APOD: The Reappearance of Mars (2020 Sep 11)

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APOD: The Reappearance of Mars (2020 Sep 11)

Post by APOD Robot » Fri Sep 11, 2020 4:06 am

Image The Reappearance of Mars

Explanation: Mars reappears just beyond the Moon's dark limb in this stack of sharp video frames captured on September 6. Of course to reappear it had to disappear in the first place. It did that over an hour earlier when the sunlit southern edge of the waning gibbous Moon passed in front of the Red Planet as seen from Maceio, Brazil. The lunar occultation came as the Moon was near apogee, about 400,000 kilometers away. Mars was almost 180 times more distant. It was the fourth lunar occultation of Mars visible from planet Earth in 2020. Visible from some southern latitudes, the fifth lunar occultation of Mars in 2020 will take place on October 3 when the Moon and Mars are both nearly opposite the Sun in planet Earth's sky.

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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by orin stepanek » Fri Sep 11, 2020 11:32 am

MarsReappearanceDuarte1024.jpg

Aw! Mars was just playing hide & seek! It came out at ali ali free! :lol2:
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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by Ann » Fri Sep 11, 2020 2:18 pm

orin stepanek wrote:
Fri Sep 11, 2020 11:32 am
MarsReappearanceDuarte1024.jpg


Aw! Mars was just playing hide & seek! It came out at ali ali free! :lol2:
🤷‍♂️¯\_(ツ)_/¯ :? :?:

Swedish confusion

???

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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by bystander » Fri Sep 11, 2020 2:41 pm

Ann wrote:
Fri Sep 11, 2020 2:18 pm
orin stepanek wrote:
Fri Sep 11, 2020 11:32 am
Aw! Mars was just playing hide & seek! It came out at ali ali free! :lol2:

🤷‍♂️¯\_(ツ)_/¯ :? :?:

Swedish confusion

???

Ann
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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by Sa Ji Tario » Fri Sep 11, 2020 3:54 pm

Another greeting between Ares and Selene, what would the Chaldeans, Akkadians, Sumerians think of these celestial phenomena?

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problema bovinum

Post by neufer » Fri Sep 11, 2020 4:34 pm

bystander wrote:
Fri Sep 11, 2020 2:41 pm
Ann wrote:
Fri Sep 11, 2020 2:18 pm
orin stepanek wrote:
Fri Sep 11, 2020 11:32 am

Aw! Mars was just playing hide & seek! It came out at ali ali free! :lol2:
  • 🤷‍♂️¯\_(ツ)_/¯ :? :?:
https://en.wikipedia.org/wiki/Archimedes%27s_cattle_problem wrote:
<<Archimedes's cattle problem (or the problema bovinum or problema Archimedis) is a problem in Diophantine analysis, the study of polynomial equations with integer solutions. Attributed to Archimedes, the problem involves computing the number of cattle in a herd of the sun god from a given set of restrictions. The problem was discovered by Gotthold Ephraim Lessing in a Greek manuscript containing a poem of forty-four lines, in the Herzog August Library in Wolfenbüttel, Germany in 1773.

The problem, from an abridgement of the German translations published by Georg Nesselmann in 1842, and by Krumbiegel in 1880, states:
...................................................................................
Compute, O friend, the number of the cattle of the sun which once grazed upon the plains of Sicily, divided according to color into four herds, one milk-white, one black, one dappled and one yellow. The number of bulls is greater than the number of cows, and the relations between them are as follows:

White bulls = ( 1/2 + 1/3 ) black bulls + yellow bulls,
Black bulls = ( 1/4 + 1/5 ) dappled bulls + yellow bulls,
Dappled bulls = ( 1/6 + 1/7 ) white bulls + yellow bulls,
White cows = ( 1/3 + 1/4 ) black herd,
Black cows = ( 1/4 + 1/5 ) dappled herd,
Dappled cows = ( 1/5 + 1/6 ) yellow herd,
Yellow cows = ( 1/6 + 1/7 ) white herd.

