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Re: Earth will be transformed into magnetic field, if we will not sto
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David Williams
Nov 19, 2008, 11:17:44 AM11/19/08
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-> 7.5 km/s will get us 1 lightyear closer in 40 million years.
The speed of light is 3e5 km/s. That's 40,000 times faster than 7.5
km/s. So we'd get 1 light year closer in 40,000 years. I guess you
dropped a factor of 1000 someplace.
Another little calculation...
The escape velocity of the sun at the distance of the earth is about 50
km/s. If the sun were as massive as Sirius, the EV would be about
200 km/s. But Sirius is about 5e5 times further away than the sun. The
escape velocity is inversely proportional to the square-root of the
distance, so the escape velocity of Sirius at our distance from it
would be about 200/sqr(5e5) which comes to about 0.3 km/s. So, even if
there were no other stars nearby (such as Alpha Centauri, which is only
half as far from us as Sirius is), the sun could be in orbit around
Sirius, as BG contends, only if the relative velocity between the two
stars is less than 0.3 km/s. If they are approaching each other at 7.5
km/s, they are moving about 25 times too fast, even neglecting any
trnsverse velocity. So there is absolutely no way that the sun can be
in orbit around Sirius.
-> When do
-> you figure we will be closest to Sirius and how close will we be
-> then?
Good questions.
dow
The speed of light is 3e5 km/s. That's 40,000 times faster than 7.5
km/s. So we'd get 1 light year closer in 40,000 years. I guess you
dropped a factor of 1000 someplace.
Another little calculation...
The escape velocity of the sun at the distance of the earth is about 50
km/s. If the sun were as massive as Sirius, the EV would be about
200 km/s. But Sirius is about 5e5 times further away than the sun. The
escape velocity is inversely proportional to the square-root of the
distance, so the escape velocity of Sirius at our distance from it
would be about 200/sqr(5e5) which comes to about 0.3 km/s. So, even if
there were no other stars nearby (such as Alpha Centauri, which is only
half as far from us as Sirius is), the sun could be in orbit around
Sirius, as BG contends, only if the relative velocity between the two
stars is less than 0.3 km/s. If they are approaching each other at 7.5
km/s, they are moving about 25 times too fast, even neglecting any
trnsverse velocity. So there is absolutely no way that the sun can be
in orbit around Sirius.
-> When do
-> you figure we will be closest to Sirius and how close will we be
-> then?
Good questions.
dow
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