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bio website dotancohen.com
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age 37
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Nov
24
accepted How would I measure that I'm at a pole?
Nov
21
awarded  Commentator
Nov
21
comment Doesn't gravity attract objects in space until they collide?
@astromax: Right, but that is in addition to the momentum component of the orbiting body (assuming m<<M). Otherwise, as the OP stated, the objects would collide.
Nov
21
comment Can I see comet ISON from Saudi Arabia?
On what basis do you calculate the absolute magnitude of the cometary system? Surely not as a rocky object I hope! Don't forget that the coma and tail are mostly empty space, thus there is no crescent and the light is very diffuse. You would need to know the amount of particles in the material as well, which we don't know. Even the albedo of the particles we don't know as we don't know which type of particles there will be (ice, methane, etc.).
Nov
21
revised How can only 1 magnetic pole of the Sun change at a time?
added 625 characters in body
Nov
21
revised Doesn't gravity attract objects in space until they collide?
added 15 characters in body
Nov
21
comment Can I see comet ISON from Saudi Arabia?
@AstroFloyd: Please put that up on Github! I would love to see that, no matter what language it is written in.
Nov
21
awarded  Teacher
Nov
21
comment Can I see comet ISON from Saudi Arabia?
I also highly recommend Stellarium.
Nov
21
comment Can I see comet ISON from Saudi Arabia?
By 'most visible' I infer the greatest visual magnitude difference between light originating from the comet components (nucleus, coma, tail) to between sunlight reflected from out atmosphere or direct from the Sun.
Nov
21
awarded  Editor
Nov
21
revised Can I see comet ISON from Saudi Arabia?
deleted 1 characters in body
Nov
21
answered Can I see comet ISON from Saudi Arabia?
Nov
21
answered How can only 1 magnetic pole of the Sun change at a time?
Nov
21
answered Doesn't gravity attract objects in space until they collide?
Nov
21
comment How would I measure that I'm at a pole?
Thank you! I have read how Amundsen measured the Sun's altitude while searching for the South Pole, so obviously there exists a daytime method as well. However, I believe that he know which day of the year he was in, so he would know the expected changes in altitude due to the Earth's orbit around the sun.
Nov
20
asked How would I measure that I'm at a pole?
Nov
17
comment Might Oort cloud comets be exchanged between solar systems?
@Rory: Congrats on the 1000!
Nov
17
accepted Might Oort cloud comets be exchanged between solar systems?
Nov
17
comment Might Oort cloud comets be exchanged between solar systems?
The Oort cloud is about 1 LY from the sun, or 1/4 the distance to the current nearest star. That means that the gravitational pull of the current nearest star is 1/16 that of the sun: hardly insignificant. I don't believe that planets could have a stable orbit with that type of perturbation.