Current Astronomical events
Highlights of the Month
13th September:
A lunar occultation of Neptune in the early morning.
27th September:
Saturn and a waning Crescent Moon
Find M31 - The Andromeda Galaxy
September's Stars
Observe the International Space Station
The Moon
The Planets this month
The Jodcast
September 3rd to 19th:
A trio of planets and a daylight conjunction
on the 11th and 12th.
|
Close grouping of Venus, Mars and Mercury
(Click image to enlarge)
Image: Stellarium |
During the first part of September, Venus, Mercury and Mars remain within an angular separation of 5 degrees - so encompassed within a binocular field of view.
They can be seen low in the west just after Sunset and Venus, at magnitude -3.8, will be the easiest to spot first.
During this period there are three conjunctions (both planets have the same right ascension) of pairs of planets: Venus is just 18 arc minutes north of Mars on the 11th, Mercury is ~3.5 degrees south of Mars on the 12th and again on the 19th. It might be interesting to attempt to spot them during the day on the 11th and 12th.
(Binoculars will be needed so be sure to look well away from the Sun which will be ~25 degrees away.)
They will be due south at 14:30 UT, so if you locate due south with a compass you can lift up your scope or binoculars to an elevation of ~ 30 degrees (that's a third of the way up to the zenith!) you should be able to spot Venus with Mars close by and Mercury ~3.5 degrees below.
Worth a try if its clear!
13th September:
A lunar occultation of Neptune in the early morning.
|
Cassini Image of Jupiter
(Click image to enlarge)
Image: Ian Morison |
If it is clear during the early hours of the morning of the 13th September you have a chance of seeing the Moon, just two days before full, pass in front of the planet Neptune.
At about 02:00 BST they will be about 13 degrees in the horizon in the west with Neptune just under 1 degree (two moon widths) up to Moon's left.
The Moon gradually moves towards Neptune and at about 03:24 (dependent on where you live in the UK) it will be occulted.
As Neptune has a disk with an angular size of 2.3 arc seconds, it will take a moment or two to disappear - in contrast to a star which vanishes instantly.
You will need binoculars or a small telescope to spot Neptune which has a magnitude of +7.8.
27th September:
Saturn and a waning Crescent Moon
 |
Wide angle and telescope images of a thin waning crescent Moon.
(Click Image to enlarge)
Image: Ian Morison |
In the pre-dawn sky on the 27th September just after 05:30 BST you may have a chance to see Saturn just a few degrees to the left of a thin crescent Moon just 51 hours before new moon and only 4% illuminated.
If you managed to spot the Moon at the same time next day it will be just 1% illuminated and only 27 hours before new moon - quite an achievement.
I was able to photograph (through my hotel window in China) the moon just 36 hours before a total eclipse of the Sun (by definition at new Moon!) on the morning of the 31st of July.
Find M31 - The Andromeda Galaxy
 |
How to find M31
(Click Image to enlarge)
Image: Stellarium |
In the late evening, the galaxy M31 in Andromeda is visible in the south-east. The chart above provided two ways of finding it:
1) Find the square of Pegasus. Start at the top left star of the square - Alpha Andromedae - and move two stars to the left and up a bit. Then turn 90 degrees to the right, move up to one resonably bright star and continue a similar distance again in the same direction. You should easily spot M31 with binoculars and, if there is a dark sky, you can even see it with your unaided eye. The photons that are falling on your retina left Andromeda well over two million years ago!
2) You can also find M31 by following the "arrow" made by the three rightmost bright stars of Cassiopeia down to the lower right as shown on the Chart. Good Hunting!
The Stars
The late evening September Sky
|
| The September Sky in the south - late evening. |
This map shows the constellations seen towards the south in late evening. To the south in early evening moving over to the west as the night progresses is the beautiful region of the Milky Way containing both Cygnus and Lyra. Below is Aquilla. The three bright stars Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila) make up the "Summer Triangle". East of Cygnus is the great square of Pegasus - adjacent to Andromeda in which lies M31, the Andromeda Nebula. To the north lies "w" shaped Cassiopeia and Perseus.
