Text 29650, 79 rader
Skriven 2012-06-14 23:06:22 av Michiel van der Vlist (2:280/5555)
     Kommentar till en text av alexander koryagin (2:5020/2140.2)
Ärende: Transit of Venus
========================
Hello alexander,

On Saturday June 09 2012 12:40, you wrote to me:

 ak> The Earth's orbital speed is the result of its moving energy. If the
 ak> Sun is vanished, the Earth would fly straight ahead at the speed of
 ak> 29.7 km/sec.

But the sun will not vanish, it will merely expand....

 ak>  But what would happened to the Earth after the Sun expands to the
 ak> Earth's orbit?

Ignoring loss of mass by solar wind and the mass equivalent of the radiated
energy nothing will happen.

The external gravitational field of a body with spherical symmetry is the same
as that of a point mass. So as long as sphericak synnetry is maintained and it
sstays within the earth orbit, the sun can expand 9or shrink) and nothing will
happen to the earth orbit.

 ak> The Sun's acceleration at 150 mln km distance will have decreased! It
 ak> means that the Sun  (after expansion) will NOT be able to keep the
 ak> Earth at its present day orbit. And the Earth will fly away from the
 ak> Sun to the interstellar space, as a rock hurled from a sling.

Nope. Nothing like that will happen.

when the sun expands beyiond the earth orbit two competing factors will occur.

1) The eart will slow down because of the friction of the solar atmosphere,
causing it to lose energy and spiral inwards.

2) The internal gravitational field of a body with spherical symmetry at
distance X from the centre is the same as that op a point mass with the mass
that is contained with the part of the body within X fron the centre.

So when the sun expands beyond earth robit only that part of the sun within
earth orbit will conribute to the gravitational pull and the earh will go into
a higher orbit.

But even without friction, it will never go so high as to be above the surface
of the sun again. Because when it rises that high, the gravitation pull will
again be that of the total solar mass and then a higher orbit means it has a
higher orbital energy. There is no source for that enery, so that will no
happen.

 ak> Nothing bad will happen to the people. People will live inside the
 ak> Earth for thousands years until the Earth arrives to another star.

At 300.000 km/s it takes 4 light years to reach the nearest star. At 30 km/s it
takes 300.000/30 X 4 years = 40.000 years to reach the nearest star. The
nearest star (Proxima Centauri) os not a vey suitable host for the earth.

Anyway, doom will hit the earth much sooner. Althoug the surface of the sun
will cool down during the expansion to the red giant fase, the total radiated
energy will increase due to the increased radiating surface. In about 10^9
years, the oceans will boil dry and that will be the end of the earth as we
know it.

It does no have to mean the end of the human race though. A lot can happen in
10^9 years. We may find a way to survive without the earth. Or - more likely -
we will come to an end in another way.

 ak> There is no doubt that the people of that time will be able to correct
 ak> the Earth's way and shorted it.

Who knows...

 ak> That's how it will be. ;-)

I am tempted to bet against, but  I don't see how I can ever cash in, so I will
refrain. ;-)


Cheers, Michiel

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