Full moon first & then straight into a crescent

Optimatic

I came across this Youtube video and its left me puzzled as to how the moon can play this trick. it moves from being a full moon to a crescent moon in a matter of moments?

Please Youtube the following video: Nibiru PlanetX #24 - Crazy Old Moon

I was on solarsystemscope to go back to the date an time and there is never a point that it displays the moon transitioning from full to Crescent.

ThunderCat

Optimatic wrote: »

I came across this Youtube video and its left me puzzled as to how the moon can play this trick. it moves from being a full moon to a crescent moon in a matter of moments?

Please Youtube the following video: Nibiru PlanetX #24 - Crazy Old Moon

I was on solarsystemscope to go back to the date an time and there is never a point that it displays the moon transitioning from full to Crescent.

Firstly, it's important to remember that this is being viewed through a webcam and not by the naked eye at that actual location.


What is happening here is that the before sunrise, the luminosity of the moon is far greater than after sunrise. Before sunrise, the luminosity of the crescent moon is enough to wash out the lunar disc when viewing through a webcam making it appear like a full moon. After sunrise, the luminosity of the moon decreased to such a degree that the webcam is able to clearly resolve the crescent shape of the moon.


I want you to pause the video at 34 seconds. You will see that the brightness of the moon is more intense around that crescent shape, which of course is not the case for a full moon as the brightness of the whole disc would be equal.


It is all down to the fact that the camera cannot resolve the crescent moon before sunrise as it is too luminous for that cameras ability. This is not the case for the naked eye which is why you would never see it with the naked eye.


Here is the link to the video the OP references - https://www.youtube.com/watch?v=Uo2dNNjV-Jo

Optimatic

Hi ThunderCat,

I appreciate you replying to me there, what you're saying makes a lot of sense, a webcam is completely inadequate to receive an accurate visual on the varying degrees of luminescence thrown out by the interacting bodies of light.
I think the inaccuracy of the WebCam is show up further by the double crescent the speaker talks about in the later part of the video.
I must say though, I do like the view transmitted and the glare adds to the drama of it all!

Thanks again!

ps200306

Hi Optimatic,

Thundercat is basically right that the disc of the moon is getting washed out in the pre-sunrise images. Also, as he or she points out, if you zoom in on any of the pre-sunrise images, you can see that what eventually becomes the illuminated crescent of the moon after sunrise is also by far the brightest part in the pre-sunrise images. There are two parts of his/her description I'd take issue with (but in fairness they are probably just down to a bit of vagueness of language).

Firstly, the luminosity of the moon does not change before and after sunrise. It is exactly the same. Think about it -- we are looking at the sun reflecting off the moon. Put yourself on the moon, 240,000 miles or so away. What difference could it possibly make to the light reflecting from the moon's surface around you that the sun happens to have just risen on a particular part of the earth, a quarter of a million miles away? There's no difference. So we can rule out any changes in the reflectance of the moon. Is it possible then that something has changed about how much of the moon's light gets through the earth's atmosphere? Again, no! The transparency of the earth's atmosphere does not change just because the sun has risen. In short, there is absolutely no physical reason why the luminosity of the moon would be different before and after sunrise ... and it isn't! What has changed is the luminosity of the sky, and we'll talk about the effects of this in a moment.

The second piece of terminology I'd take issue with is that it is "the luminosity of the crescent moon [that] is enough to wash out the lunar disc". It isn't. Why would the crescent wash out just the lunar disc? Why wouldn't it wash out a circular area of the sky around itself? In fact, we do see a lot of flare around the lower left of the moon where the crescent eventually appears. Some of this is bleeding of overexposed pixels into adjacent pixels, which is a feature of the CCD chip in the camera. Most of it, though, is just the atmosphere (air, and most especially water vapour) scattering the light coming from the direction of the moon. Nevertheless, in addition to both these effects you can clearly the full disc of the moon itself, separate to the flare coming from the crescent part, both before and after sunrise.

So what's going on? Two things -- one to do with the camera, and the other to do with the moon. The camera issue is very straightforward, and is all down to exposure levels. It looks to me that the camera is on an auto exposure setting (although it makes no difference to the argument if it is manually timed: it just means someone changed it before and during/after sunrise). First read a bit about auto exposure -- here -- which explains things quicker and better than I could, especially the stuff about averaging. Look at the image with the black background and how the centre objects are over exposed. That's what's going on with the moon in the pre-sunrise images. How can we tell? One sure sign is the streaking of the stars. The exposure is so long that the sky has rotated during the exposure and the stars appear as lines instead of dots.

