The Autumnal Equinox on Sept 23rd at 01h55 marks the official start of autumn. Day and night are almost equal in length again, and in
the northern hemisphere, autumn lasts for 89.85 days. The Earth - Sun distance at this time is 150 125 903 kms.
The Sun begins the month in the constellation of Leo, but on the 17th at 02h, crosses the astronomical border which separates
Leo from Virgo, in which constellation it remains till the month ends.
September is the best month to observe the ethereal Zodiacal Light during the early mornings when the Moon is not present in the sky and you are well away from light
pollution. Look towards the east before the onset of morning twilight, around 03h30, and you should see a faint cone of light pointing southwards at a steep angle of 60°. This phenomenon is caused by the Sun illuminating the disc of fine dust, which is
the remnant of solar system formation 4.5 thousand million years ago. The best days to observe this morning cone are from the 10th to the 24th of the month.
The Moon is at apogee,
its farthest from the Earth, on the 20th at around 00h00 (diameter of the Moon - 29’32’’ arc) and at perigee (nearest to the Earth) at 01h00 on the 8th (diameter of the Moon 32’52’’
Last Quarter Moon is at 02h38 on the 3rd in Taurus, near the bright star Aldebaran. At 01h00 the Last Quarter Moon passes just 6 arc minutes (0.109°) to the north of this star. This is one of the highest LQ
Moons of the year (60 degrees), when it crosses the meridian at sunrise, (despite the Moon being south of the ecliptic at this time).
New Moon is on the 9th at 18h02, in the constellation of Leo, passing just over 2°
north above) the Sun.
First Quarter Moon takes place at 23h16 on the 16th, in Ophiuchus, and is the lowest FQ Moon of the year, and may be seen at 15° altitude in the south just before sunset on this day.
Moon at 02h53 on the 25th, is at the junction of the Pisces/Cetus/Aquarius border. This Moon is called the “Harvest Moon”, since before the days of mechanisation, harvest was a long process and the labourers would have to work
well into the night. For several nights before and after Full, the Moon rises at about the same time each evening as the sun sets and so its light enabled the harvesters to continue their labours into the night. Look for the Harvest Moon rising almost due
east at sunset at this time.
Earthshine may be seen on the dark hemisphere of the waning crescent Moon from the 1st to the 9th, and it may also be glimpsed on the night hemisphere of the waxing crescent from
the 10th to the 15th.
As September starts, Mercury rises 90 minutes before the Sun in the constellation of Leo, and is best seen above the eastern horizon in brightening
twilight at around 04h when it is 5° above the ENE point on the horizon. It should be possible to glimpse Mercury at this time with the unaided eye, when it has the appearance of a bright star at visual magnitude -0.87. The planet may be seen in
this direction during the first week of September, but gradually sinks lower as it moves towards superior conjunction with the Sun on the 21st.
During September Venus sets less than an hour after the Sun, and as the month
progresses it becomes difficult to observe. However, in binoculars, Venus takes on the appearance of an extremely thin miniature crescent moon. During the first week of September the planet may be seen low (3° altitude), in the WSW sky at around 19h00,
and it may also be possible to glimpse Spica, the brightest star in Virgo nearby in the same binocular field.
On the first of the month, Mars sets at 01h, but at the month’s end the planet is setting just before 00h, so the planet
has now become an evening object as Earth leaves the planet behind. However Mars, on the Capricornus/Sagittarius border is still shining brightly with its ochre coloured light. During September the planet fades from visual magnitude -2.1 to -1.3. So for almost
all of the month it is brighter than Sirius (the brightest of all true stars, after the Sun). There is a conjunction with the Moon at 04h00 on the 20th, by which time the planet will have set. However the gibbous waxing Moon will lie 5° to the
west (right) of Mars at 23h00 the previous night (19th) as the two objects are setting in the SW.
