The night sky in September 2019

posted 30 Aug 2019, 05:46 by Pete Collins   [ updated 30 Aug 2019, 07:57 ]
by Anne Holt

Sunrise     1st:    06.17      30th:   07.08
Sunset      1st:   19.59       30th:   18.48

Astronomical darkness
1st:   22.12  to  04.06       31st:  20.46  to  05.12

Full Moon:  14th at 05.32     New Moon;  28th at 19.26

Lunar apogee:   13th at 13.33  (406377km)
Lunar perigee:   28th at 02.28  (357802km)

September's full Moon is the Harvest Moon as it is the closest to the Autumnal Equinox.  Other names are the Corn Moon,  the Full Corn Moon and the Barley Moon.

The equinox, when the centre of the Sun is at the point where the ecliptic crosses the celestial equator, is on 23rd at 08.50.  This day is actually 12 hours 10 minutes and 14 seconds long.  This is because sunrise is the moment when the top of the Sun's disc appears above the horizon and sunset is when the top of the disc disappears below the horizon. The extra 10 minutes and 14 seconds is the time between the top and the centre of the Sun appearing at sunrise and disappearing at sunset.  The days closest to 12 hours are 25th at 12 hrs 01' 49"  and 26th at  11hrs 57' 37".

Highlights

We now have a reasonable amount of astronomical darkness - nearly 6 hours at the start of the month and 8 and a half at the end.  It begins at a reasonable time too, soon after 10pm on 1st.  We have a couple of comets which might become bright enough to be seen in binoculars, though comets are very unpredictable and current estimates of their magnitudes vary.  Jupiter is still hanging on in the early evening sky, bright but very low and setting before midnight.  Saturn is also low, much fainter but setting a couple of hours later.  The distant ice giants are well placed for binocular and telescopic observation and we have several minor meteor showers with the possibility of bright fireballs.

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 -1.8
Appears very close to the Sun throughout September therefore very difficult to see. On 1st it rises at 05.50, less than half an hour before the Sun, and is only separated from it by 3 degrees.  It reaches superior conjunction, when it is on the opposite side of the Sun to the Earth, on 4th. On this day it passes only 1 degree above the Sun. It then starts to move away, becoming an evening object but still very low. On 11th it moves into Virgo and on 25th reaches its highest point in the evening sky but, because of the very shallow angle of the ecliptic, is only 3 degrees above the horizon at sunset.  On 30th it sets 20 minutes after  the Sun, at 19.10, but has sunk below the horizon by the time the sky darkens.

Venus:  in Leo, mag -3.9
Another planet which is very low in the evening sky, therefore difficult to spot despite its brightness.  On 1st it sets soon after sunset, at 21.14, and appears only 5 degrees from the Sun.  It moves into Virgo on 10th.  On 29th the very thin crescent Moon passes 3.2 degrees above the planet around sunset, with Mercury 6 degrees to the left of Venus.
Remember:  DO NOT attempt to view these through binoculars until the Sun has fully set. Catching even a couple of the final rays will cause instant irreversible damage to the eyes.
On 30th Venus is on the horizon at dusk but might be visible for a short time in the bright twilight sky before setting at 19.12.

Mars:  in Leo, mag 1.7
Again appears too close to the Sun to be seen for most of the month, as it is at Solar conjunction on 2nd.  It then becomes a morning object, still very close to the Sun. On 25th, when it moves into Virgo, they are separated by 7 degrees. On 30th it has increased to 9 degrees, the planet rising at 06.05, and maybe visible from a site with a clear dark eastern horizon. 

Jupiter:  in Ophiuchus, mag -2.2
Visible low in the early evening sky this month.  On 1st it is 13 degrees above the southern horizon as the sky darkens, setting at 23.11. The Moon passes on 5th & 6th, closest, 2 degrees 15', at 08.40 on 6th.  The pair should be visible on the evening of 5th, with the Moon to the west, and on 6th when the Jupiter is to the west. On 30th it sets at 21.27 and is only visible for a short time from around 19.00, when it is only 11 degrees above the horizon.

