The Night Sky in September 2024
Don’t forget our 1st meeting on the 23rd September is the AGM, please attend. This is your society and we need you!
The nights have certainly drawn in, with sunsets increasingly earlier and sunrises increasingly later. Great for astronomy, we can get observing and imaging earlier in the evenings. Pity the weather is not as obliging.
September is one of the months where an equinox occurs, this month it is the Autumnal Equinox and marks the day when the Sun crosses the celestial equator from North to South. The reason for this latitudinal movement is because the Earth axis of rotation is inclined at 23.5° to its path around the Sun. Without it we would not have seasons. The Solstice occurs on 22nd September and our nights will get longer and longer up until the Winter equinox.
Though the event occurs when the Sun is in Virgo, the position is still referred to as the First Point of Libra, which is where is was first plotted by ancient astronomers and was in Libra, but due to precession has moved to Virgo.
It is also, for you Tolkien fans, Bilbo Baggins birthday..and mine.
The Moon
The Moon starts is new phase and is visible from 4th September and reaches its full phase on the 15th September, this is the Barley Moon in Saxon times. It is sometimes called a Harvest Moon but the true Harvest Moon is the first full moon after the Autumn Equinox, that will actually happen in October. A once every three year occurrence.
On 17th September the near full Moon will be very close to Saturn..a nice opportunity for the astrophotographers.
On September 18th the is a very small partial eclipse starting at 01:47 BST and ending at 05:47 BST. The Moon will just clip the Earths shadow and a very slight colour change might be seen. As it is mostly for us a penumbral eclipse. The darker umbral part of the eclipse occurs at03:44 BST and just a small part of the northern pole area will darken.
The waning gibbous Moon will cover the Pleiades on the 22nd September.
The Planets
There is a decent parade of the brighter planets this month. Such a change to the start of the year.
Mercury: Reaches around 15° on the Eastern horizon and between 1st-11th September will be at its highest before heading back down again.
Venus: very low in our sky so not a good target this month.
Mars: Shining at +0.7 magnitude and on 9th September is 52 arc minutes south of M35.
Jupiter: Starts to offer late evening views object and is getting brighter shining at -2.4. It is also at quadrature, 90° angle to the Sun. This means that shadow transits of the Galilean Moons will be more visible, this also means that shadow occultations of those moons will be occurring.
Saturn: Saturn will be at opposition on 8th September, it’s rings are only just tilted so we are looking at them more or less edge on. On September 17th it will be just 0.3° south of the Moon
Its altitude is about 30°, much better for imaging. It is still a very lovely object in small telescopes and even binoculars.
Uranus: It will be in the constellation of Taurus and due to our smaller inner orbit around the Sun we pass it and it appears like the other outer planets to go backwards. Retrograde motion. Apparent retrograde motion – Wikipedia
When it was thought that the solar system was Earth Centred the believers in that system had the outer planets have their own mini orbits around an imaginary point in order to describe this clockwise then anti clockwise motion against the back ground stars.
Neptune: Neptune is currently in Pisces and so is a sunset to sunrise object. It is at opposition on September 20th and has a magnitude of +7.8 so not a naked eye object but in a small telescope appears as a bluish tiny disc. On 18th September it will be 0.7° south of the Moon making it slightly easier to find.
The Constellations
The Winter constellations start making their appearance earlier in the evening, the Pleiades and Taurus are visible before midnight towards the end of the month. Old friends returning and longer nights to observe and image.
By 05:00 Orion is full visible in the east, always a favourite of mine and very distinctive, but more of the Hunter later in the year.
Though the constellations of Pegasus and its companion Andromeda are still nicely visible high in the South East. Its W shape makes it very distinctive, find that and south of it you will find Andromeda and Pegasus.
To the west of Cassiopeia is the large cross of Cygnus the Swan. Both these constellations lie in the Milky Way. This is the visible arm of our home galaxy. A pair of binoculars will reveal that the visually misty band in the sky is in actual fact made up of billions of stars.
The summer triangle is still very prominent. And the dark lane of gas in the Milky Way runs through the triangle formed by Deneb, Vega and Altair.
Perseus and the Double Cluster will be high in the sky. That will please Alan our Chairman..
The Plough (Ursa Major) is now low in the North in its horizontal position.
A good guide to the night sky with small telescopes and binoculars can be found at www.binocularsky.com
Clear Skies!
Frank Dutton
