APOD: Lunations (2018 Sep 12)

[APOD Robot]

Lunations

Explanation: Our Moon's appearance changes nightly. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The featured video animates images taken by NASA's Moon-orbiting Lunar Reconnaissance Orbiter to show all 12 lunations that appear this year, 2018. A single lunation describes one full cycle of our Moon, including all of its phases. A full lunation takes about 29.5 days, just under a month (moon-th). As each lunation progresses, sunlight reflects from the Moon at different angles, and so illuminates different features differently. During all of this, of course, the Moon always keeps the same face toward the Earth. What is less apparent night-to-night is that the Moon's apparent size changes slightly, and that a slight wobble called a libration occurs as the Moon progresses along its elliptical orbit.

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[BillT]

Nice animation. Northern hemisphere centric though

[ihowarth]

Absolutely brilliant animation -- so much information packed into such an elegant presentation.

Not really "N-hemi-centric", beyond the universal convention that N is "up", but a version without the (distracting, barely legible) labels would be nice.

[DomeLord]

Magnificent work! Well done!

[Kelleher]

Beautiful

[Half-empty]

As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible.

The visibility of the sunlit side greatly depends on when you start watching it. If you start watching when the moon is full, it first becomes decreasingly visible, then increasingly visible.

[Case]

What is less apparent night-to-night is that the Moon's apparent size changes slightly, and that a slight wobble called a libration occurs as the Moon progresses along its elliptical orbit.

The Wiki describes nicely why the wobble is a perceived oscillation from our vantage point. I do wonder how it changes over extreme long time, as some of the components (eccentricity of the orbit, axis of rotation) could have been different in the far past.

[starsurfer]

I think it's time to go on a moon safari!

[dduggan47]

Absolutely brilliant animation -- so much information packed into such an elegant presentation.

Not really "N-hemi-centric", beyond the universal convention that N is "up", but a version without the (distracting, barely legible) labels would be nice.

Absolutely agree that it's brilliant and that it could do without the labels.

[edgardine]

Earthshine is missing, isn't it ?

[BDanielMayfield]

Awesome APOD!

And it even shows Earth's Artic ocean as it soon will be, free of almost all ice.

Bruce

[Chris Peterson]

Earthshine is missing, isn't it ?

Our displays are incapable of simultaneously displaying Earthshine and the illuminated part of the Moon. There's far too much dynamic range. It is possible, of course, to distort the brightness curve in such a way that both are shown, but presumably they chose to simply use a linear scaling, meaning no visible Earthshine (even if their model includes this source of illumination).

[BDanielMayfield]

I note that the frame rate of this video is one frame per real time hour. Is it possible to slow down the display rate of YouTube videos? The names of features on the moon and the stats flash by too fast to read.

Bruce

[Chris Peterson]

I note that the frame rate of this video is one frame per real time hour. Is it possible to slow down the display rate of YouTube videos? The names of features on the moon and the stats flash by too fast to read.

I don't know of a way to do it from inside YouTube. But you can easily download the video, and play it with any of a number of players which support slow motion playback.

[SeedsofEarth]

Love the allusion to 2001, Space Odyssey. Always loved what Stanley Kubrick did to that movie with the music. Perfect!

[first98@sonic.net]

No credit to the performers of the Strauss waltz? Shame!

[edgardine]

Earthshine is missing, isn't it ?

Our displays are incapable of simultaneously displaying Earthshine and the illuminated part of the Moon. There's far too much dynamic range. It is possible, of course, to distort the brightness curve in such a way that both are shown, but presumably they chose to simply use a linear scaling, meaning no visible Earthshine (even if their model includes this source of illumination).

Thank you for this answer.

[neufer]

No credit to the performers of the Strauss waltz? Shame!

https://c8.alamy.com/comp/B6TYDJ/spike- ... B6TYDJ.jpg

[RJN]

No credit to the performers of the Strauss waltz? Shame!

Good point. It was provided for free by YouTube without obvious attribution. Here is a link: https://www.youtube.com/watch?v=4ntn86KbtG4 . If anyone can track down the performers please post it here.