The Moon
| Current Lunar Phase |
|
Current position of the International space Station
For more information on the ISS and visible pass information, please click here or click the 'Space station visible passes' button on the index.
|
|
| The Planets |
 |
Venus
Image: NASA |
|
Mercury reaches what is called Eastern Elongation on the 11th September when the angular separation from the Sun is greatest. However, at this time of year, the ecliptic - the path of the Sun across the sky close to which the planets are found - is at a very shallow angle to the horizon so that it will be seen very low above the horizon making it difficult to pick out. The best chance is probably at the beginning of the month when it is at 0th magnitude.
Care should always be taken when looking for Mercury as it is often very close to the sun.
Don't scan around the sky with binoculars whilst the Sun is still above the horizon as you could accidentally look at the Sun itself and cause serious and permanent damage to your eyes in a split second. |
|
| |
 |
Venus
Image: NASA |
|
Venus can be seen very low in the west after sunset shining at magnitude -3.8 so it is possible to spot it without the use of binoculars. It is gradually moving further in angle from the Sun so will remain in the evening sky for longer after the Sun has set as the month progresses whilst its brightness increases fractionally to a magnitude of -3.9. It starts September with an angular size of 10.8 arc seconds and its disk is 92% illuminated. By the end of the month, the angular size has increased to 12 arc seconds but the percentage illuminated has dropped to 86%. These two effects tend to cancel out in the way they affect its apparent brightness which is why the brightness remains almost constant. |
|
 |
A Hubble Space
Telescope
image of Mars.
Credit: Jim Bell et al.
AURA/STScI/Nasa) |
|
Mars lies to the upper left of Venus at the beginning of the month very low in the western sky after sunset. At magnitude +1.7 and with an angular size of just 3.9 arc seconds it will probably need binoculars to pick it out. |
|
| |
 |
A Cassini image
of Jupiter.
Credit: NASA |
|
Jupiter is seen in the south as nightfall begins. Due to the Earth’s motion around the Sun “on the inside track” Jupiter has been seen to move westwards relative to the stars – called retrograde motion – but on September 7th it begins to move eastwards again above the handle of the “Teapot” in Sagittarius. It begins September with an angular size of 43.5 arc seconds which slowly reduces to 40 arc seconds as the month progresses. In like manner, its brightness reduces from -2.5 to -2.3 magnitudes during the month.
Jupiter is now at the lowest point of the ecliptic in the sky and will only rise to about 16 degrees elevation when it is in the south. Thus, sadly, this year our views of Jupiter from northern latitudes will be rather poor. Despite the low elevation, even a small telescope will show the Galilean Moons as they weave their way around it. Due to refraction, we see Jupiter at very slightly different elevations in the different colours of the spectrum, thus bluring the image. A cleaner image may seen if one observes through a narrow band filter such as a green filter or, even better, if you have an 8" scope or above with a filter like an OIII filter only letting a very narrow band of light through. |
|
| |
 |
Saturn:
Taken by the
Cassini Spacecraft
Credit: NASA |
|
Saturn is in conjunction with the Sun on September 4, lying on the far side of the Sun so is not visible during the first two weeks of September, but it will reappear in the pre-dawn sky by month’s end and will then rise 2 hours before the Sun with a magnitude of +0.9. This is significantly less than it often appears as the rings will then be at an angle of just 4 degrees from edge on! As we move towards the end of the year, this angle will reduce until the rings are edge on to us and become invisible to us. Saturn is close to the thin crescent Moon on the 27th Serptember.
|
|
The Jodcast
Listen to the Jodcast (or Jodrell Bank Podcast) for a monthly update on the Sky
http://www.jodcast.net/
Read Popular Astronomy's Sky Diary for this quarter by clicking here. This is is Adobe Reader format (PDF).
If you do not have Adobe Reader installed please click 
to download software. Please note this is FREE to download.
International Space Station and lunar phase images reproduced courtesy of Heavens-Above GmbH
