APOD: The Lunar X (2016 Dec 10)

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APOD: The Lunar X (2016 Dec 10)

Post by APOD Robot » Sat Dec 10, 2016 5:09 am

Image The Lunar X

Explanation: The striking X appearing in this lunarscape is easily visible in binoculars or a small telescope. Yet, not too many have seen it. The catch is this lunar X is fleeting, only apparent in the hours before the Moon's first quarter phase. At the terminator, or shadow line between lunar day and night, the X illusion is produced by a configuration of the craters Blanchinus, La Caille and Purbach. Near the Moon's first quarter phase, an astronaut standing close to the craters' position would see the slowly rising Sun very near the horizon. Temporarily, the crater walls would be in sunlight while the crater floors were still in darkness. Seen from planet Earth, contrasting sections of bright walls against the dark floors by chance look remarkably like an X. This sharp image of the Lunar X was captured at approximately 16:45 UT on December 6, 2016. For extra credit, sweep your gaze along the lunar terminator and you can also spot the Lunar V.

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JerryO

Re: APOD: The Lunar X (2016 Dec 10)

Post by JerryO » Sat Dec 10, 2016 9:32 am

The Lunar V is also known as the lunar guitarist, a.k.a. Elvis. Independently discovered by Alister Ling and myself about the same time, and reported by Glenn Chaple in the August 2013 issue of Astronomy magazine, the V looks remarkably like a rock 'n' roll guitarist with legs spread wide. (It's the shadow within the V, not the bright V, that makes up the guitarist.) Like the X, this only lasts for a few hours at most.

heehaw

Re: APOD: The Lunar X (2016 Dec 10)

Post by heehaw » Sat Dec 10, 2016 11:24 am

Even better stuff is available on TeaLeavesOfTheDay!

heehaw

Re: APOD: The Lunar X (2016 Dec 10)

Post by heehaw » Sat Dec 10, 2016 3:43 pm

heehaw wrote:Even better stuff is available on TeaLeavesOfTheDay!
Here it is:
http://www.thedailytea.com/inspiration/ ... ea-leaves/

E Fish

Re: APOD: The Lunar X (2016 Dec 10)

Post by E Fish » Sat Dec 10, 2016 7:09 pm

Now, what I want to know is what's buried under that X. I'll volunteer to go up there and start digging...if someone will give me a ride.

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Re: APOD: The Lunar X (2016 Dec 10)

Post by Chris Peterson » Sat Dec 10, 2016 7:42 pm

RenaissanceMan wrote:How frequently can we detect meteorite impacts on the moon, and how large are they typically?
During showers, under favorable observing conditions, a single observer with a small telescope and a video camera might detect 5-10 per night. My friend who runs NASA's monitoring system has detected several hundred over the last few years. The smallest observed impacts involve bodies massing perhaps 50g. I believe the largest routinely observed are several kilograms. There have been at least a few which were much larger- several hundred kilograms- and which have new craters associated with them.
Chris

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Re: APOD: The Lunar X (2016 Dec 10)

Post by Chris Peterson » Sat Dec 10, 2016 9:02 pm

RenaissanceMan wrote:50 grams, come on now! No way. Less than two ounces? Not with a small telescope, I'm pretty sure.
Verification! I want some pictographic verification. That's what I'm talkin' about.
Well, you could take a look at the pages put up by the folks at NASA who are doing this routinely. They say "greater than 10s of grams". They use 14" telescopes of the sort routinely used by amateurs.

The maximum impact speed on the Moon is about 72 km/s. A 50g object striking at this speed releases about 130 MJ. Since these events only last a fraction of a second, you can get a sense of the brightness by considering that a MJ is also a wattsecond. Or if you like, it's the energy given up by 30 kg of TNT. Even if the luminous efficiency is fairly low, that's still a lot of light.
Finally, this. I wrote to Carl Sagan after reading several of his books, like Cosmos and Pale Blue Dot. I noticed two problems in them generally.
1. He has a very distinct left-wing bias, which is most unseemly for scientists.
Why? Scientists are allowed social and political opinions like anybody else. Are you suggesting that his biases resulted in him arriving at false scientific conclusions?
Chris

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Re: APOD: The Lunar X (2016 Dec 10)

Post by Chris Peterson » Sat Dec 10, 2016 9:29 pm

RenaissanceMan wrote:Why? Scientists are allowed social and political opinions like anybody else. Are you suggesting that his biases resulted in him arriving at false scientific conclusions? - Chris

There ya go! You got right to the bottom of that, didn't you.
Tell me how "scientific" it is to consistently criticize and make fun of Republican presidents and Republicans, but never Democrat presidents and liberals? Is that "scientific"?
It isn't scientific at all. But nobody is claiming it is. Something would be terribly wrong with a society where scientists had to remain neutral about their political opinions.
Chris

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Re: APOD: The Lunar X (2016 Dec 10)

Post by FLPhotoCatcher » Sat Dec 10, 2016 11:20 pm

OK, back to the X on the moon.
Does anyone think it looks like the "X" in SpaceX?

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Re: APOD: The Lunar X (2016 Dec 10)

Post by gadieid » Sun Dec 11, 2016 6:25 am

My own (not as good) version of the X and V. I Guess just few hours after the "right time". Should try again
2016-03-16-LunarXV.png
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Re: APOD: The Lunar X (2016 Dec 10)

Post by DavidLeodis » Sun Dec 11, 2016 12:34 pm

It's a nice image. I like such images of the Moon because I can also see by naked eye the large features on its side that faces Earth.

I may not have spotted the Lunar V without the annotated image brought up through the "For extra credit" link. In the inset image on the APOD there is a diamond shape a little above the Lunar X, so perhaps that could be called the 'Lunar Diamond'. OK, it's easy to 'spot' shapes but there does seem to be a lot of Lunar Os :wink:.