Jupiter is an evening object in the constellation of Libra and may be seen low in the SW sky in the early evening. By the end
of September the planet sets at around 19h00. Its appearance is that of a star shining brightly and steadily at magnitude -1.8. The waxing crescent Moon may be seen approaching Jupiter on the 13th, when at 19h00, Jupiter lies 5° to the east
(left) of the Moon, and the following night the 14th, when the waxing crescent and the giant planet are 8° apart. On this latter occasion Jupiter lies 8° to the west (right) of the Moon. Using binoculars look out for Jupiter’s moons
and their nightly dance around the planet.
Mid-month, Saturn culminates (crosses the south meridian) at around 19h00, when its altitude is around 12° (from Scarborough). Again, despite the favourable presentation of the northern
surface of the rings towards Earth, the low altitude of the planet affects the clarity of the view through a small telescope. However modern techniques in imaging using software to ‘stack’ images of the planet produce excellent results. Saturn’s
largest moon Titan is at its greatest elongation east of the planet on the 2nd and 18th and western elongation on the 10th and 26th. The gibbous waxing Moon passes close to Saturn on the evening of the 17th,
when at 19h00 the two objects are just over a degree apart in the south. See if you can spot Saturn in the same binocular field as the Moon, in the fading twilight.
Uranus in the constellation of Aries the Ram rises during the early
evenings of September and may be seen in binoculars for the rest of the night. It culminates (crosses the meridian) at around 02h00. Uranus lies 8° south of Mesarthim (gamma Arietis), and has a visual magnitude +5.71 Uranus is on
the threshold of naked eye visibility, so is best seen through a small telescope. There is a location chart showing the movement of Uranus on the Aries/Pisces on the Remote Planet page accessible from the MENU (MORE) above.
is at opposition and its nearest to the earth this year on the 7th. Despite this, the planet is very faint and is below naked eye visibility at magnitude +078. The planet lies 41 minutes of arc to the NW of the visual magnitude +5.43 star 82 Aquarii.
It is theoretically visible all night long and there is finder chart on the Remote Planets page, mentioned above.
A minor meteor shower peaks during the early morning of the 9th, when through the night, you may see about 10 Piscid
shooting stars an hour. The radiant, or apparent origin is in the constellation of Pisces, hence the name.
Constellations visible in the south around midnight, mid-month, are as follows: Aquarius, the western fish of Pisces, sometimes known as ‘The
Circlet’ because of its shape, and the large autumn square of Pegasus. Almost overhead are the great galaxy in Andromeda and the ‘W’ shaped constellation of Cassiopeia.
All times are GMT 1°
is one finger width at arm’s length.
SEPTEMBER EVENTS SUMMARY (Using Coelix Software).
The phenomena of the month : September 2018
Times are given in UT for SCARBOROUGH (0°
25' 0" W, 54° 16' 3" N, zone 0 UT).
Date Hour Description of the phenomenon
yyyy mm dd hh:mm
2018 09 01 03:25 Meteor shower : Alpha Aurigids (6 meteors/hour at zenith; duration = 8.0 days)
2018 09 01
11:46 Close encounter between Venus and Spica (topocentric dist. centre to centre = 1.2°)
2018 09 02 07:09 Minimum of the variable star Algol (beta Persei)
2018 09 02 10:00 Mercury at its perihelion (distance to the Sun = 0.30749 AU)
09 02 12:29 Opposition of the asteroid 115 Thyra with the Sun (dist. to the Sun = 2.123 AU; magn. = 9.9)
2018 09 03 00:52 Close encounter between the Moon and Aldebaran (topocentric dist. centre to centre = 0.4°)
2018 09 03 02:38 LAST QUARTER
OF THE MOON
2018 09 03 18:58 Simultaneous transits on Jupiter: shadows of two satellites.