If thou canst give, O friend, the number of each kind of bulls and cows, thou art no novice in numbers, yet can not be regarded as of high skill. Consider, however, the following additional relations between the bulls of the sun:


White bulls + black bulls = a square number,
Dappled bulls + yellow bulls = a triangular number.

If thou hast computed these also, O friend, and found the total number of cattle,
then exult as a conqueror, for thou hast proved thyself most skilled in numbers.
...................................................................................
The problem remained unsolved for a number of years, due partly to the difficulty of computing the huge numbers involved in the solution. The general solution was found in 1880 by Carl Ernst August Amthor (1845–1916), headmaster of the Gymnasium zum Heiligen Kreuz (Gymnasium of the Holy Cross) in Dresden, Germany. Using logarithmic tables, he calculated the first digits of the smallest solution,

showing that it is about 7.76 × 10206544 cattle,

far more than could fit in the observable universe.>>
https://en.wikipedia.org/wiki/Cattle_of_Helios wrote:
<<In Greek mythology, the Cattle of Helios (Greek: Ἠελίοιο βόες, Hēelíoio bóes), also called the Oxen of the Sun, are cattle pastured on the island of Thrinacia (sometimes identified with Sicily).

Helios, also known as the titan of the sun, is said to have had seven herds of oxen and seven flocks of sheep, each numbering fifty head. In the Odyssey, Homer describes these immortal cattle as handsome (ἄριστος), wide-browed, fat (εúρυμέτωπος) and straight-horned (ὀρθόκραιρος). The cattle were guarded by Helios’ daughters, Phaëthusa and Lampetië, and it was known by all that any harm to any single animal was sure to bring down the wrath of the titan.

Tiresias and Circe both warn Odysseus to shun the isle of Helios. When Eurylochus begs to be allowed to land to prepare supper, Odysseus grudgingly agrees on condition that the crew swear that if they come upon a herd of cattle or a great flock of sheep, no one will kill any of them. They are held on the isle for a month by an unfavorable storm sent by Poseidon.

When Odysseus goes up the island to pray to the gods and ask for help, Eurylochus convinces the crew to drive off the best of the cattle of Helios and sacrifice them to the gods: "if he be somewhat wroth for his cattle with straight horns, and is fain to wreck our ship, and the other gods follow his desire, rather with one gulp at the wave would I cast my life away, than be slowly straitened to death in a desert isle." When he returns to the ship, Odysseus rebukes his companions for disobeying his orders. But it is too late, the cattle are dead and gone.

Lampetie tells Helios that Odysseus' men have slain his cattle. In turn, Helios orders the gods to take vengeance on Odysseus' men. He threatens that if they do not pay him full atonement for the cattle, he will take the sun to the Underworld and shine it among the dead. Zeus promises Helios to smite their ship with a lightning bolt and cleave it in pieces in the midst of the ocean.

Soon the gods show signs and wonders to the Odysseus' men. The skins begin creeping and the flesh bellowing upon the spits, both the roast and raw, and there is a sound like the voice of cattle. For six days, Odysseus's company feast on the kine of Helios. On the seventh day, the wind changes. After they set sail, Zeus keeps his word and the ship is destroyed by lightning during a storm and all of his men die. Odysseus escapes by swimming to Calypso's island.>>
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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by Chris Peterson » Fri Sep 11, 2020 4:45 pm

Sa Ji Tario wrote:
Fri Sep 11, 2020 3:54 pm
Another greeting between Ares and Selene, what would the Chaldeans, Akkadians, Sumerians think of these celestial phenomena?
They would have been interpreted astrologically.
Chris

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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by orin stepanek » Fri Sep 11, 2020 5:29 pm

bystander wrote:
Fri Sep 11, 2020 2:41 pm
Ann wrote:
Fri Sep 11, 2020 2:18 pm
orin stepanek wrote:
Fri Sep 11, 2020 11:32 am
Aw! Mars was just playing hide & seek! It came out at ali ali free! :lol2:

🤷‍♂️¯\_(ツ)_/¯ :? :?:

Swedish confusion

???

