About Christopher Watson Expertise Can nearly always answer general astronomy questions, and can get much more specific in the areas of stellar evolution, variable stars, astronomical information systems and celestial cartography. Hard astrophysics is not my bag, though.
Experience Have been involved in observational and computational astronomy for 20 years. Member of and/or contractor to several astronomical organizations. Former officer for one of the largest and most active amateur astronomical associations in the United States. Creator of SkyGX, the most comprehensive and accurate atlas of the sky. Creator of The International Variable Star Index (VSX) at the American Association of Variable Star Observers (AAVSO). Contributing member of The NGC/IC Project. I regularly help professional astronomers with their computational and database needs.
Organizations American Association of Variable Star Observers (www.aavso.org), The NGC/IC Project (www.ngcic.org), The SkyGX Project (www.skygx.com).
Publications Several peer-reviewed astronomical journals.
Education/Credentials None in the field of astromomy. All self-taught.
Awards and Honors The Special Recognition Award, American Association of Variable Star Observers (AAVSO) [http://www.aavso.org/news/fall06awards.shtml].
Question What color is the moon? Do you know of a book or website to support your answer?
Answer Hello Jon,
Thank you very much for your interesting question about the Moon. I'll see what I can do about answering it for you.
Almost everyone who has looked at the Moon from the surface of Earth will tell you that it appears either white, grey or yellowish. They're all pretty much correct, because that just about all our eyes can pick up of the true color of our natural satellite. Many say that the Moon looks pale yellow at night, more so than in the day, and that a daytime Moon just looks white. That's just the effect of sunlight scattering through our atmosphere and toying with our eyes. The brighter background during the day affects the way our eyes perceive color, and the yellowish hue some say appears at night just can't be picked up by our eyes during a bright day in blue skies.
But the truth of the whole matter is that the Moon is actually a lot more colorful than our eyes can attest to. Abundances and absences of different types of minerals on the lunar surface cause light to be absorbed and reflected in different ways. It's just that these subtle color differences can't be picked up by the human eye. They can, however, be brought out using photographic techniques, such at those described here:
By digitally accentuating the subtle color information that does exist in light reflecting from the lunar surface, the differences can be made more visible. And those colors are real. It's just that they exist at such low levels, comparatively, that we can't see them by just looking at the Moon.
It has been discovered that the bluish areas of the Moon correspond to fields rich in the element Titanium, while the orangish areas relate to Titanium poor fields.
Back in 1962, astronomer Sidney van den Bergh published a paper in The Astronomical Journal titled "The Color of the Moon". In it, he cites the differences in color between 14 different regions of the Moon by viewing it through specialized filters, taking brightness (magnitude) readings in different light wavelengths, and then making comparisons using a "color index", or the difference in magnitude between the different filters. His findings scientifically substantiate the colors seen in digitally enhanced photography. So the colorations seen in the images presented on the web page noted above are actually there.
