Expert: Tom Whiting - 11/13/2008

Question
Time viewed: after 10:30pm, Nov. 12, 2008 from Glenville, NY (near Schenectady, NY) with the naked eye. Full moon with very large, vaporous ring, perfectly circular, around the moon. The moon is in the exact center. The ring is significantly far away from the moon. Proportion: If the ring is a dinner plate, the moon would be the size of a quarter. No stars are visible anywhere. What am I seeing? I have never seen anything like this before!

Answer
Hi Jeanne,
You are seeing the very common 22 degree halo around the bright moon, caused by ice crystals in the upper atmosphere (we had it here last night in Erie, PA too).  It's caused by thin cirrostratus clouds very high with it's ice crystals oriented preferentially.
See
http://en.wikipedia.org/wiki/Halo_(optical_phenomenon)
for this, and other atmospheric phenomena too.

Still rarer is the much bigger and dimmer 46 degree halo around the moon.  So next time, look for that ring too.
And the reason there were few stars visible was due to both light
pollution from the moon itself, and the thin deck of cirrostratus
clouds.
Cirrostratus clouds either precede a front, or sometimes come
after a front. So if you see a halo around the moon, and it's been
fair weather, you can generally expect stormy weather from 24-48 hours later because a frontal zone is approaching you.
The American Indians used this method for weather forecasting, and
we can do it today too.  If it follows bad weather, then you can generally expect fair skies the next day.
It also happens around the sun too, but it's a little harder to see
because you usually have to block out the sun with your hand, to see it.  So it's an atmospheric event, not astronomical event.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA

FOLLOW UP:
Opps...wrong URL..try
http://en.wikipedia.org/wiki/Halo_(optical_phenomenon)
Tom

Ok, that didn't work either, so try
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/ice/halo/22.rxml
tom

I'm having a horrible time with URL's tonight...tell you what, just
google 22 degree Lunar Halo ....and see what pops up.
tom

FOLLOW UP:
BTW,  since you are a homeschool mom, and I was a teacher too,
if you ever have any additional astronomy or science questions in general,  feel free to contact me directly at
bwhiting@velocity.net
if you wish.  And don't forget to teach your children the constellations
too.....it was Thomas Carlysle's complaint that rings down thru the
ages, "Why did no one teach me the constellations when I was a
child?"
Clear Skies,
Tom Whiting
Erie, PA