Dark Sky Wales astronomer Martin Griffiths takes a look at the August night sky and provides you with an incite into what you can enjoy this month.
August sees the return of darker evenings and the glories of the summer Milky Way stretching from northern horizon to southern horizon. Sagittarius is at its best in early evening and the planets Jupiter and Saturn still dominate the evening whilst Venus dominates the morning skies.
Moon in August:
New: 21st August
First quarter: 29th August
Full: 7th August
Last Quarter: 15th August
Planets in August:
Mercury: is barely visible after sunset, setting low on the horizon in Virgo at the beginning of the month until it reaches inferior conjunction on the 26th August.
Venus: is a morning object rising in the early morning in the constellation of Gemini and is a brilliant object shining at magnitude -4
Mars: Draws toward the Sun in Leo this month and may be glimpsed by keen eyes observers in the first week of August rising just before the Sun but it is otherwise not well placed for observation.
Jupiter: still shines as a bright object in the constellation of Virgo, lying close to the first magnitude star Spica. Shining at magnitude -2 the planet is visible for just a over an hour after sunset.
Saturn: Is still in Ophiuchus after sunset and shines brightly at magnitude 0.1 Although it is low in British skies it is still a wonderful object and the rings look wonderful. Look out for the satellites, especially the bright moon Titan
Uranus: Is in Pisces and rises in the late evening, shining at magnitude 5.9 but still only subtends a small disk just under 4” across.
Neptune: The furthest planet from the Sun remains in Aquarius and rises in the evening shining at a miserable magnitude of 7.9. It has a small 2” disc.
Meteor showers in August.
The Perseid meteor shower peaks on the 12th August at 19:00 hours and this year the moon is 19 days old and rising with the best part of the radiant so many of the fainter meteors may be drown out. Nevertheless, the shower still has surprises, a bright bolide was observed over the UK just at the star of the shower in July 2017 and with a ZHR of over 80 meteors per hour, the show may well have some beautiful meteors to image or see. Local astronomical societies will have events to mark the occasion so look at their webpages. In Brecon, there is an event at the National Park Visitor Centre so see this webpage to book tickets: http://www.breconbeacons.org/events/9026
Interesting Events in August
There is a partial Lunar eclipse on the 7th August but from the UK the moon will rise in Eclipse and the southern portion of the Moon may well have a “bite” taken out of it but the maximum depth of the eclipse will be at 18:40UT but sunset is not until 19:38 UT and the eclipse may be over. If you are travelling to the continent, the entire partial phase may be observed dependent on location.
In the early morning of the 21st August the crescent moon is just 1.5 degrees from Mars in the Morning sky and may make a good photo opportunity.
Comets in August
There are no bright comets available for viewing in August.
Constellation of the Month: Scutum Sobeiski
This is one of the smallest constellations in the northern sky, yet it is packed with all manner of deep sky objects that are guaranteed to thrill and captivate the observer. The constellation was created by Hevelius and is supposed to represent the shield of the Czechoslovakian king Johann Sobeiski, who made a spirited defence of Vienna during the Turkish invasion in the 16th century. Unlike most of Hevelius’ creations, Scutum is not some obscure blank area of the sky, but is one of the brightest parts of the Summer Milky Way, as it is composed of a radiant star cloud that is perceived as the brightest patch of nebulous light along this rivulet of stars.
As one has come to expect, the proximity of the Milky Way ensures that the constellation is a delight for observers with binoculars or small telescopes, whist owners of giant binoculars will have a wonderful time sweeping the star clouds of this rich region of the sky.
One of the showpiece objects of the summer sky can be found close to a knot of bright stars at the northern end of the constellation, where b Scuti is the brightest of these stars. Lying in the same low power field is a blaze of starry light that is extremely compressed, looking an almost solid object through binoculars. This is the incomparable M 11, the “Wild Duck” star cluster, so called by the amateur observer Admiral Smyth, as its “V” shape reminded him of a gaggle of ducks in flight. M 11 is an astounding cluster that probably contains over 800 stars, making it the richest galactic star cluster in the Messier catalogue. It can be resolved in a telescope as an eighth magnitude cluster of stars with a central blaze of half resolved objects in a very crowded region, with a lovely red star just at the apex of the “V”. The cluster is very remote; about 6200 light years, hence its crammed appearance in the eyepiece.
