Colored regions - Part 2

Colored regions on the moon's surface: Part 2

Part 1 is an overview of telescopic observations and photographs of subtle colorations on the moon's disc, and orbital observations and photographs performed by Apollo astronauts and previous unmanned orbiters.
Part 2 is a rather curious look at the moon's colors, plus all sorts of rare observing techniques, thoughts, and hypotheses (the possible cause of the reddish-colored Transient Lunar Phenomena, TLP). It is also an enthusiast's look the visual perception of colors.
Part 3 is an exploration of the moon's surface and the variety of subtle colorations on boulders, rocks, and regolith. Photographs by the Apollo astronauts and previous unmanned landers.

Purkinje effect, Earthshine, and Total Lunar Eclipses

In semi-darkness, all colors at and near the red part of the spectrum are seen as "dark", while the colors at and near the blue part of the spectrum are seen as "bright" (the Purkinje effect). The Earthshine on the nocturnal part of the moon's near side (as seen from Earth itself) looks quite bright because of its slightly bluish coloration and the retro-reflectivity of the moon's regolith. On the other hand, during a Total Lunar Eclipse, the reddish/brownish colored lunar disc doesn't look as bright as it really is! (note: the actual brightness of a Total Lunar Eclipse is not always the same, hence the Danjon scale).
  Red-orange colored Cool Carbon Stars, such as S-Cephei or T-Lyrae, are typical examples of the "dark" look of red-colored objects observed in darkness. A bluish-white star in the neighbourhood of a red-colored Cool Carbon Star (both the same magnitude) looks much more brighter than the red star.
 
 

Curious color-contrast phenomena: the Green Moon and the Blue Moon

- When there's lots of volcanic ash in the upper layers of Earth's atmosphere (after a major volcanic explosion), the colors of the morning- and evening-twilight look very Magenta-red or purple. A crescent moon surrounded by this diffuse purplish twilight glow looks abnormally "green". This greenish coloration is a typical color-contrast phenomenon (Magenta and green are each other's "antipodal" colors on the color-circle).
  - Forest fires produce lots of smoke which look remarkably "dirty yellowish". A gibbous moon surrounded by yellowish looking translucent smoke has a typical lilac or blue appearance. This too is a color-contrast phenomenon (Lilac and "dirty yellow" are each other's "antipodal" colors on the color-circle).
  See also:
  - J.W.Goethe's Farbenlehre.
  - M.G.J.Minnaert's Light and Color in the Outdoors.
 
 

Albireo (beta Cygni), the Vesuvius, and the Full Moon's remarkable green color

A remarkable observation, printed on pages 99 and 100 of T.W.Webb's Celestial Objects for Common Telescopes, Volume 2; The Stars :
  - Beta Cygni (Albireo: yellow-blue).
  One of the finest in the heavens. I have seen the colors beautifully by putting the stars out of focus. Sm. observes that they are actually different, not, as may sometimes be the case, complementary, from mere contrast; an effect which is seen when the bright yellow light of a lamp makes the moon appear blue, and which Schm. witnessed to a remarkable degree at his observatory on Vesuvius during the great eruption of '55, when the sky was as green as bottle glass, and the Full Moon a lively green through openings in red clouds of smoke and steam. A similar result may take place with some double stars, but not with all, as is proved by hiding the larger star behind a bar in field. Hence artificial light is misleading in estimating star colors.
 
 

Chromatic dispersion phenomena observed shortly after moonrise and/or shortly before moonset

This optical phenomenon is something which could be the cause of many so-called Transient Lunar Phenomena at and near bright high-albedo craters such as Aristarchus. Chromatic dispersion is also the reason why the upper limb of the moon looks remarkably green-blue, while the lower limb looks orange-red, hence the optical effect known as the Green Flash (the sun's upper limb which looks fluorescent green, observed shortly after sunset or shortly before sunrise).
  See also:
 LPOD 17-10-2008 (low Full Moon with upper green limb).
  To avoid this "disturbing" color effect (chromatic dispersion at the moon's limb and craters) one has to observe the moon through a green filter (which is the central color of the spectrum).
  Related:
 Moonrise and moonset observed from Earth orbit
 Moonrise from Skylab
 Moonset from the International Space Station (ISS)
 Full Moon's distorted image, observed from the ISS
 Les Cowley's -Today's Feature: Impossible Moon-
 
 

Rare bluish and greenish streaks and patches in a Total Lunar Eclipse's Umbra

A typical Total Lunar Eclipse looks always dark copper-red colored. But sometimes there are rare bluish and greenish colored streaks and patches in the Umbra. The cause of these curious colorations is unknown. Could it (the rare bluish and greenish colorations) be a result of the atmospheric optical effect known as the Green Flash in Earth's atmosphere? In other words; is there sometimes a "projection" of the Green Flash phenomenon on the surface of the Totally Eclipsed moon? - DannyCaes Aug 10, 2008
  See also:
  - W.R.Corliss, Mysterious Universe, a handbook of astronomical anomalies (The Moon; Eclipse phenomena).
 
