Earthshine blog

Earthshine blog

"Earthshine blog"

A blog about a system to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

What colour is the Earth, then?

Real World ProblemsPosted by Peter Thejll Feb 13, 2014 07:16PM
An artist, Jeremy Sharma, in Singapore, has asked us what Pantone colour code the earthshine colour corresponds to. He heard of us through the Guardian story.

I can see two ways to answer him: One is via a conversion from colour temperature to Pantone code (or, equivalently, hexadecimal RGB code), another is to take a realistic image of Earth and averaging the RG and B channels.

I cannot, yet, find a conversion from colour temperature to Pantone code or RGB intensities, but the temperature to use is given by B-V=0.44 which is near 6400K, I think.

For these images of Earth:

http://news.bbc.co.uk/2/hi/8547114.stm

I can take the average of the R G and B channels of both images - omitting the black sky around earth.

the RGB averages are:

89.5127 92.4462 115.971

or, rounded to nearest integer

90 92 116

The hexadecimal equivalent of this triplet is #595C73
(use IDL 'Z' format to work that out ...)

On this page

http://goffgrafix.com/pantone-rgb-100.php

(and links thereon) it is possible to find Pantone colour codes and the equivalent hexadecimal code. The above value does not appear on these pages - but a tool at

http://goffgrafix.com/colortester.php

allows you to type in the above hexadecimal number and see the corresponding colour as shown on a computer terminal.

The above colour can be 'brightened' or 'darkened' by multiplying each of the RG and B values by some number (same for all three) and then converting to hex code. In doing this avoid saturating any of the three (they must be smaller than 255).

I did this so that a lighter rendition of the same colour would appear, and the result is

#BAC0F0

which you can also type into that page and see (they allow showing of two such colours next to each other).

Real earthshine is thousands of times fainter than moonshine so I doubt you can 'see' the colour if you make the numbers realistic (in fact, RG and B would be 0 in such an image since the numbers are integers and cannot be smaller than 1 without being 0). The two above colours have the same tones but differ in brightness.

I expect that a dye maker or a paint shop with a smart machine can mix your colour according to the hexadecimal code, instead of the Pantone colour code.

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