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Much like our street lights but using lasers we can light the Moon even from the distance of the Earth. Most of the light reflected from the Moon will spread in all directions and not come back to Earth. So, even using lasers, the amount of light you'd need to shine on the Moon to see a spot on the Moon from Earth is the same amount as you'd need for streetlights - except - that if it is a visibly extended patch, covering much of the Moon, you get the issue that celestial objects that produce enough light to be visible as a single spot can become invisible to the naked eye if spread out, say, as a galaxy, over an extended area of the sky because of low surface brightness.

In short, this way around, it is very hard. If you could focus the lasers right down to a single city on the Moon - it could be useful perhaps, as a way to provide "street lighting" from Earth but if you did that, then as for our street lighting calculation, for even a large city the resulting spot won't be bright enough to be seen from Earth. There's an entertaining discussion here of the question "If every person on the Earth aimed a laser pointer at the Moon at the same time, would it change colour?

Shining laser light from the Moon to the Earth seems rather pointless, except perhaps for advertising. More examples here: Space Advertising wikipedia. The lasers would need to be spread over thousands of kilometers of the lunar surface to make a logo you could recognize from Earth, it's a mega project.

There would be much easier ways to advertise. Because they are closer to Earth, they wouldn't need to be nearly as bright, so cost far less to construct.

Put in a near polar low Earth orbit, and everyone on Earth would see your logo fly over at some time or another. I don't think there is anything in international law to prohibit this, in the Outer Space Treaty. But surely we'd have legislation to stop it if it became practical. Well I'd vote to prohibit it anyway - would anyone except the advertisers themselves vote for it? Hopefully if it ever becomes practical, illuminated signs on the Moon bright enough to be seen from Earth are not going to be permitted in the future :.

Sky writing and Aerial advertising is legal though, just not used that much, maybe because of the expense, see Aerial advertising wikipedia. The only examples I can think of are blimps and hot air balloons carrying messages, have seen those sometimes. And - you can put logos and advertising on the spacecraft and habitats themselves of course. So if this becomes a matter for legislation, I expect the laws will be quite complex, what you can and can't do by way of space advertising - and it would need international agreement world wide - a tricky thing to manage with space issues.

As I said in the article, not sure how likely any of this is. The fields seem the most likely in a way - but there are a lot of "if"s there - if the future Moon has extensive fields of 32 acres or more illuminated brightly with lights as bright as the sun, with the light being broad spectrum so including green light for the plants to reflect, and with the greenhouses not covered up at night?

As for deliberately shining a light on Earth - yes they could do it, but one wonders why anyone would attempt it. Even with advertising, it would probably be made illegal, and if not, there are much easier ways to advertise for much less expense. What is your best bet for some form of lighting on the Moon that might in the future be visible from Earth if we had large scale settlement there? This is just a fun calculation, and not meant to answer either way whether we should build such cities.

With the Moon, then it's much easier for planetary protection than, say, Mars. But it does have a few issues. This may mean we need some caution even for small numbers of astronauts living there and some of these will need serious thought if we ever have large populations even on the Moon. It certainly needs to be talked over, and not something that should just be "left to the scientists" to decide, as it is an ethical rather than a scientific decision.

So, anyway that's not the main focus of this article, whether or not we ever have big cities on the Moon, just fun to work out what we could see from the Earth with the naked eye. But it's interesting to note, that even the Moon, is not without some planetary protection issues as well, and ethical issues to discuss, if you have large numbers of people visiting it. This came up on quora a while back, as " When we colonize the moon, will people on earth be able to see the settlements' lights on its surface facing us even during a crescent moon?

What Are Days and Nights Like on the Moon? | HowStuffWorks

The anonymous questioner continues: "In other words, say it was a crescent moon, but there was a well-lit civilization on the part of the moon we wouldn't normally be able to see in the sky that night. Would we be able to see those lights from Earth? Would they light the surface well enough for us to see the surface like a full Moon as well?

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Please say in the comments if you spot any errors however minor, including typos and interested in any ideas or thoughts on any of this. Some of them are also available as kindle books. I have had a long term special interest in astronomy, and space science since the s, and most of Full Site.

