590 reputation
28
bio website dotancohen.com
location
age 37
visits member for 1 year, 1 month
seen Nov 18 at 15:01

Sep
4
comment How is space-time bent by black holes?
Actually, you can get nearer to the geometric center of the mass, which accounts for the higher local gravity field (and tidal forces). Note that at the same distance from the (center) of the black hole and the (center) of the star, the black hole's gravity will be lower.
Jul
28
comment Escaping a black hole
Mitchell, you might want to accept the answer as given. It answers your question very well.
Jun
10
comment How does the evolution of a solar system not break the second law of thermodynamics?
The statement "the radiated photons are out there somewhere" really does make it clear.
Jun
10
comment How does the evolution of a solar system not break the second law of thermodynamics?
So where was the corresponding increase in entropy to offset the creation of the solar system? Heat loss?
May
5
comment What would happen if an ice cube is left in space?
This is a terrific answer.
May
1
comment Would a Phobos full impact make Mars temporary habitable?
I am intrigued and I wish to subscribe to your newsletter.
Feb
5
awarded  Nice Question
Jan
9
answered Are nebulae only visible from a distance?
Dec
27
comment How would the night sky look from inside a globular cluster?
The Asimov story Nightfall describes this very situation.
Dec
16
comment Doesn't gravity attract objects in space until they collide?
@Envite: Thanks. I edited the post to remove that simplification with a better, more accurate, simplification.
Dec
16
revised Doesn't gravity attract objects in space until they collide?
added 8 characters in body
Dec
9
comment Could any known, living organisms on Earth survive on Mars?
No problem! I'm also hoping to see some other interesting answers.
Dec
6
answered Could any known, living organisms on Earth survive on Mars?
Nov
24
comment Can I see comet ISON from Saudi Arabia?
Very nice, Astro! Thanks!
Nov
24
comment How would I measure that I'm at a pole?
That is a beautiful last picture, especially how the trails and the roofline are parallel.
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