Rainbow

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Rodney Blackall

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Nov 14, 2000, 3:00:00 AM11/14/00
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In article <8uosau$or7$1...@lure.pipex.net>, Les
<sundogs...@dial.pipex.com> wrote:
> > As the view opened up I could see it was a full rainbow but because
> > of the darkness could only make out the colours at each end - but
> > they were clear
> -snip-
> > is it a common phenomenon?


> Rainbows produced by the moon are fairly rare because they are much
> fainter than their solar companions and so go unnoticed. Colour
> vision is not very effective for dim objects so they usually appear
> uncoloured. You were lucky!

QUESTION: what colour is moonlight? Is it white, i.e. all colours mixed
and hence capable of giving a rainbow, or is it changed by the Moon's
surface?

Anyone seen a spectrum of moonlight?

--
Rodney Blackall (retired meteorologist)
London, ENGLAND
Using Acorn SA-RPC with ANT INS and Pluto

Stephen Tonkin

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Nov 15, 2000, 3:00:00 AM11/15/00
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[follow-ups reset as this is an astronomical, more than a weather,
topic]

Rodney Blackall <rbla...@rodsrisc.demon.co.uk> wrote:
>QUESTION: what colour is moonlight? Is it white, i.e. all colours mixed
>and hence capable of giving a rainbow, or is it changed by the Moon's
>surface?

It is essentially reflected sunlight -- the lunar surface reflects light
in a manner that approximates to tarmac.

>
>Anyone seen a spectrum of moonlight?

Yes -- both in a spectroscope, and in parselene photographed by Bob
Mizon. It is a continuous spectrum. If you don't have a spectroscope,
you can make a simple one using a CD. All you need is some arrangement
by which light from a slit is diffracted from the surface of the CD. My
"CD" one uses a CD fragment and a couple of flock-lined section of waste
pipe, with a slit at the end of one, all held together with gaffer tape.

I've just photo'd it -- if I remember, when I post this, I'll upload it
to:
http://www.aegis1.demon.co.uk/spectroscope.jpg

As an alternative, Dave Randell has a much simpler system that uses a
complete CD, and the CD box to form the slit!

Noctis Gaudia Carpe,
Stephen

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Tim Hicks

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Nov 15, 2000, 3:00:00 AM11/15/00
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Lernout & Hauspie: www.LHSL.com <http://www.LHSL.com>
Stephen Tonkin <s...@nospam.demon.co.uk> wrote in message
news:FFdSVAAu...@aegis1.demon.co.uk...

> >Anyone seen a spectrum of moonlight?
>
> Yes -- both in a spectroscope, and in parselene photographed by Bob
> Mizon. It is a continuous spectrum. If you don't have a spectroscope,
> you can make a simple one using a CD.

Out of curiosity, is there any way to "visualise" spectroscopic data other
than actually looking at the spectrum itself. I guess what I mean is; is
there a way to obtain a spectrum in a data format without serious scientific
instruments costing the earth. Perhaps with some sort of CCD plus
appropriate software?
The reason I ask is that I am quite badly colour blind, so while the
spectrum is pretty, I seriously doubt I would be able to interpret it in any
useful way (not that I'd know how anyway).

Tim

Stephen Tonkin

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Nov 15, 2000, 3:00:00 AM11/15/00
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Not at all OT, Tim. (IMNSHO, of course.)

Tim Hicks <tim....@lhsl.co.uk> wrote:
>Out of curiosity, is there any way to "visualise" spectroscopic data other
>than actually looking at the spectrum itself.

Yes. If, for example, you project the spectrum onto a CCD chip, you can
read out the count for each pixel to produce a line graph. Obviously the
wavelength axis needs to be calibrated, but this is possible against
fluorescent lamps (e.g. mercury, neon) or stars (known emission or
absorption lines).

I ought to state now that I am a relative beginner at this game -- I've
been mucking about with home-made stuff for decades, beginning with
using a vinyl record (a Monkees one I "borrowed" from my sister on the
grounds that it was useless musically and therefore it was entirely
moral to investigate its scientific potential, if you must know <g>) as
a reflection grating, and graduating recently to a Rainbow Optics
grating, which I am still experimenting with when weather permits.

If you want to see what is possible with amateur kit, try the Forum for
Amateur Astro-Spectroscopy site (http://www.erols.com/njastro/faas) or
Maurice Gavin's website (http://astroman.fsnet.co.uk), both of which are
pregnant with information from experienced people and both of which have
numerous links to other spectroscopers.

Tim Hicks

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Nov 16, 2000, 3:00:00 AM11/16/00
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Stephen Tonkin <s...@nospam.demon.co.uk> wrote in message
news:i5qbqBAw...@aegis1.demon.co.uk...

> Not at all OT, Tim. (IMNSHO, of course.)
>
> Tim Hicks <tim....@lhsl.co.uk> wrote:
> >Out of curiosity, is there any way to "visualise" spectroscopic data
other
> >than actually looking at the spectrum itself.
>
> Yes. If, for example, you project the spectrum onto a CCD chip, you can
> read out the count for each pixel to produce a line graph. Obviously the
> wavelength axis needs to be calibrated, but this is possible against
> fluorescent lamps (e.g. mercury, neon) or stars (known emission or
> absorption lines).
<snip>

Thanks Stephen. There looks some interesting stuff there for the "spectrally
challenged"!
I'm not sure I know anyone who would admit to owning a monkees album, but a
particular member of my family has a Cher CD. Would you consider that fair
game?

Tim


Steve Jarrett

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Nov 17, 2000, 2:31:24 AM11/17/00
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Tim Hicks <tim....@lhsl.co.uk> wrote:

| I'm not sure I know anyone who would admit to owning a monkees album,
but a
| particular member of my family has a Cher CD. Would you consider that
fair
| game?

Don't you get CDs mailed to you from ISPs begging you to sign up with
them? I regularly find my doorway cluttered with the darn things.

And just think all this time, they weren't really sending me free internet
offers, but free spectroscopes! ;-)


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