Physical Sciences. Subscribe to the newsletter. Just For Fun. Robert Walker. It's a fun question to answer I think, so let's give it a go. We can work it out backwards from the brightness of the full Moon. I'll indent the rest of this calculation so you can skip it easily if you want. Magnitude Example Patch width in meters 7 Faintest stars visible from dark rural area at least miles from a city meters 6 from dark rural area at least miles from a major city meters 5 from dark rural area at least 40 miles from a major city meters 4 Faintest stars visible from suburbs meters 3 Faintest stars visible from the smaller cities meters 2 Polaris, the pole star meters 1 Pollux - head of the left-most of the twins in Gemini, or Spica, brightest star in Virgo meters 0 Arcturus or Vega - so amongst the brightest stars in the sky though not quite as bright as Sirius meters See "Astronomical magnitude scale" from the International Comet Quarterly - of course what you see depends a lot on your eyesight as well as your location.

Probably like this: JSC lunar base concept, Also, I rather expect that human habitats would have few windows, and the windows all tiny, as in this Bigelow mockup. Bigelow moon base mockup At most you might have occasional larger ones like the Cupola on the ISS but they would be rare, surely - that's because windows are really hard to construct when you have to hold in ten tons per square meter of outwards atmospheric pressure. The full movie, in restored colour , with machine translation subtitles for part of it but sadly not this section. A very large field, perhaps half a kilometer in diameter or more, if fully lit up with artificial light equivalent to the sun, on the Moon, would be as bright as a sixth magnitude star.

This is a photo I took myself, so copyright Robert Walker. It is of the corner of a field in the Scottish Borders - not sure of its acreage. We needed eleven million of them for equivalent of a sixth magnitude star.


Earth lights as seen from space - from the Earth observatory. Our calculation suggests these lights are not visible from the Moon to naked eye, and similar lights on the Moon would not be visible from Earth. Which is backed up by direct observation by the Apollo observations Back at the time of Apollo, our cities weren't as bright. A very rough calculation again, the Moon subtends 0. A whole sphere has 41, square degrees.

A one watt laser is very powerful and we need 3, of them. Or to be as bright as Arcturus, six magnitudes brighter, about 62, of them. Or about 31, of these 2 watt lasers. Of course you have the problem then of getting them to the moon. More examples here: Space Advertising wikipedia The lasers would need to be spread over thousands of kilometers of the lunar surface to make a logo you could recognize from Earth, it's a mega project.

Or off- piste skiing? The very thin lunar atmosphere, or exosphere. For instance, does the Moon have a water cycle? Does it get any water from the Earth also? Just one large landing by astronauts would change the entire atmosphere, it is so thin. There is no risk of Earth life replicating on the Moon but a landing by humans will leave spacecraft and human waste products locally around the lander , from their air, rocket fuel, and also from their own wastes. A city with millions of people would of course have a huge wastes problem on the Moon though probably most of it would be recycled.

A footprints and tracks problem. If you have millions of people there, eventually the entire surface around every settlement would get covered by tracks and footprints, which would not be erased by natural processes, even after millions of years. We have never explored a place quite like that before. So what would we do if the Moon gets really popular? Keep humans to special tracks, or sweep the surface after you walk or drive over it, or what?

At present anyway it is much more expensive to live anywhere else outside of the Earth - so seems people on the Moon or elsewhere would be supplied mainly from Earth. Still, with a population of rising to perhaps 11 billion people on Earth, and the Moon so close, once transportation to the Moon gets as easy as present day transportation to another continent - you might well get millions of people on the Moon as tourists, even with it costing far more to live on the Moon than on Earth. And where you have millions of visitors, probably get a few hundred thousand people at least living there permanently.

His contributions are also discussed in a biographical page in about. Thank you for your interest in this question.

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Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site the association bonus does not count. Would you like to answer one of these unanswered questions instead? Read more. Home Questions Tags Users Unanswered. Who discovered first that the Moon does not have its own light? Ask Question. Asked 6 years, 8 months ago. Active 2 years, 11 months ago. Viewed 27k times. Who and when discovered first that the Moon does not have its own light?

Shouldn't this be asked at History of Science SE? Cited source: Burnet J.

Black, London SEP's page on Anaxagoras has this note : The sun is a mass of fiery metal, and the moon is an earthy lump with no light of its own. I don't get what Rice has with middle-aged, weather-beaten cowboys, but it doesn't do it for me and I was annoyed to find that my third attempt with a Rice novel included yet another one.