A good example is in the close-up at 0:43, in which we can see several interesting features. First, the stars are clearly moving during the exposure. Second, in addition to the over-exposed crescent of the moon and the halo around it, we can also still see that disc of the moon above and right of the crescent. Another item to mention in passing is the greenish "gas" to the lower left. Notice that it has it's own little upside-down crescent in it? That gives away what it is -- a reflection from inside the barrel of the camera or telescope. Many cheap devices have this: an annoying internal reflection that is invisible most of the time except during night time viewing, and especially on long exposures.

Ok, so now we know the moon is way overexposed due to the scene averaging features of the camera's exposure setting. Watch the sequence from 1:00 onward. Zoomed out, we can only barely see the star streaks, but notice how they get shorter as the sky get brighter. Also, look at the hills on the horizon. Before sunrise we can see at least two ridges in shades of grey, but after sunrise they become almost undifferentiated solid black due to the hugely shorter exposure. Now look at 1:35 where the narrator exclaims in surprise "guess what! we got our moon back -- our normal moon". Well it doesn't look normal to me. I can still clearly see the full disc of the moon, even more clearly in the zooms leading up to the 2:00 mark.

Just a note on the times, by the way. It doesn't take much forensic Googling to discover that he has just ripped this footage off the webcam of a hotel in the Italian Alps, just south of the Austrian border. You can look at it yourself here and very pretty it is too. You can also see that its clock is set to GMT, an hour earlier than local time in Italy. We can also look up the times of sunrise for that exact location on that exact day last Monday ... 7.06 AM. So the frame at 1:35 is four minutes after sunrise.

So what's going on with the moon? No big mystery there either. We're looking at earthshine. Monday was two days before yesterday's new moon. The old moon was rising about two and half hours and thirty-odd degrees ahead of the sun. It was five per cent illuminated. From the moon's point of view, the earth was nearly opposite the sun, and full. So earth light was beaming down on the unlit part of the moon. How brightly? Well if you were watching the lunar eclipse on September 27th and saw the conspicuous blood red moon, it was lit up by only the earth's atmosphere refracting the light of the sun which was otherwise eclipsed from the moon's point of view. Earthshine reflecting off the moon around the time of new moon is many times brighter than that eclipsed moon was. It's way brighter than any of the stars -- in fact, if you were able to turn off that lit crescent part of the moon, the "dark" part of the moon would be far and away the brightest thing in the sky. So if the exposure level is high enough to capture stars, you can absolutely bet that it's high enough to not only capture the earthlit part of the moon, but to be overexposed by it. And that's what we're seeing, the whole way through the video. It's only in the short exposures after sunrise that it starts to look "normal" but even then we can very easily see the earthshine (which the narrator somehow never mentions).

If you had been looking at that moon yourself, it would look very different. Your eye is not a webcam. For a start, it doesn't have equal sensitivity throughout your field of view, so it's not doing the same averaging as the webcam. A bright moon at the centre of your field of view would cause your pupil to narrow so that you would have quite a high contrast with the black sky. As a result you'd see fewer stars than the webcam (although more than on a night of full moon, when the moon blots out all but the brightest stars). You also have two different "cameras" in your eye -- in low light levels you're using your "scotopic vision" which is more light sensitive but has low colour sensitivity, whereas in daytime you're using a different set of cells for "photopic vision". In bright moonlight you're in an overlapping regime called "mesopic". But in either case you'd probably quite easily see the earthshine because it is so bright at this time of month. Indeed, the moon is just after new now, and in the unlikely event that you get a clear evening just after sunset anytime in the next few nights, look for the young crescent moon toward the west and you'll easily spot the earthshine on its unlit part. But you'll be able to distinguish the bright sunlit crescent from the more dimly earthlit disc much better than the webcam managed in that video.

If you'd like to know more about earthshine, there's a little history lesson here about how it was first described by no less than Leonardo da Vinci in 1510, just over 500 years ago. Then there is this lovely little paper from over seventy years ago by "Dr. Jackson" calculating the brightness of earthshine on the moon. And finally here is a more heavyweight paper.

