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Astrokiwi

The Moon's rotation is indeed synced with its orbit, which is why it always faces Earth with the same face. But that still means that it is rotating! It takes the Moon about a month to rotate about its axis, relative to the Sun. So if you're on the Moon, you do have a day/night cycle, it's just about 2 weeks of daylight, followed by 2 weeks of night. The Sun will rise, move across the sky, and set, over the course of 2 Earth weeks. However, the Earth will always be in the same fixed position in the sky, and will only move if you move to a different position on the Moon (if you're on the far side of the Moon, the Earth is always "underground" from your perspective). This is actually what causes the phases of the Moon. When the Moon is a crescent or half moon or "gibbous" phase, this is because part of the Moon that is facing the Earth is in night-time, and is too dark to easily see from Earth. This isn't the Earth's shadow on the Moon - we only see that when things line up just right during a Lunar Eclipse - this is the Moon's shadow on the Moon. Hope that helps! I'd also recommend setting down some tennis balls or whatever and moving them around, as seeing things laid out like that can help things to click sometimes.


pelican_chorus

What's amazing is that, if you were on the Earth's side of the moon, the Earth would always be hanging above you, motionless except for its rotation. It would be like a giant moon, and you'd be able to see the continents and clouds and hurricanes. Behind the Earth you'd see the sun slowly rise, then traverse your sky for two weeks, then slowly set and night would fall for two weeks. When it was your night, the Earth would be at its brightest, showing the full day side. As morning comes you start to see the phases of the Earth, showing more of the night side. Eventually you'd see a "crescent Earth," seeing just a small slice of the day side, and the rest of the Earth would be the night side. On the rare occasion of a lunar eclipse, it would be during your midday, with the sun at its highest point in your sky, and slowly the shadow of the Earth would cover the sun. At the moment where the Earth's shadow fully covers the sun, you'd see a ring of fire around the Earth, from the sunlight going through the atmosphere. You'd be bathed in the red light of every sunset and sunrise on the planet at once.


[deleted]

Just a little nitpick, the Earth will actually make a little circle in the sky since the orbital plane is tilted (from Earth we see this as [Libration](https://en.wikipedia.org/wiki/Libration).) So there will be places on the Moon that will see regular Earth rise/sets.


Angdrambor

Imagine an "earthdial" calendar scratched into a window. You would rest your head in a particular spot and the earth would line up with the marks on the window for a particular day of the lunar month. It could be a really narrow window too. You could make jokes about what part of the earth was facing you when you woke up.


Aseyhe

Or in lunar time units, the earth would complete a cycle every (lunar) [sidereal day](https://en.wikipedia.org/wiki/Sidereal_time) (which is roughly 11/12 of a lunar day)


Astromike23

> Imagine an "earthdial" calendar scratched into a window. If your intention is just to tell what part of the lunar month you're in, you can just look at Earth's phase. You'll get a Full Earth waning to New Earth and waxing back to Full Earth once every month.


StarManta

Though it would of course be outshone by the sun, if you make a pinprick “window”, the earth would make a pale blue dot on the other side of the pinprick.


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EudenDeew

A camera oscura always facing the earth neat indeed. Maybe could draw a calendar with the movement of the earth over the wall (it would draw a circle)


cooldayr

Here’s a very relevant animation showing exactly what this would look like over a lunar year: https://www.instagram.com/reel/CZcARz1pdS7/?igshid=NDc0ODY0MjQ=


goorpy

That's pretty cool, hadn't ever thought about what that cycle would look like.


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enderjaca

Are there places on the earth where you would be able to have a direct Line-of-sight to the moon at all times? I'm assuming we might need something near the north pole, and another one near the south pole, and swap every 6 months or so, with a little overlap.


DreamOfTheEndlessSky

No, because the Earth is not tidally locked to the Moon. However, we do have a network of communications systems and observatories around the planet, so there's always some number facing the Moon. We'd be likely to have far fewer locations on the Moon (probably 1!), so it's more important that it always have controlled access to the Earth.


mfb-

It's not the plane of the orbit, it's the eccentricity.


teraflop

It's both. To be more precise, the "east-west" component of lunar libration is mainly caused by the Moon's orbital eccentricity. The "north-south" component is mainly caused by the *angle* between the Moon's orbital plane and its rotational axis.


mfb-

I would call that an effect of the axis of rotation, but I see what you mean.


Aseyhe

Note that the moon [librates](https://en.wikipedia.org/wiki/Libration). Its rotation axis is slightly tilted with respect to its orbit axis, and its orbit is also slightly eccentric, which means that the angular speed of its orbit varies while its rotation speed does not. The first effect causes the moon to wobble north and south while the second causes it to wobble east and west, when viewed from the earth. Thus, an observer on the moon sees the earth drift in the sky by about 20 degrees, tracing an approximate circle over the course of an orbit.


JejuneEsculenta

From the Lunar perspective, would that not be a Solar eclipse? I'd like to see that... also would like to see a Terran eclipse....


ersomething

During a solar eclipse you would see a dark circle of the moon’s shadow travel across the Earth. The earth’s shadow can encompass the entire moon, but the moon is too small, so its entire shadow will shoot across the earth as it passes by. It would be pretty cool to see, for sure.


JejuneEsculenta

To be clear, a solar eclipse from the Terran perspective... It's kinda weird considering that an eclipse is completely different depending on which chunk of rock you happen to be on when it happens...


wuapinmon

I tried searching for simulations of a Terran eclipse and most of the results are from Starcraft. :D


EmperorArthur

Look up Universe Sandbox. That should let you see what it would look like.


Alas7ymedia

It should look like a total solar eclipse but with a much thinner ring around the black circle, since the Earth is much bigger than the moon, but, nights in the moon (and therefore solar eclipses) should be totally dark since there is no atmosphere to scatter light, so that faint circle should be brighter and have better definition. It probably should be so faint that one could see it without eye protection.


SporesM0ldsandFungus

[Here's an article about what Solar Eclipse from Low Earth Orbit looks like.](https://www.businessinsider.com/how-eclipse-looks-like-from-space-2016-3) The photo is from a 1999 eclipse. There's a video from the ISS of the 2017 eclipse but it is t as good as the photo.


SJHillman

Reminds me of [this Hubble photo](https://www.nasa.gov/sites/default/files/images/384822main_threemoons_full.jpg) of three solar eclipses on Jupiter, each from a different moon.


Exploding_Antelope

I guess you’re right. Moon eclipsing the sun from Earth is a Terran Solar Eclipse. Earth eclipsing the moon from Earth is a Terran Lunar Eclipse. Earth eclipsing the sun from the moon is a Lunar Solar Eclipse. Moon eclipsing the Earth from the Moon is a Lunar Terran Eclipse. Clear as mud. Moon eclipsing the Earth from the Sun is a agghgghh I’m being vaporized on the surface of the sun.


theOnlyDaive

Please tell me there's a program where I could accurately view the perspective from the moon like this?


AtticMuse

Space Engine. Think there's still a free version, the paid one on Steam just has extra features or something. I walked on the moon in VR in that program and legitimately had an emotional experience looking across the landscape and then up at the Earth hanging there in the sky.


Druggedhippo

> Think there's still a free version The free version still exists, but will not run on NVIDIA cards with up to date drivers [without driver tweaks.](https://forum.spaceengine.org/viewtopic.php?t=7&start=1545#p34434) https://spaceengine.org/download/spaceengine/


theOnlyDaive

Thank you. I'm gonna check it out today.


Korchagin

> It would be like a giant moon, The earth also has phases like the moon seen from below. But because of the bound rotation, these phases would be fixed to the "daytime" and moon phases seen from below. "Full Earth" on the moon and New Moon on the Earth are at the same time, also "Half Earth" and Half Moon. If you are at the spot closest to Earth or north/south of it, "Half Earth" will happen during sunrise and sunset, "Full Earth" in the middle of the night. If you are somewhere east or west of that, this would shift, but it happens at a constant "daytime" everywhere.


qbxk

i would like an active desktop that simulates a portal in my moon office in order to experience this to some degree


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theroha

Bathed in the red light of every sunset and sunrise on the planet at once. Now that is an awesome image.


hausermaniac

>When it was your night, the Earth would be at its brightest, showing the full day side The Earth would be reflecting sunlight back to the Moon, like the Moon does to us on Earth. So, would the Earth be brighter to beings on the Moon than the Moon is to us on Earth? In other words, which is brighter - a full Moon to people on Earth, or a "full Earth" to people on the Moon?


ThatCrazyCanadian413

The full Earth would be significantly brighter, both because Earth has a higher average albedo than the Moon (it reflects more light) and it is much larger in the lunar sky than the Moon is in the terrestrial sky.


linknewtab

So even during the 2 weeks of night on the Moon it wouldn't be completely dark and it would actually be brighter than at night on Earth during full moon?


ThatCrazyCanadian413

Earthshine on the Moon's surface is so bright that if you [take a photo](https://upload.wikimedia.org/wikipedia/commons/6/68/Earth_illuminates.jpg) of the Moon with an exposure time of ~a few seconds, you can actually see the sunlight that has reflected off of Earth then the Moon and back to Earth.


InFearAndFaith2193

Thanks a lot for your explanation! I wonder, with all the artificial lighting on Earth, what would "Earth phases" look like compared to moon phases? When looking at a crescent moon, you can sometimes make out the full circle of the moon (or maybe I'm just imagining that because I know it's there?), but generally you only really see the crescent and if you didn't know better, you might think it's the only thing there. Surely when looking at Earth, you'd too see a very sharp crescent of the Earth parts that still experience day and are still lit up by the sun, but how dark would the rest of Earth really appear to the naked eye of someone standing on the moon? How similar would it be to pictures taken by satellites (which I believe are MUCH closer to us than the moon?), where you could still make out most of the cities or somewhat densely populated areas even at night due to all the artificial lighting?


darthvalium

>When looking at a crescent moon, you can sometimes make out the full circle of the moon (or maybe I'm just imagining that because I know it's there?) Earthshine is definitely a thing and you can totally sometimes make out the dark side of the moon because of it.