[MoonSmith]

I note that the frame rate of this video is one frame per real time hour. Is it possible to slow down the display rate of YouTube videos? The names of features on the moon and the stats flash by too fast to read.

Bruce

If you open the video on YouTube, in the lower right corner there is a gear wheel, select that and you can reduce or speed up the video.+

[Pat42]

I note that the frame rate of this video is one frame per real time hour. Is it possible to slow down the display rate of YouTube videos? The names of features on the moon and the stats flash by too fast to read.

Bruce

From the cog wheel (settings) you can select diferent sepeeds, from x0.25 (slower) to x2 (faster).
However this does not work reliably. Whenever you pause and restart the video is back on standard speed, even though it shows a different speed !

Btw, there is a fault on the video on July 27th, around 20 UTC. The lunar eclipse is missing !

[alter-ego]

...
Btw, there is a fault on the video on July 27th, around 20 UTC. The lunar eclipse is missing !

At first glance that seems to be true. It is not evident from the description that LRO did not take those pictures as real-time snapshots. In fact, it's likely there is no image in that video that was acquired in 2018. Probably all the lunation animations (2011 to present) were derived from the Wide Angle Camera (WAC) near-side mosaic made in 2011 from data (including South-up versions ) The WAC acquires a 60km-wide swath of images (at 50km altitude that's about a 114° field of view!). At that resolution about 600,000 images are required to cover a single hemisphere!

You can see that over a full hemisphere, it's not possible for the LRO to capture a lunar eclipse. Given the mosaics are likely many years old, you could say the images are "faults". A lot of calculations and morphing went into those images, but rest assured, though, the representations are very accurate. However,it would have been better to add a sentence in the description stating the images are not snapshots but instead are mosaics built from LRO WAC images taken over the years.

[geckzilla]

...
Btw, there is a fault on the video on July 27th, around 20 UTC. The lunar eclipse is missing !

At first glance that seems to be true. It is not evident from the description that LRO did not take those pictures as real-time snapshots. In fact, it's likely there is no image in that video that was acquired in 2018. Probably all the lunation animations (2011 to present) were derived from the Wide Angle Camera (WAC) near-side mosaic made in 2011 from data (including South-up versions ) The WAC acquires a 60km-wide swath of images (at 50km altitude that's about a 114° field of view!). At that resolution about 600,000 images are required to cover a single hemisphere!

You can see that over a full hemisphere, it's not possible for the LRO to capture a lunar eclipse. Given the mosaics are likely many years old, you could say the images are "faults". A lot of calculations and morphing went into those images, but rest assured, though, the representations are very accurate. However,it would have been better to add a sentence in the description stating the images are not snapshots but instead are mosaics built from LRO WAC images taken over the years.

I would go a step further and say that this is not only comprised of many thousands of images to create a mosaic, but that mosaic is applied as a fully 3D model combined with elevation data to render it as realistically as possible. Fun fact: it's hard to create the flat color mosaic at the poles because the Sun never illuminates the terrain from directly above, so shadows are always present.

Anyway, it's totally possible to put the eclipse into the simulation. One need only include a properly placed Earth...

[neufer]

You can see that over a full hemisphere, it's not possible for the LRO to capture a lunar eclipse. Given the mosaics are likely many years old, you could say the images are "faults". A lot of calculations and morphing went into those images, but rest assured, though, the representations are very accurate. However,it would have been better to add a sentence in the description stating the images are not snapshots but instead are mosaics built from LRO WAC images taken over the years.

I would go a step further and say that this is not only comprised of many thousands of images to create a mosaic, but that mosaic is applied as a fully 3D model combined with elevation data to render it as realistically as possible. Fun fact: it's hard to create the flat color mosaic at the poles because the Sun never illuminates the terrain from directly above, so shadows are always present

• Feast your eyes on comet 67P's surface, with depth cues added.

[alter-ego]

...
Anyway, it's totally possible to put the eclipse into the simulation. One need only include a properly placed Earth...

Yes, but it would be a simulation needing additional image data to be accurate. I can see a telescopic image from Earth taken at an animated image frame time, and then overlaid on the modeled 2D mosaic. LRO imagery alone won't provide enough information to accurately render an eclipse.