And one final thought. Any youtube video with "Nibiru" in the title is very unlikely to be scientifically reliable. It is one of the most "out there" wacky internet memes. If you watch other vids on the same channel such as this one you will see that it is a mishmash of scientific gobbledygook and apocalyptic foreboding, along with the usual warning that anyone telling you different is a government spy. :pac:

ThunderCat

ps200306 wrote: »

Hi Optimatic,

Thundercat is basically right that the disc of the moon is getting washed out in the pre-sunrise images. Also, as he or she points out, if you zoom in on any of the pre-sunrise images, you can see that what eventually becomes the illuminated crescent of the moon after sunrise is also by far the brightest part in the pre-sunrise images. There are two parts of his/her description I'd take issue with (but in fairness they are probably just down to a bit of vagueness of language).

Firstly, the luminosity of the moon does not change before and after sunrise. It is exactly the same. Think about it -- we are looking at the sun reflecting off the moon. Put yourself on the moon, 240,000 miles or so away. What difference could it possibly make to the light reflecting from the moon's surface around you that the sun happens to have just risen on a particular part of the earth, a quarter of a million miles away? There's no difference. So we can rule out any changes in the reflectance of the moon. Is it possible then that something has changed about how much of the moon's light gets through the earth's atmosphere? Again, no! The transparency of the earth's atmosphere does not change just because the sun has risen. In short, there is absolutely no physical reason why the luminosity of the moon would be different before and after sunrise ... and it isn't! What has changed is the luminosity of the sky, and we'll talk about the effects of this in a moment.

The second piece of terminology I'd take issue with is that it is "the luminosity of the crescent moon [that] is enough to wash out the lunar disc". It isn't. Why would the crescent wash out just the lunar disc? Why wouldn't it wash out a circular area of the sky around itself? In fact, we do see a lot of flare around the lower left of the moon where the crescent eventually appears. Some of this is bleeding of overexposed pixels into adjacent pixels, which is a feature of the CCD chip in the camera. Most of it, though, is just the atmosphere (air, and most especially water vapour) scattering the light coming from the direction of the moon. Nevertheless, in addition to both these effects you can clearly the full disc of the moon itself, separate to the flare coming from the crescent part, both before and after sunrise.

So what's going on? Two things -- one to do with the camera, and the other to do with the moon. The camera issue is very straightforward, and is all down to exposure levels. It looks to me that the camera is on an auto exposure setting (although it makes no difference to the argument if it is manually timed: it just means someone changed it before and during/after sunrise). First read a bit about auto exposure -- here -- which explains things quicker and better than I could, especially the stuff about averaging. Look at the image with the black background and how the centre objects are over exposed. That's what's going on with the moon in the pre-sunrise images. How can we tell? One sure sign is the streaking of the stars. The exposure is so long that the sky has rotated during the exposure and the stars appear as lines instead of dots.

A good example is in the close-up at 0:43, in which we can see several interesting features. First, the stars are clearly moving during the exposure. Second, in addition to the over-exposed crescent of the moon and the halo around it, we can also still see that disc of the moon above and right of the crescent. Another item to mention in passing is the greenish "gas" to the lower left. Notice that it has it's own little upside-down crescent in it? That gives away what it is -- a reflection from inside the barrel of the camera or telescope. Many cheap devices have this: an annoying internal reflection that is invisible most of the time except during night time viewing, and especially on long exposures.

Ok, so now we know the moon is way overexposed due to the scene averaging features of the camera's exposure setting. Watch the sequence from 1:00 onward. Zoomed out, we can only barely see the star streaks, but notice how they get shorter as the sky get brighter. Also, look at the hills on the horizon. Before sunrise we can see at least two ridges in shades of grey, but after sunrise they become almost undifferentiated solid black due to the hugely shorter exposure. Now look at 1:35 where the narrator exclaims in surprise "guess what! we got our moon back -- our normal moon". Well it doesn't look normal to me. I can still clearly see the full disc of the moon, even more clearly in the zooms leading up to the 2:00 mark.

Just a note on the times, by the way. It doesn't take much forensic Googling to discover that he has just ripped this footage off the webcam of a hotel in the Italian Alps, just south of the Austrian border. You can look at it yourself here and very pretty it is too. You can also see that its clock is set to GMT, an hour earlier than local time in Italy. We can also look up the times of sunrise for that exact location on that exact day last Monday ... 7.06 AM. So the frame at 1:35 is four minutes after sunrise.

