Starship Asterisk*

http://apod.nasa.gov/apod/ap081116.html

So, let's understand this: The view is to the east and the Sun is setting in the west behind the observer. Parallel light rays from the Sun were refracted by Earth's atmosphere so that they appear to converge at infinity in the east. Correct?

I remember seeing something similar but opposite in western North Dakota. We were driving east at about 1 AM (in July) and observed bright rays of what we took to be Sunlight radiating upward from the northern horizon. At first we thought it might have been light pollution from a town north of us, but couldn't decide which one it might be. Besides, ND doesn't have all that many cities large enough to produce what we were seeing. We finally decided that we were seeing Sunlight reflected (diffracted?) off the polar ice and refracted through the atmosphere.

zbvhs wrote:So, let's understand this: The view is to the east and the Sun is setting in the west behind the observer. Parallel light rays from the Sun were refracted by Earth's atmosphere so that they appear to converge at infinity in the east. Correct?

Not exactly. First, you're not seeing light rays, you're seeing the shadows of clouds. And there is no refraction involved. The shadows are actually pretty much parallel to each other; they appear to converge because that's what parallel lines do as they get more distant (think railroad tracks).

It isn't uncommon when you see anticrepuscular rays like this to see crepuscular rays in the west as well. That is, you can follow the shadows from where they converge in the east (the antisolar point), up and overhead, where they are spread out, and back down to the west where they converge again, on the Sun (which is likely to be behind the clouds, but isn't always).

As to your second paragraph,
At 1am in North Dakota Light radiating from the northern directions could have been the Aurora or noctilucent clouds

Today's APOD 2008 Nov 16 "Anticrepuscular Rays Over Colorado":

http://antwrp.gsfc.nasa.gov/apod/ap081116.html

... and "Anticrepuscular Rays Over Florida" by way of APOD and a stint as my wallpaper:

http://antwrp.gsfc.nasa.gov/apod/ap060917.html

... and "Anticrepuscular Rays Over Horseshoe Canyon" also by way of APOD:

http://antwrp.gsfc.nasa.gov/apod/ap030226.html

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Three more titles like that and you could start your own chain of theme parks.

BMAONE23 wrote:At 1am in North Dakota Light radiating from the northern directions could have been the Aurora or noctilucent clouds

crepuscular http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... repuscular
noctilucent http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... octilucent
aurora http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... rch?aurora

apodman wrote:Three more titles like that and you could start your own chain of theme parks.

Then, there is the rival park, APOD: 2005 August 31 - Crepuscular Rays Over Utah

I knew this image looked familiar....

http://antwrp.gsfc.nasa.gov/apod/ap011030.html

bystander wrote:Then, there is the rival park

Yes, strictly "anti", like placing the Scorpion and the Hunter on opposite sides of the sky because they don't get along.

Gee whizz, every time I've ever driven west to Boulder or its environs, the horizon has been well up in the sky over some magnificent Rocky Mountains. Pray tell, how did you ever make them disappear?

Ok, I've seen both types before, but can anyone tell me if there is a name for those streaks in the sky that look like black or just slightly darker than background streaks?

Kind of like anti-anticrepuscular rays?

I've seen them in the upper midwest over the past 10 years, even taken pictures where they kind-of show up. Very hard to describe as they are not usually set in a geometric pattern. In fact they seem to be shadows of some (now) unseen flight vapor left earlier?

I'll look for some of my pictures and try to post.

Hello reboots,

Yeah, I know what you mean. They even look lower than what one would expect from a vapor trail. ICBW but I, not being familiar, attributed the phenom to vapor-trail shadows landin on a rising lower but warmer layer of water vapor.

reboots wrote:Ok, I've seen both types before, but can anyone tell me if there is a name for those streaks in the sky that look like black or just slightly darker than background streaks?

(snip)

A Condensation Trail (contrail) shadow was the first to come to mind too

I've seen noctilucent clouds and I've seen auroras. The former are usually irregular in shape and the latter have a shimmery, variable appearance. What we saw were light rays radiating fan-like upward from the horizon. The air in ND is usually pretty clear so phenomenon might have been city lights from a source over the horizon. We were on I-94 in western ND at the time so light from Wahpeton is a possibility. I remain dubious, however.

If anticrepuscular rays in the photo are cloud shadows, why are they brighter than the ambient sky?