APOD: Eclipsosaurus Rex (2017 Oct 07)

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APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby APOD Robot » Sat Oct 07, 2017 4:06 am

Image Eclipsosaurus Rex

Explanation: We live in an era where total solar eclipses are possible because at times the apparent size of the Moon can just cover the disk of the Sun. But the Moon is slowly moving away from planet Earth. Its distance is measured to increase about 1.5 inches (3.8 centimeters) per year due to tidal friction. So there will come a time, about 600 million years from now, when the Moon is far enough away that the lunar disk will be too small to ever completely cover the Sun. Then, at best only annular eclipses, a ring of fire surrounding the silhouetted disk of the too small Moon, will be seen from the surface of our fair planet. Of course the Moon was slightly closer and loomed a little larger 100 million years ago. So during the age of the dinosaurs there were more frequent total eclipses of the Sun. In front of the Tate Geological Museum at Casper College in Wyoming, this dinosaur statue posed with a modern total eclipse, though. An automated camera was placed under him to shoot his portrait during the Great American Eclipse of August 21.

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby Boomer12k » Sat Oct 07, 2017 5:32 am

Imaginative... and creative... I am sure the dinosaur enjoyed the view as he "POSED" for the shot....

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby neufer » Sat Oct 07, 2017 9:50 am

One wonders what Rex thought of the Moron Moon back then.
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby Guest » Sat Oct 07, 2017 11:01 am

We live in an era where total solar eclipses are possible because at times the apparent size of the Moon can just cover the disk of the Sun.

As has everyone that has ever lived on Earth. Duh.

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby neufer » Sat Oct 07, 2017 12:25 pm

Guest wrote:
We live in an era where total solar eclipses are possible because at times the apparent size of the Moon can just cover the disk of the Sun.

As has everyone that has ever lived on Earth. Duh.

That's the "We" being referenced. Duh.
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby Steve Dutch » Sat Oct 07, 2017 7:04 pm

Now THAT is neat!

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby ta152h0 » Sat Oct 07, 2017 7:35 pm

There seems to have been a lot of diversity in those creatures, even flying ones 64999999 million years ago. And all the creatures that ended up in the bottom of the ocean never to be found.
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby neufer » Sat Oct 07, 2017 8:05 pm

ta152h0 wrote:
There seems to have been a lot of diversity in those creatures, even flying ones 64999999 million years ago. And all the creatures that ended up in the bottom of the ocean never to be found.

64999999 million years :?:
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby kcairns » Sat Oct 07, 2017 8:19 pm

Seems to me the moon is held in orbit by the balance between centrifugal and gravitational forces. it is expending energy dragging tides around, so it must be slowing down, so the centrifugal force must be getting smaller and it should be coming closer to Earth?

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby kcairns » Sat Oct 07, 2017 9:24 pm

The laser measuring scheme must be influenced by scattering of photons both in space, which is not entirely empty, and air.
It is acknowledged that Earth is moving closer to the sun for the same reasons that the moon must be moving closer to Earth
The density of air must be increasing making the distance between moon and Earth measured by laser appear to be increasing when it is really decreasing.
Same argument - scattering of photons in space - might apply to the expanding universe conclusion, which I understand is based on red-shifted light, and defies logic.

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby neufer » Sat Oct 07, 2017 10:22 pm

kcairns wrote:
Seems to me the moon is held in orbit by the balance between centrifugal and gravitational forces. it is expending energy dragging tides around, so it must be slowing down, so the centrifugal force must be getting smaller and it should be coming closer to Earth?

The ocean tidal bulge lifted by the Moon actually ends up preceding the Moon in space as the Earth rapidly rotates beneath it.

The lagging Moon is thereby pulled forward by the very ocean tidal bulge it has generated and hence the Moon gains angular momentum at the expense of the Earth's rotation.
Last edited by neufer on Sat Oct 07, 2017 10:24 pm, edited 1 time in total.
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby heehaw » Sat Oct 07, 2017 10:24 pm

kcairns wrote:Seems to me the moon is held in orbit by the balance between centrifugal and gravitational forces. it is expending energy dragging tides around, so it must be slowing down, so the centrifugal force must be getting smaller and it should be coming closer to Earth?

I'm no expert but the sun is involved, too. Newton was intently focused on the motion of the moon, angry with the first Astronomer Royal for focusing first on an accurate grid of stars against which to measure the moon's motion.

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby Chris Peterson » Sat Oct 07, 2017 11:16 pm

kcairns wrote:The laser measuring scheme must be influenced by scattering of photons both in space, which is not entirely empty, and air.