So what's going on with the moon? No big mystery there either. We're looking at earthshine. Monday was two days before yesterday's new moon. The old moon was rising about two and half hours and thirty-odd degrees ahead of the sun. It was five per cent illuminated. From the moon's point of view, the earth was nearly opposite the sun, and full. So earth light was beaming down on the unlit part of the moon. How brightly? Well if you were watching the lunar eclipse on September 27th and saw the conspicuous blood red moon, it was lit up by only the earth's atmosphere refracting the light of the sun which was otherwise eclipsed from the moon's point of view. Earthshine reflecting off the moon around the time of new moon is many times brighter than that eclipsed moon was. It's way brighter than any of the stars -- in fact, if you were able to turn off that lit crescent part of the moon, the "dark" part of the moon would be far and away the brightest thing in the sky. So if the exposure level is high enough to capture stars, you can absolutely bet that it's high enough to not only capture the earthlit part of the moon, but to be overexposed by it. And that's what we're seeing, the whole way through the video. It's only in the short exposures after sunrise that it starts to look "normal" but even then we can very easily see the earthshine (which the narrator somehow never mentions).

If you had been looking at that moon yourself, it would look very different. Your eye is not a webcam. For a start, it doesn't have equal sensitivity throughout your field of view, so it's not doing the same averaging as the webcam. A bright moon at the centre of your field of view would cause your pupil to narrow so that you would have quite a high contrast with the black sky. As a result you'd see fewer stars than the webcam (although more than on a night of full moon, when the moon blots out all but the brightest stars). You also have two different "cameras" in your eye -- in low light levels you're using your "scotopic vision" which is more light sensitive but has low colour sensitivity, whereas in daytime you're using a different set of cells for "photopic vision". In bright moonlight you're in an overlapping regime called "mesopic". But in either case you'd probably quite easily see the earthshine because it is so bright at this time of month. Indeed, the moon is just after new now, and in the unlikely event that you get a clear evening just after sunset anytime in the next few nights, look for the young crescent moon toward the west and you'll easily spot the earthshine on its unlit part. But you'll be able to distinguish the bright sunlit crescent from the more dimly earthlit disc much better than the webcam managed in that video.

If you'd like to know more about earthshine, there's a little history lesson here about how it was first described by no less than Leonardo da Vinci in 1510, just over 500 years ago. Then there is this lovely little paper from over seventy years ago by "Dr. Jackson" calculating the brightness of earthshine on the moon. And finally here is a more heavyweight paper.

And one final thought. Any youtube video with "Nibiru" in the title is very unlikely to be scientifically reliable. It is one of the most "out there" wacky internet memes. If you watch other vids on the same channel such as this one you will see that it is a mishmash of scientific gobbledygook and apocalyptic foreboding, along with the usual warning that anyone telling you different is a government spy. :pac:

Spot on ps200306, thanks for the clarification.


I'm male by the way!

ps200306

Speak o' the devil. Heartstoppingly gorgeous fingernail-thin crescent moon five degrees above western horizon right now, with glorious earthshine on the rest of the disc. Just got a break in the clouds between Storm Abigail and Storm Beelzebub (or whatever's comin' next). :pac:

EDIT: 4% illuminated, according to Stellarium which gives me these params (note the magnitude -- 100 times brighter than Sirius, even at 4% lit, and according to Dr. Jackson's calculations the earthshine should be below magnitude -3, so perhaps 5% to 10% as bright as the crescent part, and thus easily visible):



EDIT2: Horizon is staying spectacularly clear and I'm getting a great binocular view. Whole lunar disc is a very faint yellow-gray. Set time is 18:06.

ps200306

ps200306 wrote: »

Speak o' the devil. Heartstoppingly gorgeous fingernail-thin crescent moon five degrees above western horizon right now, with glorious earthshine on the rest of the disc. Just got a break in the clouds between Storm Abigail and Storm Beelzebub (or whatever's comin' next). :pac:

Well they seem to have named the next storm 'Barney' which is a bit less intimidating. But once again there was a good moon view this evening. It's now 33% illuminated, and I have to confess I couldn't discern any earthshine through binoculars. The magnitude is probably just too low, the contrast with the lit crescent too high, and my optician's appointment too overdue. So that's it for another lunar cycle, then. I'm not sure if an overexposed webcam couldn't still conjure up Niburu the winged wonder. :pac: