APOD: Moonquakes Surprisingly Common (2019 Jul 21)

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APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by APOD Robot » Sun Jul 21, 2019 4:09 am

Image Moonquakes Surprisingly Common

Explanation: Why are there so many moonquakes? Analyses of seismometers left on the moon by the Apollo moon landings reveals a surprising number of moonquakes occurring within 100 kilometers of the surface. In fact, 62 moonquakes were detected in data recorded between 1972 and 1977. Many of these moonquakes are not only strong enough to move furniture in a lunar apartment, but the stiff rock of the moon continues to vibrate for many minutes, significantly longer than the softer rock earthquakes on Earth. The cause of the moonquakes remains unknown, but a leading hypothesis is the collapse of underground faults. Regardless of the source, future moon dwellings need to be built to withstand the frequent shakings. Pictured here 50 years ago today, Apollo 11 astronaut Buzz Aldrin stands beside a recently deployed lunar seismometer, looking back toward the lunar landing module.

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RocketRon

Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by RocketRon » Sun Jul 21, 2019 5:57 am

Great photo, history for all time...

Could the moon still be cooling and shrinking ?
How long would that process continue after its formation ?

I'm still mystified that with no atmosphere, the sky should be ablaze with stars, even in the daytime ?
Did the camera ever point upwards and take a shot ?
One of the missions they pointed one at the sun - and fried it !?

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by orin stepanek » Sun Jul 21, 2019 10:57 am

My wife and I were at the drive in the day they landed on the moon! Good luck Mr Gorsky! :mrgreen:
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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by De58te » Sun Jul 21, 2019 1:52 pm

RocketRon wrote:
Sun Jul 21, 2019 5:57 am
I'm still mystified that with no atmosphere, the sky should be ablaze with stars, even in the daytime ?
If I recall my Kodak Instamatic camera back in 1969 had an exposure time of 1/60th a second. Fast enough to stop people when moving from blurring, but still designed for photographing in the sun. If you wanted to take a picture indoors you had to attach a flash cube. Stars, besides the Sun, are rather dim and won't show up at 1/60th a second exposure.
Notice Neil Armstrong is actually in sunlight. If they wanted to capture the stars which meant an exposure in minutes, then Armstrong would have been an overexposed blob of white light.

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by BDanielMayfield » Sun Jul 21, 2019 2:12 pm

RocketRon wrote:
Sun Jul 21, 2019 5:57 am
Great photo, history for all time...

Could the moon still be cooling and shrinking ?
How long would that process continue after its formation ?
Yes the Moon is still cooling. In fact, its inner core might still be partially molten. Per wikipedia:
The Moon is the second-densest satellite in the Solar System, after Io.[55] However, the inner core of the Moon is small, with a radius of about 350 kilometres (220 mi) or less,[1] around 20% of the radius of the Moon. Its composition is not well defined, but is probably metallic iron alloyed with a small amount of sulfur and nickel; analyses of the Moon's time-variable rotation suggest that it is at least partly molten.
And this continued cooling would be a cause for moonquakes. Cooling also leads to shrinkage.
The discovery of fault scarp cliffs by the Lunar Reconnaissance Orbiter suggest that the Moon has shrunk within the past billion years, by about 90 metres (300 ft).[62] Similar shrinkage features exist on Mercury. A recent study of over 12000 images from the orbiter has observed that Mare Frigoris near the north pole, a vast basin assumed to be geologically dead, has been cracking and shifting. Since the Moon doesn't have tectonic plates, its tectonic activity is slow and cracks develop as it loses heat over the years.
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by Chris Peterson » Sun Jul 21, 2019 2:30 pm

