[BAA 00309] Regulus grazing occultation. 2007 October 7

[Rick]

BAA electronic bulletin No. 00309   http://www.britastro.org/

Early on Sunday morning, October 7th, the bright star Regulus will be occulted by the moon south of a line from Lancashire to Lincolnshire. Observers near that line will see a 'grazing occultation', where the star appears to 'graze' the northern limb of the moon: it may disappear and reappear several times as it passes behind mountains, crater walls, and valleys, on the limb.  Such events can be spectacular (although not as spectacular as southern limb grazes).  This will be the last grazing occultation of Regulus visible from the UK for many years.

The central graze track crosses south Lancashire, west and south Yorkshire, and north Lincolnshire.  Spode's Law dictates that it misses most large centres of population.  But in more detail, it crosses Lytham St. Annes (~05:35 UT), Freckleton, south Preston, south of Blackburn, north Haslingden, Rawtenstall, Bacup, Ripponden, north of Huddersfield, south of Wakefield, Askern, south of Thorne, Scunthorpe, Brigg, Waltham (Grimsby), and over the east coast south of Grimsby and Cleethorpes (~05:38 UT).  (N.B. add 1 hour to convert these times to British Summer time.)

The waning crescent moon is well placed for observation at about 30 degrees elevation in the ESE direction.  It will be only 14% sunlit and the graze takes place against the bright northern limb near the terminator, at cusp angle 7 degrees.  The Sun will be around 7 degrees below the horizon, so the event occurs in significant twilight.  The event may be visible in binoculars, but because of the above factors, a telescope would be a safer option.  Multiple events will only be possible in a narrow band from about 0.5km north to 1km south of the central track.  However, owing to remaining uncertainties in the lunar profile, some events may be visible up to 2km north of the centre line. Regulus has a significant apparent diameter and so, from previous experience, the disappearances and reappearances may appear to be gradual.

Because of the possibility of multiple events, observers wishing to make serious visual timings (to better than 1 second) will need a multi-lap stopwatch or a voice recorder linked to an accurate time signal.  Those with sensitive video cameras, camcorders or webcams may also be able to record the events, but will need an accurate method of time-stamping the video.  Serious timings would be welcomed by the undersigned, including any from just north of the expected zone (see above).  Accurate timings are valuable scientific data which can help to refine our knowledge of the limb profile of the Moon.

In order to see *precisely* where the track passes, you might like to click the following link, which displays a high precision track on 'Google Maps', at all zoom levels.  The opening screen is centred on continental Europe but it is a simple matter to pan to the UK and zoom in to any level:-

http://www.dangl.at/maps/2007/gr071007/g071007e.htm

This link is courtesy of Gerhard Dangl of the International Occultation Timing Association (IOTA).  The web page also has further details about the graze although the information is optimised for central Europe.  Please email the undersigned if you want detailed track coordinates, including OS map references for easier plotting, and a profile plot, for the UK.

Clear Skies,

Andrew Elliott

Occultation Coordinator, Lunar Section

[Tony G]

On Sunday morning when this occultation is happening, the Moon is placed nicely between Saturn and Venus.
Cameras at the ready.

Tony G