Imagine... a new unmanned lunar lander at Sinus Medii, north of the remains of something which was once a 43 kilometer diameter crater, thanks to the I.A.U. officially known as Oppolzer. Now, this lander has only one purpose: to aim a beam of reflected sunlight toward Earth, via a disc shaped flat mirror on top of the lander. Telescopic observers on Earth could see a starlike dot of light just after local sunrise (the sunrise terminator at Sinus Medii). At the lander itself, the sun's disc is already visible just above the eastern horizon. The lunar surface around the lander is still very dark (perhaps here and there a sunlit rock or boulder). Now here's a question for enthusiasts of mathematics and optics: what should be the diameter of this disc shaped mirror to observe such a starlike dot of reflected sunlight? One meter? Ten meters? Less than one meter? Just fifty centimeters? More than ten meters?
Note: a rather small mirror called a Heliotrope is capable of reflecting a beam of sunlight over ten or more kilometers. The diameter of such a small mirror is only five centimeters. An observer at ten or more kilometers distance could see a rather bright point of light: the beam of reflected sunlight from the Heliotrope. Also note that such an experiment is always performed in broad daylight, when everything around the observer is illuminated by bright sunlight. The sunlit surface of the moon, when seen at First Quarter, is way too dark compared with the sunlit daylight circumstances on Earth. Which means: the starlike point of reflected sunlight, coming from the mirror on the moon, is much more distinct. The telescopic observers watch the First Quarter Moon when their sunset (at their location on Earth) happened more than two hours ago: they are in nocturnal circumstances and their eyes are adapted to darkness.
To make sure that the telescopic observers on Earth are watching an artificial object from Earth, the mirror on the lunar lander should move a little bit, to "shift" the beam of sunlight across the face of Earth, in repetitive motion. Projected toward Earth, the angular diameter of the beam of sunlight is the same as the angular diameter of the sun's disc, seen from Earth and/or the moon. Now, what would the telescopic observers see? A pulsating point of light slightly to the east of the moon's morning terminator. Question: can they see such a point of light during Full Moon too? Yes, but it would look not at all that distinct as during First Quarter Moon.
If I was the "big boss" of NASA, I would send an unmanned lunar lander (with movable disc shaped mirror) straight to Sinus Medii on the Moon, a.s.a.p., because the number of people who can't or won't believe the fact that something from planet Earth is capable of performing a landing on the moon's surface is growing day by day! Telescopes aimed at the moon could change their way of thinking.
Note: if NASA has a plan to launch such an unmanned lunar lander with movable disc shaped mirror on top of it... I already have a name for it: Project PHAROS.
Again: is all of this something brand new or is such a lunar mirror already an old proposal? I know of Carl Sagan who wanted to drop a nuclear bomb on the moon, to see what would happen up there (believe it or not, he really wanted to do this!). I keep it much more "gentle" by sending a lander with sunlight reflecting mirror toward the moon's Sinus Medii...
Needless to say that I want to talk about this topic on the daily workfloor. Alas, my colleagues are still waiting for 'THAT' moment when I start talking about Earthly subjects, such as... soccer, or... the trade-union, or... vacation.
Note: a rather small mirror called a Heliotrope is capable of reflecting a beam of sunlight over ten or more kilometers. The diameter of such a small mirror is only five centimeters. An observer at ten or more kilometers distance could see a rather bright point of light: the beam of reflected sunlight from the Heliotrope. Also note that such an experiment is always performed in broad daylight, when everything around the observer is illuminated by bright sunlight. The sunlit surface of the moon, when seen at First Quarter, is way too dark compared with the sunlit daylight circumstances on Earth. Which means: the starlike point of reflected sunlight, coming from the mirror on the moon, is much more distinct. The telescopic observers watch the First Quarter Moon when their sunset (at their location on Earth) happened more than two hours ago: they are in nocturnal circumstances and their eyes are adapted to darkness.
To make sure that the telescopic observers on Earth are watching an artificial object from Earth, the mirror on the lunar lander should move a little bit, to "shift" the beam of sunlight across the face of Earth, in repetitive motion. Projected toward Earth, the angular diameter of the beam of sunlight is the same as the angular diameter of the sun's disc, seen from Earth and/or the moon. Now, what would the telescopic observers see? A pulsating point of light slightly to the east of the moon's morning terminator. Question: can they see such a point of light during Full Moon too? Yes, but it would look not at all that distinct as during First Quarter Moon.
If I was the "big boss" of NASA, I would send an unmanned lunar lander (with movable disc shaped mirror) straight to Sinus Medii on the Moon, a.s.a.p., because the number of people who can't or won't believe the fact that something from planet Earth is capable of performing a landing on the moon's surface is growing day by day! Telescopes aimed at the moon could change their way of thinking.
Note: if NASA has a plan to launch such an unmanned lunar lander with movable disc shaped mirror on top of it... I already have a name for it: Project PHAROS.
Again: is all of this something brand new or is such a lunar mirror already an old proposal? I know of Carl Sagan who wanted to drop a nuclear bomb on the moon, to see what would happen up there (believe it or not, he really wanted to do this!). I keep it much more "gentle" by sending a lander with sunlight reflecting mirror toward the moon's Sinus Medii...
Needless to say that I want to talk about this topic on the daily workfloor. Alas, my colleagues are still waiting for 'THAT' moment when I start talking about Earthly subjects, such as... soccer, or... the trade-union, or... vacation.
