The night sky in August 2016

posted 28 Jul 2016, 08:59 by Pete Collins
by Anne Holt

Sunset   1st:   21.04     31st:    20.00

New moon   2nd     Full moon  18th

Highlights

The Perseid meteor shower, peaking on the night of 11th/12th (see below) and a lengthening period of astronomical darkness - an hour and a half at the start of the month and almost 6 hours at month end.

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

Still not a very good time for planetary observation, as the naked eye planets are all very close to, or even below, the horizon during the hours of darkness.

Mercury:  In Leo, moving into Virgo on 21st. Not easily seen this month as, because of the angle of the ecliptic, it remains close to the horizon.  Even when it is at greatest Eastern elongation on 16th, it sets only half an hour after the sun.

Venus:  in Leo, moving into Virgo on 25th. Again, not easily seen despite having a magnitude of -3.9, as it sets around 40 minutes after the sun throughout August.

Mars:   mag 0.8, in Libra, moving into Scorpio on 3rd. At the start of the month Mar is 11 degrees above the southern horizon as the sky darkens, setting at around midnight.  By month end, when it will be on the border of Scorpio and Ophiuchus,  it will have dimmed to -0.3 and be setting soon after 10.30.
On 24th it will pass between Saturn and Antares, about 2 degrees north of the red supergiant.

Jupiter: mag -1.8,   in Leo, moving into Virgo on 10th. Best seen in early August, when it is 7 degrees above the horizon at dusk, setting just before 10.30.  By month end it will be only 1 degree above the horizon at dusk and setting half an hour after the sun. On 27th it will be just 8 arcminutes (one quarter of the moon's diameter) from Venus.  The pair might just be visible, very low on the Western horizon, about 20 minutes after sunset.
Apparently this will be a spectacular sight - if you should happen to be viewing it from Brazil!

Saturn:  mag 0.4,  in Ophiuchus. Setting soon after 1am at the start of August, when it is best seen between 10 & 11pm.   By month end it will be setting just after 11pm.

Uranus:  mag 5.8, in Pisces. Quite well placed this month, rising around 11pm in early August and soon after 9pm at the end of the month, when it will reach its highest point (45 degrees) at around 4am.  It will also be slightly brighter at mag 5.7 so, if you have a very dark, clear sky, it might be worth testing your eyesight by trying to spot it without optical aid.   A chart of its position can be found at www.nakedeyeplanets.com/uranus.htm

Neptune:  mag 7.8,  in Aquarius. Too faint to be seen with the naked eye but worth viewing through a scope this month.   Rises at 10pm at the start and by 8pm in late August.   Reaches its highest point (28 degrees) at 3.20am on 1st, and soon after 1.15 on 31st.   Exact position on any day can be found on https://in-the-sky.org/ephemeris.php

Pallas, the third largest asteroid, and the second to be discovered - in 1802 - is at opposition on 22nd.   At mag 9.2, it should be visible in amateur scopes. Probably best viewed on 13th, when it will be slightly more than 1 degree SE of globular cluster M15, in Pegasus.

Meteor Showers

August is dominated by the Perseids.  These are bright, fast moving meteors often leaving persistent trails, caused when the Earth passes through debris from comet Swift-Tuttle.   They are active between 17th July and 24th August but with fairly low activity for most of that time, although it's always worth looking out for them a few days either side of the peak. The peak is on the night of 11/12th when ZHR is usually said to be around 80.  However, this year is predicted to be particularly good, with a peak which could be as high as 160, as the Earth travels through a large cloud of debris which it encounters every 12 years. There could also be a lesser peak, of faint meteors, at around 10.30 on 11th, as we pass through a cloud of smaller dust particles. Best viewed between Moonset, at 00.30, and dawn.

Minor Showers

Kappa Cygnids
Peak 18th,  ZHR 1 - 5  Slow moving but very bright meteors with occasional brilliant fireballs.  This year, the shower will be adversely affected by the full moon on that day.

Alpha Aurigids
Peak 31st,  ZHR 5.  A minor shower which sometimes produces a good display.  No moon interference this year.

There are also several minor showers having their radiants on the ecliptic, low in the sky so better seen from further South.    Because they are low activity and similar in appearance, with radiants close together,  it can be difficult to separate them so most are referred to together, as the Summer Antihelion Source.

Alpha Capricornids: 
Peak August 1st,  ZHR 4 - 5.  Bright, slow moving yellow coloured meteors leaving long trails.  Some fireballs.


Southern Delta Aquarids:
Peak 6th,  ZHR  between 1 and 8.  Faint, medium speed.

Northern Delta Aquarids:  peak 13th, ZHR 1 - 2.  Faint, medium paced.

Northern Iota Aquarids:   peak 25th/26th.  ZHR 1-5.  Again faint, medium speed.
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