I'm curious about the impact of having a moon composed primarily of a material with a strong optical property: calcite, diamond, glass or something else similar. Would the traditional spherical shape pose any dangers in terms of magnifying the light coming from the sun?

What if it was actually a lens shaped moon?

Would a Solar eclipse be a giant-moon-ray apocalypse type scenario?

  • $\begingroup$ Even if you made such, it would become pitted and covered with the ground-up bits as regolith. $\endgroup$
    – JDługosz
    Sep 29, 2015 at 16:26

3 Answers 3


Even if you did have a moon made completely out of carbon, it would not be completely made of diamond. You are neglecting the role of gravity here. You are expecting a highly refractive, transparent cosmic body which is not practically possible. Only the innermost layers would be composed of diamond, the outer layers would be buckminsterfullerene powder or huge layer of opaque graphite. Furthermore, the asteroids hitting the surface would be depositing a large amount of opaque dust on the surface which would further decrease it's role as a colossal lens.

A lens shaped moon-sized body is not practically possible due to gravity, which tends to squeeze things in a form where most matter can be compressed in a shape that has the least surface area. It happens to be a sphere. A lens shaped body has a much larger volume to surface area ratio. The sides of this lens (even if it happen to form) would be crushed in and after sufficient amount of time (a few hundreds of millions of years), it will crack into a spherical form we see today.

Even if you did have a colossal lens shaped body (extremely improbable) which tends to be made of transparent material (severely improbable) which also happens to be at 90° angle against a planet (next to impossible), still the chance of getting metal-boiling temperatures would be very low, because, as you know, the planet surface would have to be exactly (or a few hundred plus or minus) kilometers to the focal point of that colossal lens.


Assuming that the objections noted by YoustayIgo about the form of the material being transparent don't apply (lets assume a bored god decided to play marbles), and also assuming that the material is cold and not going to undergo heating due to compression (as radiating objects are, to all intents and purposes, opaque in the wavelengths they radiate) it could be possible to engineer a situation where it could be an issue at certain distances from your transparent planetoid.

On the other hand: You've got to have a seriously bored god on your hands to engineer such a situation.


One short note, that will make you question the transparency of the planet-sized bodies. Transparency is defined as the relation between the intensity of passed through and incident light. It is always in the range [0..1], and is 1.0 only for the ideal vacuum. Solid materials have much lower transparencies, for example optical quartz glass plate that is just 10mm thick has transparency of about 0,999. 1 meter plate will only transmit 90% of the incident light. This is a part of why we use thin lenses anywhere.

  • $\begingroup$ Welcome to Worldbuilding! So you're essentially saying that a quartz glass moon would transmit a negligible amount of light? Are there any nonlinear effects that would need to be taken into account? $\endgroup$ Nov 25, 2017 at 8:32
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    $\begingroup$ @Mithrandir24601, yes, high quality glass moon will still be opaque. Best example would be modern optical fibers, that are specially engineered to be able to transmit single frequency optical signal over maybe 100km before the next repeater, and it will be several orders of magnitude weaker on arrival. Non-linear effects can take place, but I'm not familiar with this area enough to make judgements. $\endgroup$
    – ZuOverture
    Nov 25, 2017 at 9:09

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