Night Sky Notes – August 2018

Night sky notes for August 2018            Geoff Mitchell

As we head into August the evening twilight noticeably fades an hour earlier throughout the month.

Look to the NW  from 90 to 120 minutes  after sunset  or similarly  to the NE  hours before sunrise  i.e. when the Sun just below the horizon during the summer months when extremely high clouds at 80 km altitude known as Noctilucent Cloud (NLC) may be seen. NLC’s show a bluish colour and also show filamentary structure.  Late August marks the end of the season for seeing NLC’s.

Venus may be seen low in evening twilight, reaching 50% phase (Dichotomy) mid month  around the time of greatest elongation , visual observers may note the Schroter effect , prominent using a blue (wratten 80 ) filter to determine the exact date of Dichotomy .

Jupiter is also low in the south west aspect but is heading into twilight skies . In the southern aspect the ringed planet Saturn is located amongst the rich star fields of Sagittarius and is telescopically is a fine sight with the famous rings prominently displayed.  Also the Red Planet Mars shines brightly low in the south east,and moves in retrograde motion ( westward) during the month on the border between Sagittarius and Capricornus . Mars was closest to Earth around 57.5 million km on July 31st, the closest distance since 2003. At 24 arc seconds apparent diameter, the lelescopic views from the southern hemisphere should be impressive , however Mars is very low in UK skies and so the image quality is relatively poor. A white polar cap and some dark markings may be seen in moderate sized telescopes (20cm) – However recent reports suggest the Martian summer dust storms have started, which can obscure the surface features.  Mars is also in the headlines at the time of writing due to the announcement of the discovery by orbital radar mapping of a possible salty water lake kilometres beneath the frozen CO2 polar cap.

Periodic Comet 21P Giacobini-Zinner  is a binocular object , a small fuzzy patch , brightening to around 7th magnitude  as it moves through Cassiopeia and heads towards perihelion  in mid September , The comet is found close to the bright star Capella at the end of the month  – See Notes [ LAS newsletter No 198 ] .

Comet 2017 S3 Panstarrs heads for perihelion mid month, currently it has shown brightening to binocular brightness. A new visitor to the inner solar system, the comet will pass within 0.2 AU of the Sun – In late July and early August the comet moves south into pre dawn twilight. A difficult observation in our twilit skies.

The August night sky shows the summer constellations prominently in the south east from early evening.

Our own Milky Way galaxy stretches from the constellation of Auriga[ The Charioteer]  marked by the bright star Capella low in the north  up  through the constellations of Perseus [ and Cassiopeia  rising  low in the north east  Overhead the Milky Way can be seen on moonless nights as a faint band of light in the constellation of Cygnus {The Swan or Northern Cross]  and down towards the southern aspect , through the constellation of Auriga and the star rich fields in the constellation of Scutum [ The Shield]  and into the southern horizon and the constellation of Sagittarius [The Archer]. If you are lucky enough to holiday in a dark sky site, remember to pack your binoculars and enjoy looking these rich star fields on clear moonless evenings and be amazed.

Sagittarius is best seen in early August but the constellation  known for the `Teapot` asterism of stars has  both rich star fields and some fine star clusters  located above the spout of the Teapot  asterism; however you do need a good southern horizon and finder chart to spot some of these.  Pluto is located just above `the handle of the teaspoon asterism` .

Up until to August 23th observers may also catch the Perseid meteor shower, with peak occurring late on the  evening of August 12th.and early hours August 13th  Conditions this year are very favourable.  If you have clear conditions in the  late  evening of the 12th/ 13th and a dark site,  sit back on a sun lounger  and keep a look out for these bright meteors with persistent trails. Meteors originate from the dust debris trail of comets and these sand grain size meteoroids burn up in Earths upper atmosphere causing the streak of light we see as a meteor. In the case of the Perseid shower, these are seen to peak around August 12th each year as Earth passes through the meteoroid stream from Comet Swift Tuttle (1862 III). Each time the comet orbits the Sun, another stream is laid down, resulting in a complex set of streams, rather like the stands of a rope – Meteor activity can therefore vary from year to year.  Due to perspective the meteors appear to radiate from a single point in the sky, the Radiant, in the case of the Perseids this is in the constellation Perseus hence the name – Perseid. Refer to the website for details of the LAS Perseus Meteor Watch event (Weather permitting)