RocketRon wrote:
Sun Jul 21, 2019 5:57 am
I'm still mystified that with no atmosphere, the sky should be ablaze with stars, even in the daytime ?
Film is rather insensitive compared with modern electronic sensors. If you'd like to take a film image at night (when the sky is dark) which captures stars, you'll need an exposure of at least a few seconds (possibly tens of seconds with the film used by the astronauts). Use this same exposure during the day on the Moon, and everything lit up by the Sun will be massively overexposed. Film simply lacks the dynamic range to capture stars and sunlit landscapes in the same image. The difference in brightness is too great. You expose for one or you expose for the other. (To some extent, this remains true even with electronic sensors. But when we combine those sensors with the right electronics and software, we can rapidly capture several exposures and combine them into a single high dynamic range image- the HDR process we now find incorporated into many digital cameras.)
One of the missions they pointed one at the sun - and fried it !?
This would not have harmed their film cameras. But they also used video cameras, and the technology at the time used vidicons or other image tubes which had photocathodes which could be directly damaged by bright light, or which could be damaged by high currents flowing through them when exposed to bright enough light. You had to be careful with those cameras. The surface video camera used for Apollo 12 was seriously damaged by being pointed (accidentally) at the Sun.
Chris

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by bystander » Sun Jul 21, 2019 2:43 pm

BDanielMayfield wrote:
Sun Jul 21, 2019 2:12 pm
RocketRon wrote:
Sun Jul 21, 2019 5:57 am
Great photo, history for all time...

Could the moon still be cooling and shrinking ?
How long would that process continue after its formation ?
Yes the Moon is still cooling. In fact, its inner core might still be partially molten. Per wikipedia:
The Moon is the second-densest satellite in the Solar System, after Io.[55] However, the inner core of the Moon is small, with a radius of about 350 kilometres (220 mi) or less,[1] around 20% of the radius of the Moon. Its composition is not well defined, but is probably metallic iron alloyed with a small amount of sulfur and nickel; analyses of the Moon's time-variable rotation suggest that it is at least partly molten.
And this continued cooling would be a cause for moonquakes. Cooling also leads to shrinkage.
The discovery of fault scarp cliffs by the Lunar Reconnaissance Orbiter suggest that the Moon has shrunk within the past billion years, by about 90 metres (300 ft).[62] Similar shrinkage features exist on Mercury. A recent study of over 12000 images from the orbiter has observed that Mare Frigoris near the north pole, a vast basin assumed to be geologically dead, has been cracking and shifting. Since the Moon doesn't have tectonic plates, its tectonic activity is slow and cracks develop as it loses heat over the years.


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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by neufer » Sun Jul 21, 2019 4:05 pm

Click to play embedded YouTube video.
BDanielMayfield wrote:
Sun Jul 21, 2019 2:12 pm


Yes the Moon is still cooling. In fact, its inner core might still be partially molten. And this continued cooling would be a cause for moonquakes.

Cooling also leads to shrinkage.
Isn't that Surprisingly Common knowledge :?:
Art Neuendorffer

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by BDanielMayfield » Sun Jul 21, 2019 8:03 pm

neufer wrote:
Sun Jul 21, 2019 4:05 pm
Click to play embedded YouTube video.
BDanielMayfield wrote:
Sun Jul 21, 2019 2:12 pm


Yes the Moon is still cooling. In fact, its inner core might still be partially molten. And this continued cooling would be a cause for moonquakes.

Cooling also leads to shrinkage.
Isn't that Surprisingly Common knowledge :?:
Depends on your gender. Elaine didn't know. :wink:
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by Boomer12k » Sun Jul 21, 2019 9:55 pm

I wonder if there would be enough cavern collapses to account for it...

I wonder if tidal forces from Earth... as The Moon produces Tides on Earth... THAT is a real constant ever changing pressure... a transference of Energy.

Or has that already been ruled out...
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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by Chris Peterson » Sun Jul 21, 2019 10:22 pm

Boomer12k wrote:
Sun Jul 21, 2019 9:55 pm
I wonder if there would be enough cavern collapses to account for it...

I wonder if tidal forces from Earth... as The Moon produces Tides on Earth... THAT is a real constant ever changing pressure... a transference of Energy.
While the actual tidal force on the Moon from the Earth is greater than that of the Moon on the Earth, keep in mind that there is very little movement of the tidal bulge on the Moon. Other than a very slight wobble because of libration, and a small variation in magnitude because of the eccentricity of the Moon's orbit, not much is changing. The stress is fixed- quite unlike what happens on the Earth, where the tidal bulges rotate around the planet daily. So I doubt that tides on the Moon have much of a geological impact.
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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by neufer » Mon Jul 22, 2019 2:58 am

Chris Peterson wrote:
Sun Jul 21, 2019 10:22 pm
Boomer12k wrote:
Sun Jul 21, 2019 9:55 pm

I wonder if there would be enough cavern collapses to account for it...

