The night sky in September 2020

posted 30 Aug 2020, 09:08 by Pete Collins   [ updated 30 Aug 2020, 14:39 ]
by Anne Holt

Sunrise   1st:    06.18      30th:    07.09
Sunset    1st:    19.57      30th:    18.47

Astronomical darkness    1st:  22.09  to  04.08     30th:  20.44  to  05.13

The Autumnal Equinox, when the Sun crosses the celestial equator, is on 22nd at 14.30.  However, despite the name meaning equal night, we do not have a 12 hour day and night at this time.  The day is actually 12hrs 11minutes 14 seconds long.  The difference is partly because of refraction of sunlight by our atmosphere, so we can see the Sun for a few minutes before it rises and for a few minutes after it sets. This adds about 6 minutes to the day length.  The rest of the difference is because, on this day, the centre of the Sun is above the horizon for 12 hours but sunrise is the time when the upper edge becomes visible, which is slightly later, and sunset is when it sinks below the horizon, a few minutes after the centre does so.
The day which is closest to 12 hours is the 25th at 11hr 58mins 30 seconds.

Full Moon:   2nd at 06.22       New Moon: 17th at 12.00

Lunar apogee:     6th  at  06.32  (405605km)
Lunar perigee:   18th  at  14.45  (359080km)

The new Moon is the day before perigee, so the waxing crescent will appear slightly larger than average.

September's full Moon is known, according to the Farmers' Almanac, as the Corn Moon or Barley Moon,  the Celtic names are the Singing Moon or Blood Moon, the Chinese call it the Chrysanthemum Moon, to the Cherokee it's the Nut Moon and for the Chocktaw, the Mulberry Moon.  The Dakota Sioux have what must be one of the best of all the full Moon names - the Moon when the calves grow hair.
This year's September full Moon isn't the Harvest Moon.  That will be in October as it is closer to the Autumnal Equinox.

Highlights

As always in September, one of the main highlights for astronomers is the lack of light.  On the night of 1st/2nd we have just one minute short of 6 hours, increasing to almost eight and a half hours by month end.  Venus is still shining brightly in the morning sky, and Jupiter in the evening, albeit very low.  Mars is brightening rapidly as it gets closer to us and is much higher in the sky, so easier to see, and they all have some close visits from the Moon.
We don't have much in the way of meteor showers but could see some fireballs later in the month, and, unless something new turns up, no bright comets. 
But all those who believe in a****logy, beware!   Mars, Jupiter and Saturn are all retrograde for part of the month, and Uranus and Neptune, plus dwarf planets Ceres, Pluto and Eris, for the whole of September.  For a couple of days towards the middle of the month, all of them appear to move from east to west across the sky.   

Constellations

The Milky Way is 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 -0.6
An evening object, very low so hardly visible this month.  On 1st, it is on the horizon at dusk, setting only 35 minutes after the Sun.  It moves into Virgo on 3rd, and on 9th reaches its highest point in the evening sky - still only 4 degrees in the east at sunset and just below the horizon as the sky darkens.  On 18th, the one day old Moon passes 6 degrees 25' north of the planet at 22.53, an hour after it has set.  It will now be at mag -0.1, very low at sunset, setting less than half an hour later.  It reaches perihelion on 19th, at a distance of 0.47AU.  On 30th, now at mag zero, it is 2 degrees below the horizon as the sky begins to darken.

Venus:  in Gemini, mag -4.2
Now fading slightly but still brilliant in the morning sky, starting the month a little to the south of Castor and Pollux.  On 1st it rises at 02.09 and should be easily visible from around 03.15, reaching 31 degrees in the east before the sky brightens. It is in Cancer from the 5th and is at its highest point in the morning sky on 7th, when it is at 35 degrees at sunrise.  From 11th to 15th it is to the south of the Beehive cluster.  On 14th the 13% Moon passes north of Venus, closest, 4 degrees 21', in daylight at 07.23.  The pair should be visible before dawn, with the Beehive between them.   All three should be in the same field of view of 10 x 50 binoculars. The planet moves into Leo on 23rd, when it rises at 02.52 and reaches 30 degrees in the east by dawn.  On 30th it rises at 03.10, still getting to 30 degrees before the sky brightens. 

Mars:  in Pisces, mag -1.8
Visible for much of the night, brightening as it gets closer to Earth, its red colour now very obvious.  On 1st it rises at 21.31 and reaches 43 degrees in the south by 04.14.  On 6th, at 05.44, the 85% Moon passes only a couple of arcminutes north of the planet.  Observers in some parts of Central and South America, West Africa and southern Europe will see an occultation.  From 10th, Mars is retrograde, moving across the sky from east to west.  Of course, it doesn't actually change direction, it's a visual effect caused by the Earth appearing to overtake the outer planet as it approaches opposition. On 30th it rises at 19.29 and culminates at 02.11, now at 42 degrees in the south.  Much brighter at mag -2.5, it is now outshining Jupiter.

Jupiter:  in Sagittarius, mag -2.6
Now an early evening object, still very bright but very low.  On 1st it should be visible from around 20.20, 13 degrees above the southern horizon.  It culminates at 21.59, not much higher, and sets at 01.30.  For the last few weeks it's apparent movement across the sky has been from east to west - retrograde -  but from 13th it reverts to prograde motion, west to east.  On the evening of 24th the 62% Moon will be 7 degrees SW of the planet as it culminates at 20.08. They are closest, 1 degree 35', at 07.57 on 25th, and at 20.00 that evening the now 68% Moon will be 7 degrees to the SE.  On 30th Jupiter culminates only an hour before sunset and will be at 13 degrees in the south as the sky darkens, setting at 23.34.  Now at mag -2.4 it is slightly fainter than Mars.