Ann
Olly olly oxen free

Hey! It's been a long time; can't expect me to remember everything! 😁
Orin

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Re: problema bovinum

Post by Ann » Fri Sep 11, 2020 5:57 pm

neufer wrote:
Fri Sep 11, 2020 4:34 pm
bystander wrote:
Fri Sep 11, 2020 2:41 pm
Ann wrote:
Fri Sep 11, 2020 2:18 pm
  • 🤷‍♂️¯\_(ツ)_/¯ :? :?:
https://en.wikipedia.org/wiki/Archimedes%27s_cattle_problem wrote:
<<Archimedes's cattle problem (or the problema bovinum or problema Archimedis) is a problem in Diophantine analysis, the study of polynomial equations with integer solutions. Attributed to Archimedes, the problem involves computing the number of cattle in a herd of the sun god from a given set of restrictions. The problem was discovered by Gotthold Ephraim Lessing in a Greek manuscript containing a poem of forty-four lines, in the Herzog August Library in Wolfenbüttel, Germany in 1773.

The problem, from an abridgement of the German translations published by Georg Nesselmann in 1842, and by Krumbiegel in 1880, states:
...................................................................................
Compute, O friend, the number of the cattle of the sun which once grazed upon the plains of Sicily, divided according to color into four herds, one milk-white, one black, one dappled and one yellow. The number of bulls is greater than the number of cows, and the relations between them are as follows:

White bulls = ( 1/2 + 1/3 ) black bulls + yellow bulls,
Black bulls = ( 1/4 + 1/5 ) dappled bulls + yellow bulls,
Dappled bulls = ( 1/6 + 1/7 ) white bulls + yellow bulls,
White cows = ( 1/3 + 1/4 ) black herd,
Black cows = ( 1/4 + 1/5 ) dappled herd,
Dappled cows = ( 1/5 + 1/6 ) yellow herd,
Yellow cows = ( 1/6 + 1/7 ) white herd.

If thou canst give, O friend, the number of each kind of bulls and cows, thou art no novice in numbers, yet can not be regarded as of high skill. Consider, however, the following additional relations between the bulls of the sun:


White bulls + black bulls = a square number,
Dappled bulls + yellow bulls = a triangular number.

If thou hast computed these also, O friend, and found the total number of cattle,
then exult as a conqueror, for thou hast proved thyself most skilled in numbers.
...................................................................................
The problem remained unsolved for a number of years, due partly to the difficulty of computing the huge numbers involved in the solution. The general solution was found in 1880 by Carl Ernst August Amthor (1845–1916), headmaster of the Gymnasium zum Heiligen Kreuz (Gymnasium of the Holy Cross) in Dresden, Germany. Using logarithmic tables, he calculated the first digits of the smallest solution,

showing that it is about 7.76 × 10206544 cattle,

far more than could fit in the observable universe.>>
It's a good thing that the Universe is so much bigger than we can see, then, so that we would have some place to store all those cattle.

I'm sure I heard someplace that the minimum diameter (or was it radius?) of the non-observable Universe is 150 Hubble spheres. A Hubble sphere, by the way, is the size of the observable Universe.

Ann
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a bowl of mush

Post by neufer » Fri Sep 11, 2020 7:38 pm

Chris Peterson wrote:
Fri Sep 11, 2020 4:45 pm
Sa Ji Tario wrote:
Fri Sep 11, 2020 3:54 pm

Another greeting between Ares and Selene, what would the Chaldeans,
Akkadians, Sumerians think of these celestial phenomena?
  • They would have been interpreted astrologically.
Goodnight Moon and the Red Balloon :?:
https://en.wikipedia.org/wiki/Goodnight_Moon wrote:

