All eyes are on Comet Ison this weekend
TODAY’S the day then. The morning when we will know whether Comet Ison is going to be a real goer or not. Yesterday it zipped past the sun at a distance of 0.012AU – 100 times closer than we are – and if it survived that encounter should have emerged this morning as a very bright object.
When first spotted it was deemed to have the potential to outshine the moon but, as I predicted, expectations have been progressively downgraded since.
Nevertheless, it should be of Venus-like luminescence and readily visible in the pre-dawn sky, and to a lesser extent in the evening sky after sunset, giving double the opportunity to see it. This morning, and for the first few days of December, it will still be very near the sun so great care should be taken in looking for it, especially in telescopic or telephoto attempts at observation as catching a glimpse of the sun through a magnifying lens will have bad effects on your sight. (As Galileo discovered!) The sun will have risen at about 08.37UT today and will rise later every day until it flat lines for a few days from the 23rd at about 09.07.
Try to catch the last of the morning darkness from about 07.00 onwards for good views of Ison in the east-south-eastern sky during the first half of December. Its period on view will progressively increase as the month goes on but it will fade simultaneously so take advantage of any clear morning or evening sky from today onwards. Ison originated in the Oort Cloud, which forms a sparsely populated shell of largely water-ice material approximately a light year away from the sun, which no-one has ever seen but which is known to exist.
Though widely dispersed on the fringes of the solar system, this area of space contains not just billions, but trillions of objects, of which Ison was one. This comet’s brief visit to the system’s power centre will probably project it completely beyond the sun’s gravitational influence to languish in the even emptier arena of interstellar space.

That is, unless its nucleus has been reduced to dust as it rubbed shoulders with our parent star in which case none of what I have told you above will be true.
t Jim A Johnston would welcome suggestions for future topics for the Skywatching column. He may be contacted by e-mail at jimajo@btinternet.com