Re: pinhole rainbow halos on pavement

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From: pauld@exploratorium.edu
Date: Wed Jun 05 2002 - 11:02:28 PDT 

Message-Id: <200206051802.g55I2Qp20002@isaac.exploratorium.edu>
From: pauld@exploratorium.edu
Subject: Re: pinhole rainbow halos on pavement
Date: Wed, 5 Jun 2002 11:02:26 US/Pacific

Hi Regan

The halo around the shadow of your head is most likely caused by the highway crew
that just repainted the white lines on the road.

When they paint the lines they throuw on top of the wet paint handfulls of
spherical glass beads.

These glass beads get scattered all over the road and act just like raindrops do
in the sky...they produce rainbows centered around the shadow of your head. But
because the index of refraction of glass is different from water, the angular
diameter is smaller for the glass bead rainbow.

Good observing!

Paul D

> as i was biking home i saw a rainbow around my shadow on the pavement yesterday. i have
often taken this route before on similarly sunny days and never noticed this
rainbow. it
followed me for about three blocks and it was about one hand's width (fingers and
arm
extended) away from the center of the shadow of my head. is this related to the
sunhalos
or does this probably happen all the time?
>
> also, are sundogs just chunks of sun halos? i saw one on memorial day (interestingly,
i
saw it on I-80, near davis, where I have seen 2 before).
>
> thanks.
> -Regan
>
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