Let's say there is a HUGE orbit for planet x, and somewhere in the orbit, there are some debris or clouds or anything else.

Can any of these block the light and stop it from reaching the planet x?


  • $\begingroup$ You mean like, lets say, a moon during an eclipse? $\endgroup$ – Anedar Jun 10 '17 at 22:36
  • $\begingroup$ yes exactly like that but without the moon or a planet. something like a cloud of debris or a gas cloud ... $\endgroup$ – Maxwell Jun 10 '17 at 22:42
  • $\begingroup$ the light for our sunny days is blocked by a myriad of particles ranging on different sizes, from atomic to dust to human sized, both natural and artificial, and there also are larger objects such as the space attestation. But the dark spot they would create is so blurred and so filled with skylight, that the contrast of their shadow is imperceptible to us. $\endgroup$ – user126422 Jun 11 '17 at 1:14

I mean, it depends on the relative sizes of everything involved, of course.

Sometimes, Venus transits across the Sun from Earth's perspective. It's a pretty big thing to pass across the Sun, but it's very far away and so it appears to us as a small dot blotting out only a speck on the Sun. (Feel free to look up images of this, there are a bunch.) Lunar eclipses, by contrast, blot out nearly the whole Sun, because the Moon is closer to us.

So the "huge orbit" thing helps because the Sun gets smaller in the sky as you get further away from it. But you still need things to be near you in order to really obscure it, so presumably the things that are blocking the Sun will be orbiting the planet in question.

That's where things get very difficult, because it's not stable for a single big rock to just sit between the Sun and the target planet causing a permanent eclipse -- there's even a point at which the gravitational forces of the two bodies and the centrifugal force of orbit all happen to coincide and there is 0 net force, called the L1 point, but unfortunately it is a "saddle point": perturbations in the angular orbit will be sucked back to the L1 point (this is called "negative feedback" and stabilizes systems) but perturbations towards or away from one of the two gravitating bodies will be lightly sucked towards whichever body you move towards (a "positive feedback loop" that will lead to this thing leaving the L1 point and not coming back for an extremely long time, if ever).

But a lot of rocks could orbit the planet stably and still cast a shadow on it. For this, I have some slight bad news for you: those systems seem to quickly become 2-dimensional, like Saturn's rings. Now Saturn's rings do cast a massive shadow on Saturn, but the problem is, you can't get more than a little under a quarter of the planet's surface that way (half of the lit half).

  • $\begingroup$ Thank you, it was very informative. and thanks for talking about L1. and the star in that system can be bigger and brighter than our sun .what if a big giant like Jupiter was swapped with Venus? $\endgroup$ – Maxwell Jun 11 '17 at 9:20

Well CR Drost covers it correctly but I would like to answer some other ways due to which starlight fails to reach a planet so here goes (sorry if it does not answer your question ): 1. If the star originally on the edge of light cone of an event ( in this case a planet ) moves out of it , its light ceases to reach the planet due to acceleration of space being much greater than speed of light. 2. In presence of super large galactic clusters or black holes in path of light which cause starlight to undergo gravitational lensing. 3.Due to a specific relative rotational movement of star(its parent galaxy) and the point of observation. Well there are more but these are more established phenomenons , however I just wanted to provide more info for a casual viewer wanting more out of this question.


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