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Venus Express
ljk4-1
post Nov 7 2005, 04:03 PM
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QUOTE (RNeuhaus @ Nov 7 2005, 10:54 AM)
Besides, the other intrigating thing is that Venus sluggishly rotates on its axis once every 243 Earth days, while it orbits the Sun every 225 days - its day is longer than its year!

On the other hand, Venus rotates retrograde, or "backwards," spinning in the opposite direction of its orbit around the Sun. From its surface, the Sun would seem to rise in the west and set in the east.

The other odd thing is that its Equatorial Inclination to Orbit is 177.3 degrees. By comparison, it is: 7.56 x Earth. That is its north pole is almost pointing to the south pole.

These are at least one of the oddies things that I would like to understand:

Why does the day is longer than a year?
Why the planet rotates on backwards?

Rodolfo
*


A whomping big celestial impact is my guess.


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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RNeuhaus
post Nov 7 2005, 04:26 PM
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QUOTE (ljk4-1 @ Nov 7 2005, 11:03 AM)
A whomping big celestial impact is my guess.
*

Interesting but...why no a moon. After an impact to Venus and that should have a moon like the Earth's case.

I thought that the Venus' slow rotation might be caused by a very heavy atmosphere that circulates the planet in the opposite side to its rotation.

Or perhaps that is a normal for physics' law since its neigboor planet Mercury rotates around 58 Earth days and orbits around the Sun 88 Earth days. That is more or less a very long day that approach to a "planet of close one year" for both Mercury (less days) and Venus (more days).

Rodolfo
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ljk4-1
post Nov 7 2005, 04:30 PM
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QUOTE (RNeuhaus @ Nov 7 2005, 11:26 AM)
Interesting but...why no a moon. After an impact to Venus and that should have a moon like the Earth's case.

I thought that the Venus' slow rotation might be caused by a very heavy atmosphere that  circulates the planet in the opposite side to its rotation.

Or perhaps that is a normal for physics' law since its neigboor planet Mercury rotates around 58 Earth days and orbits around the Sun 88 Earth days.  That is more or less a very long day that approach to a "planet of close one year" for both Mercury (less days) and Venus (more days).

Rodolfo
*


Actually, should a large impact create a moon? My guess is that if Venus did get hit by something massive and powerful enough to practically flip it over, slow down its spin rate, and have it rotate in the opposite direction of most other major worlds, Venus was lucky enough to have survived intact, forget having a moon in the outcome.

Or maybe Venus was hit BY its own moon.


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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djellison
post Nov 7 2005, 04:57 PM
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Moons tend to orbit their parent planet in the same direction as the planets rotation - so were a moon to colide with its parent planet, the likely impact would be an increase in rotation I'd have thought.

Perhaps it's a symptom of planet formation closer to the centre of the protoplanetary disk - further out from the sun, the local gravity from chunks of whatever is the major force, but closer in, the suns gravity is dominant.

It's a complex process, that's for sure.


Doug
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JRehling
post Nov 7 2005, 05:26 PM
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QUOTE (ljk4-1 @ Nov 7 2005, 09:30 AM)
Actually, should a large impact create a moon?  My guess is that if Venus did get hit by something massive and powerful enough to practically flip it over, slow down its spin rate, and have it rotate in the opposite direction of most other major worlds, Venus was lucky enough to have survived intact, forget having a moon in the outcome.

Or maybe Venus was hit BY its own moon.
*


There are good sources on the Net for things being wildly speculated about here.

To pick just one: the angular momentum of a planet-moon system would remain the same after an impact as before. Such a collision couldn't make the system go backwards unless it was going backwards in the first place.

For the Moon to be created from a collision, it had to be a glancing blow. A straight-on punch would not liberate a lot of material.

A collision would be necessary if Venus's rotation was set in place as its formation concluded. But there are suggestions that tidal and thermal dynamics of its massive atmosphere may have "set" the rotation at the current rate. If so, the initial rotation is irrelevant/unknowable. In fact, the low inclination suggests that there is some sort of sun-driven factor: a collision that reordered Venus's rotation radically would be unlikely to leave the axis so nearly perpendicular to its orbit -- although that kind of coincidence is not impossible.

The rotation is only one oddity, not two or more. Given that the rotation is so slow, the reversal is not so odd -- the difference between rotating slowly E-W or slowly W-E is not nearly so big a difference as the slow rotation in the first place. Consider that a point on Venus's equator is rotating at about the speed of a fast *walk*!!! If it were moving the other direction, but just as slowly, that would only be a difference of a few km/h.

Also, the relative relationship between the day and year of Venus is not an "extra" oddity. Given the slow rotation, that follows as a logical consequence.

There is a second mystery regarding Venus's rotation, however, and that is why it is [almost] synchronized so as to show [almost] the same face towards the Earth at every conjunction. Mathematically, it would seem impossible for the tidal attraction to make this happen... but if this is a coincidence, it is a remarkable one.
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The Messenger
post Nov 7 2005, 05:46 PM
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QUOTE (JRehling @ Nov 7 2005, 10:26 AM)
There is a second mystery regarding Venus's rotation, however, and that is why it is [almost] synchronized so as to show [almost] the same face towards the Earth at every conjunction. Mathematically, it would seem impossible for the tidal attraction to make this happen... but if this is a coincidence, it is a remarkable one.
*


I'm filing this gem right next to the thermal energy in the Tiger stripes of Enceladus.

One thing is clear: The Solar System loves to throw us curve balls.
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Guest_BruceMoomaw_*
post Nov 7 2005, 09:20 PM
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Well, as Chesterton said, the most remarkable thing about coincidences is that occasionally they DO occur. The classic one in the Solar System is the disks of the Moon and Sun being virtually the same size as seen from Earth, which is the only thing that makes solar eclipses as we know them possible.

The trouble comes when the fact that the human (and presumably animal) mind is designed to specifically look for patterns leads us to jump to the conclusion that a genuine coincidence is more than that. Arthur Koestler once wrote an infamous crank philosophical book based on precisely that logical fallacy.
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RNeuhaus
post Nov 7 2005, 09:57 PM
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Anyway, at the beginning of the planetary formation, all planets is formed orbiting around the sun in the counter-clockwise, all have the same plane inclination with respect to the sun, all planets has their axis in perpendicular position to the planetary plane and all rotate the same way as it is orbiting around the sun, it is counter-clockwise.

are those all above suppositions affirmative or not?

Rodolfo
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ljk4-1
post Nov 7 2005, 10:08 PM
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QUOTE (JRehling @ Nov 7 2005, 12:26 PM)
There are good sources on the Net for things being wildly speculated about here.

*


There was this guy a long time ago named Aristarchus who wildly speculated that Earth went around the Sun and that the stars were other suns very far away.

The powers that be of his era accused him of religious impiety. His ideas were effectively buried for 1,500 years.

These ideas may "just" be speculation, but they are not wild. Uranus has been thought by many sober, rational astronomers to be in its present state due to major collisions by natural objects in its past, so why not for Venus to explain its current different state?


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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imran
post Nov 9 2005, 02:41 AM
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Less than one hour from launch!

Live webcast should be here:
http://www.starsem.com
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Waspie_Dwarf
post Nov 9 2005, 03:06 AM
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Alternative link for the live webcast of the launch: ESA's Venus Express Site


--------------------
"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space."

The Hitch-Hikers Guide to the Galaxy
Douglas Adams 1952 - 2001
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jamescanvin
post Nov 9 2005, 03:11 AM
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QUOTE (imran @ Nov 9 2005, 01:41 PM)
Less than one hour from launch!

Live webcast should be here:
http://www.starsem.com
*


Anybody getting a feed from here yet?

Just wondering if the error message I'm getting is because it hasn't starting or if there is an incompatibilty with the OSX version of Media Player.

James


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Waspie_Dwarf
post Nov 9 2005, 03:14 AM
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The live feed won't start until 03:28 GMT, at least on the ESA site. I assume it is the same on the Starsem site.


--------------------
"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space."

The Hitch-Hikers Guide to the Galaxy
Douglas Adams 1952 - 2001
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jamescanvin
post Nov 9 2005, 03:14 AM
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QUOTE (Waspie_Dwarf @ Nov 9 2005, 02:06 PM)
Alternative link for the live webcast of the launch: ESA's Venus Express Site
*


Ah, cross posting, a much more useful site.smile.gif

Starts only 5 mins before launch...


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imran
post Nov 9 2005, 03:22 AM
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Both webcasts are working now although you get better resolution from the Starsem site.
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