Lunar Heliotrope Project

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Lunar Heliotrope / Lunar Heliograph (Project PHAROS)

We just want a common sunlight-reflecting mirror on the moon, NOT a retro-reflector for laser beams!

This page describes a possible lunar project to aim a ray of reflected sunlight from a relatively small common mirror on the surface of the moon toward earth (a mirror on top of a lunar lander or rover); to observe the minute speck of reflected sunlight through all sorts of common and powerful amateur telescopes.
The spark (the very first idea) to create the so-called Lunar Heliotrope or Lunar Heliograph was conceived during the mid nineties of the foregoing century. In these years the dedicated lunar observer Danny Caes went to his city's Public Observatory to observe the moon, planets, orange-red colored Cool Carbon Stars (C-type stars), star clusters, etcetera...

The name of this project (Project PHAROS) is derived from the legendary Lighthouse of Alexandria (or Pharos of Alexandria).

Here's a couple of mails to Kipp Teague's Project Apollo Group, in which Danny Caes described his idea of the Lunar Heliotrope or Lunar Heliograph:

Sunday the 20th of january 2013:
To be honest, I can't get rid of this thought, because as I see it, it must be possible to observe the speck of reflected sunlight through common amateur telescopes on earth, as long as it is reflected by a slightly adjustable common mirror the size of a table (on top of a lunar lander or rover).
See, the disc-shaped reflected image would have the same angular diameter as the true sun. Of course, from the moon there would be nothing visible of that reflected image, BUT... it would be visible in telescopes on earth (as a minute speck of light).
And because of the small angular sun-sized reflected image (about one-fourth of the earth's angular diameter), that mirror should "dance" a little bit to cover the whole of the earth's disc (read: the mirror's repetitive movement of mere millimeters "out of alignment").
We on earth would see the "on-off-on-off-on-off-on-off" effect of the sun's reflection created by the slightly "dancing" mirror.
There's no need to make that mirror slightly concave or convex, because the sun's reflected image would become too weak to be observable in telescopes.
Just a common mirror "as flat as possible" (to create a perfect disc shaped reflected image of the sun, with the same angular diameter as the true sun).
I wish some NASA personnel could read this message.

To get the best results of this project, the mirror should be placed at a location very near the crashed lander Surveyor 4 and soft-landed lander Surveyor 6 (at approximately 0 degrees latitude and 0 degrees longitude, in Sinus Medii, between craters Bruce and Oppolzer, very near Oppolzer's satellite crater Oppolzer A).
It (the mirror) should only reflect the sun's light shortly after local sunrise and shortly before local sunset, in other words: shortly after First Quarter Moon and shortly before Last Quarter Moon. Why? Because during these moments the surrounding lunar surface (around the rover with its mirror) would look dark (not black), and this could create a good contrast to observe the speck of reflected sunlight!
Note: during Full Moon it would become invisible because of the powerful Retro-Reflection of the moon's regolith (the "white moon" effect).

Flemish letter to Ivo Demeulenaere (dedicated investigator of terminator-related clair-obscur phenomena on the moon's surface). Tuesday the 21st of march 2017:
Wat ik mij vooral afvraag in verband met zo'n zonlichtreflekterende spiegel op de maan is hoe klein die eigenlijk mag zijn, om ons alsnog het ultrazwakke puntje zonlicht te kunnen laten waarnemen, en dan wel met behulp van een niet al te kleine amateurtelescoop (let wel: die spiegel zou enkel zonlicht naar de aarde reflekteren als de zonneschijf zelf net boven de maanhorizon staat, dus als er genoeg contrast zou te zien zijn ten opzichte van het donkere omringende maanlandschap in de terminator-zone). Ikzelf schat dat een ronde vlakke spiegel van 100 cm diameter voldoende groot zou zijn om iets te laten zien dat te vergelijken is met een ster van Magnitude 7 (waargenomen met de telescoop). Het kan ook zijn dat ik er geheel naast zit en dat de magnitude in werkelijkheid veel zwakker is (?), of veel helderder is (?). Ikzelf ben niet goed in het berekenen van zoiets (ik ben geen wiskunde-knobbel), maar ik veronderstel dat wiskundigen ondertussen reeds weten wat een zonlichtreflekterende vlakke spiegel van een meter diameter (op de maan) zou te zien geven... (misschien bestaat er een soort tabel met verschillende diameters van zo'n spiegel, gerelateerd aan de verschillende magnitudes van het telescopisch waargenomen zonnereflectiepuntje) (?). In ieder geval laat dat concept van die maanspiegel mij niet los sinds de jaren 90!
De gemiddelde afstand van de maan tot de aarde is iets van een 384.402 kilometer, zeg 384.000 kilometer. Gedeeld door duizend is dat 384 kilometer voor een duizendmaal kleinere maan (een bol van ongeveer 3 en een halve kilometer diameter) met daarop een piepklein spiegeltje van slechts 1 millimeter diameter. Kan zo'n minuscuul klein zonlichtreflekterend spiegelkorreltje nog te zien zijn op zo'n goeie 384 kilometer afstand? (mits contrasterende zwarte of egaal donkergrijze achtergrond, en een waarnemend oog dat zich voldoende heeft aangepast aan de duisternis, kijkend doorheen een krachtige amateurtelescoop).
Het zou interessant zijn om eens wat experimenten te doen m.b.v. een spiegeltje van 1 millimeter diameter (om te bepalen tot op welke afstand de zonnereflektie daar nog in te zien is, tijdens daglicht-omstandigheden en overbelichte waarnemende ogen). U zult er verbaasd van zijn, te zien dat zo'n minuscuul spiegeltje toch nog tot op verre afstand waarneembaar is!
Zie ook: Lunar Distance

