Occultation of a Bright Star by Asteroid (502) Sigune
01:19 BST Sunday 24th June 2007
Between 00:18 and 00:20 UT (01:18 - 01:20, local BST time) on the morning of Sunday June 24, the magnitude 14 asteroid (502) Sigune is predicted to occult the m (v) +4.9 star 74 Ophiuchi (SAO 123377, HIP 89918). The duration of the occultation is expected to be just 1.2 seconds at the centre of the "shadow" path. For this reason the prediction does not appear on the Occultation Section's list of UK events, where the limiting duration is 1.5 seconds. The short duration is due the asteroid's small diameter (of around 16km). This also results in a path that is not much wider than the asteroid's diameter.
However, because of the brightness of the star on this occasion, an observer equipped with nothing more than a pair of binoculars, and a stop watch, should be able to see the star wink out and come back on again very easily, if on the occultation path, and make a valuable timing of the moment when the occultation takes place.
The latest predictions seem to indicate that the path will cross the UK from east to west, hitting the mainland on the North Sea coast between Scarborough and Bridlington, in Yorkshire. The path then proceeds through York, Leeds, Huddersfield, Manchester, Warrington, and Chester to Aberystwyth, and leaves the mainland in Cardigan Bay. Remember though, that with small bodies such as Sigune, predictions as to where the occultation will be seen are not always accurate, and observers living a considerable distance north or south of the predicted path could pick up the occultation instead. So, this is a general appeal for as many members as possible to attempt to observe the disappearance of this fairly bright star in the early hours of Sunday morning, June 24. Like the National Lottery, you could pick up the top prize, and you alone may observe a very rare event. Worth a go? ---------- I hope so!
Please, if you do attempt an observation, and I hope you will, can you send me a short report, stating your name, your location and whether the star was occulted or not. A negative result is just as important, as it tells us where the occultation wasn't seen. In this way we can put limits on the actual path. If you can start a stopwatch at the moment the star goes out, and stop it later against an accurate time signal, or accurate radio controlled clock, so much the better; this will tell us when the event took place from your location. My e-mail address is: jonvran@aol.com.
74 Ophiuchi lies almost midway between Beta Ophiuchi (Cebalrai) and Theta Serpentis (Alya), near the Aquila border. It is the first bright binocular star to the east of the asterism in Ophiuchus, known once as "Poniatowski's Bull", consisting of the stars: 66, 67, 68, 70 and 73 Ophiuchi. The resemblance of this asterism to the chief stars of the Hyades, making up the face of Taurus the Bull, is remarkable; although the stars in Ophiuchus are much fainter.
A star chart showing the position of 74 Ophiuchi, and also the most up to date "Winoccult" generated path, computed by Steve Preston, are shown below.
 Occultation Shadow Path |
 Finder Chart for HIP 89918 |
Please have a go at observing this special event!
Report from Members of York Astronomical Society
5 dedicated members of the York AS turned out at the YAS Observatory on Saturday night/Sunday morning in an attempt to observe and time the predicted occultation of 74 Ophiuchi.
The sky was very cloudy with only the occasional view of Arcturus and Jupiter from time to time. However, just after midnight there was some general clearing and we were able to observe some brighter deep sky objects such as M13 and M57 with a 10" Dob, an 80mm F5 refractor, and some 10x50 and 15x70 binoculars.
We located the target star quite easily in all telescopes and binoculars, and as the minutes ticked by after 1am, we were hopeful of observing the occultation - if it lay on the predicted centre line.
However . . . . . . . . as the minutes slowly passed the clouds began to intrude on that part of the sky, and at 1:12am (BST) the star began to be obscured and was finally occulted by the clouds at about 1:14am (BST). We waited until 1:25 with no reappearance of the star.
Interestingly, we packed up and left just as light rain began from the offending thick cloud bank that had obscured the target star. A case of close but no coconut! I guess it was all in the timing. Hope you had better luck closer to the coast?
We would be interested to hear if you have any information about the observation of the occultation, and any times and locations of the actual track compared to the predictions, i.e. would we have seen it from York if the sky had remained clear for another 10 minutes?
Please keep us informed of any future occultations as we have a taste for them now.
Very best wishes and clear, dark skies
Paul Buglass, Chairman - York AS, York, UK. York Astronomical Society www.yorkastro.co.uk