Hercules is noted for the Globular cluster M13 containing some 750,000 stars, a nice view in a small telescope

The bright star Vega in the constellation of Lyra [The Lyre] is seen high above the north east horizon and Altair in the constellation of Aquila low in the south east. Vega, Altair and Deneb, in the constellation of Cygnus form the `Summer Triangle` asterism, a useful sign post for the summer skies.

Look low in the south early evening to find the distinctive `T` shaped asterism of stars of the `head` of Scorpius. To the east of Scorpius find a yellow star. This is the ringed planet Saturn, although rather low as seen from the UK, Saturn’s ring system is now wide open, a classic view of this gem of the solar system. Small telescopes will show the rings and the brightest moon Titan. Larger telescopes show up to six or so fainter moons and any white oval features on the planets disk.  Look below the `T` head of Scorpius to see the `blood red` coloured star Antares.  Antares name means `The rival of Mars`, a red super giant star, with a mass of some 20 solar masses. It has a diameter that, on the scale of our solar system, would be greater than the orbit of Mars.

High in the south the bright orange star Arcturus in the constellation of Bootes [The Herdsman] is the brightest star in the northern hemisphere of the sky.

The stars of the Summer Triangle asterism, the position of the Milky Way star fields and dark rifts through the constellations of Cygnus, Sagitta and Aquila.

 

Planets in August 2018

Mercury Inferior conjunction on August 9th ,  returns to dawn twilight from mid month .

Venus is visible low in evening twilight skies, Venus and thin crescent moon , August  13th greatest elongation Aug 18th , 50% phase – Telescopically observe phase from August 11th onwards to record – Schroter  effect .

Mars is now positioned in our daytime skies.

Jupiter heads towards the daytime skies by late August, with conjunction on October 26th.

Saturn now visible early evening low in the south in Ophiuchus  – a good time to see this ringed `gem`.

Uranus rises by late evening in the constellation of Pisces   – best views in autumn skies.

Neptune now rises mid evening in the constellation of Aquarius – best views in autumn skies.

Moons phases in August

New Moon          August 11th        Moonless, best time for deep sky observing. and meteor watching (see notes)

First Quarter     August 18th         Best days to see shadow details in lunar craters (early evening)

Full Moon           August 26th         Best days to see bright ray craters like Copernicus / Tycho.

Last Quarter      August  4th         Moon visible in daytime skies.  Do not look directly at the Sun.

Meteor shower s                             Perseid   range July 23rd to August 20th, Maxima August 12th (late evening)

Visually 30 to 50 per hour at peak – Fast meteors with bright persistent trails.

Delta Aquarids, range July 15th to August 20th, maxima August 6th, ZHR 10/ hr

The highlights of the month.

Perseid Meteor Shower, very favourable  Maxima August 12th/ 13th (Refer to web site)

Mars close to Earth (July 31st) , shines bright red low in the south aspect in Sagittarius / Capricornus

Venus at 50% phase  (Dichotomy) – low in evening twilight

Saturn  very low in south in Scorpius , rings open at 26.8° DE [tilt] showing Saturn’s North Pole.

Jupiter low in evening twilight , four Galilean Moons and cloud belts visible in modest telescopes.

Noctilucent cloud – watch the NW skies from 90 minutes to 120 minutes after sunset (see text)

Milky Way star fields, visible from dark sites on moonless evenings Remember the binoculars if your on holiday in a dark site and trace out the star fields and dark rifts through Cygnus, Aquila, Scutum and down into Sagittarius.