I wonder if tidal forces from Earth... as The Moon produces Tides on Earth...
THAT is a real constant ever changing pressure... a transference of Energy.
While the actual tidal force on the Moon from the Earth is greater than that of the Moon on the Earth, keep in mind that there is very little movement of the tidal bulge on the Moon. Other than a very slight wobble because of libration, and a small variation in magnitude because of the eccentricity of the Moon's orbit, not much is changing. The stress is fixed- quite unlike what happens on the Earth, where the tidal bulges rotate around the planet daily. So I doubt that tides on the Moon have much of a geological impact.
The monthly Earth tidal shear oscillation on the Moon is actually
~3 times the (twice daily) lunar tidal shear oscillation on the Earth
thanks primarily to the elliptical lunar orbit.

However, the small ocean tidal variations on Earth vs-a-vi the actual
size of the Earth means that such tidal oscillations are negligible overall.
Art Neuendorffer

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by neufer » Mon Jul 22, 2019 3:06 am

BDanielMayfield wrote:
Sun Jul 21, 2019 8:03 pm
neufer wrote:
Sun Jul 21, 2019 4:05 pm
BDanielMayfield wrote:
Sun Jul 21, 2019 2:12 pm

Yes the Moon is still cooling. In fact, its inner core might still be partially molten.
And this continued cooling would be a cause for moonquakes.

Cooling also leads to shrinkage.
Isn't that Surprisingly Common knowledge :?:
Depends on your gender. Elaine didn't know.
It's frightened turtles all the way down.
Art Neuendorffer

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by TheOtherBruce » Mon Jul 22, 2019 3:20 am

RocketRon wrote:
Sun Jul 21, 2019 5:57 am
I'm still mystified that with no atmosphere, the sky should be ablaze with stars, even in the daytime ?
Keep in mind that with no atmosphere, the sunlight is much brighter than you could find anywhere on earth. How much brighter? On the wikipedia page for the Moon, it's mentioned that the albedo (a measure of how much light is reflected from the surface) is about the same as road tar. And yet the lunar surface seen close up is, on average, a sort of medium grey. Look at it from Earth, and it seems almost white.

The sunlight's bright enough to wash out the dark dust and rocks. Sunlight reflected from the surrounding lunarscape is bright enough to illuminate the shadowed side of the astronauts and the LM. Look at the sunlit sides, and they're so bright all the colours are distorted. You can set the camera exposure for that, or you can set it to catch the much fainter stars.

I know the Apollo cameras were excellent quality (Hasselblads, I've got one) but at least back in the 60s they couldn't handle that sort of brightness range. It might be different now if you stuck the right kind of CCD back with the right programming onto a Hasselblad.

RocketRon

Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by RocketRon » Mon Jul 22, 2019 3:33 am

The Earth would always be in the background sky, and even it doesn't seem to feature.
Were they so blasé already that it didn't even feature ?
Even an ordinary exposure should show it.

Someone must have noticed the sky viewing, for a later moon mission left a telescope there.
Which doesn't seem to get much attention.

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Re: APOD: Moonquakes Surprisingly Common (2019 Jul 21)

Post by Chris Peterson » Mon Jul 22, 2019 5:06 am

TheOtherBruce wrote:
Mon Jul 22, 2019 3:20 am
RocketRon wrote:
Sun Jul 21, 2019 5:57 am
I'm still mystified that with no atmosphere, the sky should be ablaze with stars, even in the daytime ?
Keep in mind that with no atmosphere, the sunlight is much brighter than you could find anywhere on earth.
Not much different, actually. The Earth's atmosphere doesn't absorb all that much light in the visible spectrum. Our eyes wouldn't notice the difference.
Chris

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