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Date: Thu, 14 Nov 1996 08:32:00 -0500 (est)
From: "Cornette, William - (I)" <CornetteW_at_nima.mil>
Subject: Opposition effect
To: owner-meteoptic_at_LISTSERV.FUNET.FI
Cc: "Cornette, William - (I)" <CornetteW_at_nima.mil>
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<snip>
From: Paul Schlyter <pausch_at_saaf.se>
> This "opposition effect" is also responsible for the full moon being
> about ten times brighter than the half moon, and not merely twice as
> bright as could be naively expected, or PI times as bright as if it
> would be if the lunar surface was a perfect diffusor (a "Lambertian"
> reflector).
Do you have any references for this -- or better yet some data.
I have constructed a lunar exoatmospheric irradiance model, which is
combined with a solar and lunar ephemeris model. I compensate for:
- Amount of lunar surface illuminated by sun
- Variation in earth-moon and moon-sun distance during lunar
cycle.
There is a total variation in the irradiance of about
26 percent from this.
- Variation in the albedo of different portions of the moon
surface. The irradiance is about 20 percent brighter
at first quarter (waxing) than at third quarter
(waning) due to differences in the lunar surface.
- Spectral variation in the lunar albedo (averaged over the
whole lunar surface).
The correction factor for the third factor as a function of lunar
elongation is:
DATA ELONG / 0., 10., 20., 30., 40., 50., 60., 70.,
+ 80., 90.,100.,110.,120.,130.,140.,150.,160.,170.,180.,190.,
+ 200.,210.,220.,230.,240.,250.,260.,270.,280.,290.,300.,310.,
+ 320.,330.,340.,350.,360./
DATA CORREC /0.255,0.259,0.263,0.267,0.271,0.275,
+ 0.284,0.307,0.326,0.361,0.393,0.429,0.465,0.499,0.545,
+ 0.613,0.706,0.829,1.000,0.829,0.662,0.574,0.484,0.422,
+ 0.384,0.354,0.332,0.314,0.305,0.295,0.294,0.292,0.286,
+ 0.267,0.248,0.229,0.210/
If you have some quantitative values for this brightening due to the
opposition effect, which I assume is a sharply peaked value, falling off
sharply if the lunar elongation is more than a couple of degrees off from
full (180 deg), and any reference, I would appreciate it.
Bill
Cornette
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