I don’t know if any of you had more luck than me but I didn’t achieve my own challenge of seeing Mercury during May. With so much rain and cloud cover, and the usual haze close to the horizon observing has been very difficult but I have managed to see Venus on the odd clear night and I still have two evenings left in May to catch Mercury. Several people have mentioned the ‘super’ moon on the 26th so that always attracts attention especially in those parts of the world where a lunar eclipse was observed.
It is the summer solstice in the northern hemisphere on the 21st June so we have long light evenings and need to do our sky observations later than usual and the following charts represent the night sky at 11.59pm BST on the 8th of June and at 10.59pm BST on the 23rd June. 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.
Starting from The Plough like last month we follow the arc of the plough handle down to the bright star Arcturus in the constellation Bootes- The Herdsman. Easily identified by its kite shape. Note that The Plough has continued on its anti-clockwise journey about the Pole star and is now ‘standing on its handle’. Just for interest I’ve named another star in Bootes- Izar, which can be resolved with a small telescope to reveal an orange giant of magnitude 2.7 and a fainter blue star. Something to look out for when we get back to group observing again and the opportunity to make use of a telescope.
Now, while still facing south, look to your left by about 30 degrees (about 3 clenched fists at arm’s length) and you will see a group of four relatively faint stars in the form of a quadrilateral. This is an asterism called The Keystone and is part of the constellation Hercules- the strong man from Greek mythology. Although quite a large constellation, Hercules is relatively faint but The Keystone gives us another signpost in the sky. I can see no likeness to a strong man and in fact Hercules is generally depicted upside down.
Lying halfway between The Keystone and Arcturus is a small but distinctive constellation, Corona Borealis- The Northern Crown. It consists of seven faint stars (but the brightest is of average magnitude 2.2) in a horseshoe shape if you cannot envisage a crown. Corona Borealis forms a very attractive grouping of stars.
The second diagram shows three constellations and the stars are mostly faint but these constellations deserve a mention because they lie on the zodiac, a region of the sky either side of the ecliptic- the apparent path of the Sun as it traverses the celestial sphere. By definition therefore the Sun passes through all the constellations on the zodiac. Historically the zodiac was divided into twelve equal regions each with its own sign of the zodiac and corresponding approximately to twelve zodiacal constellations. These were mostly used by astrologers about which we shall say no more. In the early part of the 20th century the International Astronomical Union defined boundaries for the constellations by coordinates in the sky and irrespective of the star patterns. The zodiacal constellations were no longer of equal size and there were thirteen rather than twelve. The odd one out is Ophiuchus which is a constellation but not a sign of the zodiac. That might be useful as the answer to a quiz question sometime!
Follow a line from the right side of the Keystone down to the horizon and you will see a bright reddish star with an average magnitude of about 1.4. This star is Antares, the brightest star in the constellation Scorpius- The Scorpion. Most of Scorpius and specifically its fish-hook tail is not visible from our latitude. Antares is the 10th brightest star visible from the northern hemisphere and that is because it is a red supergiant and if it were to replace our sun, its surface would lie between the orbits of Mars and Jupiter. It is said to represent the heart of the scorpion.
Having located Antares, the small and faint constellation Libra- The Scales lies towards the right.
Between Antares and the Keystone lies the large but faint and indistinct constellation Ophiuchus- The Serpent Bearer. Ophiuchus does not have much to offer the casual observer but its claim to fame is that it is the home of Barnard’s Star, the fastest moving star in the sky and at a distance of only 6 light years is the fourth closest star to the Sun after the three in the Alpha Centauri system.
Something to look out for
The big attraction in our skies this month is the solar eclipse which takes place on the 10th June. It will appear as an annular eclipse in some parts of the world but as the Moon passes in front of the Sun we will see a partial eclipse starting about 10.00am and finishing just after 12 noon. At maximum coverage at our location the Moon will extend across almost a quarter of the Sun’s diameter between 11.00am and 11.30am.Remember never to look directly at the Sun as this could result in permanent eye damage. Solar eclipse glasses are available if not locally then definitely online. Don’t risk using any unreliable method. Some of you may wish to try projecting an image of the Sun using a pinhole camera. For an image diameter of 1cm you will need a projection tube more than a metre long. Let’s hope the weather stays good.
On the 13th June there will be a close approach of the Moon and Mars with the Moon passing just over 5 Moon diameters to the north of Mars. You will be able to observe this from 10.00pm as dusk fades 16 degrees above the western horizon.
At long last we have been able to enjoy some clear skies and the Moon was prominent high in the sky last month with a close approach to Mars in the middle of April and a super moon on the 27th April.
The following charts represent the night sky at 10.00pm BST on the 8th of May and at 9.00pm BST on the 23rd May. 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.
We’ll start from The Plough which we discussed last month and you will notice that it has continued on its anti-clockwise journey round the pole star and is now slightly west of south with the middle of its handle at your zenith. Follow the arc of the handle of the Plough downwards round to the star, Arcturus, which has the distinction of being the second brightest star visible in the northern hemisphere at magnitude -0.05. Also known as alpha Boo (alpha meaning it is the brightest and Boo a short form of Bootes). It is an orange giant nearing the end of its life and relatively close at a distance of 36 light years. It is the brightest star in the constellation Bootes (The Herdsman) and again it is difficult to distinguish such a figure whereas the Kite asterism is easier to see and is what most people recognise as Bootes.
In mythology the constellation Coma Berenices is supposed to represent the locks of Queen Berenice of Egypt but it contains no stars brighter than magnitude 4 so doesn’t present much to observation with the unaided eye. I recall that it was an answer to a quiz question so if it comes up again at least you will have heard of it.
Carry on following the curve of the arc from Arcturus for about the same distance again until you see another bright star. This is Spica the brightest star in the constellation Virgo- The Maiden. Virgo is of course one of the zodiacal constellations as it lies on the ecliptic. Spica is a blue-white star with an average magnitude of about 1 and is 260 light years from Earth.
It may be easier to memorise these two star hops using the expression (Arc on to Arcturus and Speed on to Spica).
Now look to your north west and from last month you should recognise Leo- The Lion with Regulus shining brightly. Turn to face Leo then look up and you are back at the Plough.
Something to look out for
The challenge this month is to spot the planet Mercury. This is always quite tricky because it is low in the sky and only visible for a short time after sunset in the North West sky. It will be at its brightest early in the month but close to the Sun and it will be at its highest altitude on the 16th May. You will need a clear view to your West/North West horizon and if you have the use of binoculars so much the better. On the 4th May it will be on its easterly journey just below the Pleiades and above and to the left of our old faithful Venus which is significantly brighter. A better opportunity to spot it arises on the 13th May when a crescent Moon, Mercury and Venus form an isosceles triangle about 40 minutes after sunset. I can’t finish without saying how good it is to have Venus back in the evening sky and it will be just above a crescent on the 12th May. Clear skies.