Once again, Kurt, you've proven your worth. ;-) Thanks - I appreciate all the info. It helps a lot. Kim -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Kurt Fisher Sent: Sunday, September 02, 2007 8:21 PM To: utah-astronomy@mailman.xmission.com Subject: RE: [Utah-astronomy] Aurigid report Kim asked:
Is there a specific technique for estimating meteor brightness?
Kim, As a general rule because estimating meteor brightness is so subjective and imprecise, the official IMO counting method does not use meteor brightness as a parameter. The IMO limiting magnitude charts are used to estimate sky brightness (NELM or naked-eye limiting magnitude) in the observing FOV. Since you see fewer meteors in a brighter sky, the NELM information is used to normalize the raw real-time meteor flux to a ZHR under an ideal sky at about mag 6.2. The IMO has the 30 charts of their limiting magnitude areas well hidden on their website: http://www.imo.net/visual/major/observation/lm These charts, in an easier to use format, can also be found at: http://obs.nineplanets.org/lm/rjm.html Before the invention of the Sky Quality Meter ( http://www.unihedron.com/projects/darksky/ ) I used the IMO limiting magnitude charts to estimate ZLM during general observing. I still ocassionally use them for NELM (naked-eye limiting magnitude) estimates for off zenith fields. Tke Sky Quality Meter only works on the zenith. The IMO limiting magnitude method is a star counting game. How many stars can you count in the defined region - usually about 5 x 8 degrees? Count the stars and then look up the limiting magnitude in the table. The fields were charted carefully to yield 0.1 magnitude intervals. The system was created by professional astronomer Alistar McBeath. (If you want a humbling reminder of how age dims visions, do a count-off with your 9 or 10 year old children or grandchildren.) As you can see on the IMO Live Count page, the observers look at and count in the region of their 35-40 deg diameter for normal vision around a constellation - AUR in this case. ("SPO" on the reporting form means sporadics seen in the FOV.) For ZHR counting purposes, anything you can see counts as a hit without regarding to magnitude. IMO observers provide supplemental notes on the magnitudes seen, but these are not used for modeling purposes. Estimating meteor magnitudes is too subjective and imprecise. The limiting magnitude charts are used to determine the NELM in the observing field. As a practical matter you pick an LM field about 20 degrees off the radiant and center your observing for a 20 deg radius (40 deg diameter) around that LM field. But you can also use the LM reference stars to estimate the brightness of a particular meteor. The IMO Meteor Live Count ( http://www.imo.net/live/alpha-aurigids2007/ ) normalized the observed rate at 112 ZHR - basically close to Vaubaillon's prediction but way lower than Jenniskens's 200 p/h prediction. The NASA Ames Aurigids Mac page has a number of good photographs ( http://aurigid.seti.org/ ) as does Chris Peterson's (a retired professional) meteor cam website ( http://www.cloudbait.com/science/aurigid2007.html ). On Cloudy Nights, Chad Moore - the Park Service light pollution guy - reported a max real-time flux rate of 60 p/h with an peak report time of at 5:15 AM UTC from Bryce Canyon. This is similar to the ~42 peak flux rate and same peak time reported by the NASA Ames Aurigid Mac project. Other amateurs in internet reports (including myself) saw a different peak near 5:45am. Chris Peterson's meteor count records two peaks - one at 11:20 UTC and a second at 11:40 UTC (5:20am and 5:45am) at around a real time flux rate of 70 p/h each. I saw a max rate of 50 p/h from the Moon washed out 3.5 ZLM sky at Little Mountain centered 2 minutes off the predicted peak of 11:37 UTC (5:37 am MDT). Total count was 17 between 5:15am to 6:00am - capped by a nice v0-1.0 mag fragmented three part bolide at 11:39 UTC. The 11:39 UTC bolide was very similar to the 1998 image shown in your September copy of Sky and Telescope at page 56. Really a very pretty but short shower, a nice night, and a good 3rd quarter Moon - followed by an really impressive sunrise featuring a bright Venus. All in all a great night out. I'm still typing up my notes on this one and will have a further report in a separate webpage in a few days. The shower has the usual diminished expectations quiping associated with it - which is intended as a general observation and not as a negative comment directed at this listserv. The RV and lawn chair types at Little Mtn griped that "That's all it was. I got up at *@$# 4:00am for that! What a disappointment!" Instead of living in the here and now and taking life's events for what they have to teach, many continue to measure things against a some distant once-in-a-lifetime event - that "Leonid shower that I saw a few years ago. Now that was a shower!" - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.utahastronomy.com ______________________________________________________________________ This e-mail has been scanned by Cut.Net Managed Email Content Service, using Skeptic(tm) technology powered by MessageLabs. For more information on Cut.Nets Content Service, visit http://www.cut.net ______________________________________________________________________ Internal Virus Database is out-of-date. Checked by AVG Free Edition. Version: 7.5.484 / Virus Database: 269.12.1/963 - Release Date: 8/20/2007 5:44 PM Internal Virus Database is out-of-date. Checked by AVG Free Edition. 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