Just above b Scuti is a famous long period variable star known to observers as R. Scuti. This is an intensely red star that can be followed through its rather irregular period with either binoculars or a small telescope. The duration is not well known but appears to fluctuate between magnitude 6 and 8.5 in roughly 140 to 150 days. It is yellow supergiant of G0 type lying at a distance of 1500 light years and shimmering with a luminosity over 9000 times greater than the Sun.
Travelling south into the heart of the constellation, the observer comes to another bright object lying southeast of the star e Scuti. This is M 26, a compact star cluster of some 25 bright stars in a very rich field of the Milky Way. So lavish is this region that it is hard to discern where the cluster ends and the Milky Way begins. It is a fairly remote cluster, apparently lying at a distance of 5000 light years. It can be seen with binoculars as a misty patch of light, but a small telescope will bring out the best in this lovely cluster, revealing the stars to be bright O and A type giants shining with luminosities thousands of times that of our Sun.
To the east of this cluster can be found a small globular cluster; NGC 6712. This small ball of light can be seen with a properly mounted pair of binoculars as a round conglomeration of stars against the concentrated starlight of the Scutum star cloud. In a small telescope it looks like an unresolved mottled sphere of white light, nice and compressed and separated from the Milky Way. It is uncertain whether NGC 6712 is a foreground object compared with the cloud or if it is actually passing through it, if it is a foreground cluster then its distance must be between 5,000 and 8,000 light years.
Close to the star a Scuti is a cluster of 25 tenth magnitude stars in a scattered group known as NGC 6664. a Scuti is not an actual member of this star cluster; it is merely a foreground object that is another one of nature’s chance alignments. Binoculars should show this rather large and faint cluster, whilst a small telescope will show it up nicely. In the same binocular field may be found another star cluster, the group NGC 6649, a pleasing assembly of some 35 stars, most of which are of 11th magnitude, but shining collectively at magnitude nine. Through a telescope the cluster is a lovely rich object with a beautiful sixth magnitude double star to its southwest that is easy to split, although both components do not exhibit much difference in colour, as they are both bluish B type giants.
The whole area of Scutum is a brilliant blend of star clouds and deep sky objects in perfect balance. The observer will be drawn to this area all summer long as the beacon of this incredible galactic condensation draws the eye. The Scutum star cloud is relatively easy to capture photographically as it glows at fourth magnitude with the collective light of billions of stars. Along the western edge of the cloud is the dark lane of the “Cygnus Rift”, and where it meets the cloudy fringe of stars, it breaks up into dark streamers and intrusions that are easily visible on a photograph. Some of these dark clouds can be seen if you carefully scan with binoculars along the periphery of the star cloud, where the wealth of stardust suddenly gives way to the empty blackness of the rift.
The distance to the Scutum star cloud is not well known, but it must be well in excess of 7000 light years, whereas the Cygnus rift probably lies between 5000 to 5500 light years away, although these figures can by no means be taken as the last word in the galactic distance scale. Within the cloud are two bright condensations that have been allocated NGC numbers. These are NGC 6682 at RA 18h 41m 36s Dec -04°46m and NGC 6683 at RA 18h 42m 12s Dec -06°17m. These objects are in all probability not true galactic clusters in the full sense of the word, but are probably dense areas of the cloud, perhaps containing a higher than average concentration of bright stars, or simply bright clumps of stars lying on the closest edge of the cloud to us.
Considering the beauty and detail shown in the Scutum star cloud, it would be a particularly fruitful place to search for nova; indeed, several novae have been discovered here in the not too distant past. The confusion of stars in this rich area is one that will take a little patience to learn, but is a worthwhile project.