September 2019

 

 

 

The Sun begins the month in the constellation of Leo, but on the 17^th at 02h00, crosses the astronomical border which separates Leo from Virgo, in which constellation it remains till the month ends.

 

 

 

The Autumnal Equinox on Sept 23^rd at 07h51 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 km.

 

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 Aug 30^th to Sept 13^th, and again on the last two days of the month.

 

 

 

The Moon

 

The Moon is at apogee, its farthest from the Earth, on the 13^th at around 13h (diameter of the moon 30’ of arc) and at perigee (nearest to the Earth) at 02h00 on the 28^th (diameter of the moon 33 mins of arc).

 

 

 

First Quarter Moon takes place at 03h11 on the 6^th, in Ophiuchus, and is one of the lowest FQ Moon of the year, and is near to Jupiter.

 

 

 

Full Moon at 04h34 on the 14^th, is in the  eastern part of Aquarius, beneath the ‘Great Square of Pegasus’ and the circlet of stars outlining the ‘western fish’ of Pisces. 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.

 

 

 

Last Quarter Moon is at 02h42 on the 22^nd almost exactly on the Taurus/Orion/Gemini borders. This is one of the highest LQ Moons of the year.

 

 

 

New Moon is on the 28^th at 18h27, in the constellation of Virgo, passing 5° above the Sun.

 

 

 

Earthshine may be seen on the dark hemisphere of the waning crescent Moon from the 23^rd to the 28^th, and it may also be glimpsed on the night hemisphere of the waxing crescent from the first and last few days of September.

 

 

 

The Planets

 

 

 

Although Mercury lies to the east of the Sun, the planet sets only 20 mins after the Sun and cannot be seen due to the bright twilight. Superior conjunction is on the 4^th of September.

 

 

 

Venus also lies too near to the Sun to be observed during this month, although you may be able to locate it in binoculars very near the horizon at around 18h00 at the end of the month in the western sky after the Sun has set.

 

 

 

Mars is in conjunction with the Sun on the 2^nd, and so will be difficult to observe before sunrise in the bright twilight of the morning sky.

 

 

 

Jupiter lies in the constellation of Ophiuchus and is visible in the SSW sky as night falls. The Moon will be seen approaching Jupiter on the evening of the 5^th, when at 21h they are just over 5° apart, parallel with, and 5° above the SW horizon. Take the opportunity to observe the Galilean satellites; Io, Europa, Ganymede and Callisto as the configuration changes on a nightly basis. Identification of the satellites is to be found on the Front Page of the Sky Notes.

 

 

 

Saturn, in the constellation of Sagittarius, culminates in the early evening at around 20h at the south meridian. Its angular altitude from northern England, is some 15° above the horizon. Any small telescope will show the widely opened rings at this time. Also, try to spot the largest of Saturn’s moons, Titan, when it is at eastern elongation from the planet on the 5^th and 21^st, and when it is at western elongation on the 13^th and 29^th. Titan has a visual magnitude of +8. The Moon lies to the east of Saturn on the 8^th. At this time the two are separated by an angular distance of 3°, Saturn lying to the upper right of the waxing gibbous Moon. The two objects lie directly beneath the ‘Summer Triangle’ of stars, made up by Vega, Altair and Deneb.

 

 

 

Uranus lies in Aries beneath the stars Hamal and Sheratan in that constellation. See the Remote Planets page to find its position. The visual magnitude of Uranus during the month is +5.7, and through an astronomical telescope has the appearance of a tiny greyish green disc

 

 

 

 

 

Neptune is at opposition and its nearest to the earth this year on the 10^th.  It lies in the constellation of Aquarius, beneath the circlet of stars which makes up the pattern of the ‘western fish’ of the neighbouring constellation of Pisces. The opposition magnitude of Neptune is +7.83. like Uranus, Neptune presents an even smaller disc and is bluish in colour.

 

In order to locate this remote planet, you are encouraged to visit the Remote Planets page accessible via the MENU above. The planet is visible all night and culminates (crosses the south meridian) around midnight at an altitude of 29°.

 

Therefore in September there are four planets visible during the hours of darkness to be observed;  Jupiter and Saturn which are readily visible to the unaided eye, and the remote planets Uranus and Neptune,  planets which require optical aid in order to identify and locate them.

 

 

 

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.