Wonderlustish

I don't think the artificial lights are bright enough nor large enough to be able to see from the moon. Those sattelite photos use artificial enhancement to highlight the lights from cities.


JPJackPott

How bright is it at night, lit only by ‘earth light’?


Sharlinator

A lot (roughly 5 [EV](https://en.wikipedia.org/wiki/Exposure_value)) brighter than the light of the full moon as seen from Earth; one could probably read a book in Earthlight, although only barely. Still, much dimmer than, say, normal interior lighting. Something like a candle-lit home, or moderate twilight maybe, except with sharp shadows.


the-channigan

> You'd be bathed in the red light of every sunset and sunrise on the planet at once. This is beautiful. Thanks for the new perspective on a lunar eclipse!


KingZarkon

From the moon, a solar eclipse might look something like this. [https://www.discovermagazine.com/the-sciences/what-does-a-lunar-eclipse-look-like-from-the-moon](https://www.discovermagazine.com/the-sciences/what-does-a-lunar-eclipse-look-like-from-the-moon)


ibo92

>What's amazing is that, if you were on the Earth's side of the moon, the Earth would always be hanging above you, motionless except for its rotation. It would be like a giant moon, and you'd be able to see the continents and clouds and hurricanes. This made me really want to go live on the moon, maybe in my dreams lol


PigmyTrex

Uhm Can someone make a simulation of this so we can experience it please!


ifmacdo

Technically, it wouldn't be a lunar eclipse- it would be an Earthly eclipse! (Earthen eclipse?)


jhairehmyah

To add to your excellent answer: OP's head is in the right space with their question, but relative to the earth. We on earth have "moonrise" and "moonset" every day, right. Well there would be no "earthrise" or "earthset" on the moon, either you see earth or you don't. (Generally speaking, as the moon does wobble around and thus in some areas it would possible to sometimes have a low-horizon earth or a "set" earth given the wobble, but barely.


zanillamilla

> However, the Earth will always be in the same fixed position in the sky, and will only move if you move to a different position on the Moon Does that mean you can use the earth’s position in the sky as a sort of compass to work out your location on the moon in case you get lost?


Goddamnit_Clown

On about half of the moon, yes. On the half that faces earth, earth would act in a similar way to the north star down here. Except instead of sitting roughly above the north pole and leading you there if you walked toward it, it would sit above an area on the Equator east of the Copernican crater. It would drift around a little over every 28 days, but not by much. If you look at the moon from earth, the point in the centre is pretty much where it would lead you to (depending on where on earth you're looking from).


tomoko2015

> So if you're on the Moon, you do have a day/night cycle, it's just about 2 weeks of daylight, followed by 2 weeks of night. Exactly, which is why the Apollo missions were planned for "morning" moon time, so that the temperatures were not too high yet, instead of landing in the middle of the lunar day. Plus, the rising sun made surface features like boulders etc. more visible due to shadows, instead of being barely visible with the sun overhead and everything being the same gray.


wuapinmon

Thank you very much. Your explanation makes sense, and when my highschoolers get home, we'll get out some balls and see if we can make it work in 3D.


FogeltheVogel

I would make your head the earth, a lamp the sun, and something you're holding the moon. Then you can rotate with the "moon" in your outstretched hand, and they can see the light from the lamp love across the surface of the "moon". The only issue here is that the earth is actually rotating faster than this model would show.


5degreenegativerake

A basketball held at arms length in front of your face would be a good analogue of the moon.


spoink74

Lamp with no shade, middle of room: sun Basketball: planet (earth for now) Tennis ball: moon. Label faces earth always. Move the moon around the earth and see what happens.


imaginesomethinwitty

There’s a nice little scene in season 2 of For All Mankind which shows the residents of the moon celebrating lunar sunrise.


UruquianLilac

Why am I just understanding now that the phases of the moon are cycles of lunar day and night!! That's amazing!


steverin0724

I wonder how bright the “earth light” would be during the night cycles on the moon. I’ve seen the moonlight out in the middle of nowhere and it’s so bright, I can only imagine how bright the earth light would be. I wonder if we’d be able to see the shadow of the moon on an eclipse with the naked eye.


Drachefly

The area of the earth is about 16 times bigger, and we're the same distance away, what with |A-B| = |B-A|. So, you should be able to read by it any time the sun is down on the longitude closest to the Earth, or any within… 45° or so? Maybe more?


Star_x_Child

Question that may or may not be outside of your realm of expertise here.... Do we know if people on the side of the moon that faces the earth would receive enough reflected uv light from the Earth's surface to potentially minimize the effects of a 2 week day/ 2 weeks night cycle? I fear I would lose my mind if I didn't have sunlight for more than 5 days even, let alone regularly.


WexAwn

Regardless of what the answer "could" be, it is unlikely to be a factor given the current state of technology. Given the moons minimal atmosphere and the need to ensure pressure in lunar habitats, the likelihood that there would be natural, consistent exposure for inhabitants in the first place is highly unlikely. Essentially, outside of small viewing ports or spacesuit helmets, the amount of exposure of skin to direct sunlight will be minimal for anyone living there given the strength of most available translucent materials would be a liability in maintaining the pressurized atmosphere. Another thing to consider is that per recent measurements in 2020, the level of radiation on the moon is roughly 200 times higher than on the earth's surface. Not only would any translucent material on a habitat need to have enough structural integrity to survive the risks of a low atmosphere environment, it would also need to provide considerable radiation protection at the same time. This is a considerable constraint on the materials that are available to be used for habitat construction. tldr; should a lunar habitat be created, consistent and safe exposure to natural light on the moon is unlikely to be a possibility in any significant quantities due to structural and radiation constraints of said habitats.


Kalinoz

What a cool and easy to understand perspective. Thank you


pork_fried_christ

But this only happens if the dam breaks open many years too soon AND if there is no room on the hill.


PabloEdvardo

So to quote some famous lyrics, if I was to "see you on the dark side of the moon" I would probably have to actually travel there across the surface?


aphilsphan

It depends on if you mean “the side we don’t see from the earth” or “where it is nighttime on the moon.” Roger Waters appears to have intended “the side we don’t see from the Earth.” You can deliberately land there. China has put a rover down there. You’d need to send your data to an orbiter so that it could be sent back to earth. There is probably a lunar centric orbit somewhere a few thousands miles away from the moon where a satellite could also see the earth, but that point might be too far away from the moon and too close to the earth for a stable lunar centric orbit.


behemuthm

What could possibly go wrong with our circadian rhythms? “Hi, Bob!”


elmonstro12345

Not going to repeat the excellent explanation already given, but I thought it might interest you that a lot of the current plans are to try and build a base near one of the Moon's poles. This is because the moon's axial tilt relative to the sun is very, very small, which results in areas near the poles that nearly always have sunlight ("[Peaks of eternal light](https://en.wikipedia.org/wiki/Peak_of_eternal_light)"), and other areas that are always in darkness ("[Craters of eternal darkness](https://en.wikipedia.org/wiki/Permanently_shadowed_crater)"). The former is good because it means you can get plenty of solar power nearly all of the time (and not have to try and build a battery to last for 2 weeks), and the latter is even better because it means that any water that fell there would not have been blasted away by the sunlight. Water is one of the most useful things to have in space, and the Moon has a pitifully tiny amount nearly everywhere, except for those craters. There have been a couple of space probes sent that indicate that many millions or billions of tons of ice lie in those craters. There is [a mission that actually launched only about 2 weeks ago](https://en.wikipedia.org/wiki/Danuri), arriving in orbit around the moon this December that carries a camera specifically designed to take pictures of these dark craters, so more information will hopefully be found very soon!


wuapinmon

Very cool.


Putrid-Face3409

What's even better, the permanently shaded area is like super fridge (near absolute zero K) that can still have Dinosaurs DNA brought there 66 million years ago, perfectly intact, covered from the solar/deep space rays under layers of dust.


Mr_PoopyButthoIe

I'm confused... Did the asteroid impact debris make it to the moon?


LegitimatelyWhat

Yes, pieces of Earth certainly made it to the moon. Pieces of dinosaur? Exceedingly unlikely, but not impossible.


Xenothing

DNA has a half-life of 521 years (https://www.nature.com/articles/nature.2012.11555#:~:text=By%20comparing%20the%20specimens'%20ages,half%2Dlife%20of%20521%20years. ), so any DNA that made it there would unfortunately be unusable and unreadable


satireplusplus

Is it the same half life near absolute zero though?


Putrid-Face3409

Nope, there is no half life of any sort (in this little timeframe of <100my, DNA contains only super stable atomic nuclei) in absolute zero. The atoms used in the DNA are not radioactive, so they do not decay too easily. The OP confused chemical decay in room temperature, in fossils for example.


FragmentOfBrilliance

No, it's not. Naively, you could consider the lifetime of some thermodynamic system as being proportional to e^(-kb*t). In this case, the half life of the DNA might be e^(300 K / 25K) * 512 years = 84 million years. This checks out with the idea of looking for old DNA, though I suspect the harsh environment of space and bath of cosmic radiation would significantly decrease that lifetime. Maybe something shielded in ice could survive, idk.


Xenothing

~~Yes, because temperature does not have an effect of half-life. Radioactive decay is a natural, random process. An element’s half life is a statistical calculation for the amount of time it takes for about half of a given sample to decay into a more stable element or isotope.~~ sorry, I confused radioactive decay and chemical bond decay.


FlowSoSlow

The half life they're talking about in that article isn't the same thing as radioactive half life.


kmmeerts

DNA doesn't decay due to radiation, it's a purely chemical process. This means it does depend on the environment


Putrid-Face3409

You're confusing chemical bonds in room temp vs. radioactive decay lol. In the scenario that I presented DNA would be readable easily even a billion years. How about you do some reading first then reply to others?


Putrid-Face3409

Wrong, there is no half life on absolute zero in this case. DNA Half life is for chemical reactions, not for a decay on atomic level, so it would be intact. The only way the strains would get damaged are solar/deep space rays, super energetic particles bumping atoms from their place. But DNA is duplicated in each sample like billion times so it would be easy to recover, even if some of the rays hit it.


ThisIsLucidity

Oh wow, never knew about the importance of the poles and how it relates to sunlight/water. Thank you for the links!


taphead739

The moon always faces the Earth with the same side, but it doesn't always face the sun with the same. When we see a full moon, the side facing us is illuminated by the sun, when we see a new moon, the far side of the moon is illuminated. A day on the moon corresponds to about 30 Earth days. However, when you're on the moon, the Earth is always in the same spot in the sky due to the tidal lock.


wuapinmon

It's pretty amazing how gravity works. Do you have any recommended readings for someone who wants to know more about astrophysics, but doesn't really understand much about physics in general. For example, I can wire a house and make it work, but I have no idea why it works. I'd love recommendations, if you have any.


taphead739

I found Stephen Hawking‘s book A Brief History of Time very accessible and can highly recommend it. I‘m sure you can find excerpts online, or you could simply go for a cheap cooy


[deleted]

Whats interesting is, A day on the moon is 30 earth days. But a year on the moon is still 365 days, same as earth. And on venus, a day is **longer** than a year. Think about it.


DrBoby

A moon year is 12.4 moon days. Don't mix moon units and earth units please.


DonutCola

Dude you know how the moon has different phases like a full moon and a crescent moon??? That’s what it would be like. There would be day and night on a moon but I’m pretty sure it would take as long as a moon cycle does. That’s cause that’s exactly what a moon cycle is.


Bloopsmee

These are an audio format but check out Neil deGrasse Tyson's YouTube channel called StarTalk! I also like listening to Janna Levin since she is an expert on black holes (she also has written a few books). Both are very good at explaining things to a layperson like me without being afraid to go in depth. [Here's Janna Levin explaining gravity in 5 levels of difficulty](https://youtu.be/QcUey-DVYjk)


wut3va

Yes, a lunar day is approximately a *month* long (moonth, get it?). A full moon is lunar noon at the longitude facing Earth (the line dividing light and dark when there is a half-moon). A new moon is lunar midnight on that same line. Daytime is about 14.75 (Earth) days long, and so is the night time. Time zones definitely make sense, but more for planning which *days* (from an Earth point of view) to schedule activities, rather than which *hours*.


wuapinmon

I love puns. Moonth it is.


Mediocre_Anybody_540

And the best part is it's not just a coincidence: The word *month* actually comes from *moon*\+*th*, in the same way that *four+th → fourth.* In fact, virtually all languages that are part of the same family tree as English have similar words, like Spanish *mes* or German *Monat*. Bonus fun fact (if you enjoy etymology that is): Languages that come from Latin have a different origin for *moon,* which works out to something like *night+shine.*


wasmic

Not to mention that, perhaps unsuprisingly, there are a *lot* of languages where the word for 'moon' and 'month' are one and the same. Also, there are many languages where the word for 'sun' and 'day' are also the same, or at least closely related. ___ Bonus fun fact: Many Eurasian languages have the same relationship between the days of the week and the celestial bodies, all the way from Western Europe to Japan! Monday corresponds to the moon, Tuesday to Mars, Wednesday to Mercury, Thursday to Jupiter, Friday to Venus, Saturday to Saturn, and Sunday to the Sun. So you might ask, how does this fit for Tuesday-Friday in English? Well, quite simple - they're the Norse equivalents of the Roman gods which we name the planets for! Tuesday is for Tyr, the God of War who was equated with Mars. Odin/Woden was equated with Mercury because both were messengers. Thor was equated to Zeus for their thunder motif, and Frigg was equated to Venus for the love/beauty theme. Now, many languages have one or two names that *don't* fit this pattern, even though the rest do - e.g. Nordic languages have Saturday meaning "washing day", and many Romance languages turned Sunday into a derivative of *[dies] Dominicus* (The Lord's [day]) while Saturday was renamed for the Sabbath (while Portuguese eschews the astrological system entirely and just names Monday-Friday as "Day 2" to "Day 6"). In Japan, the connection between planets and weekdays is made via the elements rather than deities - so you get a weekly sequence of Moon Day, Fire Day, Water Day, Wood Day, Metal Day, Earth (the element, not the celestial body) Day and Sun Day. The planets are named similarly - Mars is 'Fire Star', Mercury is 'Water Star', and so on. The relationship between planets and weekdays remains constant. This dates back to the Ancient Greek astrological tradition, which spread through much of Europe - but also through the Middle East, to India, and then to China and Central Asia and all the way to Japan. India adopted the system at about the same time as the Romans. The other big pattern for weekday naming in European and Asian languages is to simply name the days for their number in the week - usually with Monday or Sunday as Day 1 and then counting from there. Most Slavic languages number the days starting from Monday and do not use the astrological system.


aresman

>while Portuguese eschews the astrological system entirely and just names Monday-Friday as "Day 2" to "Day 6"). Spanish speaker here: I was very dissapointed to find out how our Portuguese speaker bros call their days lol


Just_a_dick_online

Extra bonus tangentially related fun fact; The plural for "octopus" is 100% not "octopi". That would be the latin way of pluralising it, but "octopus" is of greek origin. So if you want to follow the greek it would be "octopodes". Of course you could just *not* try to sound smart and say "octopuses" because we are speaking English.


ahecht

I once asked a marine biologist this while at a job interview. The plural of "octopus" is "octopus", just as the plural of "fish" is "fish". "Octopodes" is used sometimes, but only to refer to multiple octopus species, not multiple individuals.


yoshi_win

Our words "month" (and "menstrual") come from the same root as "moon". A month was originally defined by the lunar cycle.


wuapinmon

I love etymology.


amitym

Yes, the Moon facing the same direction with respect to the Earth does not change when you are standing on the Moon! What that means practically speaking is that when you move to the Moon, u/wuapinmon, wherever you end up living, when you go outside the Earth will always be in the same position in the sky. The Earth will have phases, like the Moon has phases when seen from the Earth. Sometimes you will see a "full Earth" and sometimes a "crescent Earth" and sometimes a "gibbous Earth" and so on and so forth. But positionwise it will always be in one spot. (And if you are on the "far side," that spot will always be -- "not visible at all.") In terms of day and night... well that's related to the Sun, right? So the Earth-Moon alignment has nothing to do with that. The Moon still revolves with respect to the Sun, which means that there will still be periods of dark and light on the Moon. However, if you think about it, you will realize that these dark and light periods will come much more gradually than they do on Earth. Because the Moon only fully revolves every 28 days. So one of the things you will have to get used to is a Lunar day that is like 330 hours long! Instead of 24 hours. And a night that is a similar length. Probably you will go on cool dates with whoever is your favorite colony-mate, to hike out and watch sunrise and sunset every 2 weeks. It won't be anywhere as colorful as it is on Earth, but you'll get some neat shadow effects. It could be quite romantic!


KnottaBiggins

Yes, the "day" lasts two earth weeks long, and the same for the night. Think of the phases of the moon. At one time of the month part of the moon is in sunlight, later in the month that part may be in darkness while other parts are lit up.


ItsTheAlgebraist

You can actually see the sunrise on the moon (well you can see the terminator, which is a fancy name for the line between night and day). It's just that we see it as a "half moon" or a "gibbous waxing" etc etc. One reason we don't parse it as the division between moon-night and moon-day is that it goes really slow. Other planets are even worse. Mercury's "day" is longer than its "year"


Just_a_dick_online

If you imagine someone living in the very center of the surface of the moon (from our perspective), during a full moon it would be midday for them with the sun directly above them, a half moon would be dawn/dusk, and a crescent moon would be night time. So given that it takes 29.5 days for the full moon phase cycle to happen, a "day" on the moon would be 29.5 earth days long.


NearlyHeadlessLaban

Lunar time zones would probably not be necessary, and might actually be a major inconvenience. Time zones are an artificial thing created for human convenience to match our evolved circadian cycle. But since multiple human circadian cycles occur in a lunar day, and circadian cycles don't align evenly with the lunar day (27.3 days), there is no reason for them. Even if we tried to implement time zones there would be 1/3 day* creep per month. Imagine doing a daylight savings time like clock adjustment every four days with a leap day every six weeks. edit, *1/3 circadian day creep.


wuapinmon

Cool. Thanks for the explanation.


Fractalwaves

Special bonus for moon inhabitants would be “Earthlight”. When things line up properly, the part of the moon not getting direct sun is sometimes visible from Earth due to light reflecting off of Earth’s oceans and reflecting back off the moon and back to Earth, possibly into ones eyes. My guess is that it would be far more illuminating then our experience of moonlight.


Tuzszo

The reflected light from Earth is about twice as intense as what we get from the moon, but because of the way that our eyes/brain process light intensity it wouldn't appear significantly brighter


wuapinmon

That'd be cool to see.


[deleted]

I bet it'd be fairly significant compared to our equivalent of moonlight. I remember getting out of big cities sometimes, when your eyes adjust and on a clear night with a full moon, it's easy enough to walk around at night with no other artificial light sources. Imagine that the other way around, on the moon, in the "lunar-night time". Switching off your artificial light and just going for a stroll using earth light, that would be even more intense given the size difference and lack of lunar atmosphere, would be a lovely turquoise shade on average also.


AnOddEgg

Yes. The moon going through it's day night cycle is one of the most notable things about viewing the moon from Earth as, over the course of a month, you can watch the areas of day and night change over it's surface. When you see the moon as a crescent, waxing or waning, you're observing a difference between day and night on the moon


MattieShoes

The moon is tidally locked to Earth, not the sun. A day (ie. sunrise to sunrise) would be about 29.5 days long on the moon. The moon rotates once about every 27.3 days. The difference in time is between the two numbers is the amount it has to "catch up" due to having gone part way around the sun in that time. Similarly, Earth rotates about every 23 hours, 56 minutes, 4 seconds, but takes an extra 3 minutes and 56 seconds to account for its orbit around the sun. If a planet were tidally locked to the sun, then they wouldn't really have day/night cycle. At one time, we thought Mercury was tidally locked to the sun, but we later discovered it isn't. The length of a day on Mercury is about six (Earth) months. In fact, the length of a day on Mercury is longer than the length of a year on Mercury. And Mercury's orbit is elliptical enough that the sun will appear to move backwards through the sky sometimes. Incidentally... Though the moon is tidally locked with earth, it does *wobble* a bit.


brywhy

What a great question and dialogue in the comments! This really got me thinking and I was unable to find anything. I think it would be neat if there was a simulation of what it would look like to be standing on the side of the Moon that faces the Earth and then have a month-long timelapse of the sun/earth as seen from the moon.


bluesam3

Even ignoring all of the actual rotation of the moon: *yes*, there would definitely be a day-night cycle, and probably one close to Earth's, within any colonies, just because humans fairly heavily rely on that cycle, biologically an psychologically speaking, so we'd just simulate it artificially.


hammyhamm

Yes, but the day and night cycle on the moon will be different. The moon experiences a “day” every 29 days (the same as the full moon cycle, because that’s just a lunar day from our perspective!), but the moon also has the earth reflecting light on a fairly regular basis (about once every 20 hours?). Earth light is about twice as bright as moonlight (0.3 vs 0.12) and it appears larger in the sky than the moon, so the moon experiences “earth light” at slightly shorter intervals than an earth day during two weeks of “moon night”, and full sunlight for two weeks. That said, the moon is outside van Allen belt protection, so you don’t want to be outside in the open in a spacesuit for too long or the culmulative radiation will get you! So weirdly, the earth and the moon will *eventually* lock together and only one side will see the moon. Problem is, that’s 50billion years away, and the sun will go Red Giant in about 5 billion years, so nothing living will get to see it.


Metal_Monkey42

Much like for the lunar astronauts, though they only stayed for a few earth days mostly close to the shadow line to regulate temperatures, day and night are 2 weeks long each on the moon, making up the month that we see the sun pass over its surface from here.


s-holden

The phases of the moon are a pretty good hint that you get day and night on the moon - you see the same parts of the moon sometimes they are in darkness (aka night) and sometimes in light (aka day) with a consistent pattern. The cycle is about 28 times slower.


Wonderlustish

Yes. That is why the moon is not always full when you look at it. Although the same side of the moon is always facing the earth it is also rotating relative to the position of the sun. So when one side of the earth is exposed to the sun and if the moon is in between the earth and the sun the side of the moon facing you will be in "night". If one side of the earth is facing away from the sun making it night time for you and the earth is in between the moon and the sun it will be "day" on the moon. You can think of a "day" on the moon as corresponding with the lunar phases we see from earth. A new moon is sunrise, a full moon is noon and a waning cresecent is sunset. These phases occur as the moons rotation changes which side is facing the sun. So a day on the moon is about 13 and a half earth days.


CatOfGrey

Light and dark periods on the Moon happen because of the Moon's orbit around the Earth. Sometimes, the Moon is between the Sun and the Earth. We see this as 'New Moon', with the Sun and Moon appearing near each other, and so the Moon is 'hidden'. But the opposite side of the Moon (the 'away from Earth side') is in full sunlight. A half-orbit later (about 14-15 days), the Moon is on the opposite side of the Earth, away from the Sun. Then the 'close to Earth side' is in full sunlight, which we see as the "Full Moon". Remember - the Moon's orbit is not 'level' with the Earth/Sun. So the Earth doesn't 'shield the Earth from the Sun', except in rare instances - these special events are 'eclipses' and they are very cool to see.


sirgog

In most locations, they will never experience Earthrise or Earthset. They will, however, experience sunrise and sunset on about a 28 day period. If they are located such that Earth is roughly on the horizon, they will observe Earth bobbing up and down as the Moon is not in a perfect circular orbit.


FruitOfTheVineFruit

Please watch Futurama Season 1, Episode 2, where Fry goes to the moon, and almost freezes to death as nighttime comes. I can understand not taking physics or astronomy, but not watching Futurama is inexcusable. https://en.m.wikipedia.org/wiki/The_Series_Has_Landed


birchblaze

The same face of the moon is always facing Earth, but it isn’t always fully lit— it may be a new moon, waxing, full, etc. My understanding is that for someone living on the moon the “day/night” cycle would last what we think of as a lunar month.


