CDAA

Written by David Pugh

Dear CDAA Members

Hope you are all keeping well and have had a reasonable late summer. This coming Thursday at 7.30pm will be CDAA's September meeting. After a brief AGM it will be Members' Night with some five members giving short astronomy related talks. So, there should be plenty of variety. Hope you can make it.

In the night sky this month there is some improvement regarding the planets although some of the action is still in the pre-dawn sky. However, in my view, the evening night sky is at its best at this time of year with the Milky Way overhead (if you can get away from the light pollution!), and plenty of deep-sky objects to observe or image. Plus temperatures are still comfortable for observing without too many layers of clothes!

Mercury, (mag -1.1),the inner-most planet is at its best for the year, reaching greatest western conjunction on Sept 5. However, it is a pre-dawn object in Leo. Venus (mag -3.9) remains very close to the western horizon after sunset and will be difficult to observe despite its brightness. Mars, the red planet, (mag +0.6), lies in Gemini and will start to rise before midnight early in the month. Jupiter, king of the planets, (mag -2.4), lies in Taurus in the east, rising late evening at the start of the month and mid evening by month's end..

Saturn, the lovely ringed planet, (mag +0.6) is at opposition, (its brightest for the year) on Sept 8. It is located in Aquarius and can be observed for most of the night so do have a look. Although the rings currently appear almost edge on, this is a good opportunity to try to observe telescopically some of Saturn's smaller moons close to the planet that are sometimes lost in the glare of its rings. If conditions allow, increase the magnification of the eyepiece to darken the background sky a bit may help you to detect several of the inner moons. Titan, the largest and brightest moon in contrast is always easy to observe and it is often well away from the planet.

The ice giant Uranus (mag +5.7) is a mainly morning object in Taurus, lying south of the Pleiades star cluster. It can be observed with binoculars but you will need a telescope to resolve its greenish disc. Neptune (mag +7.8) reaches opposition on Sept 21 and lies in Aquarius. You will need a small to medium sized telescope to resolve its small bluish disc.

Comet C/ 2023 Tsuchinshan-ATLAS is unlikely to be on view from the UK this month unless it brightens dramatically but could become a naked eye object during October. However, comets are extremely unpredictable and sometimes do not survive their perihelion passage close to the Sun. Still nothing happening with recurrent Nova T Corona Borealis as of two days back when I observed the area with binoculars.

There will be a partial lunar eclipse on Sept 18. However, it all happens in the early hours from 01.41 - 05.47 BST, peaking at 03.44 BST. However, the Moon will only be 8.5% eclipsed so hardly worth the early hours effort in my view!

All of the deep sky objects and constellations mentioned last month are still on view, especially Cygnus the Swan riding high above us in the northern Milky Way, its principal stars forming the shape of a cross, hence its alterative name of the Northern Cross. In this Night Sky Watch I thought that I would cover a constellation that I have not referred to before. Cepheus the King. It lies in the northern sky above Cygnus the Swan, between it and Cassipeia the W- shaped constellation that represents the Queen i.e the wife of Cepheus. Its principal stars, of magnitude 2 and 3, form the shape of a house with a pitched roof.

Cepheus contains no Messier objects but does, nevertheless contain several noteworthy objects. Delta Cephei is a very famous cepheid variable star where the giant yellow star pulsates in a very regular period. It is the protype Cepheid variable, a class of star where each star's luminosity and period of variability are so precisely linked that they can be used as standard candles in the determination of distances in the local Universe, the first stepping stone in determining the size of the Universe. Another fascinating star is Herschel's Garnet Star Mu Cephei. This is a ruddy coloured star that William Herschel likened to the colour of a garnet. It is a red supergiant semi-regular variable star of mag 3.4 - 5.1 that, if placed where our Sun is, its surface would extend to beyond the orbit of Jupiter!

Mu Cephei lies on the northern edge of a massive but very faint emission nebula IC1396. It spans over 3 degrees across and is really a photographic object requiring a telephoto lens or small refractor to get it all in. It is sometimes wrongly called the Elephant's Trunk Nebula but this name actually applies to the small narrow dark nebula IC1396A on its western side. Lastly there is the fascinating Iris Nebula NGC 7023. This a blue reflection nebula surrounding a 7th mag star but surprisingly bright for this type of object, well worth observing or imaging.

Good Hunting and hope to see you Thursday. Should be a good meeting.

Best Regards

David