<<Goodnight Moon is an American children's book written by Margaret Wise Brown and published on September 3, 1947. The text is a rhyming poem, describing an anthropomorphic bunny's bedtime ritual of saying "good night" to various inanimate and living objects in the bunny's bedroom: a Red Balloon, a pair of socks, the bunny's dollhouse, a bowl of mush, and two kittens, among others. Goodnight Moon contains a number of references to Brown's The Runaway Bunny. For example, the painting hanging over the fireplace of "The Cow Jumping Over the Moon" first appeared in The Runaway Bunny. However, when reprinted in Goodnight Moon, the udder was reduced to an anatomical blur to avoid the controversy that E.B. White's Stuart Little had undergone when published in 1945. In 2005, publisher HarperCollins digitally altered the photograph of illustrator Hurd, which had been on the book for at least twenty years, to remove a cigarette. Its editor-in-chief for children's books, Kate Jackson, said, "It is potentially a harmful message to very young [children]." HarperCollins had the reluctant permission of Hurd's son, Thacher Hurd, but the younger Hurd said the photo of Hurd with his arm and fingers extended, holding nothing, "looks slightly absurd to me." Brown, who died in 1952, bequeathed the royalties to the book (among many others) to Albert Clarke, who was the nine-year-old son of a neighbor when Brown died. Clarke squandered those millions of dollars.>>
https://en.wikipedia.org/wiki/Moon_rabbit wrote:
<<The moon rabbit or moon hare is a mythical figure who lives on the Moon in Far Eastern folklore, based on pareidolia interpretations that identify the dark markings on the near side of the Moon as a rabbit or hare. The folklore originated in China and then spread to other Asian cultures. In East Asian folklore, the rabbit is seen as pounding with a mortar and pestle, but the contents of the mortar differ among Chinese, Japanese and Korean folklore. In Chinese folklore, the rabbit often is portrayed as a companion of the Moon goddess Chang'e, constantly pounding the elixir of life for her; but in Japanese and Korean versions, the rabbit is pounding the ingredients for mochi or other some other type of rice cakes. In some Chinese versions, the rabbit pounds medicine for the mortals. Unrelated moon folklore arising among native cultures of the Americas, also have rabbit themes and characters.>>
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Re: problema bovinum

Post by neufer » Fri Sep 11, 2020 8:20 pm

Ann wrote:
Fri Sep 11, 2020 5:57 pm
neufer wrote:
Fri Sep 11, 2020 4:34 pm
https://en.wikipedia.org/wiki/Archimedes%27s_cattle_problem wrote:
<<Archimedes's cattle problem (or the problema bovinum or problema Archimedis) is a problem in Diophantine analysis, the study of polynomial equations with integer solutions. Attributed to Archimedes, the problem involves computing the number of cattle in a herd of the sun god from a given set of restrictions. The problem remained unsolved for a number of years, due partly to the difficulty of computing the huge numbers involved in the solution. The general solution was found in 1880 by Carl Ernst August Amthor (1845–1916), headmaster of the Gymnasium zum Heiligen Kreuz (Gymnasium of the Holy Cross) in Dresden, Germany. Using logarithmic tables, he calculated the first digits of the smallest solution,

showing that it is about 7.76 × 10206544 cattle,

far more than could fit in the observable universe.>>
It's a good thing that the Universe is so much bigger than we can see, then, so that we would have some place to store all those cattle. I'm sure I heard someplace that the minimum diameter (or was it radius?) of the non-observable Universe is 150 Hubble spheres. A Hubble sphere, by the way, is the size of the observable Universe.
It hardly matters.

A Hubble sphere has a volume of only 10185 cubic Planck lengths.

The universe would have have 4 × 1068,786 Hubble sphere diameters to hold even Planck cattle.
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Re: problema bovinum

Post by orin stepanek » Fri Sep 11, 2020 10:23 pm

Ann wrote:
Fri Sep 11, 2020 5:57 pm

It's a good thing that the Universe is so much bigger than we can see, then, so that we would have some place to store all those cattle.

I'm sure I heard someplace that the minimum diameter (or was it radius?) of the non-observable Universe is 150 Hubble spheres. A Hubble sphere, by the way, is the size of the observable Universe.

