Saturday, June 7, 2008

Venus racing towards the solar limb, still caught today ...

Eight hours from now Venus will slip behind the limb of the Sun, a rare event that happens only every 8 years and only for a few decades (in the vicinity of the transit of Venus 'seasons'). As already explained here observing the "show" may or may not be possible at all, will definitely require special equipment and is very risky for both equipment and observer. Then again, Venus has been imaged again today, just 25 arc minutes from the solar limb and 13 hours before disappearing behind it! Owners of prominence coronagraphs and full-disk H-Alpha telescopes alike might give it a try, and if Venus won't show up at all in raw images which show prominences (there is a good one near the Eastern limb right now, and on June 4 a spectacular one was observed) and/or the chromosphere well, try to overexpose. Experiments with other (wider-band) filters are at your own risk, of course. Now here is the timeline, calculated with Horizons for Bonn, Germany:
  • First contact (Venus and Sun limbs touch) - 5:07½ UTC - solar elevation 14°
  • Mid-entry - 5:14 UTC - solar elevation 15°
  • Second contact (Venus gone) - 5:20½ - solar elevation 16°
The times should be approx. true everywhere. The solar diameter will be 1890.8", Venus' diameter is 9.6", and the whole disappearing act will last 13 minutes. For Europe the exit on June 10 will be at night as will be both entry and exit in 2016. In the years 2024 and 2032, however, both entry and exit will be observable from Europe each time, and especially in 2032, the Sun will be high in the sky for both events. One can only marvel at the technical possibilities in our hands then. Looking back, by the way, coronagraphs have been used during planetary transits before: Searching several data bases yours truly found a report about Mercury being seen against a solar prominence just outside the 1970 transit as is mentioned briefly in this paper on page 4. But no reports of successful or unsuccessful attempts to image Venus or Mercury in superior conjunction "anti-transits" at the solar limb with a coronagraph could be found.

In other news we have a nice video of a stellar occultation by (618) Elfriede, the young Moon on June 4 (again) and Jupiter on June 2. • A detailled - but controversial - paper on Holmes' outburst has been published in the ICQ while there are new thoughts on the origin of the Kappa Cygnid meteors and the famous fresh Carancas crater has been visited again, 8 months after the bizarre mini-impact in Peru. • A 5 gigapixel IR image mosaic of the Milky Way has been published in several ways: through a viewer and as a mega-poster at at conference. • And here is the ISS on June 3 (also reported internationally).

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