ASTRONOMY IRELAND MAILING LIST - www.astronomy.ie (The all-Ireland astronomy club, magazine and Shop) --------------------------------------------------- 1. Terry Moseley provides the following information about an asteroid passing in front of the star 31 Piscium (mag. 6.4) as seen from most of Ireland on the night of July 20/21 (Tuesday night). This is an extremely rare event and so well worth watching. The star will appear to vanish for just a few seconds as viewed in anything from a pair of binoculars or even a small telescope. The star is 30 degrees up in the East and the Sun is 16 degrees below the horizon so morning twilight will barely have begun. 31 Piscium is only 7 degrees (one field of view of our 10x50 binoculars) to the lower right of Algenib (the bottom left star in the Square of Pegasus) so any good star map will show it. And do try, even if you only have binoculars. Even video camera owners may be able to zoom in enough to show the star. There is a map showing the expected track at: www.asteroidoccultation.com/2004_07/0721_773_1842_MapE.gif but everyone in Ireland should watch in case the track is slightly off but also because satellites of asteroids have been found in this way. To this end even if you do not see the star disappear at the appointed time then this fact is very important and the start and end time of your watch should be reported. This would be an ideal project for those of you who have bought Philips ToUcam webcams from us recently. You can get exact time signals from the speaking clock by dialling 1191 (in the Republic of Ireland) even on your mobile phone and record it on to the sound track with your webcam for analysis later. Here are Terry's comments:

1. Further to last email, the asteroid (773 Irmintraud) is moving from SSE to NNW, so the track actually enters Ireland at the SE Coast, and exits at Sligo/Mayo.

The exact predicted central track over Ireland is as follows, with times in UT. Add 1 hour for BST ! ! !

Longitude Latitude Time (UT) Long. 5 deg 0m 0s W; Lat. 51 deg 14m 03s N; 01h 19m 03s. Long. 6 deg 0m 0s W; Lat. 52 deg 03m 33s N; 01h 19m 11s. Long. 7 deg 0m 0s W; Lat. 52 deg 49m 54s N; 01h 19m 19s. Long. 8 deg 0m 0s W; Lat. 53 deg 33m 23s N; 01h 19m 25s. Long. 9 deg 0m 0s W; Lat. 54 deg 14m 14s N; 01h 19m 32s.

The nominal track width is 112km, with an uncertainty (1 sigma) of about 40km either side of the track.

The following towns are near the centre of the track (SE to NW): Wexford, Enniscorthy, Carlow, Tullamore, Moate, Roscommon, Charlestown, & Ballycastle (Mayo).

Dungarvan & Galway lie just W of the predicted limit, and Dublin & Sligo lie just E of the predicted limit, but all four cities are within the uncertainty limits, so it's still worth observing from there.

For those of you who have never observed a similar event (which is most of you!), you WON'T see the asteroid at all, unless you have a very big telescope, or CCD imaging - it's magnitude 13.8, and the sky isn't totally dark at that time! So it will be an 'invisible' object, moving across the sky, which will, if predictions are correct, pass in front of a 6m.3 magnitude star, making it disappear. If you are on the centre of the track, the star will suddenly disappear for up to 10 seconds (if our assumptions of the diameter of Irmintraud are correct). If you are off centre, the duration will be less, down to just a fraction of a second if you are right on the edge of the track.

So you just keep observing, or imaging, the star, starting preferably 10 minutes before the predicted time, and observe/image continuously until 10 minutes after the predicted time. If you can't manage that length of time, concentrate on the predicted time +/- 5 minutes.

Record the time of disappearance & re-appearance as accurately as possible. Be prepared for the possibility of a 'double disappearance & re-appearance', which could happen if the asteroid is a close binary, or even hour-glass shaped and you lie a bit off the centre of the track. This is where continuous imaging is best - it will record all fluctuations in light. If you just have one stopwatch, you can only record 2 times (use the 'stop' & the 'elapsed' or 'lap' time functions - and practice beforehand!).

If we get a series of accurate timing from various locations we can determine the size & shape of the asteroid to a high degree of accuracy. Do have a go - after all, the star will be visible even in binoculars! If you are using binocs, it will be MUCH easier if you mount them on a tripod. The star is also designated 31 Piscium, and it lies 0.5 deg N of 32 Psc (mag 5m.7), which itself lies 1.8 deg NNE of Omega Psc (mag 4).

REMEMBER - it's at about 02.19 BST. Be ready to observe no later than 02.10 BST!

See www.asteroidoccultation.com for more details also, and do email us if you try to watch, even if cloudy! 2. NAKED-EYE SUNSPOT Seamus Bonner in Dublin reports seeing 4 large sunspot groups today (Saturday) with one of our Celestron Firstscope 80EQ telescopes fitted with AstroSolar filter. The new 4th sunspot is huge and has just rotated in to view. If it's clear take a look - this sunspot is sure to be big enough to be seen with the naked-eye (protected by AstroSolar filter that is! NEVER LOOK AT THE SUN OTHERWISE) as it rotates more in to view in the coming days. If it's cloudy check it out on the SOHO website: http://sohowww.nascom.nasa.gov/data/realtime/mdi_igr/512/ and click on the image for an even bigger image. This sunspot should be on view for 2 weeks so if you want to view it by eye, binoculars or telescope call the Shop to order your AstroSolar filter. 3. MISCELLANEOUS I.S.S. continues to blaze across the sky for the coming week. The times to see it on Saturday night are 10:46pm and 12:21am. For the times to see it every night until July 24 call our Newsline on 1550-111-442 after 12noon each day for the time to see it that night. Virtually all of the GR17 Public Lecture 'FREE tickets for young people (including students)' have been allocated. There are only 4 left for Monday and 1 for Friday if you know anyone interested who qualifies? Our thanks to the organisers. Everyone else can book tickets on www.gr17.com where you'll also find details of the July 19 & 23 talks. Note that Stephen Hawking's paper about black holes (correcting his 1976 work) is on Wednesday and with literally hundreds of media reports already on the net (do a search!) it's likely to make the news that day as the great man speaks in Dublin. (Note that this paper is part of the professional scientists' conference and not a public lecture by Hawking but there is an abstract of his paper at www.gr17.com if you can understand the jargon). While Lecture mania sweeps Ireland I note that very few of you have BOOKED for the next Public Lecture in Dublin, that by Alan Fitzsimmons who designed parts of the Cassini-Huygens probe now in orbit about Saturn and due to start its historic landing on Titan on Christmas Day. "TITAN BLINKS" is on August 9 in Dublin City University and IS organised by Astronomy Ireland. We are very lucky to get someone who has 'touched' the probe that is now at Saturn so go to www.astronomy.ie/lecture0408.html and click the link to reserve your seats NOW (then pay at the door on the night, only 5euro, that's 4 times less than the GR17 talks so bring a few friends!). Don't miss this one! Click today! Star-B-Q, the highlight of our Summer Programme is on Friday August 13. Details and online booking for Ireland's biggest annual viewing event at: www.astronomy.ie/sbq.html Regards and clear skies, David Moore, Chairman, Astronomy Ireland. Editor "Astronomy & Space" magazine. www.astronomy.ie Astronomy Shop: Tel (01) 847 0777 Mon-Sat