Public Open Nights at the Institute of Astronomy : 7th November 2007

Institute of Astronomy http://www.ast.cam.ac.uk & Cambridge Astronomical Association http://www.caa-cya.org/home/index.php Any comments or suggestions please to Carolin Crawford [email protected]

This week’s fascinating fact: We all know it’s the winter solstice coming up on 22nd December, but did you know that the shortest afternoon occurs during the next week (13/14 December), with the shortest morning not occurring till a couple of weeks later (30 Dec)? You might have noticed this in previous years, in that the sunset starts getting later again a couple of weeks before the sunrise starts getting earlier. The explanation is complicated, but it’s all related to the fact that the Earth goes round the in an ellipse rather than a circle. Perhaps surprisingly, the Earth is closest to the Sun during our winter, and thus moving at its fastest in its orbit. This means it has to rotate just that little bit further to get to when the sun is directly overhead again each day. The net effect is that the Sun isn’t precisely overhead at noon on every day of the year – in fact sundials only tell the correct time four times a year. The correction between the sun and official clock time is known as the equation of time, and it changes fastest at the winter solstice. The situation is compounded by the fact that the Earth rotates about a tilted axis, which means this effect is even more pronounced at lower latitudes than Cambridge.

This week’s talk : Zoe Leinhardt is telling us about Things that go bump in the night: the life of an asteroid Next week’s talk : Dan Zucker will be Building galaxies on our doorstep

Goodbye to Comet Holmes, which has put on a good show for us; it is now fading and can only really be seen through binoculars or a telescope. It appears as a faint, diffuse cloud to the lower right of Mirfak, the brightest star in the of Perseus (its approximate position is shown as the grey circle on the map left).

Venus is S unmissable in the s early morning (ie before 6.30am), as a brilliant bright star low in the SE. It will be by the moon tomorrow morning. By then Mars will be over high in the West; half- way between Mars and Venus lies Saturn, just under the constellation of Leo the Lion. The map (right) shows the sky for 6.30am tomorrow (6th December) morning.

There are only a few early evening Iridium flares visible from Cambridge during the next week: Day Time Altitude & Direction 06 Dec 17:13:34 59° NE 07 Dec 17:07:27 60° NE 11 Dec 16:48:09 67° ENE For more details look at www.heavens-above.com

Targets we intend observing tonight (weather permitting, of course): Coming up to new moon now, so the skies are nice and dark * Mars (finally) * The variable star Mira, and the eclipsing binary stars Zeta Auriga and Algol * Mirfak, the brightest star in the constellation of Perseus, and its surrounding open cluster Merlotte 20; also the in Perseus, and the and Pleaides open clusters in the constellation of Taurus. And while we’re nearby, I’m sure we’ll take a last look at Comet Holmes * The spiral galaxy M77 * The planetary nebulae M1 (the Crab Nebula) and M97 (the Owl Nebula) * The NGC 2419

Chart of the night sky from Cambridge for 8pm on Wed 5th December (taken from www.heavens-above.com)

So while we bid adieu to the comet, we can say a warm hello to Mars – unmistakable as a bright orange object to the East in the early evening, crossing to more overhead and SE during the night. It’s going to continue to get brighter as we approach closer to it throughout December.

And finally, a site map to help you find your way back to the car in the dark!

Gravel car park

Public observing happens here

Enter the IoA here for the talk

You have probably parked here

suggested route back to the car park ; follow the red rope light which marks your path back to the road.