The night sky in August 2019

posted 31 Jul 2019, 09:02 by Pete Collins   [ updated 31 Jul 2019, 12:02 ]
by Anne Holt

Sunrise    1st:  05.24       31st:  06.15
Sunset     1st:  21.05       31st:  20.01

Astro darkness
1st:  00.40 to 01.50        31st:  22.15 to 04.03

New Moon:    1st at 04.13     30th at 11.37
Full Moon:     15th at 13.29

Lunar perigee:    2nd at 07.10  (359397km)   30th at 15.59  (357175km)
Lunar apogee:   17th at 10.51  (406243km)

August full Moon is known as the Sturgeon Moon, named after the large numbers of these in the lakes where the Algonquin tribe fished.  Other names are the Green Corn Moon, Barley Moon, Fruit Moon and the Anglo Saxon Grain Moon.

Highlights

At last we have some astronomical darkness, especially towards month end - there's only 70 minutes on the night of 1st/2nd but almost 6 hours by 31st/Sept 1st.  There's a Super Black Moon on 30th, when the new Moon is only a few hours after Lunar perigee - the second closest of the year.  It's also the second new Moon in the calendar month, hence the name 'Black'.  However, as always at new Moon, you won't actually see anything.
Not much else of note, one of the best meteor showers of the year will be seriously marred by bright moonlight and the naked eye planets are all very low in the sky, some aren't visible at all in the latter part of the month. The two ice giants are well placed for binocular and telescopic observation.
Experienced astrophotographers fare much better, a couple of the dwarf planets are quite high in the sky for part of August, 3 asteroids reach opposition at magnitudes of around 8 or 9,  and there are 4 comets brighter than mag 12.
And the nights should be reasonably mild - observers should be able to manage without wearing all their thermals.


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.

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 Gemini, mag 2
Should be visible in the morning sky after the first few days in August from a site with a good unobstructed eastern horizon.  On 1st it rises at 04.22 but is still 4 degrees below the horizon when the sky starts to brighten.  It moves into Cancer on 10th and also on this day reaches greatest western elongation, separated from the Sun by 19 degrees.  It reaches its highest point on 12th when it is 8 degrees above the horizon by dawn, brighter at mag -0.3. It moves into Leo on 24th, now at mag -1.3 but lower in the sky, only 5 degrees, in reasonable darkness.  By 31st it won't be visible, despite now being at mag -1.7, as it is only 4 degrees from the Sun.


Venus:  in Cancer, mag -3.9
Not visible in August.  It starts the month at 3 degrees from the Sun and moves in even closer during the next couple of weeks.  It moves into Leo on 12th, when the separation is only 1 degree.  After superior conjunction on 14th, it does start to move away but the two are only 4 degrees apart by month end.
 
Mars:  in Leo, mag 1.8
On 1st it sets at 21.33 and might be seen for a short while, low in the west soon after sunset.  On this evening it is less than 1 degree SSW of the very thin crescent Moon.   Not visible after the first few days of the month as the apparent separation from the Sun decreases.  By month end they are only 1 degree apart.

Jupiter:  in Ophiuchus, mag -2.4
An early evening object, now past its best.  On 1st it is at 14 degrees in the south at 21.30 and should be visible until around midnight, setting at 01.16.  On 9th the 72% Moon passes 1.5 degrees to the north of the planet.  In early August it appears to move from east to west against the background stars, known as retrograde motion.  It resumes prograde motion (west to east) on 11th.  Of course it doesn't actually change direction, it's a similar effect to being in a car which overtakes another vehicle.  For a short time the slower one appears to be going backwards.  By 31st the planet will be 13 degrees above the western horizon as the sky darkens, setting at 23.15.

Saturn:  in Sagittarius, mag 0.2
On 1st it should be visible from a few minutes before 22.00 as the sky darkens, at 10 degrees in the south east.  It reaches its highest point, 14 degrees, in the south at 23.34 and sets at 03.29.  On 11th and 12th the gibbous Moon passes close to the planet, to the west on 11th and to the east on 12th.  On 31st it culminates at 21.30 in astro twilight, setting at 01.23.

Uranus:  in Aries, mag 5.8
Much better positioned than the brighter planets.  On 1st it rises at 23.25, becoming visible around 2am and reaching 32 degrees by 03.32 when the sky starts to brighten.  It is retrograde from 12th, though it moves so slowly against the background stars that the change is unlikely to be noticed.  On 21st and 22nd it is close to the waning gibbous Moon and on 31st it reaches 49 degrees in the south by dawn, culminating at 04.48 when the sky has started to brighten. It is a naked eye object given the usual caveat of needing a good dark sky site and good eyesight.  For everyone else binoculars are needed, or a scope to show the small blue-green disc.

Neptune:  in Aquarius, mag 7.8
The second distant ice giant's position is also improving.  On 1st it rises at 22.11 and reaches 30 degrees in the south by dawn.  On 31st it rises at 20.12 and is at 21 degrees in the east by 23.00. It culminates, 30 degrees above the southern horizon, in darkness at 01.45.  It is much fainter than Uranus and needs the aforementioned good site and good sight to be seen with binoculars.  A decent amateur scope is necessary if you want to see its rich blue colour - and maybe even large moon, Triton.

