September brings the darker nights of late summer and the Milky Way still shimmering overhead. The autumn constellations begin to dominate the skies and the evenings are colder with plenty of dew so make sure your instruments are checked for dewing!
Moon in September:
New: 20th September
First quarter: 28th September
Full: 6th September
Last Quarter: 13th September
Planets in September:
Mercury: Is at its greatest western elongation on the 12th September and will be a bright object shining at magnitude -0.4 in the morning sky after dragging itself away from inferior conjunction in late August.
Venus: is a morning object rising in the early morning in the constellation of Leo and is a brilliant object shining at magnitude – 3.9
Mars: Draws toward the Sun in the morning sky and is not far from the bright Star Regulus at 2:00am in the first week of the month. Its tiny disc is not well placed for observation.
Jupiter: Is in conjunction with the Sun in the constellation of Virgo and is not well placed to observe in September though it may be glimpsed low down on the western horizon after sunset early in the month.
Saturn: Is still in Ophiuchus after sunset and shines brightly at magnitude 0.1 Although it is low in British skies it is still a wonderful object and the rings look fabulous. It sets quickly after the Sun.
Uranus: Is in Pisces and rises in the late evening, shining at magnitude 5.9 but still only subtends a small disk just under 4” across.
Neptune: The furthest planet from the Sun remains in Aquarius and rises in the evening shining at a miserable magnitude of 7.9. It has a small 2” disc.
Meteor showers in September.
There are no bright meteor showers in September although sporadic meteors will be seen on any clear night. The only shower that may be visible is the relatively unexplored September Epsilon Perseid shower, but with a Zenithal Hourly Rate of just 1 meteor per hour, it will be difficult to separate it from sporadic meteor activity. This shower peaks on the morning of 9th September at around 5:00am UT
Interesting Events in September
The Autumn Equinox will occur on Friday 22nd September at 21.02 in the northern hemisphere and will herald the start of astronomical autumn.
In the early morning of the 5th September the planet Mars is just 0.8 degrees from the bright star Regulus in Leo in the early morning. The same star is joined by the bright planet Mercury on the 10th September and on the 16th September the waning crescent moon joins Mercury in the morning sky and is almost touching it at a separation of only 0.06 degrees. There are several good photographic opportunities for conjunctions this month.
Comets in September
There are no bright comets reported for September although Comet 213P Van Ness may attain 11th magnitude as it comes to perihelion on the 12th September.
Constellation of the Month: Delphinus
This lovely little constellation is easily envisaged as the dolphin it is meant to represent. In one Greek tale, it is the dolphin that came to the rescue of the famous Greek poet Arion, who was returning by ship from a competition in which he had won a large sum of money. The avaricious sailors robbed him of the prize and cast him overboard, hoping to hide their crime. But Zeus sent a dolphin to rescue him, and then destroyed the ship with a thunderbolt. Arion was saved and the dolphin thereafter was placed in the sky. Delphinus contains a few objects that merit the attention. Its position close to the eastern border of the Milky Way ensures that it is a place of interest to the nova and supernova hunter.
The trapezoid shape of the body of the dolphin contains the lovely coloured double star g Delphini, a superb sight through a telescope. The primary is blue – white in colour whilst the companion is a glowing yellow, which has sometimes been described as pale green, due to the contrast with the primary. It lies relatively close to our solar system at 101 light years.
Delphinus contains two globular clusters that are worthy of amateur attention, although it must be stated that neither object is particularly bright or detailed. The first of these objects is the ninth magnitude NGC 6934, RA: 20h 34m 12s Dec 07°24m; a small round bundle of white light lying directly below the tail of the dolphin in a rich field of the Milky Way. It should be well seen in good binoculars, whilst a small telescope will show it to be slightly mottled with many field stars seemingly making a ragged “resolved” edge of pinpoints to the cluster. NGC 6934 is approximately 52,000 light years away.
The real celebrity of Delphinus is the very distant cluster NGC 7006, an object on a par with its distant cousin NGC 2419 in Lynx. The globular NGC 7006 shines feebly at 11th magnitude and is a rather small, difficult object to capture against the Milky Way star fields, but from a dark sky site, with a small telescope, you should be able to pick up this elusive ball of light. NGC 7006 is very distant, over 185,000 light years from our solar system, making the separation between it and NGC 2419 to be over 300,000 light years! It is not known if NGC 7006 is actually a member of the Milky Way cloud of globulars, or if it is an “Intergalactic Tramp”. It has a luminosity of 130,000 times that of the Sun and possibly contains more than 80,000 stars.
Lying amongst the stars in the northern part of the constellation is the planetary nebula NGC 6905, a beautiful vivid blue little nebula with an elongated axis. It is known as the “blue flash” nebula due to this wonderful colour and is located 3000 light years away and yet is quite large at that distance, subtending 1.2 arc-minutes. It can be found at RA 200h 22m 23s Dec 20o 06m 18s.
Delphinus accommodates a few variable stars of interest to the observer the best of which is R. Delphini, a “Mira” type long period variable, which alternates between mag 7.7 and 13.7 in 264 days, it can therefore be followed part way in binoculars. Delphinus is also a good hunting ground for nova observers, the bright nova HR. Delphini becoming a remarkable naked eye object in 1967, after its discovery, with binoculars, by the brilliant British amateur observer G.E.D. Alcock. This discovery was a boon to professional observers, as HR Delphini remained bright for over one year after discovery, the slowest fading nova on record. So never give up! Increase your knowledge of star patterns and fields to increase your chances of unearthing this beautiful type of object.