Ann

I've often wondered about that; and came to the conclusion that we will never know! How can there be an end to the universe? Like; what's there? What could possibly be there? Like more universe! 8-)
A big bug had little bugs upon their backs to bite them; and little bugs had lesser bugs, and on and on to infinitum! (not my saying)
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Re: problema bovinum

Post by Chris Peterson » Fri Sep 11, 2020 10:26 pm

orin stepanek wrote:
Fri Sep 11, 2020 10:23 pm
Ann wrote:
Fri Sep 11, 2020 5:57 pm

It's a good thing that the Universe is so much bigger than we can see, then, so that we would have some place to store all those cattle.

I'm sure I heard someplace that the minimum diameter (or was it radius?) of the non-observable Universe is 150 Hubble spheres. A Hubble sphere, by the way, is the size of the observable Universe.

Ann

I've often wondered about that; and came to the conclusion that we will never know! How can there be an end to the universe? Like; what's there? What could possibly be there? Like more universe! 8-)
A big bug had little bugs upon their backs to bite them; and little bugs had lesser bugs, and on and on to infinitum! (not my saying)
Where is the end of a circle? Or the edge of the surface of a sphere? Or of the volume of a hypersphere?
Chris

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Re: problema bovinum

Post by orin stepanek » Fri Sep 11, 2020 10:35 pm

Chris Peterson wrote:
Fri Sep 11, 2020 10:26 pm
orin stepanek wrote:
Fri Sep 11, 2020 10:23 pm
Ann wrote:
Fri Sep 11, 2020 5:57 pm

It's a good thing that the Universe is so much bigger than we can see, then, so that we would have some place to store all those cattle.

I'm sure I heard someplace that the minimum diameter (or was it radius?) of the non-observable Universe is 150 Hubble spheres. A Hubble sphere, by the way, is the size of the observable Universe.

Ann

I've often wondered about that; and came to the conclusion that we will never know! How can there be an end to the universe? Like; what's there? What could possibly be there? Like more universe! 8-)
A big bug had little bugs upon their backs to bite them; and little bugs had lesser bugs, and on and on to infinitum! (not my saying)
Where is the end of a circle? Or the edge of the surface of a sphere? Or of the volume of a hypersphere?

I was thinking outside the circle or globe or whatever: like a bag full of marbles! What's outside the marble? Another marble , or the marble's yet bigger? on to infinitum?
Orin

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Re: problema bovinum

Post by Chris Peterson » Fri Sep 11, 2020 10:37 pm

orin stepanek wrote:
Fri Sep 11, 2020 10:35 pm
Chris Peterson wrote:
Fri Sep 11, 2020 10:26 pm
orin stepanek wrote:
Fri Sep 11, 2020 10:23 pm

I've often wondered about that; and came to the conclusion that we will never know! How can there be an end to the universe? Like; what's there? What could possibly be there? Like more universe! 8-)
A big bug had little bugs upon their backs to bite them; and little bugs had lesser bugs, and on and on to infinitum! (not my saying)
Where is the end of a circle? Or the edge of the surface of a sphere? Or of the volume of a hypersphere?

I was thinking outside the circle or globe or whatever: like a bag full of marbles! What's outside the marble? Another marble , or the marble's yet bigger? on to infinitum?
There is no outside.
Chris

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Re: problema bovinum

Post by orin stepanek » Sat Sep 12, 2020 12:07 am

Chris Peterson wrote:
Fri Sep 11, 2020 10:37 pm
orin stepanek wrote:
Fri Sep 11, 2020 10:35 pm
Chris Peterson wrote:
Fri Sep 11, 2020 10:26 pm

Where is the end of a circle? Or the edge of the surface of a sphere? Or of the volume of a hypersphere?

