Observatory Logo


From: TerryMoselaol.com
Date: Sat, 17 Jul 2004 11:32:16 EDT
Subject: Ast. Occ, Sunspopts

Hi all,

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!

2. Huge Sunspots!  Wow! Do look at the Sun if you can do so safely - if you 
are not sure, DON'T! There are 4 large spot groups, and other small ones, now 
on the disc. One is just past the meridian, two are just approaching it, and 
the biggest of all has just come round the East limb. It's a whopper - mainly a 
single large very dark umbral spot & good penumbra - The umbra alone is 
comparable in size to Venus during its recent transit! Use a PROPER solar filter if 
you have one, otherwise project the image through the telescope onto a piece 
of white card held about 1 foot behind a low-power eyepiece. DON'T Look at it 
directly, or through any other sort of filter.
 
Good luck to all.

Terry Moseley










---------

Last Revised: 2004 July 19th
WWW contact:webmaster@arm.ac.uk
Go to HOME Page Home Page