Four occultations in September 2012

Four unusual occultations were described in the September 2012 issue of Sky & Telescope, page 51. Here are links to the promised maps and further information:

• The naked-eye star Alpha2 Librae, magnitude 2.7, will be occulted for up to 2.6 seconds by the faint asteroid 363 Padua on September 16th along a path from Washington State to Florida — in the daytime! If the blue sky is especially clear and clean you may be able to see the star in a telescope, especially at high power, if you can get aimed exactly right. Alpha2 is the brighter star of the wide Alpha Librae pair. But can you hold it in continuous view well enough to tell an occultation from an atmospheric shimmer or an eye twitch? Some observers will surely try. Map and details.

• Far beyond the asteroid belt, the trans-Neptunian object 2000 PD30 may occult an 8.0-magnitude star in Aquarius for up to 6 seconds somewhere in the Americas, sometime around 6:38 September 20th Universal Time. . . plus or minus an hour or more! Objects that far away cast very uncertain occultation tracks, but timings of these events are especially desirable because these remote objects are otherwise hard to study.

Here's a map showing the very rough path and times, and finder charts for the star. Check for any late improvements to the predictions by watching the IOTA Yahoo discussion group, and ask about it if no one there brings it up. Or write to Steve Preston at his link on the map page.

If enough observers all across the hemisphere keep watch, one or more may get lucky. This cold outer object is estimated to be 75 miles (125 km) across.

• The Moon occults Jupiter on September 8th for central and southern South America in the daytime (around sunrise on the west coast). Map and timetable.

• The Moon occults Mars on September 19th — but again only for central and southern South America, and partly in daytime (in evening twilight for some of the Atlantic coast). Map and timetable.

Predictions for lots more asteroid occultations worldwide are at

To learn about today's asteroid-occultation timing world and join the party, see Worldwide Asteroidal Occultation Observations and Resources. Video is now the standard method. For information on video recording and time extraction, see the "Equipment" heading.

For human advice and help, join the International Occultation Timing Association (IOTA) Yahoo discussion group, say hi, and ask for help.

Here are results of past asteroid-occultation timing campaigns (in the "Results of Observations" box at top).

Free e-book: Chasing the Shadow: The IOTA Occultation Observer’s Manual (the preview page).

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