 

Lunar rocks and indigo colored black light

What if... the moon is illuminated by a giant black light (deep indigo colored light) instead of the sun's yellowish-white light.
  Related questions:
  - Are there lunar samples (moonrocks) and meteorites which are (or were) investigated under black light? (to look for differences in composition and structure).
  - Is it possible to create an equivalent of black light during telescopic observations of the Full Moon? (use of a special filter perhaps?).
  In certain stone-shops there are special "dark rooms" with typical indigo black light inside it, to show curious fluorescent colorations on minerals. I wonder if such colorful fluorescence is also noticeable on moonrocks and meteorites. - DannyCaes Jul 27, 2008
  It's very interesting to explore Wikipedia's page Black Light (an overview of all sorts of tubes and bulbs). - DannyCaes Jul 21, 2014
 
 

Perception of colors

There is an old prescription among painters for seeing more life and greater richness in colors of a landscape, and that is to stand with your back to the landscape, your legs wide apart, and bend forward so far as to be able to see between them. The intensified feeling for color is supposed to be connected with the greater quantity of blood running to the head. Vaughan Cornish suggests that lying on one's side would produce the same effect. He ascribes this to the fact that the well-known overestimation of vertical distances is neutralized, so that the tints apparently show steeper gradients. The question is whether this applies also to the much stronger effect while bending.
 - M.G.J.Minnaert, Light and Color in the Outdoors, page 134, $ 95: Observation of Color while bending down.
 
 Don Davis' thoughts on Color Pictures and Color Filters; an exploration and investigation of color photography.
 
 

Charlie Duke's color-photograph on the moon's surface, Apollo 16, april 1972

AS16-117-18839 (extreme high-resolution scan).
Thanks to Kipp Teague of the Project Apollo Archive, and Eric M. Jones of the Apollo Lunar Surface Journal.


Color photograph of Earth by lunar orbiter Zond 7, august 1969

The colors of Meteorites (Aerolites)

Dhofar 961 and it's remarkable purple coloration:
http://www.nature.com/news/2008/080625/full/4531160a.html (source: JohnMoore2).

Transparent glassy spherules in lunar regolith, and the Primary Lunar Glass-Spherule Bow

In the early 1990s, the explorer of spectral colored optical phenomena Danny Caes came up with a hypothesis to explain the red-colored glows which are sometimes noticed by dedicated lunar observers (often called Transient Lunar Phenomena). According to D.Caes, these reddish colored glows are nothing more than the appearance of the most distinct spectral color in sunlit transparent glassy spherules on the moon's regolith (the top-surface layer of lunar dust). In other words, these reddish glows are very small parts of the Primary Glass-Spherule Bow (circle), of which most of it is invisible due to its latent state (read: when there are no glassy spherules at an angle of 22°30' around the anti-solar point, one can't see this optical phenomenon).
  As mentioned above, to see parts of the possible reddish coloration on the moon's regolith, the lunar observer should aim the telescope moonward when the moon itself is at an angle of 22° to 23° of the anti-solar point (that is: about 44 hours and 25 minutes before Full Moon, and again about 44 hours and 25 minutes after Full Moon).
  Good Luck!
  360° : 22°30' = 16
  29.5 days (one lunation) X 24 hours = 708 hours : 16 = 44 hours and 25 minutes ( = 22°30').
 
 

Photographs of the Primary Glass-Spherule Bow (or Circle) :

Complete Primary Glass-Spherule Bow (almost a complete circle!).
Identify This Phenomenon (a VERY bright Primary Glass-Spherule Bow).
Bow in Asphalt Paint (note the error in the angular value of the bow, which should be 22°30').
Glass Bead Bows
Road Bow
Very bright Glass Spherule Bow (source: Flickr).
Glass Bead Rainbow on Kitchen Table (by Alexander Haussmann).
The Primary Glass Spherule Bow (circle) is also noticeable on (sunlit) movie projection screens made of a white plastic sheet with countless transparent glassy spherules glued on it.
The Secondary Glass Spherule Bow (circle) is also noticeable on such screen, at an angle of almost 90° around the anti-solar point! This bow (circle) is very broad and very weak. An experienced eye is needed to observe this sort of bow! (and a linear polarizer).

A linear polarizer in the (rotating) eyepiece of a telescope

The Primary and Secondary Glass Spherule Bows (circles) and also common rainbows emit polarized light, and should be observed through a rotating linear polarizer. To detect traces of possible reddish coloration on the moon's surface, one has to add a linear polarizer in the eyepiece of the telescope (a Celestron-polarizer for example). The eyepiece should be rotated around its axis. If a reddish glow is indeed observable, it (the colored region) should "blink" on-and-off while the observer is rotating the eyepiece. During observations through a rotating eyepiece (and polarizer) one shall notice the yellow-lilac colored Haidinger's brush. The source of this vaguely colored secondary optical phenomenon is the rotating polarizer and the human eye, and not the lunar surface!
 
 

Where to look?