The irradiation illusion
A very tiny white speck on a black background is much more detectable than a very tiny black speck on a white background.
Thanks to the optical illusion known as irradiation it is possible to detect very dim stars against the black background of space. Sunlit geostationary satellites at 36.000 kilometer distance are easily detectable in common telescopes (for example, telescopes in Public Observatories). Geostationary satellites "pop up" against the westward progressing starry background sky. I don't know much about the magnitudes of those geostationary satellites, I guess most of them appear at something like magnitude +9 or +10, or perhaps +11. Although very weak, they are still detectable through most telescopes.

Further thinking...
Would it be possible to aim a ray of reflected sunlight from a large terrestrial mirror (or a group of large mirrors) toward a geostationary meteorological satellite such as METEOSAT?
In other words; the possible detection of one white pixel at the location of a sunlight reflecting mirror somewhere in a low-albedo part of central Europe, visible on an online METEOSAT photo made during a cloudless noon (at exactly 12:00 U.T. on (or around) the 21st of june, when the sun is at its most northern declination and its highest culmination).
- DannyCaes Jan 20, 2013

Much further thinking...
A mirror aboard one of the geostationary satellites could aim a ray of sunlight toward the nocturnal part of earth, to be visible as a stationary "new star" through common amateur telescopes, and perhaps also through small binoculars and/or the unaided eye.
- DannyCaes Jan 20, 2013

The Heliotrope and the Heliograph
The Heliotrope (invented by Carl Friedrich Gauss) is also mentioned on pages 17, 18, and 19 in the book Light and Color in the Outdoors by M.G.J.Minnaert (Springer Verlag, 1993).
Derived from C.F.Gauss' Heliotrope is the Heliograph (which could create some sort of repetitive Morse-signals from reflected sunlight). This must be the most ideal way to convince telescopic observers on earth about the presence of human technology on the moon!!!

See also:
Gauss and his lunar heliotrope

Related, but... it's not the ideal kind of lunar reflectors, certainly not for observers with common telescopes in Public Observatories
Lunar Laser Ranging experiment (most people would say: "Well, there are laser reflectors on the moon, we don't need a common mirror up there") (I don't want to say this, but, they don't think a little bit further...) (Lunar Laser Reflectors are invented only for scientists in professional observatories, not for common moon observers with small backyard-telescopes or amateur telescopes in small home-domes).

See also:
Project A119 (a rather disputable plan from G.P.Kuiper and C.Sagan to detonate a nuclear bomb on the moon, at or very near the lunar terminator, this detonation should have been observable from earth as a minute starlike flash of light).

Possible specular reflections on the Moon?

The odd case of the so-called specular reflection at crater Torricelli B, January the 29th - 1983

  • The strange behaviour of Torricelli 'B' - Marie C. Cook - Journal of the British Astronomical Association, 110, 3, 2000.
  • A Portfolio of Lunar Drawings - Harold Hill - Page 174.
What was it? Was there really an abnormal brightening of Torricelli B on January the 29th, 1983? Was it some sort of specular reflection of the sun's light on the slopes of that crater? Or was it perhaps just a mis-interpretation and erroneous location of the nearby high-albedo ray craterlet Censorinus?

Is there something like a Specular Highlight on the moon's globe?
Specular Highlight
If the moon was made of Quicksilver (a perfect sphere-shaped mirror), we would see a very bright reflected image of the sun on the (quicksilvery) moon's outer surface.
If the moon was made of the same shiny material of snooker balls, this kind of shiny moon would show us the same solar reflection, albeit much more diffuse.
Now, the moon is made of a sort of material not-at-all suitable for solar reflections. In some way, the upper surface's powdery regolith layer has the same absorbing effect as the pyramid-shaped appendages on the inner walls of a reverb-less or "echo-less" chamber. There's absolutely nothing like specular reflection on the moon. Or... ??

Possible specular reflection on a lunar rock near the landingsite of APOLLO 14
Surface Hasselblads AS14-66-9281, 9282, and 9283 were made in eastern direction, toward the slopes of the distant Cone crater. These three images show lots of shadowed dimple craterlets (upsun photographs). In each one of these three images, a curious bright dot is visible below and to the left of the sun's position (the dot is located on the lunar surface). Could it be that this bright dot is some sort of solar reflection at a rock's mirror-like flat surface? Was this bright dot noticed before?
The High-Resolution scans of these three upsun Hasselblads:

- DannyCaes Mar 30, 2017