2018 09 05 03:58 Minimum of the variable star Algol (beta Persei)
2018 09 05 08:00 Venus at its aphelion (distance to the Sun = 0.72824 AU)
05 09:18 Maximum of the variable star delta Cephei
2018 09 05 23:39 Opposition of the asteroid 27 Euterpe with the Sun (dist. to the Sun = 2.406 AU; magn. = 9.8)
2018 09 06 02:55 Close encounter between Mercury and Regulus (topocentric dist. centre
to centre = 1.0°)
2018 09 06 14:46 Maximum of the variable star eta Aquilae
2018 09 07 18:27 OPPOSITION of Neptune with the Sun
2018 09 08 00:47 Minimum of the variable star Algol (beta Persei)
2018 09 08 01:21 Moon at perigee (geocentric
dist. = 361351 km)
2018 09 09 09:32 Maximum of the variable star zeta Gemini
2018 09 09 14:20 Meteor shower : Sept. Perseids (5 meteors/hour at zenith; duration = 16.0 days)
2018 09 09 18:01 NEW MOON
2018 09 10 07:46 Comet 21P Giacobini-Zinner
at its perihelion (dist. to the Sun = 1.013 AU; magn. = 7.0)
2018 09 10 18:06 Maximum of the variable star delta Cephei
2018 09 10 18:52 Simultaneous transits on Jupiter: two satellites and shadow of one satellite.
2018 09 10 19:31 Minimum of
the variable star beta Lyrae
2018 09 10 21:35 Minimum of the variable star Algol (beta Persei)
2018 09 13 18:24 Minimum of the variable star Algol (beta Persei)
2018 09 13 19:01 Maximum of the variable star eta Aquilae
2018 09 14 20:25
Beginning of occultation of 44-eta Lib (magn. = 5.41)
2018 09 16 02:53 Maximum of the variable star delta Cephei
2018 09 16 13:00 Mars at its perihelion (distance to the Sun = 1.38144 AU)
2018 09 16 15:13 Minimum of the variable star Algol (beta
2018 09 16 23:15 FIRST QUARTER OF THE MOON
2018 09 17 18:54 End of occultation of 14 Sgr (magn. = 5.49)
2018 09 18 01:56 Opposition of the asteroid 173 Ino with the Sun (dist. to the Sun = 2.198 AU; magn. = 10.3)
2018 09 18 18:17
End of occultation of 39-omicron Sgr (magn. = 3.76)
2018 09 19 01:57 Opposition of the asteroid 30 Urania with the Sun (dist. to the Sun = 2.118 AU; magn. = 9.6)
2018 09 19 12:01 Minimum of the variable star Algol (beta Persei)
2018 09 19 13:07
Maximum of the variable star zeta Gemini
2018 09 20 00:54 Moon at apogee (geocentric dist. = 404876 km)
2018 09 20 23:16 Maximum of the variable star eta Aquilae
2018 09 21 01:51 SUPERIOR CONJUNCTION of Mercury with the Sun (geoc. dist. centre
to centre = 1.5°)
2018 09 21 11:40 Maximum of the variable star delta Cephei
2018 09 21 20:26 Beginning of occultation of 40-gamma Cap, Nashira, (magn. = 3.69)
2018 09 21 21:22 End of occultation of 40-gamma Cap, Nashira, (magn. = 3.69)
2018 09 22 08:50 Minimum of the variable star Algol (beta Persei)
2018 09 23 01:54 AUTUMN EQUINOX
2018 09 23 18:06 Minimum of the variable star beta Lyrae
2018 09 23 21:44 Beginning of occultation of 93-psi2 Aqr (magn. = 4.41)
23 23:01 End of occultation of 93-psi2 Aqr (magn. = 4.41)
2018 09 24 00:00 VENUS at maximum brightness (magn. -4.60)
2018 09 24 00:44 Opposition of the asteroid 10 Hygiea with the Sun (dist. to the Sun = 3.317 AU; magn. = 10.1)
2018 09 25 02:53
2018 09 25 05:38 Minimum of the variable star Algol (beta Persei)
2018 09 26 20:27 Maximum of the variable star delta Cephei
2018 09 27 20:26 Beginning of occultation of 73-xi2 Cet (magn. = 4.30)
2018 09 27 21:22 End of occultation
of 73-xi2 Cet (magn. = 4.30)
2018 09 28 02:27 Minimum of the variable star Algol (beta Persei)
2018 09 28 03:31 Maximum of the variable star eta Aquilae
2018 09 29 16:41 Maximum of the zeta Gemini
2018 09 30 23:16 Minimum of the
variable star Algol (beta Persei)