Saturn: in Sagittarius, mag 0.3
A very low evening object throughout September.  On 1st it should be visible from about 20.40, when it is 13 degrees above the southern horizon, culminating one degree higher at 21.26.  On 8th at about 8pm the 76% Moon should be seen 3 degrees ESE of the planet.  They are closest in daylight, only 2 arcminutes apart, at 14.42.  By 30th it should be visible for a while from around 19.30, again at 13 degrees, setting at 23.30.

Uranus:  in Aries, mag 5.7
Still very well placed, unlike the naked eye planets. On 1st it rises at 21.23 and should be visible in a small scope or binoculars from around midnight, reaching 49 degrees in the south by dawn.  On 17th at around 21.00 the Moon passes 5 degrees south of the planet.  By mid  month it should be high enough to be a good target, maybe even for the naked eye from a good dark sky site, from 23.00. On 30th it rises at 19.25, reaches 21 degrees in the east by 22.00 and culminates, 49 degrees in the south, at 02.48.  It's still around 36 degrees in the SW at dawn. 

Neptune:  in Aquarius, mag 7.8
On 1st it rises at 20.09 and is at 21 degrees in the SE at 23.00.  Reaches its highest point, 30 degrees in the south, at  01.44. Reaches opposition on 10th and on 13th the Moon passes 4.2 degrees to the south at around 22.00.  On 30th it is at 21 degrees in the SE by 22.00 and culminates at 23.43.  Could be visible in good binoculars from a dark sky site - if you know exactly where to look. Much easier to find it using a telescope with GoTo. 

Dwarf Planets

Ceres:  in Scorpio, mag 8.8
The closest and brightest of the 5 officially designated dwarf planets is now very low in the evening twilight, reaching a maximum altitude of 13 degrees, setting on 1st at 22.31.  It moves into Ophiuchus on 9th and on 30th, when it has faded to mag 9.1, sets at 20.54.

Pluto:  in Sagittarius, mag 14.7
Still very low,  too faint to be seen in all but the very best amateur scopes and too low for astrophotography - max 14 degrees.  On 1st it culminates at 21.56. on 30th at 20.01.

Haumea:  in Bootes, mag 17.4
Only high enough for imaging in the first few days of September. On 1st it is at 23 degrees in the west at around 23.30, setting at 00.20.  By 30th it is 18 degrees at above the horizon at dusk and sets at 22.32.

Makemake:   in Coma Berenices, mag 17.2
Also very low.  On 1st it is 18 degrees above the horizon at dusk, setting a few minutes before midnight.  It reaches solar conjunction on 29th but, because of the angle of its orbit to the ecliptic, passes 27 degrees north of the Sun. On 30th it sets at 22.04 but is down to 14 degrees as the sky darkens.

Eris:  in Cetus, mag 18.8
Very distant, very faint but a possible target for very good, experienced astrophotographers. On 1st it reaches 21 degrees in the SE at around 1am and culminates, 34 degrees in the south, at 04.15.  On 30th it's at 21 degrees in the SE soon after 23.00 and reaches its highest point, still 34 degrees, at 02.20.

A couple of asteroids are at opposition in September:

6th:  135 Hertha: in Aquarius, mag 9.6.  Culminates at 01.08 at an altitude of 29 degrees in the south.

28th.  21 Lutetia: in Cetus, mag 9.4.  Culminates at 01.08, at 33 degrees in the south.

And: You may have heard about a large near earth object passing Earth on Sept 16th.  Don't panic!  The definition of an NEO is any object, usually an asteroid but occasionally a comet, which comes within 149 million km (1.3 AU) of us.  This one, C2000 QW7, won't get closer than 5.3 million km - that's almost 14 times the distance to the Moon, so we aren't in any danger.

Comets

We have a couple of (possibly) fairly bright comets, and some fainter ones, this month.  However, comets are very unpredictable and estimates of their brightness do vary - sources can't seem to agree on their current brightness, never mind what it will be in the next month.

