The night sky in September 2017

posted 29 Aug 2017, 13:37 by Pete Collins
by Anne Holt

Sunrise  1st:   06.18        30th:   07.09
Sunset   1st:   19.58        30th:   18.47

Astronomical darkness 
1st:   22.10  to  04.07         30th:   20.44  to  05.13


Full Moon  (Harvest Moon)  Sept 6th at 08.02    New Moon  Sept.20th at 06.29

The autumnal equinox, when the Sun appears to cross the celestial equator, is on 22nd at 21.01.  Despite the name we do not have a 12 hour day and night then, or on any other day, though this year the 25th comes very close at only 15 seconds short.

Highlights

As always in September the highlights are on the ground rather than in the sky.  On Sunday 24th we have our Open Day,  11am to 4pm in the classroom and the Farm Centre Courtyard in Heaton Park, and the following Thursday, 28th, sees the first meeting of the new season at the Bowls Pavilion as usual.  On this day sunset is at 18.52 but astronomical darkness does not begin until 20.50 - ten minutes before our finishing time.   But never mind, if past years are anything to go by, it will probably be cloudy anyway.

We have no major meteor showers and the bright planets are becoming less prominent, however we do have a close (astronomically speaking) encounter with a large asteroid.

You'll have to get up early for bright ISS passes this month - all around 4am to 5am - see www.heavens-above.com for predictions.

Constellations

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

Milky Way & Summer Triangle from Derbyshire

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

For the best views of planets this month you need either a telescope or an alarm clock.

Mercury:  in Leo, mag 3.3. A morning object throughout September.  On 1st it rises at 05.35, about 45 minutes before the Sun, and not easily seen in the dawn glare.  On 10th it is only 38 arcminutes from Regulus.  Reaches Greatest Eastern Elongation on 12th, when it rises at 04.49, will have brightened to -0.3 and should be briefly visible before the sky gets too light.  On 16th it is only 28 arcminutes West of Mars, the following day it is even closer at 21 arcminutes.  By 22nd it will be at mag -1.1, and the following morning will form a line in the morning sky with Mars, Venus and Regulus. However Mercury will be very low.  It moves into Virgo on 27th but is unlikely to be visible.  On 30th, it rises at 06.20, only 40 minutes before Sunrise. 
 
Venus:  in Cancer, mag -4.0. Still shining brightly in the dawn sky at the start of the month.  On 1st, when it rises more than 3 hours before the Sun, it is just 1.5 degrees below the Beehive cluster.  It rises a few minutes later each day and moves into Cancer on 11th. On 18th, forms a line with Mercury, Mars and the thin crescent Moon.  By month end it rises at 04.37 so will still be quite prominent but beginning to dim, at mag -3.9.  By this time it will be 3.3 degrees from Mars.   

Mars:  in Leo,  mag 1.8. On 1st it rises at 05.03,  75 minutes before sunrise and only half an hour before Mercury.  By month end it rises only 5 minutes earlier but, because sunrise is not until after 7am should be more easily seen, as the sky is still reasonably dark. However it is very low in the sky -  only 2.3 degrees above the ENE horizon.

Jupiter:  in Virgo, mag -1.8. Now very low in the WSW sky after sunset and very difficult to see, on 1st it sets just an hour after the Sun.  On 22nd it is 5 degrees below the waxing 6% lit Moon and by month end it sets at 19.25, only 40 minutes after sunset.

Saturn:  in Ophiuchus, mag 0.4. Still very low in the SW evening sky despite being above the horizon until 20 minutes before midnight at the start of September.  On 26th it is 3.5 degrees below the 37% lit Moon at about 21.00.   By month end it will have faded to mag 0.3 and set at 21.43,  3 hours after the Sun but only visible for a short time as the sky darkens.

Uranus, in Pisces, mag 5.7. Much better placed than the closer, brighter planets, visible for most of the night throughout Sept - though binoculars will be needed unless you have excellent eyesight and are observing from a dark sky site.  On 21st it rises at 21.07 and reaches its highest point, 47 degrees, soon after 4am.  By the end of the month it rises half an hour after sunset and culminates at 02.14.

Neptune:  in Aquarius, mag 7.8. Another distant planet which is well placed again this month.  On 1st it culminates at 01.25 and sets about half an hour before sunrise.  It reaches opposition a few days later, on 5th, and the following day is 2.5 degrees NE of the full Moon.   By month end it culminates before midnight and sets just before 5am.

For more details on planetary positons see

Meteor Showers

No major showers this month but September is said to be the peak time for sporadic activity - meteors not associated with any particular shower.

Minor showers are:

Alpha Aurigids:  active Aug 28th to Sept 5th,  peak Aug 31st/Sept 1st,   ZHR 6
These are best seen after midnight when the radiant is high in the sky.  The shower occasionally produces a much better display but in some years is not seen at all. It is thought to be associated with comet C1911/N1 Kiess and may not be a permanent shower.

September, or Epsilon, Perseids: Sept 5th to 21st, peak Sept 9th,  ZHR 5 - 9
This is a faint shower which will be adversely affected this year by the presence
of a bright gibbous Moon.

Piscids:  active for most of September, actual dates vary according to source used.  Some sites say that there is no real peak, just enhanced activity between 9th and 21st, however others give 2 separate peaks, Sept 9th,  ZHR 5,  Sept 21st,  ZHR 2.    The Moon will interfere on the first of thses dates but not the second.

Southern Taurids, active Sept 7th to November 19th.  Peak is not until early October but worth looking in September as thsi shower is often rich in fireballs.  The parent object is a fragment of former comet 2P/Encke.

The Piscids and Southern Taurids are sometimes considered to be part of the Autumn Antihelion Source.  However others say that the ANT is not very active at this time and these are 2 distinct showers.

And finally ...

On Sept 1st at 13.06 a large asteroid 3122 Florence (aka1981 ET3) will pass by us at a distance of less than 8 million km/5 million miles - but don't panic:  that's more than 18 times the Earth - Moon distance. It is expected to be around mag 9 at this time, so should be visible in amateur scopes.
At 4.35km/2.7miles in diameter it is the largest near Earth object to come so close to us since NASA started tracking them in the 1990s.  By mid Sept, when it has moved from Cygnus into Draco, it will have faded to mag 12.
For more information and exact position at any time, see https://theskylive.com/florence-info
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