PHEMU09 begins tonight: a campaign of observations of the mutual phenomena of the satellites of Saturn

"Tonight (Monday 2008 Dec.08) at 23:50 UT will begin 'the campaign of observations PHEMU09 of the mutual phenomena of the satellites of SATURN in 2008-2010'," advises J.Lecacheux and refers to the PHEMU09 homepage for all details and in particular the interactive software linked there. "While trying it, you will remark that because of the late rise of Saturn tonight, the total occultation of ENCELADE (S II) by TETHYS (S III) will be observable from eastern or central Europe, but not from Great Britain, France or Spain." So what can an amateur do? "The duration of the mutual phenomena, often several minutes, allows some time integration in order to improve the SNR (Signal/Noise ratio), typically between 0.2 and 5 seconds, depending on the diameter of the telescope. Good SNR, good camera linearity and excellent UTC datation of the mid-exposures are the main requirements.

A modern CCD camera mounted at the focus of a large enough mirror is optimal regarding SNR and linearity, but often may induce variable time delay (sometimes more than 1 second) caused by the digital link between the camera and the computer in a multitask environment. In contrast video integration may provide poor linearity and modest SNR." There is a need to hurry: "In reason of the date of the conjunction of Saturn with the Sun (2009 Sep. 18), only a small number of 'phemus' will be observable from a given location during the next 18 months. Even worse : In reason of the Earth-Saturn current geometrical configuration, actually 65 % of the whole set of observable events will occur during the current month of December 2008, and the next one, January 2009!!! So please don't await that better weather condescend to return! If you possess convenient equipment, your immediate cooperation wouldbe very valuable! As early as tonight, if possible!"

In other news there was a -18 mag. fireball over Colorado early on Dec. 6, also observed elsewhere and now analyzed: It is unlikely but not impossible that the event (which was widely reported) has led to meteorites dropping. • Meanwhile the unconfirmed claim of a major (though sub-storm-level) Leonids outburst in 2009 is spreading to the most unlikely places - please refrain from distributing these "news" any further until another dust trail-ologist agrees. He actually got the 2008 Leonids at least as good as the other theorist - and sees only a modest outburst in 2009. • There was a minor panic in the comets community when someone could not find promising Lulin in SOHO images and another one couldn't either - but it is there as was eventually found out, as this image shows.

• Venus is now dominating the evening sky, together with Jupiter and later Mercury as this animation nicely shows. The Moon, which was joining the planet pair on Dec. 2, Dec. 1 and Nov. 30 (as was reported in great detail in the previous two postings) returns to the evening skies only at the month's end. Also enjoy these rare image composites of Venus in the sky (another apparition). • Mira has brightened to 3.9 mag. and is now easy to observe. • As is, apparently the lost astronaut's tool bag now flashing in the sky and discussed here - but not in the official NASA video of STS-126 ... • And finally unusual video of Orion rising.

It is also time for a reminder that this blog is being joined by a Twitter feed since nearly two months: There have already been 1018 "tweets" to date, most of them either linking to all kinds of space news and pictures practically in the moment I found them - or reporting "live" from space events on the web, be it launch broadcasts, press conferences or webinars. The usefulness of Twitter is notoriously hard to explain to the uninitiated (and yours truly had resisted the temptation to join this social network for two years - until personally given the kick by the 'voice of Phoenix' at a conference) - but once you're using the service it becomes clear pretty quickly. There are three levels of engagement possible: just check the Cosmos4U Twitter website occasionally for new tweets ("RT" there means 're-tweeting' someone else's stuff, "@" responds directly to another tweet which is then linked at the bottom), open your own account and subscribe to a few feeds (those which Cosmos4U "follows" are recommended) but stay quiet yourself (as a "twurker" = twitter lurker) - or simply join the party. Since you chose whom to listen to (other than Cosmos4U, of course :-), it's practically spam-free ...