See the International Meteor Organization calendar for details. http://www.imo.net/calendar/cal05.html#perseids http://www.imo.net/calendar/per.gif (Position of Perseid radiant for Jul 15 to Aug 25) and - NASA Headlines. The 2005 Perseid Meteor Shower (7/22/2005) http://science.nasa.gov/headlines/y2005/22jul_perseids2005.htm http://science.nasa.gov/headlines/y2005/images/perseids2005/skymap_north.gif and - Kronk's Meteor Shower Page - http://comets.amsmeteors.org/meteors/showers/perseids.html Jeremie Vaubaillon forecasts likely ZHR for many meteor showers. Here is his June 15 forecast for the 2005 Perseids - http://www.imcce.fr/page.php?nav=en/ephemerides/phenomenes/meteor/PER/2005Pe... "The expected ZHR is not expected to be higher than the annual activity (recorded by IMO), i.e. ZHR=100 /hr. From the above figure, the maximum is expected to occur on the 12/08/2005 at 3:54 UT (Solar longitude=139.478°)." In Utah, 8/12/2005 at 3:54 UTC corresponds to Thursday, 8/11/2005 at 9:54pm. On 8/11/2005, sunset is at 8:32pm, astronomical twilight is at 10:17pm, and moon set of the eight day old Moon is at 11:28pm. The IMO predicts a different time for the peak - 18:30 UTC on 8/12/2005, or around noon MDT on Friday, 8/12/2005. See discussion at the IMO calendar regarding uncertainty in the Perseid peak time. At sunset on Thursday, 8/11, Perseus is just below the horizon. Altitudes for eta Per to the nearest degree, which is a few degrees southwest of the radiant, on 8/11-8/12 are given in the following table, as well an adjusted expected meteor hourly rate. The ZHR is adjusted because the shower's radiant is off-zenith: MDT UTC Alt Adjusted ZHR 10pm 8/11 4am 8/12 14° 24 11pm 8/11 5am 8/12 19° 33 Midn 8/12 6am 8/12 26° 44 1am 8/12 7am 8/12 33° 54 2am 8/12 8am 8/12 41° 66 3am 8/12 9am 8/12 58° 85 (See the Appendix to this post for the computation converting ZHR to an meteor hourly rate where the radiant is off-zenith.) This estimated rate is not adjusted for the unknown decline of the shower in the hours after the peak at 8/12/2005 3:54 UT. My usual way of enjoying the Persieds is to sit either facing north towards the radiant or with my back to the radiant facing south. When facing south in previous years, many fainter widely dispersed meteors were seen on a broad arc. The arc traces a cone back to the radiant. I have prepared two alt-az charts, one north facing and one south facing. I use these to pass the time by roughly plotting meteors seen. These charts are for 1am MDT 8/12 (7:00 UT 8/12). http://members.csolutions.net/fisherka/astronote/finder/PerseusChart20050812... http://members.csolutions.net/fisherka/astronote/finder/PerseusChart20050812... (Right-click on the chart, save it to your desktop and then print to a full landscape page.) Enjoy - Canopus56(Kurt) ========================= Appendix - Conversion of ZHR to hourly rate off-zenith The zenith hourly rate is the rate observed when the shower is at local observer's zenith. The International Meteor Organization gives the following information regarding when the meteor shower's radiant is not on the observer's local zenith: "Table 1 gives the number of meteors an observer might expect to see at different radiant elevations if the ZHR amounted to the impressive value of 100. Now you can imagine what you will see with a radiant elevation of 10° if the ZHR is not as impressive as 100. Therefore, when planning your watch you should take care that the radiant will have a reasonable elevation for the whole watch. For several reasons the lower limit is about 20°. Table 1: Numbers of meteors visible per hour for a ZHR=100 shower and different radiant elevations h (limiting magnitude of 6.5m) h in ° | 90 | 70 | 50 | 40 | 30 | 20 | 10 n | 100 | 94 | 77 | 64 | 50 | 34 | 17 " Source: IMO. http://www.imo.net/visual/major01.html IMO Table 1 appears to follow a simple sin function - alpha = altitude of the radiant above the local horizon at a local time * pi() / 180 hr_alpha = zhr * sin(alpha) where hr_alpha is the predicated hourly rate at the selected altitude of the radiant above the local observer's horizon. ____________________________________________________ Start your day with Yahoo! - make it your home page http://www.yahoo.com/r/hs