One magnitude is a factor of 2.512. What I meant when I indicated I did not think this a serious error is that a simple orientation change in a satellite (whether due to its intrinsic orientation, or your position) could make it change dramatically. Take a look at the information for iridium satellites and looks what happens with a slight change in your position on the earth. Now I'm no expert in satellites, having just come to this type of observing in the last few months, but it seems from what I've been seeing that several magnitudes change can easily occur just from one solar panel catching the light just right. On Halloween night we saw a passage of ISS that was predicted at something like -2 mag. As usual, I had a telescope set up in front of my house to show the sky, in this case the moon, to the passing ghosts and goblins...and their parents. When it came over it flashed, in a matter of a couple seconds, to brighter than -4 mag. and I estimated it at -6 as we could see shadows. Lots of witnesses, in fact all the trick-or-treaters stopped to watch with moms and dads in tow. It had a metalic blue color too. But this flash, like and Iridium flash, lasted only a few seconds. So do we call the inability for Heavens-Above to predict this flash a serious error? I wouldn't. With the frequent changes in attitude of these things I'm amazed Chris Peat does as well as he does. I am working on getting video of ISS + STS and I will pursue any opportunity regardless of 'predicted' brightness. Now if you are _constantly_ experiencing differences like these you may want to be sure of the coordinates you are using and/or the offset from the database position from H-A. I just changed the site I was using for my predictions and it did make a noticable difference. -Rik ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Mon Apr 23 2001 - 12:40:35 PDT