The night sky in August 2017

posted 28 Jul 2017, 11:46 by Pete Collins
by Anne Holt

Sunrise       1st:     05.24              31st:     06.16
Sunset        1st:     21.04              31st:     20.00

Astronomical darkness:
1st     00.35   to   01.55         31st:   22.14  to  04.04   

Full Moon:     7th  at  19.10
New Moon:  21st  at  19.30

Highlights

Astronomical darkness is increasing throughout the month -  almost 6 hours by 31st. 
We have one major meteor shower, a faint comet passing close to the Pleiades, a penumbral lunar eclipse and, of course, a total solar eclipse - for any of you who will be in certain parts of the USA on 21st.  Here in Manchester we may, weather permitting, see a very small 'bite;' taken out of the Sun just before it sets. See lower down this page for further details of these events.

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:  in Leo, mag 0.4. At the start of August it sets about 70 minutes after the Sun and might be visible for a short while, very low in the West. On 5th it moves into Sextans, another non zodiac constellation, and spends most of August within its boundaries.  What will astrologers make of that?  It reaches inferior conjunction on 26th and goes back into Leo on 28th.  At the end of the month it rises only half an hour before the Sun and is not visible in the bright dawn sky.

Venus:  in Gemini, mag -4.0.  Shining brightly in the Eastern morning sky throughout August.  On 1st it rises more than 3 hours before the Sun and reaches an altitude of 20 degrees above the horizon before dawn.  On the morning of 19th it is close to the 8% waning Moon.  It moves into Cancer on 25th and by month end it rises around 3am and gets up to 22 degrees by sunrise.
  
Mars:  in Cancer, mag 1.7.    On 1st it rises at 05.07, just 17 minutes before the Sun, so is not visible.  It moves into Leo on 18th and by 31st will rise 70 minutes before the Sun but it is still very low in the East and too faint to be seen in the brightening sky.

Jupiter:  in Virgo, mag  -1.9.  Still bright but not now very prominent.    On 1st it sets a few minutes after 23.00 and will be only 12 degrees above the SW horizon half an hour after sunset.   On 25th it is 3 degrees below the 18% lit Moon, close to the Western horizon in the evening twilight.  By month end it will have faded slightly to mag -1.7 and be barely visible as it sets at 21.14 while the sky is still quite bright.

Saturn:  in Ophiuchus, mag 0.3.   On 1st it reaches its highest point in the sky at 21.49, 45 minutes after Sunset.  It is still very low - just 14 degrees above the Southern horizon, and sets at 01.46.  On the evening of 3rd it is 5 degrees SW of the 73% lit Moon.   It resumes prograde motion (moving from West to East against the background stars) on 25th. By month end it sets about 20 minutes before midnight.   However, despite being so low in the sky and setting early, it is still well worth viewing through a telescope - the planet's South pole is tilted towards us at an angle of 27 degrees, making it a spectacular sight.

Uranus:  in Pisces, mag 5.8.   On 1st it rises at 23.09, 2 hours after sunset, and gets to 34 degrees above the SE horizon as the sky brightens before dawn. By month end its position is even better - it rises at 21.11 and reaches an altitude of 46 degrees a couple of hours before dawn and will have brightened marginally to mag 5.7.    It is, in theory, a naked eye object - provided the eye in question has 20/20 vision and is situated in a very dark sky site. And knows exactly where to look.    Otherwise binoculars are needed,  or a scope if you want to see the small blue green disc.

Neptune:  in Aquarius, mag 7.8.   Another distant ice giant which is favourably placed this month.  On 1st it rises at 22.02, an hour after sunset and reaches its highest point, 29 degrees, in the South, at 03.30.   Around midnight on the night of 9th/10th it is 1.7 degrees North of the 94% lit Moon.  On 31st it culminates at 01.29, about 28 degrees above the Southern horizon   A decent amateur scope should show its rich blue colour.

Dwarf planet Ceres appears quite close to Venus in August, following a parallel path through Gemini, though it appears to move more slowly.  At mag 8.9 it needs to be viewed through a telescope or, better still, photographed.  It is at its closest to Venus on 12th, when it appears 2.5 degrees North of the bright planet.
 
