Timeline for Approximately what percent of the sky has nothing in it?
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25 events
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| Feb 5, 2023 at 20:24 | comment | added | Mark Morgan Lloyd | Noting the comments about Mandelbrot etc., I'd like to highlight one possible wrong answer. When I was studying elementary science in the late 1960s and early 1970s, the syllabus textbooks stated that stars were too small to be resolved as other than points in any telescope, and completely omitted any mention of nebulae and of galaxies other than our own. There is a risk that somebody whose education or reading stopped at that level would argue that since the stars appear as points, the visible part of the sky (i.e. the part not obscured by the Earth) is empty of everything other than planets. | |
| Feb 4, 2023 at 14:49 | review | Close votes | |||
| Feb 9, 2023 at 3:05 | |||||
| Feb 4, 2023 at 3:05 | comment | added | Him | @SyntaxJunkie the "looking out" analogue to the "looking in" coast of Britain paradox is apparently Olber's paradox pointed out by @ mlk above. It seems to be resolved by our current understanding that we can only look so far out. Possibly the coast of Britain paradox is resolved by our current understanding that we can only look so far in. | |
| Feb 4, 2023 at 2:46 | comment | added | Syntax Junkie | This question is reminiscent of Mandelbrot's "How long is the coast of Britain?" (users.math.yale.edu/mandelbrot/web_pdfs/…) It depends on how closely you look. | |
| Feb 3, 2023 at 22:21 | comment | added | Michael Seifert | @mlk: I took a crack at running the numbers on your idea in my answer below, but I have no idea if I did it right. | |
| Feb 3, 2023 at 22:18 | answer | added | Michael Seifert | timeline score: 8 | |
| Feb 3, 2023 at 16:37 | answer | added | fraxinus | timeline score: 1 | |
| Feb 3, 2023 at 13:52 | comment | added | mlk | I guess, you could try running Olber's paradox in reverse and compare the average brightness of the nights-sky with that of the surface of an average star. This would give you a reasonable estimate on the proportion of directions that directly face a star. I haven't been able to find any reliable numbers that aren't about terrestrial light pollution though. But it is certain that the resulting number will be tiny. | |
| Feb 3, 2023 at 10:40 | answer | added | quarague | timeline score: 3 | |
| Feb 2, 2023 at 21:18 | answer | added | Mark Morgan Lloyd | timeline score: 17 | |
| Feb 2, 2023 at 18:00 | history | tweeted | twitter.com/StackAstronomy/status/1621206838942339073 | ||
| Feb 2, 2023 at 17:51 | history | became hot network question | |||
| Feb 2, 2023 at 12:39 | vote | accept | Him | ||
| Feb 2, 2023 at 12:29 | comment | added | ProfRob | See also astronomy.stackexchange.com/questions/17990/… but note that galaxies are mostly empty space and that most photons would just go straight through them. | |
| Feb 2, 2023 at 12:25 | comment | added | ProfRob | "For a given resolution, driving the depth to infinity sends the proportion of "nothing" to 0, but for a given depth (i.e. exposure time), increasing the resolution increases the proportion of sky that has nothing? " this is an accurate summary. | |
| Feb 2, 2023 at 12:24 | answer | added | ProfRob | timeline score: 24 | |
| Feb 2, 2023 at 12:09 | comment | added | Him | @ProfRob what if we phrase it in the opposite direction: we shine a photon in a random direction. What is the probability that it hits something? This is similar, but seems to skirt these problems with resolution and exposure time. | |
| Feb 2, 2023 at 12:04 | comment | added | Him | @ProfRob so depth and resolution have opposite effects, then? For a given resolution, driving the depth to infinity sends the proportion of "nothing" to 0, but for a given depth (i.e. exposure time), increasing the resolution increases the proportion of sky that has nothing? | |
| Feb 2, 2023 at 12:01 | comment | added | ProfRob | So the question really can only be posed as what fraction of the sky is effectively empty of resolved objects down to some brightness limit. Even then it is quite hard to define what is exactly meant by that. | |
| Feb 2, 2023 at 11:59 | comment | added | ProfRob | Yes - that is indeed what I mean. Although here, "resolution" is the wrong word. Better resolution means that you can more easily resolve objects from each other so that there is a gap between them. I really mean "depth", in the sense that as your telescope collects more and more light it can see more and more (fainter) objects and eventually your finite resolution means that there are no gaps between them. | |
| Feb 2, 2023 at 11:31 | comment | added | Him | @ProfRob do you mean to imply that the proportion of sky that appears to have nothing in it approaches 0 as the telescope we use to measure it gets better and better resolution? | |
| Feb 2, 2023 at 11:30 | history | edited | Him | CC BY-SA 4.0 |
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| Feb 2, 2023 at 11:23 | comment | added | ProfRob | It's very hard to answer your question unless you provide a definitive list of stuff and how far away/how bright it needs to be. Obviously as you go deeper and deeper them more and more things become apparent at greater distances. | |
| Feb 2, 2023 at 11:23 | history | edited | Him | CC BY-SA 4.0 |
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| Feb 2, 2023 at 9:50 | history | asked | Him | CC BY-SA 4.0 |