Stupid lunar orbital issue

LazyClouds

Hi, I know v little about astronomy and there's something about the moon I really need to get straight in my mind:

Hypothetically, if I was living on the moon when would it be night and day?

I've googled it and the answer is (I think) the moon phases - depending on where you were on the surface whatever appears dark in the moon phase is experiencing night. Is this correct so far?

Meaning, there's about 2 weeks of day and 2 weeks of night on the moon. Yes?

Ok, so how exactly do the three bodies (moon, planet, sun) need to be arranged to achieve this day and night? As in, is the dark part of the moon actually the shadow of the planet as it travels between the sun and the moon? (I think I just figured that part out as I wrote it...)--> or is the other way around, that the moon between the planet and the sun so the sun is now shining on the far side of the moon?

If I'm living on the moon, which has no atmosphere I believe, do I even notice the difference between day and night? (temperature is a non-issue, this is purely a visual Q) Is the surface of the moon completely black or it is lit up by the stars?

Is there anytime where I can see the planet more clearly? Can I see it much easier during the night and, if so, how well can I see it? Can I see countries with the naked eye or do I still need a telescope?

Apologies for the stupid questions, I just can't wrap my head around this at all... If there's any handy sites out there with great pics / vids / graphics etc I'd appreciate the links.

Bit cynical

LazyClouds wrote: »

Meaning, there's about 2 weeks of day and 2 weeks of night on the moon. Yes?

Yes.

Ok, so how exactly do the three bodies (moon, planet, sun) need to be arranged to achieve this day and night? As in, is the dark part of the moon actually the shadow of the planet as it travels between the sun and the moon? (I think I just figured that part out as I wrote it...)--> or is the other way around, that the moon between the planet and the sun so the sun is now shining on the far side of the moon?

Night and day on the moon work the same as on Earth except that the moon has a 28 day rotational period as opposed to the Earth's 24 hour period.

In general the dark part of the moon is not the shadow of the Earth as it travels in front of the Sun; like on Earth, it is the part of the moon that is facing away from the Sun therefore not getting any light.

Occasionally the Earth does pass between the moon and the sun causing a lunar eclipse but this is different to the normal day/night cycle on the moon.

If I'm living on the moon, which has no atmosphere I believe, do I even notice the difference between day and night? (temperature is a non-issue, this is purely a visual Q) Is the surface of the moon completely black or it is lit up by the stars?

During the day on the moon the sun will be in the sky illuminating the surface and you would be able to see objects. Even though there is no atmosphere, you would not normally be able to see the stars because your eyes would have adjusted to the bright sunlight. However if you shielded yourself from the Sun and the moon's bright surface, you would be able to see stars once your eyes adjusted to the darkness. This is not possible on Earth due to the bright sky during the day.


During the night the only illumination would be stars and planets. If you are on a part of the moon where the Earth is visible then this would provide a lot of illumination; much more than the moon does on Earth but still a lot less than the Sun. If it is night on the far side of the moon where you can't see the Earth then the only illumination would be from the stars and planets (Mars, Jupiter etc.) It would be like a very bright clear night sky in a remote location on Earth only more so, but there would not be enough illumination to walk around without artificial light.

ps200306

LazyClouds wrote: »

Hi, I know v little about astronomy and...

Apologies for the stupid questions, I just can't wrap my head around this at all...

Actually I was really impressed with the logic behind your questions. You were well on the way to figuring it out for yourself, or at least you figured out which questions needed asking, which is half the battle. Kudos to you.

Capt'n Midnight

Instead of moonlight you'd have earthlight.

The earth is much bigger and brighter than the moon , compare clouds to coal , so nights wouldn't be quite as dark



Because the moon isn't tilted on it's axis like the earth there may be some places where the sun shines most if not all of the time
https://en.wikipedia.org/wiki/Peak_of_eternal_light

Downside is that eclipses last for hours instead of minutes.

ps200306

The Moon's a funny reflector. Maybe not quite a clouds-to-coal comparison -- see an interesting discussion here. Under the right conditions some parts of it are brighter than some parts of Earth would be as seen from the Moon.

LazyClouds wrote: »

Is there anytime where I can see the planet more clearly? Can I see it much easier during the night and, if so, how well can I see it? Can I see countries with the naked eye or do I still need a telescope?

As mentioned by Bit cynical above, you could see Earth in your sky (assuming you're on the right part of the Moon) at night time, and by blocking out the Sun and lunar surface during the day, and letting your eyes adjust.

