The night sky in September 2018

posted 31 Aug 2018, 09:23 by Pete Collins   [ updated 31 Aug 2018, 10:04 ]
by Anne Holt

Sunrise:    1st    06.17        30th   07.08
Sunset:     1st    19.58        30th    18.48

Astronomical darkness:  1st   22.11 to  04.06      30th:   20.45  to  05.12

Autumnal equinox 23rd at 02.54
The closest to 12 hours is two days later -  the 25th is 12 hours 0 minutes and 47 seconds long.

New Moon:  9th at 19.01    Full Moon:  25th at 03.52. 
Lunar perigee 8th,   apogee 20th.
This month's full Moon is known as the Harvest Moon - the one closest to the Autumnal Equinox.  Also known as the Corn Moon or Barley Moon.

Highlights

The nights are getting longer as we approach autumn,  we now have reasonable amounts of astronomical darkness - 6 hours at the start of September and almost 7 and a half hours at the end.  The naked eye planets are becoming less prominent but the two outer ice giants are very well placed for telescopic observation and photography.  The beautiful constellation Orion reappears in the morning sky, on 1st it will be above the horizon by 03.30 and by 01.30 at the end of the month.  We have one binocular and one telescopic comet but no major meteor showers.  The Moon passes through the Hyades, the V shaped asterism in Taurus,  twice this month, on the night of 2nd/3rd and again on 29th/30th.
But, as always in September, the main things we have to look forward to are firmly Earth bound - our Open Day on Sunday 23rd and the start of the new season the following Thursday, 27th.  On this day the Sun sets just 5 minutes before the start of the meeting but astronomical darkness isn't until 20.53, just as we start to pack up.
Never mind!  It'll probably be cloudy anyway.

Constellations

The Milky Way in still prominent overhead, albeit not in these parts! Find a dark sky site though, and it's spectacular.

The Summer Triangle is high in the southern sky for much of the night in early September.  By month end Aquila is setting in the west at about 2am, with Lyra and Cygnus following just before dawn.

However, on the opposite side of the sky, the Pleiades are climbing above the horizon in the east by 10.30pm at the start of September, and as darkness falls at month end. Capella, in Auriga, and the V shaped Hyades cluster at the head of Taurus the Bull are not far behind.

If you stay up until about 4am (or get up very early) you might see Orion making a welcome return to the night sky.  By the end of September, it should be above the horizon by 2am.

The ecliptic is now slightly higher across the Eastern sky, passing through Capricorn, Aquarius and Aries - though none of these are particularly bright or memorable.

Pegasus, Perseus and Andromeda are still well placed, rising in the east to north east from mid evening, as is the bright W asterism of Cassiopeia higher in the north east.

Planets

Mercury:  in Leo, mag -0.8
A morning object in early September, on 1st it rises at 04.32, one and three quarter hours before the Sun, and is 9 degrees above the horizon as the sky begins to brighten soon after 05.30.  Reaches perihelion, the closest point in its orbit to the Sun, on 2nd and on 8th the thin crescent Moon is 9 degrees north west of the planet, low in the east, just before dawn. On 19th it moves into Virgo but can't be seen, despite having brightened to mag -1.7, as it is separated by only 2 degrees from the Sun and rising 15 minutes before it.  It reaches superior conjunction on 21st then becomes a morning object.  However it won't be visible, on 30th it sets at 19.01, only a few minutes after sunset.

Venus:  in Virgo, mag -4.4
On 1st it sets at 20.44 and is only 2 degrees above the horizon at dusk.  It reaches aphelion, its furthest point from the Sun, on 5th.  By 14th it is on the horizon at dusk.  Some sites suggest looking for the planet in daytime, especially towards month end when it is at mag -4.6, but this is not recommended unless you know exactly where to look, as it will be quite close to the Sun.
WARNING: NEVER EVER sweep the sky with binoculars trying to find it.  If the Sun gets in your field of view it is very likely that you would be instantly blinded.

Mars:  in Sagittarius, mag -2.1
Now past its best as it moves away from Earth.  On 1st it culminates at 22.32, 10 degrees above the southern horizon.  It moves into Capricorn on 2nd and on 19th the 75% lit Moon passes 6 degrees north west of the planet, low in the south west just before midnight.  It continues to fade during the month but it does get slightly higher in the sky, on 26th it reaches 13 degrees in the south but is significantly fainter at mag -1.4, no longer outshining Jupiter.  On 30th it culminates at 21.05 and sets just before 01.00.

Jupiter:  in Libra, mag -1.9
On 1st it sets at 21.57, a couple of hours before sunset.  As the sky darkens it is only 10 degrees above the south western horizon.  On 13th the 7% Moon may be seen 6 degrees north west of the planet, just after sunset.  It isn't easily seen in the last week of the month, on 23rd it is only 7 degrees above the horizon when the sky begins to darken.  On 30th it sets at 20.03,  an hour and a half after sunset, before the sky is fully dark.

Saturn: in Sagittarius, mag 0.4
An early evening object this month.  On 1st it culminates at 20.35 as the sky darkens, 13 degrees above the southern horizon.  In the early evening of 17th the 58% lit Moon passes less than 2 degrees north east of the planet. It is fading slightly, mag 0.5 from 20th, but should be easy to spot from a site with a fairly low southern horizon, even in a light polluted area, as it outshines all the stars in Sagittarius.  On 30th it should be visible as the sky darkens, around 19.30, setting at 22.29

Uranus: in Aries, mag 5.7
Currently the highest planet in the night sky, visible for most of the night.  On 1st it rises at 21.15, an hour before the start of astronomical darkness, and reaches 20 degrees in the eastern sky before midnight.  It culminates at 04.28 at 48 degrees above the southern horizon.  On 26th the just past full Moon passes about 6 degrees east of the planet.  On 30th it culminates at 02.31 at an altitude of 47 degrees in the south.  It should be easily visible in decent binoculars, even from the Manchester area.  An amateur scope will show its small pale green disc.

Neptune:  in Aquarius, mag 7.8
Another planet which is well placed in September, though not as high in the sky as Uranus.  On 1st it rises a few minutes after sunset and reaches 24 degrees in the south east before midnight. It culminates at 01.34 at 29 degrees above the southern horizon.  It reaches opposition on 7th, when it culminates at 01.10.  On 23rd, in the early evening, the Moon passes 3.6 degrees south east of the planet.   On 30th it rises around sunset and should be visible before 22.00, 24 degrees in the south east, culminating at 23.34, still reaching a maximum altitude of 29 degrees.  It might possibly be seen in good binoculars from a dark sky site but for most of us a scope will be needed, especially to have a chance of seeing the small blue green disc.  Anyone using a scope of 12 inches or more may be able to spot the planet's largest Moon, Triton, currently at mag 13.4.

Minor planets and Asteroids

Ceres:  in Virgo, mag 8.7
Not a good target this month.  On 1st it sets at 21.16 before the sky is fully dark and is separated by only 20 degrees from the Sun. By month end it's even worse - 8 degrees from the Sun, setting an hour after it.

Minor planets, Pluto in Sagittarius, at mag 14.7 and Eris in Cetus, Haumea in Bootes & Makemake in Coma Berenices, all at mags of around 18 to 19, are too low to be seen in even the best amateur scopes, however could be targets for keen astrophotographers.  Eris is probably the best bet, reaching 34 degrees soon after 4am on 1st and at 2.18 on 30th.  Pluto, Haumea and Makemake are much lower, and getting worse as the month progresses.

Juno: in Taurus, mag 8.8 might be a better bet.  On 1st it rises at 23.03 and reaches 42 degrees in the south east while the sky is still quite dark.  On 30th it will be slightly brighter at mag 8.2, rising at 22.00 and culminating at 04.36.

For more information see
https://in-the-sky.org/ephemeris.php   (minor planets shown under 'asteroids')


Meteor Showers

No major showers this month but we have several minor ones, and September is said to be a good time for sporadic activity.

Alpha Aurigids:  Active August 28th to Sept 5th,  peak on the night of Aug 31st/Sept 1st,  ZHR 6.  This shower sometimes gives a much better display but some years nothing at all is seen.  There are no predictions for a good display this year.  The Moon will interfere but these meteors are very bright so a few may be visible.  Parent comet not known for sure, possibly C1911/Kiess.

Epsilon Perseids.  Active 5th to 21st, peak 9th,  ZHR 5.   Another shower which can produce occasional outbursts.  There was one in 2008 and some sources predict similar this year, on 9th at around 20.00, only 20 minutes after sunset.  Other sources say there won't be any much higher rates until 2040.  These meteors are faint but there is no Moon interference this year.

Piscids:  Low activity for most of September, dates vary according to source used, some say there is no definite peak just enhanced activity between 9th and 21st, others give 2 peaks - Sept 9th, ZHR 5 , and 21st, ZHR 2.  One site gives the very useful information that this shower is 'poorly observed due to lack of observation'. 
Can't argue with that!

Chi Cygnids:  This shower was only officially recognised in 2015 and not much is known about it.  Probable low rates throughout September with a weak maximum on the night of 14th/15th,  ZHR 2-3.  Very slow moving meteors.

Southern Taurids:  Active Sept 10th to November 19th.  The peak is not until October but it's worth looking from mid September as the shower usually includes many fireballs.  These slow moving meteors are thought to originate from a fragment from comet 2P/Encke.


Comets

Most of the current binocular comets are too far south to be seen from our latitude.

One which is high enough in the sky to be seen here is 21P/Giacobini-Zinner, visible for all of September, though it is high in the sky for much longer early in the month.  It starts Sept at mag 7.2, in Auriga, passing 1 degree south of Capella on the night of 2nd/3rd.  Until 8th it is circumpolar but is best seen from just before midnight until dawn, reaching 64 degrees in the north east.  It reaches perihelion on 10th/11th, when it will be at mag 7.1,  or maybe brighter as comets are notoriously unpredictable. It continues its southward path, moving into Gemini on 14th and Monoceros on 23rd. By 30th it will have faded to mag 7.6 (probably) and be best seen in the 90 minutes before dawn when it will be about 30 degrees above the south eastern horizon.

Much fainter comet 46P/Wirtanen is still on course for putting on a good show in December.  At mag 12.6 it is currently only visible in large scopes but is brightening.  At the moment it's low in the sky and getting lower, starting the month in Cetus,  at a maximum altitude of 17 degrees.  It moves into Fornax on 22nd and should have brightened to around mag 10 and  have a maximum height of 12 degrees.  On 30th it will be even lower, no higher than 10 degrees.
But be patient!   From early November its position, and hopefully its magnitude, will improve.

For more details on comet positions see www.cometwatch.co.uk.  Information is also given in the websites mentioned earlier.
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