Not at the whole disc of the moon! Only the regions near the terminator (grazing sunlight), because the dusty regolith at these regions is very dark compared to the sunlit transparent glassy spherules.
  It could be that Harold Hill's observation of the reddish glow near Lichtenberg (see Part 1) was indeed a small part of the Primary Glass-Spherule Bow!
  See also Richard M. Baum's observation of a reddish coloration near Philolaus on the 20th of May, 1948 (Epic Moon, page 309). According to Fred Espenak, Full Moon was on the 23th of May, at 0:37 U.T. (about two days after R.M.Baum's observation).
 
 

There are many questions...

Such as:
  - Why are there not always reddish colorations (to observe) when it's two days before and/or two days after Full Moon?
  And:
  - Is the appearance of reddish colored regions related to the changing distribution of transparent glassy spherules on the moon's regolith?
  (in other words: Are there sometimes "concentrations" of transparent glassy spherules created by the effect of levitating and migrating lunar dust?).
  And:
  - Are those transparent glassy spherules small enough to be levitated and migrated, and large enough to refract and to reflect the sun's light?
  And:
  - Why is there not the slightest trace of it (of the Primary Glass-Spherule Bow) on the surface color-photographs made by the Apollo astronauts? (only the very bright Heiligenschein phenomenon).
  Etcetera... etcetera...
 See also:
 - Greenler, Robert - Chasing the Rainbow, recurrences in the life of a scientist (Elton-Wolf Publishing, 2000), page 213: Robert Greenler's experiment with the Primary Glass Spherule Bow on a dark blue cloth.
 
 

Observing the First Quarter Moon and/or Last Quarter Moon during daylight, through a linear polarizer

Here's something for those who want to observe the First Quarter Moon (or the Last Quarter Moon) during daylight circumstances (the moon surrounded by bright transparent blue sky);
  Add a linear polarizer to your telescope's eyepiece and rotate it until you see the blue sky at its darkest! This is an extraordinary experiment!
  The F.Q. moon (or the L.Q. moon) is always at the 90 degree angle of the sun, and in this region of the blue sky there's maximum polarization; ideal for the moon to "pop up" brightly against the dark polarized blue sky!
 WARNING: this technique (polarizer on telescope's eyepiece) is not recommandable on EVERY kind of eyepiece-prism! (a simple zenith prism with mirror-image is okay).
  A series of experiments and tests are required!
  This observing technique is also ideal for planets at an angle of 90 degrees of the sun!
 
 

The riddle of the sandbow (a geophysical enigma)

James E. Talmage; Great Salt Lake, Utah. May 16 - 1901.
"On the evening of may 16, the writer was crossing the main ridge of Antelope island (the largest land body within the area of the Great Salt Lake). As he began the descent on the eastern slope, there appeared between the island and the mainland what seemed at first glance to be a segment of a brilliant rainbow of unusual width. It was evident, however, that no rain was falling in that direction. Clouds were gathering in the south and west, but the sun was not yet obscured. A wind setting toward the mainland had lifted from the dry flats large quantities of the oolitic sand, with which the lake bottom and the recently dried patches on this side of the island are covered to a depth varying from a few inches to several feet. This so-called sand consists of calcareous spherules, fairly uniform in size between the limits of No.8 and No.10 shot. The oolitic bodies are polished and exhibit a pearly luster. It would seem that the outer spherical surfaces reflected the light in such a manner as to produce the bow. The colored column appeared almost to touch the lake bed, and its ends subtended with the observer an angle of about 40°. The prismatic colors were distinct, the red being outside, i.e., away from the sun. In apparent width the column was fully double that of an ordinary rainbow. A fainter secondary bow was plainly visible beyond the primary, with the colors in reverse order. The phenomenon was so brilliant as to attract the attention of all members of the party, and it remained visible for over five minutes, then, as the sun sank lower, it rapidly died away. The production of a color bow by reflection from the outer surfaces of opaque spherules is a new phenomenon to the writer. It is inexplicable on the principle of refraction and total reflection from the interior of transparent spheroids, according to which the rainbow is generally explained".
Sources:
- Talmage, James E.; A Sand-Bow, an unusual optical phenomenon, Science, 13:992, 1901.
- Corliss, W.R.; Rare Halos, Mirages, Anomalous Rainbows, and related electromagnetic phenomena (The Sourcebook Project, 1984), pages 29-30.

Temporary colors on the moon: another theory?

The discovery of low-sun color phenomena on the moon, stimulated a review of the literature on the Alpine Glow. Conclusion: terrestrial twilight phenomena are not really well-understood. It seems possible that the mechanism producing the Alpine Glow on Earth (reflection from dust particles) might also contribute to the observed lunar phenomena.
Sources:
- Rawlings, G.C.I.; Lunar Transient Phenomena: Quasi-Alpengluhn or Twilight-Colour Theory. British Astronomical Association, Journal, 77:309, 1967.
- Corliss, W.R.; Rare Halos, Mirages, Anomalous Rainbows, and related electromagnetic phenomena (The Sourcebook Project, 1984), page 125.
See also:
Everest Alpenglow