Meteor Showers

In  August we have one of the best showers of  the year and a few minor ones.

Perseids:  active betwen July 17th and Aug 24th, peak on the night of 12th/13th, but it is also worth looking on a couple of nights either side of this date.  ZHR is given as 50 to 80 per hour but this is in ideal conditions - this year we'll be lucky if we see as many as 25 as the bright gibbous Moon will wash out all but the brightest.  On the night of 12th the Moon is 80% lit and rises at 22.49.   The good news is that the peak is on a Saturday night/Sunday morning so, for most people, work won't interfere.   Although meteor watchers are usually told that  the best time for observing is after midnight, in the case of the Perseids it could be rewarding to look earlier, when the radiant is low in the SE, as the shower sometimes includes Earthgrazers - rare, slow moving colourful meteors which streak along just above the horizon, leaving bright persistent trails.  This shower occurs when the Earth crosses the orbit of comet 109P/Swift-Tuttle and some of the debris left by the comet burns up in our atmosphere.
You may have seen, on the internet, that this shower is going to be the best since records began and there won't be anything like it for the next 99 years - there will be so many meteors that the sky will light up almost as bright as day.  Don't believe a word of it!  I've checked and no reputable site makes any mention of it - it appears to be one of these enormous Moon, bright pink Moon type urban myths which surface from time to time.

Minor Showers

Kappa Cygnids:  active August 3rd to 25th, peak 18th  ZHR 3.  Some sources give the peak as 14th, so the best bet is probably to look on both nights.  The shower has occasionally shown enhanced activity but this is not predicted for 2017.

Aurigids:  August 28th  to September 6th,  peak on the night of Aug 31st/Sept 1st,  ZHR  6.   Another shower which sometimes produces a much better show - but probably not this year.

Alpha Capricornids:  active to August 17th,  ZHR 4 to 5. The peak is sometimes given as July 30th but activity is often said to show a plateau, rather than a sharp peak, so try looking during the first few days in August.  They are slow moving yellow coloured meteors often leaving trails.  There could also be some fireballs.

There are also 3 showers which are often considered to be part of the Summer Antihelion Source, as they have radiants close together on the ecliptic.  They are all faint and medium paced, making it difficult to distinguish them from background ANT meteors.   As the ecliptic is very low at this time, these are all better seen from further south.
 
Southern Delta Aquarids:  peak 6th,    ZHR 1 to 2
Northern Delta Aquarids:   peak 13th,  ZHR 1 to 2
Northern Iota Aquarids:   peak 25th,  ZHR 1 to 5

Comets

We have one faint comet, not visible to the naked eye , magnitude somwhere between 10 & 12 (as always, sources give different info).  2015 ER61 PanSTARRS  is now reaching an altitude of 30 degrees while the sky is still reasonably dark.  It moves from Aries into Taurus on 2nd, rising at around 23.30.  During the third week of the month it passes about half a degree below the Pleiades.  

As always, for exact positions of planets, comets etc on any night see:


Eclipses

On August 7th, there is a partial lunar eclipse, however from the UK we will only see the penumbra - the faint outer part of the Earth's shadow - on the face of the Moon and probably won't notice any appreciable dimming. When the Moon rises at 20.44 a large part of it will already be in shadow, the maximum being only a few minutes later.  The Moon moves out of the shadow at 21.50.

On 21st for those who live in, or are visiting certain areas of the USA (or the Atlantic or Pacific Oceans) there is a total solar eclipse.  Here, weather and low Western horizon permitting, we might see a partial eclipse.  However, only a very small part of the Sun (6% at maximum) will be covered by the Moon.  The eclipse starts at 19.39 when the Sun is only 6 dgrees above the Western horizon, the maximum is at 20.02 when its altitude has dropped to 2.75 degrees, the Sun sets at 20.23.

REMEMBER:   NEVER look directly at the Sun without proper eye protection. SUNGLASSES ARE NOT ENOUGH, your eyes will still be permanently damaged. 
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