The Night Sky in September 2020
The nights are drawing in and the evenings cooler at the end of summer. The autumn constellations are making their appearance in late evening but the summer groups still dominate the sky.
Moon in September
New: 17th September
First quarter: 24th September
Full: 2nd September
Last Quarter: 10th September
Planets in September
Mercury: is not at its best in the evening sky at the beginning of the month and sets before sunset by mid-month becoming an early morning object of first magnitude.
Venus: Is a morning object in Cancer throughout September, rising after 03:00.
Mars: remains in Pisces and brightening to magnitude -2.1 in readiness for its opposition in October. It is visible in the late evening most of the month.
Jupiter: remains in Sagittarius but sets after 01:30 by mid month. It is still dazzlingly bright and easy to spot at Magnitude -2/3 and dominates the evening
Saturn: also remains in Sagittarius and is a bright 0.4 magnitude with its beautiful rings visible at medium powers on a small telescope. It sets an hour after Jupiter.
Uranus: is in Aries and is an evening object rising after 20:30 as a 6th magnitude star.
Neptune: Is at opposition on the 11th September and is visible all month as a faded blue star-like object amongst the stars of Aquarius, though a telescope will be needed to spot it.
Meteor showers in September
The Orionids begin their night time show after the 23rd September but they are better seen at their peak in October. Another long lasting but unremarkable shower is the Southern Taurids which go all the way from September 10th to November 20th this year. There have been some fireballs associated with the southern Taurids so keep an eye on the skies!
Interesting Events in September
On the 6th September Mars and the Moon move to within a tiny fraction of a degree of each other and provide a great photographic opportunity.
Neptune comes to opposition on the 11th September and will be at its best and brightest at magnitude 7.8 for 2020.
The autumn equinox is on the 22nd September.
Comets in September
C/2020 F3 (NEOWISE), Is fading away though larger telescopes can follow it. Comet Howell is a faint object in Scorpius after sunset but is in the twilight and shining dimly at 8th magnitude.
Constellation of the Month: Aquarius
This is a rather loose Autumn constellation with very little impression of outline, yet containing a little "Y" shaped asterism called the "Water Jar" which is generally used as the constellation's centre point, from which the observer can find the rest of this expanse of stars. The name Aquarius means "The Water Bearer" although the figure that the constellation supposedly represents has long since been lost. It is however a group of antiquity, probably being formed by the Babylonians and taken up by different cultures since. Indeed, the Romans knew the group as the Peacock of the goddess Juno, the queen of the heavens.
Aquarius is fairly rich in deep sky objects worthy of the amateur's attention plus some very interesting variable stars for those equipped with larger instruments. As it also straddles the ecliptic, occasionally some of the planets can be found adorning the field, bringing a little sparkle to this amalgam of second and third magnitude stars.
The first object on our deep sky tour is the wonderful globular cluster M 2, a bright sixth magnitude array that can be seen in binoculars some 6 degrees north of Beta Aquari. M 2 was discovered by Messier in 1760, soon after he began to formulate his catalogue, although it seems that Maraldi was the first person to set eyes on it some 16 years previously. M 2 is a fine object in a small telescope, it is a rich round blaze of white stars, which shows a little resolution along the edges, but the centre is an opaque mass of some 100,000 stars shining at magnitude 14 or 15. M2 lies over 50,000 light years away, and shows the lowest proper motion of any globular in the sky, possibly due to it reaching the furthest point in its orbit away from the galactic nucleus, and is now preparing to fall back into the galactic disc, although evidence of this scenario is scarce.
Another globular that was catalogued by Messier is the faint cluster M 72, a tenth magnitude rather bland object in the south of the constellation. It is barely visible in binoculars, but no detail is really revealed through a small telescope either, it simply remains a round haze of white light in a barren field.
M 72 apparently lies 54,000 light years away. Aquarius also holds another Messier object that is something of a curiosity. This is the object called M 73, discovered a few nights after M 72. It is not a cluster or nebulae, just a faint group of three unremarkable stars in an otherwise sparse field. Messier noted them as such, but added that they lay in a field of nebulous gas, though this must have been the shortcoming of his telescope, as no nebulae lies at this position.
One of the showpieces of the autumn sky can be found in the same general area of M72 and M 73, though how Messier came to miss it is not explained. This object is the planetary nebulae NGC 7009, a beautiful object bursting with detail in the field of a small telescope, and bright enough to be seen in binoculars as a fuzzy star.
NGC 7009 was called the "Saturn Nebulae" by Lord Rosse, the famous Irish observer who also gave M 1 and M 51 their familiar names of the "Crab" and the "Whirlpool". A glance at this object is enough to tell you why it he called it so. The nebulae is elongated and appears to have a "ring" of material surrounding the nebulous disc, exactly like the famous ringed planet. The nebulae has a high surface brightness that will take high powers well, it shines at magnitude 8 and is some 3900 light years away. Observers with large instruments may even be able to distinguish the bright rays or ansae that flash out from the central nebulae and across the "ring".
Another planetary nebulae lies well to the east of NGC 7009 and is an equally famous object of its type. This is the so-called "Helix Nebulae", or NGC 7293 as Dreyer recorded it. NGC 7293 at RA: 22h 29m 36s Dec -20°48m, has the distinction of being the largest planetary nebulae visible to us. It is slightly smaller than the full moon and has an integrated magnitude of six. This would appear from such a spectacular object, but its light is spread over such a large area that it rapidly diminishes, and the nebulae is practically invisible as a result. It is one of the few objects where binocular observers have an advantage, as the wide field of such instruments will gather all the available light to build up a picture of a ghostly blue - white ring of gas, although no detail will probably be seen.
If you are the owner of a wide field telescope, or giant binoculars, then give NGC 7293 a try, but for most small telescope users, the advice is to regretfully look elsewhere. The Helix is large merely because it is the closest planetary nebulae to our solar system, lying at a distance of 85 light years, giving the shell of ejected gas a diameter of 0.3 light years. The science fiction author Robert Silverberg speculated on the possibility of rapidly mutating, radiation eating life forms in such a fierce system as NGC 7293 in his book Tower of Glass.
One of the strangest long period variable stars lies in Aquarius, and is known as R. Aquarii, a pulsating red giant star of class M, lying close to the naked eye star omega Aquarii. It is unusual in that on some occasions the regular pulsations stop and the star remains at minimum light. R. Aquarii usually varies between magnitude six and magnitude nine in a period of 386 days; it should be visible to binocular observers at all times. As complete reports and light curves for R Aquarii are not readily available, why not try plotting your own, and sharing the results with other of similar interest. Such work is most important, and could even form a thesis for university study.
A fainter but no less interesting star is CY Aquarii, a type of dwarf Cepheid shining at tenth magnitude. In all fairness this star is a telescopic object, although its pulsations may be followed in a pair of giant binoculars. The period is the shortest known of any star, varying from magnitude 10 to 11.3 in only 88 minutes! Thus during a whole nights observing, you may be able to spot at least three or four minima and maxima, and record the appropriate light curve. CY Aquarii is a B type giant star lying 1300 light years away.