C/2017 T2 (PANSTARRS) in Taurus, mag 7.4 (or maybe 9)
Could be a binocular target especially towards the end of September. On 1st it rises at 23.22 and reaches 42 degrees in the east by dawn. predicted to reach mag 6.2 by 30th, when it rises at 21.05 and is at 63 degrees in the south as dawn breaks.

C/2018 W2 (Africano) in Perseus, mag 8.1 (or maybe 10.5)
Circumpolar for the first 3 weeks of September. On 1st it is at 28 degrees in the NE at around 21.30 and reaches 80 degrees in the east before dawn breaks. It moves south westwards during the month, going into Andromeda on 9th, crossing into Perseus on 13th then back into Andromeda on 14th.  On 20th it sets for a couple of hours and culminates at 02.12, reaching 71 degrees above the southern horizon. On 21st it briefly visits Pisces before returning to Andromeda. It is predicted to be at its brightest, mag 6.6 according to some sources, from 25th to 28th.  From 26th to 29th it is in Pegasus then ends the month in Pisces. On 30th it is at 22 degrees in the east as the sky darkens, culminating at 01.11, much lower at only 42 degrees, and slightly fainter at mag 6.7. 

Much fainter comets around are:

C/2018 N2 (ASSASSN) in Aries, mag 11.0 (or 12)
On 1st it rises at 20.30, half an hour after sunset, and reaches 39 degrees in the south by dawn.   Moves into Triangulum on 16th and on 30th reaches 22 degrees soon after 20.00, culminating at 02.31, higher at 68 degrees.  Should be slightly brighter at mag 10.6.

168P/Hergenrother:  in Auriga, mag 11.7
Circumpolar.  On 1st it is best seen for a few hours after midnight, reaching 58 degrees by dawn.  On 30th, when it will probably have faded slightly, it reaches 76 degrees in the east before the sky brightens.

260P/McNaught:  in Aries, mag 11.6
On 1st it culminates soon after astro darkness ends, and is at 57 degrees in the south as the sky begins to brighten. It moves into Triangulum on 18th, Perseus on 23rd and is circumpolar from 26th.  On 30th it is at 27 degrees in the  SE as the sky darkens, reaching 75 degrees in the south at 03.24, sinking to 62 degrees in the west by dawn.

Recommended websites for more information and exact positions of all solar system objects.


Meteor Showers

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

Alpha Aurigids:  active August 28th to Sept 5th, peak on the night of August 31st/Sept 1st, ZHR 6 or fewer. This shower does produce occasional spectacular outbursts but there are none predicted for this year. They are very bright meteors, parent comet probably C1911/Kiess.  No Moon interference on the peak night this year.

Epsilon Perseids: active 5th to 21st, peak 9th, ZHR 5.  Very faint meteors, again no increased activity predicted for this year.

Southern Taurids: active Sept 10th to November 19th.  the peak isn't till October but it's worth looking from mid September as the shower often includes very bright fireballs. These slow moving meteors originate from dust left by comet 2P/Encke.

There are also a couple of showers given in some sources but not included in the International Meteor Organisation's list.

Chi Cygnids:  Not much known about this shower which was only recognised by the IAU in 2015. They are very slow moving with low activity throughout September and a weak maximum on 14th/15th.  ZHR 2 - 3.

Piscids:  plenty of information available about this one but, unfortunately it doesn't always agree. Some sources say that there  are 2 separate streams - the northern and southern Piscids.  Some of the confusion could arise because 'this shower is poorly observed due to lack of observation'. There is possible low activity throughout Sept, maybe with a diffuse peak of ZHR 5 from 9th to 21st, or maybe a peak on 9th and a lesser one on 21st.  These slow, long lasting meteors are sometimes regarded as part of the Antihelion Source but, according to the IMO, this isn't active in September. One site gives the parent comet as possibly 46P/Wirtanen.  If this is the case 2019 could show enhanced activity, as Earth is predicted to pass through a large dust cloud left by this comet. 
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