The night sky in August 2015

posted 2 Aug 2015, 09:44 by Pete Collins
by Anne Holt

Sunset  1st Aug 21.05,  31st Aug  20.01

The return, for us in the UK, of true astronomical darkness (when the sun is more than 18 degrees below the horizon) in early August means it's time for amateur astronomers to get serious about our observing and imaging again!

Highlight of the month is the Perseid meteor shower - see below.

Constellations

When it finally gets dark enough, the Milky Way is now at its best.  From a dark sky site it can be seen stretching right across the sky and down to the southern horizon, passing almost overhead around midnight.
 
Milky Way and Summer Triangle - Vega top, Altair bottom, Deneb left

The Milky Way passes through the Summer Triangle, which is now high in the sky, with Deneb and Vega particularly prominent.  Alberio, a beautiful yellow and blue double star at the head of Cygnus the swan, is very well placed for telescopic observation.

The Plough and its host constellation Ursa Major are now very low in the Northern sky which means that the W asterism of Cassiopeia is riding high in the south east and very easy to spot.

Pegasus and Andromeda are now well above the horizon for most of the night and Perseus, followed by Auriga, are rising soon after midnight.

Planets

Mercury  mag - 0.6. An evening object, very low in the western sky after sunset, so not easily seen. On 6th August it will be only one degree from Jupiter but both will be lost in the twilit sky, setting only 20 minutes after the sun. It is at aphelion on 29th.

Jupiter in Leo, mag -1.6. Setting very soon after the sun, so barely visible this month. Superior conjuncton on 27th.

Saturn in Libra,  mag 0.6. Visible low in the SW as the sky darkens,  setting around 11.30 at the beginning of August, before 10.00 by month end. First quarter moon will be just 2 degrees NE of the planet at 21.30 on 22nd.
 
Neptune  in Aquarius,  mag 7-8. Above the horizon for most of the night, rising about 10pm at the start of August and by 8pm at month end. Not a naked eye object but should be visible through most amateur scopes, showing a small blue disc.  In larger instruments its biggest moon, Titan, can also be seen.

Uranus  in Pisces,  mag 5.8. Rising around 11pm in early August and at 9pm by month end, when it will reach its highest point in the sky (44 degrees) in the early hours.
Still a naked eye object - if you have perfect eyesight and are lucky enough to be observing from a very dark sky site.  Binoculars or a telescope are needed to see it through Manchester's murk.

Mars in Cancer,  mag 1.7. Rising about 4am, becoming more easily visible towards month end, when sunrise isn't until about 6.15.

Venus mag -4.2. Barely visible in early August as it approaches inferior conjunction on 15th. It then becomes a morning object,  on 24th it will be rising 40 minutes before the sun,  a week later this will have increased to 1 hour and 40 minutes before sunrise.

Pluto still in Sagittarius, but as ever, not easy to tell thedifference from a star.  If you have a reasonably large scope, and would like to try to spot it, the following site gives the current position -
theskylive.com/pluto-info


Meteor showers

August, of course, is dominated by the Perseids - as the Earth passes through debris from comet Swift Tuttle.They are active between 23rd July and 23rd August but for most of this time ZHR is very low.The peak is on the night of 12th/13th, when the ZHR is 80 - 100, but there could also be good displays in the early hours of 11th and 12th. Perseids are bright, fast moving meteors, often leaving persistent trails.  There could also be a few fireballs.They are best seen between 1am and dawn.  This year should be a good display, weather permitting, as the moon is a very slim waning crescent, not rising until just before dawn. From a suburban site, if you are shielded from direct light, you should be able to see one every five minutes or so.

Minor showers. There are quite a few of these this month, and there is much confusion about peak times and ZHR. Different sources give varying information.
One site had a message 'no information this month, as the web editor has had an accident on his bicycle'. At this point,  I gave up trying to find some concensus of opinion.

Several of these showers have radiants quite close together in Capricorn and Aquarius, and their activity periods often overlap, making it difficult to determine which shower an individual meteor actually belongs to,  so these are sometimes collectively called the Summer Antihelion Source shower.

Alpha Capricornids:    peak August 1st (or July 31st)  ZHR 4 -5. Bright, slow moving yellow coloured meteors leaving long trails.  Some fireballs.

Southern Iota Aquarids:  peak August 4th  (or 6th ... or 8th)  ZHR 1 - 2, maybe as many as 8. Faint medium speed.

Northern Delta Aquarids: peak August 13th, or later.  ZHR 1 -2, though one source says up to 20. Again, faint and medium paced meteors. Best seen from more Southerly latitudes.

Kappa Cygnids:  Peak August 18th,  ZHR  1 -5. Slow moving but  sometimes very bright.  This shower occasionally produces brilliant, flaming fireballs.

Nothern Iota Aquarids   peak August 25th or 26th.  ZHR 1 -3, or maybe 8. Faint, medium speed.

Alpha Aurigids: Peak August 31st   ZHR 5. A minor shower which occasionally produces a much better display.


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