The accuracy of the ranging is not impacted significantly by scattering, outside the loss of signal (virtually all of which happens within a few tens of kilometers of the surface of the Earth) reducing the signal-to-noise ratio, and therefore presumably slightly increasing the error in the measurement. But the ranging is still accurate to millimeters.

It is acknowledged that Earth is moving closer to the sun for the same reasons that the moon must be moving closer to Earth

No. Our distance is not changing significantly, because the tidal effects that result in the transfer of angular momentum are very different from the Earth-Moon system.

Same argument - scattering of photons in space - might apply to the expanding universe conclusion, which I understand is based on red-shifted light, and defies logic.

Scattering reduces the intensity of the light (the number of photons we receive). It doesn't affect either their arrival time or their wavelength.
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby kcairns » Sun Oct 08, 2017 7:29 am

Thank you, Chris, I get some of it, but not quite about the moon. The moon must be using energy to pull tides around, is it re-gaining energy from Earth by reducing it's speed of revolution as the tidal bulge tugs on the moon? So the moon is sucking energy from Earth like a parasite - I wonder if it ever considered being an Australian politician.

kcairns

Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby kcairns » Sun Oct 08, 2017 8:01 am

Chris, surely space has a refractive index, very small, but it is clearly not a vacuum, photons from distant stars must have been bounced around as they go, so have traveled further than the direct distance between here and their source. Prisms separate wavelengths into the visible spectrum due to the refractive index of glass, same with rainbows, so why is it not possible that space is acting like that. High energy violet photons might be scattered more than lower energy red ones?

Best Answer: Through any transparent or translucent material medium, like glass or air, light has a lower speed than in a vacuum; the ratio of c to this slower speed is called the refractive index of the medium (the actual speed is not affected, the speed of light is constant, the fact that the light is reflected around inside the glass will make a greater amount of time necessary for it to reach the next point). Changes of gravity, however, warp the space the light has to travel through,

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby neufer » Sun Oct 08, 2017 7:39 pm

kcairns wrote:
surely space has a refractive index, very small

    If you consider ~1.0 small.
Visible refractive index of space ~ 1.0 (+ 3 x 10-29)
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby Richard The Lion-Footed » Mon Oct 09, 2017 7:10 am

Great photo, but why would the moon being closer (600 million years ago) mean more solar eclipses? The celestial mechanics would be the same. May no annular eclipses, but the frequency of the alignment would not be different. Of course, I could be missing something. I frequently do.

Great photo however.

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby FLPhotoCatcher » Tue Oct 10, 2017 4:05 am

Richard The Lion-Footed wrote:Great photo, but why would the moon being closer (600 million years ago) mean more solar eclipses? The celestial mechanics would be the same. May no annular eclipses, but the frequency of the alignment would not be different. Of course, I could be missing something. I frequently do.

Great photo however.


If the moon was closer to Earth, it would orbit faster, and make more revolutions around Earth per year, thus more eclipses per year, on average. That's assuming its orbit was inclined about the same as it is now.

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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby neufer » Tue Oct 10, 2017 2:09 pm

FLPhotoCatcher wrote:
Richard The Lion-Footed wrote:
Great photo, but why would the moon being closer (600 million years ago) mean more solar eclipses? The celestial mechanics would be the same. May no annular eclipses, but the frequency of the alignment would not be different.

If the moon was closer to Earth, it would orbit faster, and make more revolutions around Earth per year, thus more eclipses per year, on average. That's assuming its orbit was inclined about the same as it is now.

Assuming its orbit was inclined about the same as it is now:
    Inclination = 5.145° to the ecliptic with the New Moon often
    passing 34,470 km [= 384,400 sin(5.145°)] above or below the Sun,
New Moons would of necessity:
    1) pass closer to the Sun
    2) be larger and
    3) occur more often.
However, the APOD was most likely simply suggesting that:
TOTAL eclipses would occur more often (with annular eclipses no longer being possible).
Last edited by neufer on Tue Oct 10, 2017 2:51 pm, edited 1 time in total.
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Re: APOD: Eclipsosaurus Rex (2017 Oct 07)

Postby Chris Peterson » Tue Oct 10, 2017 2:26 pm

FLPhotoCatcher wrote:
Richard The Lion-Footed wrote:Great photo, but why would the moon being closer (600 million years ago) mean more solar eclipses? The celestial mechanics would be the same. May no annular eclipses, but the frequency of the alignment would not be different. Of course, I could be missing something. I frequently do.

Great photo however.

If the moon was closer to Earth, it would orbit faster, and make more revolutions around Earth per year, thus more eclipses per year, on average. That's assuming its orbit was inclined about the same as it is now.

Also, if the Moon has a greater angular diameter, it will necessarily occlude the Sun (partially or totally) more often.
Chris

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