The Eta Geminorum Graze - Apr 9/10, 2011

This beautiful graze happens on a Saturday evening at 9:44pm PDT, and is the most spectacular graze from California in over 10 years, since the Aldebaren graze (clouded out!) from Markleville in 1998. There will be several expeditions of amateur and not-so-amateur astronomers making observations. I and my little group plan to join a team organized by Fred ___ from Stockton. He's laying out stations along Escalon-Ballotta Road just north of Farmington. The prime location is right on the predicted northern limit as can be seen from the predicted profile with past occultation timings plotted in blue and purple. The Kaguya spacecraft data closely follows the observed occultation data and show that the profile is flat for our location and promises many timings. The star is a known and challenging visual binary, with the 6.2 mag secondary almost due east of the primary. From our graze position angle, the 6.2 secondary will be slightly south of the primary, meaning it will not be possible to watch the 6.2 star graze as that will only be possible while the much brighter 3.5 mag primary remains unocculted. Here's the prediction sheet.

The star is actually an interesting triple star. It's a spectroscopic binary with a companion that has an 8 year period and is far enough away from the primary to enhance slow occultation events. The primary is red giant and a semi-regular variable with a ~250 day period, varying from V=3.15 to V=3.9. It is also a visual binary, with the 6.2 magnitude companion a famous test for splitting binaries, as its only 1.8" separated. The 6.2 companion is south of the primary for this graze, and will be difficult to see it's D and R before and after the main graze. Careful video may show the slight dip in brightness when it disappears.