Saturn: in Sagittarius, mag 0.3
Close to Jupiter in the sky, slightly higher but much fainter.  On 1st it should be visible, 12 degrees in the SE, around 20.40 and reaches its highest point, 15 degrees in the south, at 22.18.  On 25th the 68% Moon is just 2 degrees 18' to the south at 22.06, with Saturn at around 10 degrees in the SW.  The pair should be visible from 20.00, with Jupiter also close by.  Saturn is also currently retrograde, reverting to prograde motion on 29th.  It ends the month 7.4 degrees east of Jupiter, culminating at 20.18, 15 degrees above the southern horizon, down to mag 0.5 and setting at 00.19.

Uranus:  in Aries, mag 5.7
On 1st it rises at 21.29 and  and should be high enough to be visible from midnight.  It culminates, 50 degrees in the south, a few minutes after the sky begins to brighten. On 30th it reaches 21 degrees in the east by 22.00 culminating at 03.02 and down to 39 degrees in the SW by dawn.  It should be an easy binocular target, given clear skies, maybe even naked eye from a very dark sky site.

Neptune:   in Aquarius,  mag 7.8
Much fainter, and lower in the sky, than Uranus but well positioned for telescopic observation.  On 1st it is at 21 degrees in the SE by 23.00 and culminates, 31 degrees in the south, at 01.50.  It is at opposition on 11th, when it reaches its highest point at 01.10.  On 30th it culminates at 23.50, still at 31 degrees and will be reasonably high until 02.30, when it is down to 21 degrees in the SE.  May be visible in good binoculars from a dark sky site, and is an easy target for amateur scopes. 

Dwarf Planets

Ceres:  in Aquarius, mag 7.9
Above the horizon for much of the night but low, so not an easy target.  On 1st it culminates at 01.15, only 12 degrees above the southern horizon, and sets at 04.56.  It moves into  Piscis Austrinus on 15th and on 30th, down to mag 8.2. culminates at 22.59 and sets at 02.31.

Pluto: in Sagittarius, mag 15.1
Too low for successful imaging, max 13 degrees above the horizon.

Haumea:  in Bootes, mag 17.4
Now getting very low in the sky.  On 1st it may be high enough for imaging, 23 degrees in the west, for a short time around 21.30.  After the first week it is too low by the time the sky gets dark.

Makemake:  in Coma Berenices, mag 17.3
Appears very close to the Sun this month.  It is at solar conjunction on 29th when, because of its highly inclined orbit, it passes 27 degrees north of the Sun.

Eris:  in Cetus, mag 18.8
Quite high in the sky but much too faint for most amateur astrophotographers to attempt.  However, it is in conjunction with Mars twice this month, on 1st when the red planet is 7 degrees 58' to the north at 04.14, and on 19th when they are slightly further apart, 8 degrees 09', at 03.03.  This happens because Mars is retrograde from 10th and passes Eris once in each direction. So, if you look at Mars at these times, you can work out exactly where Eris is - even though you can't see it.

Asteroids

19 Fortuna is at opposition on 11th.  It starts the month at mag 9.8 in Pisces, culminating, 31 degrees in the south, at 01.31.  By 11th it has brightened to mag 9.4 and reaches its highest point, 34 degrees, at 01.04.  It moves into Aquarius on 21st and on 30th, faded to mag 9.9, reaches 32 degrees in the south at 23.31.

68 Leto is at opposition on 30th. On 1st it is at mag 10.2 in Cetus, reaching its highest point, 32 degrees, at 03.28. On 30th it is at mag 9.6, culminating at 01.13, now at 31 degrees in the south.

Comets

Not much happening this month. There are a few comets around but they are all very low, very faint, or both.
C/2020 F3 (NEOWISE) and C/2019 T2 (PanSTARRS) are getting very faint and very low in the sky after sunset.
88P/Howell is much brighter, predicted mag around 8.8, but again very low - 13 degrees at dusk in early September, down to 10 degrees by the end of the month.
C/2019 U6 (Lemmon) is high in the evening sky, but extremely faint, predicted mag on 1st, when it is 36 degrees in the west at dusk, is 12.3.  On 30th it is higher, 42 degrees, as the sky fades but much fainter at mag 14.5.

For more information and exact positions of any Solar System objects see

www.cometwatch.co.uk again hasn't been updated for a couple of months.

Meteor Showers

After last month's Perseids, which most of us missed because of cloudy skies, we only have a few very minor showers this month.

September Epsilon Perseids: active 5th to 21st, peak 9th,  ZHR 5. The radiant of these very slow meteors is closer to Algol than it is to epsilon Persei.  It's circumpolar, highest at 05.00 so the shower is best seen just before dawn.

Alpha Aurigids: active until Sept 5th, peak on August 31st,  ZHR 6.  These very bright meteors are best seen just before dawn, unfortunately the almost full Moon doesn't set until just before 5am, as astro twilight ends, on the morning of 1st.  Parent comet is C/1911/Kiess.

Piscids:  active throughout Sept, ZHR 5 (more likely 2 from light polluted Manchester skies).  Not much is known about this shower of very slow moving meteors. It is thought by some to be 2 separate showers, the Northern and Southern Piscids, one having a peak on Sept 9th, the other on 21st.  Or it could be one shower with low activity throughout September and a diffuse peak from 9th to 21st.

Daytime Sextantids: active Sept 9th to October 9th, peak Sept 27th, ZHR 5. As the name says, this shower is mainly active in the daytime, however a few may be spotted visually just before dawn around the time of the peak. 

Southern Taurids, active from Sept 10th. These don't peak until October, ZHR rarely more than 5, but worth looking out for as the shower often includes many fireballs.



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