Night sky notes for September 2018 Geoff Mitchell
The September night sky is perhaps offers some of the best observing conditions. With the autumn equinox for northern hemisphere observers on September 23rd the mix of summer and autumn contains many fine objects to view with both binocular and small telescopes. The constellations of Cygnus, Lyra and Aquila can be seen high overhead and into the south; these are noted for the bright stars of Deneb, Vega and Altair respectively forming the `Summer Triangle ` asterism.
The Milky Way stretches from Perseus rising in the north east, through the `W` shaped constellation of Cassiopeia in the north east , along the cross shaped constellation of Cygnus. This faint band of stars best seen on moonless evenings from a dark site continues down through the obscure constellation of Scutum and on in the direction of the centre of the Milky Way (not visible from the UK) low on the horizon.
Look at the constellation of Sagittarius, close to the `spout ` of the Teapot Asterism, very low in the south / south west early evening. The yellowish coloured star near to the `lid` of the teapot is in fact the ringed planet Saturn, currently the rings are wide open – the classic view of Saturn viewed telescopically.
The faint band of light of the Milky Way is seen stretching high overhead and low into the south. Use binoculars to reveal the rich star clouds that show a myriad of stars and some of the dark rifts, regions of the Milky Way spiral arm obscured by dust clouds on clear moonless evenings.
Auriga has the bright star Capella and can be seen low in the north east early evening, Capella is circumpolar from UK latitudes and so is always visible. In early September, a short period comet 21P Giacobini-Zinner passes through the constellation .On September 2nd the comet is located close to Capella; on Sept 12th it is close to the star cluster M37 before moving south into Gemini and located close to M35 on September 15th. The comet reaches perihelion on September 10th and is also closest to Earth at around 35 million km, at magnitude 7.0m it should be a round fuzzy patch with bright condensed nucleus visible in binoculars and small telescopes. (See notes)
In the east the constellation of Pegasus, noted for its `Square ` shape and the adjacent constellation of Andromeda noted for The Andromeda Galaxy (M31) , visible to the unaided eye as a faint fuzzy patch on moonless evening can now be seen mid evening . The Square of Pegasus is a useful sign post constellation and also is a good test for sky conditions, (how many faint stars you see within the square is indicates just how good your seeing conditions are). Follow the two end stars (Scheat and Markab) down to find the star Fomalhaut in the constellation of Pisces Australis (The Southern Fishes), visible very low on the southern horizon late evening at the end of the month.
In the North West Ursa Major, The Plough or The Great Bear is seen low with its handle or tail parallel to the horizon late evening Use the right hand pair of stars Dubhe and Merak (The pointers ) to find the faint pole star Polaris and hence the position of North . Follow the curve of Ursa Major’s tail to the orange star Arcturus in the constellation Bootes (The Herdsman) low in the west. To the east of Bootes find the `horse shoe ` shaped constellation of Corona Borealis (Northern Crown) and the `Keystone asterism ` in the constellation of Hercules also noted for the globular cluster M13 containing around 750,000 stars, a good view with modest telescopes.
Neptune reaches opposition on September 7th in the constellation of Aquarius and Uranus in the constellation of Pisces both visible by late evening and are objects that can be located using binoculars and a suitable finder chart. A good starting point is to locate the Square of Pegasus and the ring of stars below the Square known as the `Circlet` in the constellation of Pisces (The Fishes), then star hop using the finder chart. Uranus and Neptune are notable due to the blue and green colour, Telescopes show a tiny disc rather than the sharp pinpoints of stars in the field of view.
In the east mid evening the seven sisters’ (Pleiades, M45) star cluster and constellation Taurus heralds the forthcoming autumn skies of a new observing season.
Planets in September 2018
Mercury is poorly placed in dawn skies early Sept and at superior conjunction by Sept 21st.
Venus is now poorly placed , shining brightly low in the west after sunset.
Mars is very low in the south early evening, unmistakably red in colour, now past opposition.
Jupiter is now lost in early evening twilight –poorly placed.
Saturn visible low in the south west early evening, rings is wide open in the constellation of Sagittarius.
Uranus rises late evening in the constellation of Pisces. (Binocular / Telescope required) (See notes)
Neptune in Aquarius rises early evening (Binocular / Telescope required). The constellation of Aquarius is positioned low in the south east by mid evening Neptune is at opposition on September 7th (See notes)
Moons phases in September 2018
New Moon Sept 9th Moonless, best time for deep sky observing and Comets .
First Quarter Sept 16th Best days to see shadow details in lunar craters (early evening)
Full Moon Sept 25th Best days to see bright ray craters like Copernicus / Tycho.
Last Quarter Sept 3rd Moon visible in daytime skies. Do not look directly at the Sun.
Autumnal Equinox occurs on September 23rd 02:55 BST, Day and night being equal length
Piscids, range September to October, maxima September 9th and 21st – rather low rates.(<5 / hour)
Epsilon Perseid also peaks on September 9th rather low rates, but a small chance of increased activity.
The highlights of the month 2017
Comet 21P Giacobini-Zinner moves southward through Auriga – Binocular – see notes
September skies, Milky Way visible high over head on moonless evenings in darker skies.
Look at the Moon illusion effect at moonrise around Full Moon i.e. the Harvest Moon rising
Uranus and Neptune, binocular objects to find using suitable finder charts
M31 the Andromeda Galaxy is visible on moonless evenings, best seen in binoculars.
Double cluster, on the Perseus /Cassiopeia border, nice pair of star clusters
Albireo, the star Beta Cygnii is a nice blue/ yellow double star seen telescopically
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) and Scutum
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.
September 10th a 1.6% waxing crescent Moon sets at 20:12 BST just half an hour after sunset .Only look for the crescent Moon after the sun has completely set.
September 11th a 5% waxing crescent Moon is visible low in evening twilight with Venus to the left of the Moon – Moon set is an hour after sunset Only look for the crescent Moon after the sun has completely set.
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
Sky looking south in late September 2018 at 10pm BST
The number of stars visible inside the Square of Pegasus in dark moonless conditions is an indication of your sky conditions.
Stars shown to unaided eye limit 6th magnitude equivalent to a good dark moonless site
Sky looking east at 10pm BST early September 2018
Refer to finder charts for location of Uranus and Neptune.
Comet 21P Giacobini-Zinner moves southward (night to night) through Auriga and Gemini during September magnitude 7.0 – Binocular / small telescope (low magnification 20mm eyepiece).
Sky looking north at 10pm early September 2018
Sky looking west at 10pm early September 2018
General finder chart for locating planet Uranus ( Binocular / small telescope )
LAS general finder chart for Uranus for September / October 2018, positions shown at 5 day intervals
Note – Circles show the field of view of typical 10×50 binoculars Uranus at opposition October 24th 2018
Uranus is located in the constellation of Pisces (near Omicron Piscium) and rises in the east late evening in September. Telescopes show a tiny blue disk (magnitude 5.8m) .
LAS general finder chart for Neptune for September / October 2018, positions shown at 5 day intervals
Neptune is visible using 10×50 binocular at magnitude 7.8m at opposition September 7th 2018
Located in the constellation of Aquarius , telescopes show a tiny greenish disk.
Note – Circles show the field of view of typical 10×50 binoculars
More detailed finder charts and newsletters are available to LAS members on the member’s page