01-08-2007 September Night Sky (Article 101)

Moderator: SAC Committee

Post Reply
Simon Kenny
Posts: 527
Joined: Tue Feb 12, 2008 9:17 pm
Location: Shannon, Co. Clare, Ireland

01-08-2007 September Night Sky (Article 101)

Post by Simon Kenny » Wed Feb 04, 2009 11:19 am

September Night Sky (Article 101)

On the evening of the 2nd at about 10 pm the very distinctive star cluster called the Pleiades or the Seven Sisters (with the naked eye you can see the 7 brightest stars in the cluster) will appear above the NE horizon. The Pleiades lie in the constellation of Taurus. It will be very easy to find because it lies just left of the Moon which is 21 days old and is known as waning gibbous, with 63% of its disc illuminated by the Sun.
If you observe both the Pleiades and the Moon (preferably with binoculars) as the night progresses, by 2:45am on 3rd you will see the Moon start to pass in front of the Pleiades and by 5am the Moon will completely cover this star cluster, as viewed from our position in the Mid West. Remember that the Moon will be 368,000kms. from Earth and the Pleiades lie 400 light years away i.e. 3,784,200,000,000,000 kms. This is known as an ‘occultation’.

The Square of Pegasus remains high in the SE, with Pisces and Cetus between it and the horizon. Deneb in the Summer Triangle is almost at the zenith, Altair is prominent, while Vega in Lyra is beginning to drop westward. Though the upper part of Sagittarius is still visible in the SW, the brilliant orange star Antares in Scorpius has set. Further west, dim constellations of Ophiuchus, Serpens and Hercules are setting earlier. In the north, Ursa Major is low in the sky and bright Arcturus is hovering above the NW horizon. Yellow Capella is still high in the NE and the W-shape of Cassiopeia is higher up. The constellation Andromeda rides high in the eastern sky, to the left of the Great Square, and contains the furthest object visible to the unaided eye, the Andromeda Galaxy, M31. What should grab your attention this month, if viewing from a darker sight, is the glorious glowing band of the MilkyWay running SW through the zenith to the NE.

On the 1st Jupiter will be 13º above the horizon at 8pm and will shine quite brightly at — 2.16 magnitude, but by 10pm it will set. As the month progresses Jupiter will gradually decline so that by the 30th it will only be 4º above the horizon at 8pm. Venus will be above the horizon before the Sun and on the 1st this will be at 4:40am when it will shine brilliantly at — 4.32 magnitude, with just 7% of its disc illuminated by reflected sunlight. Mercury will lie very close to the Sun during September and too risky to try to observe. As with Venus during Sept. we give our usual warning: (Warning: do not use a telescope or binoculars with the Sun above the horizon — instant blindness will occur).

Mars will be back in our night sky and at 23:30 on the 1st if you look just above the NE horizon about 7º east of the very bright star Aldebaran in the constellation Taurus (the bull) you will spot it. It lies between the horns of the bull. If you have difficulty finding it try the night of the 3rd at 23:30 and look about 7.5º from the Moon (in the 7 o’clock position relative to the Moon). Observe mars through Sept. and note how far eastwards from Aldebaran it has moved.
Our Sept meeting in room 206, Mary Immaculate College, will have a talk by Phil Samways on ‘Astronomical influences on Earth’s climate’. Clear skies

Post Reply