I was thinking outside the circle or globe or whatever: like a bag full of marbles! What's outside the marble? Another marble , or the marble's yet bigger? on to infinitum?
There is no outside.
There has to be! IMHO! Space Doesn"t Just end! A circle goes round and round And so does a Sphere; but there has to be something outside that sphere! Infinitum! I'm not wavering on that!
Orin

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Re: problema bovinum

Post by Chris Peterson » Sat Sep 12, 2020 12:12 am

orin stepanek wrote:
Sat Sep 12, 2020 12:07 am
Chris Peterson wrote:
Fri Sep 11, 2020 10:37 pm
orin stepanek wrote:
Fri Sep 11, 2020 10:35 pm



I was thinking outside the circle or globe or whatever: like a bag full of marbles! What's outside the marble? Another marble , or the marble's yet bigger? on to infinitum?
There is no outside.
There has to be! IMHO! Space Doesn"t Just end! A circle goes round and round And so does a Sphere; but there has to be something outside that sphere! Infinitum! I'm not wavering on that!
No, there doesn't have to be anything outside a sphere. And there doesn't need to be anything outside a hyperspheric universe, either. The math is clear. If you could travel far enough in a closed universe, you'd just come back to where you started. Like on the surface of a sphere, or the edge of a circle. Don't let your inability to intuit such a geometry get in the way of reality. You are imagining a sphere embedded in a three-dimensional universe. The sphere <i>is</i> the universe. Or in our universe of spacetime, a hypersphere (or other 4D manifold).
Chris

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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by orin stepanek » Sat Sep 12, 2020 1:11 am

Who's to prove that the universe is closed? I believe it is open! But that is my Opine!
Orin

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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by neufer » Sat Sep 12, 2020 3:19 am

orin stepanek wrote:
Sat Sep 12, 2020 1:11 am

Who's to prove that the universe is closed? I believe it is open! But that is my Opine!
https://en.wikipedia.org/wiki/Shape_of_the_universe wrote:
Click to play embedded YouTube video.

<<The shape of the entire universe can be described with three attributes:
  • 1) Finite or infinite

    2) Flat (zero curvature), open (negative curvature),
    • or closed (positive curvature)
    3) Connectivity, how the universe is put together,
    • i.e., simply connected space or multiply connected.
There are certain logical connections among these properties. For example, a universe with positive curvature is necessarily finite. Although it is usually assumed in the literature that a flat or [open] universe is infinite, this need not be the case if the topology is not the trivial one: for example, a three-torus is flat but finite.

The exact shape is still a matter of debate in physical cosmology, but experimental data from various independent sources (WMAP, BOOMERanG, and Planck for example) confirm that the universe is flat with only a 0.4% margin of error. Arguments have been put forward that the observational data best fit with the conclusion that the shape of the global universe is infinite and flat, but the data are also consistent with other possible shapes.>>
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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by Ann » Sat Sep 12, 2020 4:29 am

neufer wrote:
Sat Sep 12, 2020 3:19 am
orin stepanek wrote:
Sat Sep 12, 2020 1:11 am

Who's to prove that the universe is closed? I believe it is open! But that is my Opine!
https://en.wikipedia.org/wiki/Shape_of_the_universe wrote:
Click to play embedded YouTube video.

<<The shape of the entire universe can be described with three attributes:
  • 1) Finite or infinite

    2) Flat (zero curvature), open (negative curvature),
    • or closed (positive curvature)
    3) Connectivity, how the universe is put together,
    • i.e., simply connected space or multiply connected.
There are certain logical connections among these properties. For example, a universe with positive curvature is necessarily finite. Although it is usually assumed in the literature that a flat or [open] universe is infinite, this need not be the case if the topology is not the trivial one: for example, a three-torus is flat but finite.

The exact shape is still a matter of debate in physical cosmology, but experimental data from various independent sources (WMAP, BOOMERanG, and Planck for example) confirm that the universe is flat with only a 0.4% margin of error. Arguments have been put forward that the observational data best fit with the conclusion that the shape of the global universe is infinite and flat, but the data are also consistent with other possible shapes.>>
I hope it's open. The idea that it might be closed, so that it will eventually collapse in on itself and crush itself out of existence (unless it maybe maybe rises out of the ashes like a Phoenix again, and I don't believe it will) is too horrible for a claustrophobic like me to contemplate.

