------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 1683 2001 Sep 06 15.05UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074 INTERNET: GUY@TAHQ.DEMON.CO.UK GMH at AST.STAR.RL.AC.UK WORLD WIDE WEB http://www.theastronomer.org ------------------------------------------------------------------- TITANIA OCCULTATION ON 2001 SEPTEMBER 8 Richard Miles: A very special opportunity arises next Saturday morning, when the third moon of Uranus, Titania, a medium-sized planetary satellite, almost 1600 km across, is predicted to occult the relatively bright Hipparcos star, HIP 106829 (V=7.2). Weather-permitting, the event should be visible from parts of western Europe and northern regions of South America. Positional details of the star are as follows: RA 21h 38m 14s Dec -14deg 54'36" (2000) At the time of the event, Titania and the star will be located only 14 arcsec from the limb of Uranus (3.7 arcsec app. diameter and V=5.7). Observational coverage should span the period 01:51-01:59 UT, with the expected mid-time as seen from western Europe = 01:55. Event Rating: Extremely Favourable, based on the accuracy of the astrometry, the brightness of the star, and the size of the planetary satellite. The maximum duration of the event is expected to be about 75-90 seconds. If a graze is seen then this may be over in a much shorter time interval than this. N.B. The star will dip in brightness by about 6.7 magnitudes (i.e. by a factor of about 400) and so will appear to disappear entirely if subject to a total occultation. Note that seen from the UK, the event takes place at a very low altitude above the horizon in the range, 5-12 deg. The Moon is situated well away (81 deg) from Uranus and so will not interfere with observations. However, seeing conditions may be difficult owing to the degree of extinction in the light of the star and the effects of poor seeing given the low altitude above the horizon. Observers should check for any obscuration in their horizon earlier in the night or before. The approximate azimuth will be 230 deg (i.e. close to south-west in direction). A convenient way of doing this is to observe eta Ophiuchi at 21:25 UT, when it will occupy a very similar altitude/azimuth as that of the Titania event some 4.5 hours later. Observers equipped with telescopes of 20 cm aperture or greater may wish to monitor this extremely close appulse / occultation. It will be important to be able to resolve the light of the star from that of close-by Uranus. Accurate timings referenced to a suitable standard are sought and if possible any estimates of changes in brightness of the star in the event that Titania has an appreciable atmosphere. Times should be recorded at least to the nearest 0.5 second preferably more precisely. Even better will be a video-recording possibly using a filter. Use sufficient optical magnification/aperture so as to separate the image of the star from that of Uranus. A 5-degree finder chart from Guide 7.0 is at: http://www.ast.cam.ac.uk/~baa/chart.gif A plot showing the path of the shadow across the Earth together with a small finder chart is at http://www.ast.cam.ac.uk/~baa/titania.gif Guy M Hurst