizon and looking like a plough! Clear skies.