So next time someone threatens me with a closed universe, I'll take comfort in the alternative explanation that it's turtles all the way down. Hey Art, the Universe may be too small for its cattle, but it's sure big enough for its turtles.

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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by orin stepanek » Sat Sep 12, 2020 11:46 am

Ann wrote:
Sat Sep 12, 2020 4:29 am
neufer wrote:
Sat Sep 12, 2020 3:19 am
orin stepanek wrote:
Sat Sep 12, 2020 1:11 am

Who's to prove that the universe is closed? I believe it is open! But that is my Opine!
https://en.wikipedia.org/wiki/Shape_of_the_universe wrote:
Click to play embedded YouTube video.

<<The shape of the entire universe can be described with three attributes:
  • 1) Finite or infinite

    2) Flat (zero curvature), open (negative curvature),
    • or closed (positive curvature)
    3) Connectivity, how the universe is put together,
    • i.e., simply connected space or multiply connected.
There are certain logical connections among these properties. For example, a universe with positive curvature is necessarily finite. Although it is usually assumed in the literature that a flat or [open] universe is infinite, this need not be the case if the topology is not the trivial one: for example, a three-torus is flat but finite.

The exact shape is still a matter of debate in physical cosmology, but experimental data from various independent sources (WMAP, BOOMERanG, and Planck for example) confirm that the universe is flat with only a 0.4% margin of error. Arguments have been put forward that the observational data best fit with the conclusion that the shape of the global universe is infinite and flat, but the data are also consistent with other possible shapes.>>
I hope it's open. The idea that it might be closed, so that it will eventually collapse in on itself and crush itself out of existence (unless it maybe maybe rises out of the ashes like a Phoenix again, and I don't believe it will) is too horrible for a claustrophobic like me to contemplate.

So next time someone threatens me with a closed universe, I'll take comfort in the alternative explanation that it's turtles all the way down. Hey Art, the Universe may be too small for its cattle, but it's sure big enough for its turtles.

Ann
So now you can have turtle soup ! :mrgreen:
Orin

Smile today; tomorrow's another day!

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neufer
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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by neufer » Sat Sep 12, 2020 8:45 pm

Ann wrote:
Sat Sep 12, 2020 4:29 am
neufer wrote:
Sat Sep 12, 2020 3:19 am
orin stepanek wrote:
Sat Sep 12, 2020 1:11 am

Who's to prove that the universe is closed? I believe it is open! But that is my Opine!
https://en.wikipedia.org/wiki/Shape_of_the_universe wrote:
Click to play embedded YouTube video.

<<The shape of the entire universe can be described with three attributes:
  • 1) Finite or infinite

    2) Flat (zero curvature), open (negative curvature),
    • or closed (positive curvature)
    3) Connectivity, how the universe is put together,
    • i.e., simply connected space or multiply connected.
There are certain logical connections among these properties. For example, a universe with positive curvature is necessarily finite. Although it is usually assumed in the literature that a flat or [open] universe is infinite, this need not be the case if the topology is not the trivial one: for example, a three-torus is flat but finite.

The exact shape is still a matter of debate in physical cosmology, but experimental data from various independent sources (WMAP, BOOMERanG, and Planck for example) confirm that the universe is flat with only a 0.4% margin of error. Arguments have been put forward that the observational data best fit with the conclusion that the shape of the global universe is infinite and flat, but the data are also consistent with other possible shapes.>>
I hope it's open. The idea that it might be closed, so that it will eventually collapse in on itself and crush itself out of existence (unless it maybe maybe rises out of the ashes like a Phoenix again, and I don't believe it will) is too horrible for a claustrophobic like me to contemplate. So next time someone threatens me with a closed universe, I'll take comfort in the alternative explanation that it's turtles all the way down. Hey Art, the Universe may be too small for its cattle, but it's sure big enough for its turtles.
  • Turtles make me claustrophobic.
Dark energy will keep the Universe expanding forever while simultaneously keeping it flat:
https://en.wikipedia.org/wiki/Shape_of_the_universe#Curvature_of_the_universe wrote:
<<General relativity explains that mass and energy bend the curvature of spacetime and is used to determine what curvature the universe has by using a value called the density parameter, represented with Omega (Ω). The density parameter is the average density of the universe divided by the critical energy density, that is, the mass energy needed for a universe to be flat. Put another way,
  • If Ω = 1, the universe is flat
    If Ω > 1, there is positive curvature
    if Ω < 1 there is negative curvature
Ωmass ≈ 0.315±0.018

