Feb. 19, Jurgenstock: Sirius, the brightest star in the night sky, is a Canis Majoris = HIP 32349 = SAO 151881, spectral type A0mA1.  The remaining light of Sirius A is likely to render invisible the 8th-mag. white dwarf companion, Sirius B.  The asteroid is named after Jürgen Stock, a Venezuelan astrometrist who died in 2004.

This unusual occultation of the brightest star in the night sky will occur around 10:30pm MST on Monday evening, February 18 (but on Feb. 19 U.T.).



If you are the lucky one to have the path go over your location, the star will fade over a period of several tenths of a second, probably will not disappear completely, and then will recover its full brightness over another several tenths of a second. But it could be a shallow drop in brightness lasting perhaps only half a second, if you are near the edge of the path. The angular diameter of Sirius has been measured to be 0.0060”, so theoretically, with Jurgenstock’s diameter just a little more (0.007”), at the actual center of the shadow, the start of the fade to the recovery to full brilliance should take 1.8 seconds, with the star completely occulted for 0.2 seconds. But the asteroid may be a little larger or smaller than predicted, and it’s likely to be irregularly-shaped, so there is a good chance that even at the center, the star will not completely disappear. The 1-sigma error in the time is 10s, so you should record for at least 30s before and after the predicted time for your location; to be sure, especially to compensate for any timing errors, it would be best to record from 60s before to 60s after the predicted time. Occult Watcher will tell you the predicted time for your location.


Current methods for recording occultations are described at http://occultations.org/observing/ , especially the “Observing Basics” and “Recommended Equipment” sections, and after the event, “Reporting Observations”. For the latter, most will have no occultation and can just report the coordinates of their observing location; we’ll help anyone who records the fading of Sirius by Jurgenstock. A visual observation of this event is better than nothing, but it’s best if you can record the occultation, even if only with a cell phone video. We have some information about using cell phones for recording the 2017 total solar eclipse that could be used for the Sirius occultation at http://occultations.org/eclipse2017/smartphonesimple/ - it tells about simple mounts and small magnifiers, especially useful with a photographic tripod. But you can also record the occultation with any camera that has video capability. If you record with a telescope, even a small one, you should try to prevent, or lessen, saturation of Sirius’ bright image, by covering part of the aperture and/or by defocusing; experimenting some night before the event will help for that. It would be best to use two cell phones, or one plus a video-capable camera, with one cell phone used to provide accurate audio time signals based on GPS, such as with the “Time the Sat” app for Androids and “Emerald Time” for iPhones. Another useful app is “GPS Test” that can be used to determine your geographical location; that can also be done with Google Earth, as long as you observe from a location that can be precisely located with it. If you have one of the old TimeKubes or another shortwave radio, WWV remains a good time base.

David Dunham, IOTA, dunham@starpower.net, phone 301-526-5590.
Occultation of Sirius by (4388) Jurgenstock the evening of February 18 2019
Large shift from the previous prediction
Notes by ; Bill Merline and David Dunham
The path of this event has now shifted significantly.  Sirius is a multiple star system.  Although the main star, Sirius A, is much brighter than the other stars, the center of mass for this star system has a significant offset from Sirius A.  And, unfortunately, the Hipparcos data only provides a position for the center of mass.  Today, thanks for John Irwin, we finally tracked down good estimates of the offset of Sirius A from the center of mass.  The path of the event for the Sirius A (mag -1.5) is now predicted to cross Southern Argentina, Southern Chile, Central America, and the Caribbean.
Steve Preston
More static maps of path