APOD: Craters and Shadows at the Lunar... (2018 May 22)

Comments and questions about the APOD on the main view screen.
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APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by APOD Robot » Tue May 22, 2018 4:11 am

Image Craters and Shadows at the Lunar Terminator

Explanation: Why does the right part of this image of the Moon stand out? Shadows. The terminator line -- the line between light and dark -- occurs in the featured image so that just over half the Moon's face is illuminated by sunlight. The lunar surface appears different nearer the terminator because there the Sun is nearer the horizon and therefore causes shadows to become increasingly long. These shadows make it easier for us to discern structure, giving us depth cues so that the two-dimensional image, when dominated by shadows, appears almost three-dimensional. Therefore, as the Moon fades from light to dark, shadows not only tell us the high from the low, but become noticeable for increasingly shorter structures. For example, many craters appear near the terminator because their height makes them easier to discern there. The image was taken two weeks ago when the lunar phase was waning gibbous. The next full moon, a Moon without shadows, will occur one week from today.

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Ann
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Re: APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by Ann » Tue May 22, 2018 4:42 am

Nice picture. I like the subtle colors.

The difference between the smooth, almost crater-less "mares" and the surrounding, terribly cratered and uneven moon landscape is striking indeed.

Ann
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Re: APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by Boomer12k » Tue May 22, 2018 5:10 am

Indeed a great way to see contrast...some shadows add to the scene...

Mine from earlier this month...but the terminator on the other side of Plato Crater...


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Re: APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by orin stepanek » Tue May 22, 2018 10:32 am

The shadowed craters are nice; and I love the coloration of the sunlit side of Luna! 8-)
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Re: APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by Sa Ji Tario » Tue May 22, 2018 3:06 pm

In the image of Boomer you can clearly see the Alpine Valley to the right of Plato and to the left and below, Sinus Roris but there is no Harpalo that was the first moon landing project before NASA

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Re: APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by Evenstar » Tue May 22, 2018 5:16 pm

It's a beautiful moon. I forget about the reddish (brownish) colorations--is that iron? Still, the Moon looks largely grayish. Why? Mars is redish from so much iron oxidation? Is there any dusty place on Earth where you can take a picture of a footprint that looks grayish like Apollos footprints?

When will Moonauts (Moonlings) from Earth circumnavigate the surface of the Moon? I suspect once we can successfully pull off a feat like this we will be living comfortably on Mars and other moons too?
<Evenstar>

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Re: APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by neufer » Tue May 22, 2018 5:41 pm

Evenstar wrote:
Tue May 22, 2018 5:16 pm

It's a beautiful moon. I forget about the reddish (brownish) colorations--is that iron?
Still, the Moon looks largely grayish. Why? Mars is reddish from so much iron oxidation?
https://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/lroc-20100910_color_moon.html wrote: .
<<Colors on the Moon are dominantly controlled by variations in iron and titanium content. The mare regions have low reflectance because they contain relatively high amounts of iron oxide (FeO). Some mare basalts contain unusually high amounts of titanium oxide (TiO2) in addition to iron oxide, making for even lower reflectance. TiO2 also shifts the color of the mare from red to blue.

The distinct boundary between Mare Tranquillitatis (darker and bluer) and Mare Serenitatis (lighter brown) is clearly visible in the WAC color image and results from high TiO2 in the Tranquillitatis basalts. Scientists have studied the Tranquillitatis basalts in detail from the rocks returned by the Apollo 11 astronauts; the composition of the Serenitatis rocks are known only from orbital remote sensing. One of the goals of the WAC is to provide a global map of UV and visible reflectance to help scientists better understand the distribution of iron and titanium in the mare. From the Apollo samples, we believe that titanium is dominantly held in the mineral ilmenite. However, we have not sampled the full variety of lunar basalts so we can not be sure - more samples are needed.>>
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Re: APOD: Craters and Shadows at the Lunar... (2018 May 22)

Post by MarkBour » Wed May 23, 2018 1:37 am

'Tis a lovely, crisp image of the moon!

You can so clearly see Copernicus and Tycho, and it kind of makes it look like they could have been near-simultaneous, the twin impacts of a body that had broken into two parts. From what I have seen, however, those who have dated the two craters put them far apart in time of origin. If I read correctly, Copernicus is thought to be around 800 million years old, and Tycho only about 100 million years old.

Another feature that I find beautifully highlighted here is Mare Imbrium, whose circumference ridge starts just to the east of Copernicus and curves North as one follows the ridge to the east. That had to be a real whopper of an impact! According to Wikipedia, it is theorized that Mare Imbrium was created by an impactor of about 250 ± 25 km in diameter, about 4 billion years ago. (https://en.wikipedia.org/wiki/Mare_Imbrium)
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