You could definitely see large landmasses sometimes, just as we can see major features on the surface of the Moon. The Earth would be nearly two degrees across -- near four times bigger than the Moon as seen from Earth. Have a look at this picture taken from Apollo 11 when it's half way to the Moon:



You can easily see Africa, the Arabian Peninsula, western Asia and southern Europe. If you're looking at this on a regular laptop screen (100 ppi), then if you stand back three metres from the screen you will see the Earth the actual size it would look from the Moon. You should still be able to see features. Of course, this is a particularly cloudless picture taken shortly after northern hemisphere mid summer. Add a few clouds, and maybe view at a slightly less full phase, and it gets a lot more difficult to discern anything.

Zubeneschamali

Check out the difference in colour/brightness as the moon passes in front of the Earth as seen from a satellite beyond the moon at the L1 Lagrangian point between Earth and the Sun:

Moon gif

The Moon looks weird because that is the far side, which we never see from Earth.

ps200306

I love that picture. Although I was able to grab a piece of the lunar surface and a chunk of land which I think is near Baja California, both from the same frame, and they don't look all that different:

Zubeneschamali

ps200306 wrote: »

I love that picture. Although I was able to grab a piece of the lunar surface and a chunk of land which I think is near Baja California, both from the same frame, and they don't look all that different:

Sure, but most of the Earth is not a view of dirt - it is cloud or ocean and much brighter per unit area.

ps200306

True.

LazyClouds

Thanks everyone for your answers!
One more question tho:

During the 2 week long day does the moon witness the sun's gradual progression across the sky? Is there a typical path it follows (eg. east to west) everyday? So that would mean there would be a few days of dawn and a few of dusk too?
Many thanks.

ps200306

LazyClouds wrote: »

During the 2 week long day does the moon witness the sun's gradual progression across the sky? Is there a typical path it follows (eg. east to west) everyday? So that would mean there would be a few days of dawn and a few of dusk too?

Yes, the Sun would progress across the sky on the Moon for the same reason it does on the Earth -- the Moon is rotating. The rotation of the Earth and Moon on their axes are in the same direction, as indeed are the orbits of the Moon around the Earth and the Earth around the Sun. All of them go anti-clockwise as seen from above their north poles. This is referred to as the prograde direction, and it is a good thing the Moon has a prograde orbit with respect to the Earth's rotation. If it was retrograde the two would collide due to tidal forces.

Anyway, it means the Sun goes east to west on the Moon, just like Earth, but there are two Earth weeks between sunrise and sunset. There are no dawns or dusks on the Moon in the sense of having a twilight period. When the Sun is just above the horizon there is no atmosphere on the Moon to attenuate it, and when it is just below the horizon there is no atmosphere to scatter or refract it. Shadows on the ground would lengthen toward sunset but the Sun on your face would be as strong as at lunar midday. The only attenuating effect would be due to the Sun's own dimensions -- being half a degree wide it would take approximately an hour from when its lower limb touched the horizon to when its upper limb disappeared. But due to the eye's accommodation it would still seem to disappear almost like a light being switched off -- as it does from Earth during an eclipse when the Sun goes behind the Moon with the diamond ring effect.

LazyClouds

ps200306 wrote: »

The only attenuating effect would be due to the Sun's own dimensions -- being half a degree wide it would take approximately an hour from when its lower limb touched the horizon to when its upper limb disappeared. But due to the eye's accommodation it would still seem to disappear almost like a light being switched off -- as it does from Earth during an eclipse when the Sun goes behind the Moon with the diamond ring effect.

Cool info! I had to google the diamond ring effect which is a nice term to remember What do you mean by lower and upper limb? Are you talking about the top and bottom segments of the sun? Sorry just to clarify...

ps200306

Yes, the lower limb of the Sun touches the horizon first at sunset. The upper limb is the last bit you see. (Actually, by convention sunset and sunrise are defined to be the points at which the upper limb touches the horizon). On Earth we have to distinguish between the apparent position of the Sun and its geometric position. The setting Sun shines through an ever greater thickness of atmosphere, which has a greater refractive effect. On the horizon, the effect is to shift the Sun higher by half a degree, about equal to its own width. So when the apparent position of the Sun 's lower limb is on the horizon, the geometric position is such that the entire Sun has already set:

In practice, different layers of the atmosphere do not vary uniformly in density, so the Sun's image tends to break up on the horizon, often flattened and segmented or banded:

On the moon, the apparent and geometric positions of the Sun would be the same at all times.

Capt'n Midnight

ps200306 wrote: »

On the moon, the apparent and geometric positions of the Sun would be the same at all times.

Technically speaking you'd see where the sun was between 490-507 seconds ago.

ps200306

Hah! Sneaky. I like it.

Except, not really ... the light travel time from the Sun doesn't affect the geometry due to the Moon's rotation. I guess you might see a ≈10⁻⁵ second delay corresponding to the horizon distance. :pac: