by neufer » Wed Dec 10, 2008 4:27 am
kjardine wrote:On the history of the Gould Belt ... this is all pretty controversial, and I wouldn't put this on my own site, but here's a capsule speculation:
Star formation appears to have started about 50 million years ago inside a molecular cloud shaped roughly like an American football and inclined at an angle of about 20 degrees to the galactic plane. This created what is sometimes called the Cas-Tau OB association. Stellar winds and supernovae from this association created a large bubble that eventually broke through the galactic plane (top and bottom) into the halo region, and so the denser gas formed a doughnut. Like the molecular cloud, the doughnut was tilted at an angle of about 20 degrees. Star formation was triggered inside the doughnut in several places, but especially in Orion and Scorpius to form the Ori OB1 and Sco OB2 associations (aka many of the brightest stars in those constellations).
This tilted doughnut of bright stars (within which is our Sun) is what astronomers call the Gould belt.
Eventually the Cas-Tau association dispersed, leaving only a core of stars visible around Alpha Persei (Mirfak, which is thus a sort-of mother star for our region).
One interesting question is what sparked the original Cas-Tau star formation. Some astronomers argue that the Gould Belt molecular cloud was a high velocity cloud orbiting the Milky Way and that the Cas-Tau star formation was sparked when the molecular cloud hit the galactic plane at a 20 degree angle, a little bit like a meteor hitting the moon. A little bit like because neither the cloud nor the galactic plane was solid and actually what would happen is the cloud would have gone right through the plane, and then fallen back again, oscillating up and down until it reached its current position.
Now a very few people speculate that the whole process of being attracted to the galactic plane, breaking through, oscillating, forming stars, etc, probably can be dated back a little earlier than the Cas-Tau association itself. So I suppose that you could write a science fiction novel in which the dinosaurs were wiped out by a comet dislodged from the Oort cloud as the Gould Belt cloud approached the galactic plane.
No real evidence for it, but it would be pretty cool if the same event that shaped the night sky allowed for the evolution of the human race.
That would be cosmic.
But at this point, also just science fiction.
Well.... some sorta fiction.
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http://en.wikipedia.org/wiki/Whale
<<All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulate animals). Whales are the closest living relatives of hippos; they evolved from a common ancestor at around 54 million years ago. Whales entered the water roughly 50 million years ago>>
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http://www.coldwater.k12.mi.us/lms/plan ... cetus.html
<<Cetus, in the form of a monstrous whale, set upon his mission of destruction and began the slaughter, working his way up and down the coast. The frightened people gathered and pleaded to their king to save them. Cepheus consulted an oracle--one with magical powers who could communicate with the gods when men sought their advice. The oracle told Cepheus that there was only one way to stop the slaughter: "You must offer your daughter Andromeda as a sacrifice." She was to be chained to the rocks on the coast and left for Cetus to devour. He made the bitter choice of sacrificing Andromeda, whereupon she was chained to the rocks and abandoned to await Cetus.
When Cetus discovered the prize awaiting him, he left off his wholesale destruction of the land and began swimming toward the ledge where Andromeda was chained. But then a distant figure appeared in the sky. It was Perseus, the brave son of Zeus and Danae, just returning from a journey during which he had succeeded in killing the dreaded Medusa.
It was when Perseus was flow over the coast of Æthiopia that he noticed Andromeda chained to the rocks by the sea, and not far away he could see Cetus rapidly nearing her. Down he swept to the girl's side. "Why are you thus bound?" he asked, overwhelmed by Andromeda's beauty. Andromeda told him the story of her boastful mother and the advice the oracle had given her father.
Perseus quickly turned to Cepheus and said: "I can save your daughter from the sea-monster, but for my reward I demand Andromeda's hand in marriage, and a kingdom." Cepheus promised Perseus that he would have what he asked for, whereupon Perseus unsheathed his sword and leapt into the air to the attack. One thrust of his sword found a soft spot between the armored scales of the monster. Wounded, it twisted over on its side. Perseus then inflicted another deep cut, and another. Blood now colored the water red and soaked Perseus' winged shoes. Fearful of losing his ability to fly, he settled on a rock near the shore and waited for the sea-monster to attack again. As it did, Perseus' sword plunged deeply into the monster's evil heart.>>
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Artiodactyl Neuendorffer
[quote="kjardine"]On the history of the Gould Belt ... this is all pretty controversial, and I wouldn't put this on my own site, but here's a capsule speculation:
Star formation appears to have started about 50 million years ago inside a molecular cloud shaped roughly like an American football and inclined at an angle of about 20 degrees to the galactic plane. This created what is sometimes called the Cas-Tau OB association. Stellar winds and supernovae from this association created a large bubble that eventually broke through the galactic plane (top and bottom) into the halo region, and so the denser gas formed a doughnut. Like the molecular cloud, the doughnut was tilted at an angle of about 20 degrees. Star formation was triggered inside the doughnut in several places, but especially in Orion and Scorpius to form the Ori OB1 and Sco OB2 associations (aka many of the brightest stars in those constellations).
This tilted doughnut of bright stars (within which is our Sun) is what astronomers call the Gould belt.
Eventually the Cas-Tau association dispersed, leaving only a core of stars visible around Alpha Persei (Mirfak, which is thus a sort-of mother star for our region).
One interesting question is what sparked the original Cas-Tau star formation. Some astronomers argue that the Gould Belt molecular cloud was a high velocity cloud orbiting the Milky Way and that the Cas-Tau star formation was sparked when the molecular cloud hit the galactic plane at a 20 degree angle, a little bit like a meteor hitting the moon. A little bit like because neither the cloud nor the galactic plane was solid and actually what would happen is the cloud would have gone right through the plane, and then fallen back again, oscillating up and down until it reached its current position.
Now a very few people speculate that the whole process of being attracted to the galactic plane, breaking through, oscillating, forming stars, etc, probably can be dated back a little earlier than the Cas-Tau association itself. So I suppose that you could write a science fiction novel in which the dinosaurs were wiped out by a comet dislodged from the Oort cloud as the Gould Belt cloud approached the galactic plane.
No real evidence for it, but it would be pretty cool if the same event that shaped the night sky allowed for the evolution of the human race.
That would be cosmic.
But at this point, also just science fiction.[/quote]
Well.... some sorta fiction.
-----------------------------------------------------
http://en.wikipedia.org/wiki/Whale
<<All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulate animals). Whales are the closest living relatives of hippos; they evolved from a common ancestor at around 54 million years ago. Whales entered the water roughly 50 million years ago>>
-----------------------------------------------------
http://www.coldwater.k12.mi.us/lms/planetarium/myth/cetus.html
<<Cetus, in the form of a monstrous whale, set upon his mission of destruction and began the slaughter, working his way up and down the coast. The frightened people gathered and pleaded to their king to save them. Cepheus consulted an oracle--one with magical powers who could communicate with the gods when men sought their advice. The oracle told Cepheus that there was only one way to stop the slaughter: "You must offer your daughter Andromeda as a sacrifice." She was to be chained to the rocks on the coast and left for Cetus to devour. He made the bitter choice of sacrificing Andromeda, whereupon she was chained to the rocks and abandoned to await Cetus.
When Cetus discovered the prize awaiting him, he left off his wholesale destruction of the land and began swimming toward the ledge where Andromeda was chained. But then a distant figure appeared in the sky. It was Perseus, the brave son of Zeus and Danae, just returning from a journey during which he had succeeded in killing the dreaded Medusa.
It was when Perseus was flow over the coast of Æthiopia that he noticed Andromeda chained to the rocks by the sea, and not far away he could see Cetus rapidly nearing her. Down he swept to the girl's side. "Why are you thus bound?" he asked, overwhelmed by Andromeda's beauty. Andromeda told him the story of her boastful mother and the advice the oracle had given her father.
Perseus quickly turned to Cepheus and said: "I can save your daughter from the sea-monster, but for my reward I demand Andromeda's hand in marriage, and a kingdom." Cepheus promised Perseus that he would have what he asked for, whereupon Perseus unsheathed his sword and leapt into the air to the attack. One thrust of his sword found a soft spot between the armored scales of the monster. Wounded, it twisted over on its side. Perseus then inflicted another deep cut, and another. Blood now colored the water red and soaked Perseus' winged shoes. Fearful of losing his ability to fly, he settled on a rock near the shore and waited for the sea-monster to attack again. As it did, Perseus' sword plunged deeply into the monster's evil heart.>>
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Artiodactyl Neuendorffer