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Hi Michael,
>
> Yes, I have seen some optical effects in those
> glass beads as well! Maybe
> not the actual "glass-bow" though, but they may
> be worth mentioning:
>
> I've noticed the heiligenschein (the equivalent
> of wet heiligenschein, that
> is) in traffic signs when the sun is low and
> the sign is near the antisolar
> point. I have also seen something similar to
> your observation, rainbow
> colors, but in these road signs (not marks *on*
> the road). The rainbow
> colors I saw reminded me of antisolar
> iridescence. Maybe it was actually a
> "rainbow" or glassbow for that matter. I would
> typically see these colors
> in the blue-white road signs over the highways
> in Holland, when the sun
> would be low in the back and the sign forward
> overhead or to the side (i.e.
> not exactly near 180 degrees opposite the sun).
> Closer inspection learned
> that the trafic signs are composed of the same
> kind of retro-reflecting
> glass beads as the road marks. That way they
> are always easy to see from
> your car, since you are on the light source
> itself.
>
>
> Speaking of antisolar iridescence: I haven't
> seen this term, or photos, in
> any optics book yet. Why is that? Antisolar
> iridescence is as natural an
> effect as the common iridescence, but it would
> (I guess) be caused by
> spurious glory rings instead of the corona.
> Anyway, after figuring out
> that it might occur, I have seen the antisolar
> iridescence several times in
> the mountain wave clouds here in New Mexico and
> also have a number of
> pictures of the phenomenon that I still need to
> scan in. It's one of those
> phenomena that go unnoticed unless you expect
> it and know where and when to
> look. I've seen it up to 20 degrees off the
> antisolar point, as slight
> green and pink pastel colors in the bases of
> lenticular clouds. The colors
> are even more pastel than regular iridescence.
> It's really obvious to see
> from an airplane, looking away from the glory.
> If anyone is interested I
> can maybe find and scan the photos tomorrow.
>
> Harald
Harald,
The heiligenschein was visible and the bow was
well-developed and clearly seperated with a 28
degree radius and it showed the bright colors of
a true rainbow.
Best,
Michael
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