Night Sky Notes – August 2016

Night Sky Notes for August 2016               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.

In the west some 20 minutes after sunset Venus can be seen very low but will become a more prominent feature of our autumn and winter evening skies. In early August Mercury can be seen in evening twilight, greatest elongation occurring on August 16th. Also Jupiter may be seen in twilight, before it heads into the daytime skies at the end of the month. Low in the south Mars can be seen early evening, close to the blood red star Antares in the constellation of Scorpius {The Scorpion] , which is only partially visible from UK latitudes. Just above Mars the ringed planet Saturn is just past opposition and telescopically is a fine sight with the famous rings prominently displayed.

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 July and 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 teapot asterism` and just think of NASA’s New Horizon space probe successful flyby Pluto in mid July 2015 , 4.5 light hours away !

Up until to August 20th observers may also catch the Perseid meteor shower, with maxima occurring in the early hours of August 13th. This year is not favourable in 2016 due to a 69% waxing gibbous Moon i.e. moon light, but after moon set ( around 1am) if you have clear conditions on the early morning of the 12th/ 13th and a dark site, 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.

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 a a pair of yellow and orange stars and the distinctive `T` shaped asterism of stars of the `head` of Scorpius , the yellow star is in fact the ringed planet Saturn which reached opposition on June 3rd and the orange star is planet Mars . 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 2016
Mercury returns low in the evening twilight but is poorly placed with greatest elongation on August 16th
Venus is visible low in evening twilight but will become prominent in our dusk skies later in the year.
Mars is now positioned just below Saturn and above the star Antares low in the south early evening.
Jupiter heads towards the daytime skies by late August, with conjunction on September 26th.
Saturn now visible early evening low in the south in Scorpius – 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 2nd Moonless, best time for deep sky observing.
First Quarter August 10th Best days to see shadow details in lunar craters (early evening)
Full Moon August 18th Best days to see bright ray craters like Copernicus / Tycho.
Last Quarter August 25th Moon visible in daytime skies. Do not look directly at the Sun.

Meteor shower s
Perseid range July 23rd to August 20th, Maxima August 13th (pre dawn) ZHR
80+ / hour, visually 30 to 50 per hour – Fast meteors with bright persistent
Delta Aquarids, range July 15th to August 20th, maxima August 6th, ZHR 10/ hr

The highlights of the month.
Perseid Meteor Shower, favourable only after moon set in the early hours. Maxima August 12th/ 13th

Saturn very low in south in Scorpius , rings open at 24° DE [tilt] showing Saturn’s North Pole.

Mars also in Scorpius, appears to shrink in apparent size , telescopes still show a small disk with white polar cap

Saturn, Mars and the red star Antares alight vertically, low in the south west on the evening of August 26th

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 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, 4% waxing crescent moon is visible after sunset on August 4th from around 21:00 to moonset at 21:21 BST Planet Mercury lies 0.5° north of the crescent Moon tonight.
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.