Dwarf planets

Ceres: in Scorpio, mag 8.4
Despite being the closest and by far the brightest of the dwarf planets, it isn't easy to see this month, being very low in the sky.  On 1st it is only 16 degrees above the SW horizon as the sky darkens, setting at 00.23.  By month end it is slightly fainter at mag 8.8 and at an altitude of only 14 degrees in darkness, setting at 22.34.

Pluto: in Sagittarius, mag 14.6
Still too low for telescopic viewing or imaging, reaching a maximum of 14 degrees in the south, at 00.05 on 1st and 22.00 on 31st.

Haumea: in Bootes, mag 17.4
An early evening target for good astrophotographers.  On 1st it is at 28 degrees in the west at 23.00, setting at 02.24.  By month end it is much lower, 23 degrees at 21.30 and setting at 00.24.

Makemake: in Coma Berenices, mag 17.2
Might be possible to image on 1st, when it is 23 degrees above the western horizon at around 23.00, setting 3 hours later.  By 31st it is at only 19 degrees at dusk. and sets soon after midnight.

Eris:  in Cetus, mag 18.8
The most distant of the dwarf planets is a morning object, again only suited to imaging.  On 1st it is at 23 degrees in the SE at 3am.  Its position improves during the month, on 31st it reaches its highest point, 34 degrees, in the south at 04.19.

Three asteroids reach opposition in August, and will be a better target than the dwarf planets as they are much brighter.

16 Psyche:  in Capricorn. Opposition is on 7th, when it is at mag 9.3 and reaches 21 degrees in the south at 01.14.

15 Eunomia: in Aquarius.  At opposition on 13th at mag 8.3.  Culminates at 01.13 at an altitude of 30 degrees in the south.

39 Laetitia: starts the month in Aquarius and moves into Capricorn on 8th. Reaches opposition on 17th at mag 9.1, when it is at 26 degrees in the south at 01.08.

Comets

There are 4 comets around which should be high enough and bright enough to be possible imaging targets.  Though comets are notoriously unpredictable as regards magnitude, so any one of them could become much brighter - or fade into total insignificance.

C/2017 T2 (PANSTARRS) in Taurus, mag 10.0
Quite low in the morning sky at the start of August, but its position does improve as the month progresses.  On 1st it rises at 01.29 and only reaches 14 degrees by dawn.  On 31st it rises at 23.36 and is at 42 degrees when the sky gets too bright for it to be visible.  Magnitude at this time is predicted to be around 9.1.

C/2018 N2 (ASSASSN) in Aries, mag 11.3
On 1st it rises at 23.29 and gets to 30 degrees in the east by dawn. On 31st it will be brighter at mag 10.8 and reach 59 degrees in the south before the sky brightens.

168P/Hergenrother:  in Aries, mag 11.8
Rises at 23.16 on 1st and is at 32 degrees in the east when the sky begins to brighten.It moves into Taurus on 6th and Perseus on 17th.  Becomes circumpolar on 27th and crosses the border into Auriga on 31st, when it should be marginally brighter at mag 11.7 and reach 58 degrees by dawn.

260P/McNaught : in Pisces,mag 12.1
On 1st it rises at 23.25 and gets to 31 degrees just before 03.30 as dawn breaks.  It moves into Aries on 15th.  By month end it rises at 20.39, reaching 56 degrees in the south while the sky is still reasonably dark. This one is also brightening and should end the month at around mag 11.4.

Recommended websites for more info and detailed positions of any solar system object:

Meteor Showers

There is one major shower in August, often the best shower of the year.

Perseids: active July 17th to August 26th, peak on the night of 12th/13th, ZHR could be as many as 75 to 100 from a dark sky site, probably 10 or fewer from light polluted towns.  These are swift moving meteors originating from debris left by comet 109P/Swift-Tuttle.
And now the bad news:  This year there will be serious Moon interference from the 94% Moon which doesn't set until just after 3am.  This means that the best time to see the shower will be in the hour or so before dawn.

Minor showers

Kappa Cygnids:  active 3rd to 25th, peak 18th,  ZHR 5 but sometimes much higher.  This shower, which sometimes includes fireballs, is said to be very unpredictable, not only in numbers but also in dates - there could be a second peak near the end of its period of activity.

Aurigids:  active August 28th to Sept 5th.  Peak on the night of August 31st/Sept 1st so could be said to be in August - just!    ZHR 6.  This shower of bright, slow moving meteors occasionally produces very brief strong outbursts.  Parent comet C/1911 Kiess.

And there are a couple of showers which had their peak right at the end of July, so might still show some activity.

Alpha Capricornids:  said to have a plateau like peak centred on the night of 30th/31st July.  ZHR usually fewer than 5, but could include very bright, coloured meteors.  Parent comet 169P/NEAT.  Studies of the dust clouds left by this comet have led to predictions that this shower could become very prominent between the years 2200 and 2400. 

Southern Delta Aquarids are active until 23rd but are less likely to show much activity in August as the radiant is very low and the meteors usually quite faint.

Sporadic activity is said to be reasonably high in August, and the antihelion source is also active, with a radiant in Capricorn, but the meteors from this should be easily distinguishable from Capricornids, the former being much faster.
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