"Another important occultation will occur in the next Saturday to Sunday night near 2:30 UT (i.e. on Easter morning)," advises J.Lecacheux on the PLANOCCULT mailing list: "The shadows of the big asteroid 22 Kalliope and of Linus, its 30 km satellite, will cross Near Orient and Europe diagonally, separated by 1094 km. Detecting Linus by occultation can provide a very accurate astrometric position, ten times better than the VLT or Keck Airy resolution, thus very useful to improve the satellite orbit. Only one previous successful occultation is known for Linus : when the Japanese observers caught both asteroid and satellite from the region of Tokyo on 2006 Nov.07. It allowed us to revise down the diameter of Linus from 38 to 30 km."
Here are more maps of Kalliope's path. According to Lecacheux, the 40 km path of Linus "will fly over Syria, w.Turkey, n.Grece or s.Bulgaria, all the states of former Yugoslavia, n.e.Italy or s.Austria, Switzerland or s.Germany, n.e.France or Belgium, and finally s.England and Ireland. Assuming 50 km as '1 sigma' accuracy of the Linus ephemeris relative to Kalliope, the probability of positive occultation should be 15 % for any observer staying at the middle of the Linus track [...]. For example this probability should be 7.5 % from Brussels, Bern or Paris." The path of Kalliope, 255 km wide, will be centered 500±180 km "SSW from the Linus centre line. It will cover a part of Jordania and almost whole Israel, s.Greece (Crete and Peloponnese), a part of s.Italy, and finally a large strip running across the south and west of France."
Lecacheux is a bit pessimistic, though, in his circular from yesterday, noting two circumstances that "will keep the situation far from idyllic. 1/ The bad weather now expected from many regions; 2/ The faint drop predicted, only 0.16 magnitude. The observation itself will be quite easy, even with modest telescopes and despite lunar vicinity, as the combined magnitude of the target (asteroid + star) will be V~10.7." Analyzing the measurements will be diffucult, though, and Lecacheux has an "advice: recording a two minutes dark sequence (with the telescope covered) just after the occultation, then subtracting at processing stage to every video image the so obtained 'mean dark pattern', will boost by a factor ~2 the SNR of a Watec 902x camera. This is an efficient way of improvement."
In other news Arthur C. Clarke has been laid to rest in Sri Lanka today. • More results from Hinode have been published, • auroral activity may be up a bit due to the season, • and the last Hubble Servicing Mission may face delay because there aren't enough external tanks ready. • Readers should also be aware of repeated misleading meteor 'recommendations' from one (otherwise o.k.) website.
• The particularly early Easter Sunday this year (in the western world, that is) should make us all ponder the complex rules that actually contradict astronomy one year in ten! German readers find more here or here - fortunately there are able online calculators available that obey to all the church math. • And if that's all too much, here's a celestial Easter Bunny ...