Ωrelativistic ≈ 9.24×10−5

ΩΛ ≈ 0.6817±0.0018

Ωtotal= Ωmass + Ωrelativistic + ΩΛ = 1.00±0.02

The actual value for critical density value is measured as ρcritical= 9.47×10−27 kg m−3. From these values, within experimental error, the universe seems to be flat.>>
Art Neuendorffer

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Ann
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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by Ann » Sun Sep 13, 2020 5:11 am

neufer wrote:
Sat Sep 12, 2020 8:45 pm

Dark energy will keep the Universe expanding forever while simultaneously keeping it flat:
The actual value for critical density value is measured as ρcritical= 9.47×10−27 kg m−3. From these values, within experimental error, the universe seems to be flat.>>
Snoopy with lots of dark energy around him.png
Snoopy in a dark energy universe with lots of space around him.

I hug dark energy! :D

Ann
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neufer
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Re: APOD: The Reappearance of Mars (2020 Sep 11)

Post by neufer » Sun Sep 13, 2020 9:37 pm

Ann wrote:
Sat Sep 12, 2020 4:29 am

<<So next time someone threatens me with a closed universe, I'll take comfort in the alternative explanation that it's turtles all the way down. Hey Art, the Universe may be too small for its cattle, but it's sure big enough for its turtles.>>
  • Big enough for its male turtles, at least; the females are "a bit chunkier."
https://en.wikipedia.org/wiki/Spider_tortoise wrote:
Click to play embedded YouTube video.
<<The spider tortoise (Pyxis arachnoides) is a species of tortoise in the family Testudinidae. It is endemic to Madagascar and is one of only two species in the genus Pyxis.

Very little is known about the life cycle of this endangered tortoise, which is believed to live for up to 70 years. The remaining tortoises are found only in south western Madagascar, where they inhabit the spiny vegetation of the sandy coastal areas. Here they feed on young leaves, insect larvae, and even the droppings of larger animals. When the wet season arrives, the dormancy period ends and the tortoises begin to mate. Females only lay one egg when they reproduce, and the egg is incubated for about 220–250 days. Their trade is illegal in Madagascar, but they are extensively smuggled for food, body parts, and illegal pets.>>
https://www.washingtonpost.com/local/in-a-surprise-critically-endangered-creature-appears-at-national-zoo/2020/09/12/9755dc70-f552-11ea-b796-2dd09962649c_story.html wrote:
In a surprise, critically endangered creature appears at National Zoo
By Martin Weil, The Washington Post, September 12, 2020

<<A member of a critically endangered species turned up at the National Zoo this summer in what a curator called a surprise. A tiny spider tortoise appeared July 5 at the zoo’s Reptile Discovery Center, Assistant Curator Matt Evans reported this month. It had hatched from an egg that zoo staff members suspect was laid in January. But the egg had gone unseen, Evans wrote. Nor was the hatching witnessed, he said. Clearly, the mother tortoise is among the more secretive of animals. It hid its egg under a potted cactus, obscuring keepers’ view, Evans said. Although it was known that the species could be stealthy, Evans said, only with the discovery of the hatchling did he realize just “how stealthy they could be.” More than merely startling curators, the appearance of the quarter-size creature gave them cause to celebrate. It is feared that the species will go extinct in 100 years in its native Madagascar, Evans wrote. The allure of the spider tortoise apparently contributes to its undoing. Evans wrote that the beauty of the tortoise’s shell attracts the illegal pet trade.>>
Art Neuendorffer