DSLR astrophotography – Sky photography on moonless evening – 28mm /50mm lens – manual focus to infinity.  Set ISO / ASA 1600, exposure 30s, remote cable release , tripod mounted –  Have a go at capturing some of the star fields through Cygnus  around Deneb  ( NGC 7000 N.American Nebula)  / Scutum  – you may also capture a Perseid meteor too on a moonless evening.

More detailed sky notes and LAS Newsletters, Finder charts are available to LAS members via the Members` page on the LAS Website www.lutonastrolink.org.uk  Artificial satellite and International Space Station visible passes and bright Iridium flares – check the  home page for posting s of details of favourable observing times.

 

Waxing  crescent Moon visibility    . Caution.  Do NOT look at the Sun directly with or without optical aid.

A thin, 3.2% waxing crescent moon is visible after sunset  on August 12th from around 20:50  to moonset at 21:21 BST .

An 8.5% waxing crescent Moon and Venus are seen together in evening twilight on August 13th .

Note the dimly lit part visible by Earthshine is readily seen with binoculars or small telescope.  Only look for the crescent Moon after the sun has completely set.

 

 

Sky looking south at 10pm British Summer Time (BST), mid August

In the south the ringed planet Saturn currently located in Sagittarius  above the `spout` of the Teapot asterism  , the red planet Mars to the left of  handle of the Teapot Asterism  . Jupiter is located in Libra close to the star  α Librae  (Zubenelgenubi )

From the UK we only see the head; the rest of the constellation is visible from more southerly locations. Catch a glimpse in July / August of the bright red star Antares on the stem of the `T` asterism low in the south west.

In the south the constellation of Sagittarius (noted by the famous Teapot asterism) is visible early evening. This area of sky is rich in star fields of the Milky Way and has many fine clusters but is only observable in our evening skies during the summer months. Looking  at Virgo we look outside our own Milky Way galaxy towards the external galaxies of the Virgo Cluster , look  to Sagittarius  to into the spiral arm of our own galaxy, the centre of our own galaxy is however too far south to see from the UK

 

 

Sky looking east at 10pm BST mid August

 

Around August 12th /13th keep a watch for Perseid meteors, look away from the Radiant (Perseus) to catch a glimpse of the meteors – late evening / early morning   , peaking early hours August 13th .  Typically 30 meteors per hour, but you may go for a while between seeing a meteor. With New moon conditions this years maximia is very favourable for meteor watching ( refer to the web site for Meteor Watch details )

In August, the summer constellations of Lyra and Cygnus are high overhead by late evening, the Milky Way may be visible on moonless evenings from a dark site.  Stretching from low in the south east to low in the north west, this misty band is best seen with binoculars, follow the star fields from Altair, along the galactic plane ,  down through Scutum and into Sagittarius is stunning in a dark sky.

 

 

 

 

Sky looking north at 10pm BST mid August

Perseus rising late evening – radiant of the Perseids meteor shower (see notes) typically 30 meteors / hour.

The Plough stands with its handle pointing upward follow the pointer’s Dubhe and Merek to find the polestar Polaris. The `W` shaped constellation of Cassiopeia is near to its lowest point in the north late evening.  The Milky Way follows the galactic plane and stretches from east through the constellations of Cygnus, Cassiopeia, Perseus and down into the northern horizon.  The bright star Capella is positioned almost due north and is circumpolar i.e. does not set from our latitude.

 

Sky looking west at 10pm BST mid August

The orange star Arcturus is found by following the curve of stars in the handle of the Plough down. The constellation of Bootes, resembles a `kite` or `Club ` in shape.   The star Izar is a beautiful orange/ blue double star visible in small telescopes. To the east of Bootes find the `horseshoe` shaped constellation of Corona Borealis (Northern Crown) and the `Keystone` Asterism in the constellation of Hercules. Hercules also has M13 the famous Globular Cluster, visible to the unaided eye as a misty patch; telescopes show the true wonder of this cluster with over 750,000 stars. Likewise another nice globular is M92 in Hercules.

 

 

Periodic Comet 21P, Giacobini-Zinner   currently reaching binocular visibility is placed in the constellation of

Cassiopeia {Details LAS Newsletter No198)

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