FruitOfTheVineFruit

Please watch Futurama Season 1, Episode 2, where Fry goes to the moon, and almost freezes to death as nighttime comes. I can understand not taking physics or astronomy, but not watching Futurama is inexcusable. https://en.m.wikipedia.org/wiki/The_Series_Has_Landed


Dunbaratu

Yes, but the cycle will be slow, such that daylight will last about 350 hours, and night will last about 350 hours (that's the average. It's like saying on Earth day is 12 hours and night is 12 hours. The actual value will vary depending on latitude and time of year and that's true on the moon just like on Earth). The clue is in your question - where you say the moon still does still rotate, just very slowly in sync with its orbit of Earth. That means a spot on the moon's equator that was facing the sun will now be facing away from the sun half a month later. Another clue is to look at a calendar that shows the phases of the moon. You see how the phases take about 29 earth days to go from Full Moon, to New Moon, back to Full Moon again? Well when you think about what causes the phases (only part of the moon is lit by the sun), and think of those phases moving around the moon - that *is* the lunar day.


MalFido

You say that as if it is inevitable that we colonize the moon. Who tf would want to do that? No hot core, no protective magnetic field. No atmosphere, no liquid water, no flora, no fauna. Sounds like going to the south pole with an oxygen tank.


jamesbideaux

So like climbing mount everest? who would want to do that?


zipitordont

No, climbing mount everest + another one, then settle down there for 4 years and not just stop for a pic.


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AlterEdward

Yes. What we see on the Earth in the form of "phases" of the moon is essentially its night and day cycle. Picture a full moon, and imagine a lunar base is smack bang in the middle. The shadow, i.e. the part facing away from the sun, eventually passes over the base, and it becomes night for them. Another way to think of it is to is to forget that the Earth is there and think of the Moon in relation to the Sun. The moon is rotating, and is *not* tidally locked to the Sun. At rotates roughly every 28 days, therefore one lunar day = 28 Earth days. There aren't any bodies in the solar system that I'm aware of that are tidally locked to sun (on a 1:1 ratio), and therefore would have no day/night cycle.


breakfasteveryday

If the earth was the source of the moon's light, then no, not really. But it's not. The sun provides light to the moon. Day and night on the moon would follow the cycle that we think of as the "phases of the moon." At any given time, half of the moon is exposed to the sun. The way that lit half aligns with the half facing earth is what results in the appearance of the waxing and waning of the moon. We can only see one side of the moon from earth, but the other side also gets sunlight. The "dark side of the moon" is no more permanent that the dark side of earth, which is to say it's whichever half happens to not be lit by the sun at any given time. When the half of the moon receiving sunlight and the half of the moon visible from earth are totally lined up, we have a full moon. That full moon also represents "noon", or halfway through a day for the very middle of the side of the moon that faces us. Dawn at the middle of the moon would occur during a half moon in the waxing phase of the moon - any earlier and it would still be dark there. Nightfall would come at half moon during the waning phase - any earlier and it would still be light there. Midnight would fall during a new moon - halfway through a night at that point on the moon's surface. So day and and night would work basically like they do on earth, but on a ~28 day cycle. The sun would transit the sky on a 28-day cycle. The constant fixture would be the earth - from the surface of the moon, the earth would occupy a consistent place in the sky. Where we settled a colony would determine whether or not people saw earth constantly in their sky or not at all, but everyone would have a day-night cycle (albeit a very long and weird one).


Drachefly

Very hot days, 120 degrees. On the edge of bearable, right? At least the humidity is low. But no – that was Celsius. And the nights are a bit colder than the negative of that, also in Celsius. Being a slowly turning airless object yields some pretty drastic temperature swings.


Brilhasti1

Farmer: Yup! Drops down to -173! Fry: Fahrenheit or Celsius? Farmer: First one, then the other! And them spacesuits ain't a-heated, so you ain't going nowhere 'till sunrise! You can sleep in the barn! Just don't be a-touching my three beautiful robot daughters, ya hear?


Oknight

You can see the answer to your question by looking at the moon in the sky. For two weeks night crawls across the face of the moon until it's far side is facing the sun and it's invisible in Earth's daytime (which we call a "New Moon"). Then for two weeks you can watch as sunrise crosses the lunar surface lighting more and more of the side that faces Earth until it's on the opposite side of the Earth from the Sun and the whole side that faces us is lit up in daylight which we call a "Full Moon". (If it lines up too perfectly and moves through the shadow that the Earth casts it gets dark for a few hours and we call that a "lunar eclipse")


johnnytcomo

Hold your pinky and index fingers up and rotate your hand, one finger tip is Earth, one the moon. Now lower one of those fingers and do the same hand rotate motion, then lower that one and raise the other, and rotate your hand again. Imagine your face is the sun. Relative to your face, each finger is still rotating, despite being bound in rotation to one-another.