Re: default value for altitude, blue flash?, Iridial glints

Jonathan Wojack (
Sun, 09 Aug 1998 06:28:12 PDT

>As you can see by looking at the details below, I've been following 
>glints to lower and lower altitudes.  I would like to question the 
>limit for altitude provided by glint prediction programs (IRIDFLAR, 
>John's program, GSOC, and any others).  1 or 2 degrees is probably 
>reasonable.  Individual observers will want to adjust that upward as 
>required by local conditions, but bright glints are visible at very low 
>altitudes.  I would believe a fractional altitude, i.e., less than 1 
>degree, is possible.  In DC, in the summer, the Sun sometimes 
>at 20 or even 30 degrees altitude.  Typical urban or even suburban 
>environments can make observing at low altitude difficult.  We don't 
>to frustrate newbies, but observers with good horizons shouldn't be 
>bright glints. 
>Green flash?  Green glow?  Blue flash?  Well, how about a blue-green 
>I've seen dozens of variations on the green flash and green glow, many 
>Sunrise over the land horizon from my 8th-floor apartment.  I've seen 8 
>green flashes at a single Sunset from the air over a distant cloud 
>horizon.  I've seen green flashes "brighter than flashbulbs going off". 
>But I haven't had much luck with blue.  Sunday morning, I saw the 
>event I've ever seen.  There was just a little orange haze on the 
>horizon, brighter above the orient.  As the orange brightened, a bright 
>blue-green glow appeared as not much more than a speck at the lowest, 
>brightest point of the orange.  It brightened rapidly, rapidly 
>and overwhelmed.  If I reverse the time arrow for such an event, I can 
>easily see why it is so difficult to see such events at Sunset.  You 
>to protect your eyes till the last second or two.  Maybe expose only 
>eye to the bright Sun. 

Could someone tell me what this is all about?


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