Chuck: One of my "go to" websites for nighttime viewing conditions is the U of WYO site in the link below. Click on the SLC link and you get data from the latest sounding balloon. Balloons go up twice a day at 0 and 12 Zulu time which is 6am and 6pm MDT. Of major interest is the Precipitable water [mm] for entire sounding: 12.97 at the bottom of the page. At a half inch or less (12mm) the air column is dry enough for some deep sky viewing of external galaxies. 8mm is rare during our monsoon but it happens and it's spectacular. at an inch (25mm) the air is so full of water that we will be dodging thunderstorms and the viewing is poor. I also look for layer in the sounding that have RELH% of 50 or more. even in an otherwise dry sky this layer is moist enough for the hygroscopic dust to start picking up water, forming droplets, and degrading the viewing. This usually manifests as hazy rings around brighter stars. People often mistake this for dew on their optics but if you look through a warm pair of 10x50s you will see the same rings. That tells you the stuff is in an air layer above you and not on your secondary mirror. DT http://weather.uwyo.edu/upperair/sounding.html From: Chuck Hards <chuck.hards@gmail.com>
To: Richard Tenney <retenney@yahoo.com>; Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Monday, August 18, 2014 6:58 AM Subject: Re: [Utah-astronomy] Bright object LOOK NOW!
I saw another weather balloon this morning while observing Venus and Jupiter, this one even brighter than the one last week. Amazingly bright. I think the sun-balloon-observer geometry must be just right for me this time of year, and I'm very close to the airport, where they are released. I've seen them going up in the morning on my way to work, apparently it takes about an hour for them to reach peak altitude and burst. _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
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