965 reputation
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bio website dotancohen.com
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age 37
visits member for 1 year, 3 months
seen 2 days ago

Dec
13
answered Why, in the Solar System, all the mass seems to be concentrated at the centre?
Dec
11
comment How can astronomers determine the difference between “hydrostatic equilibruim” and “just happens to be spherical”?
I'm not trusting Wikipedia even though I reference it. In university we actually modelled at what point does rock start behaving as a fluid given geological time scales. It is actually not as high as you might expect, just about mountain sized. That is, a large mountain will 'flow' over geological time scales. And this makes sense: this actually describes what we see in nature. The rock is not rigid enough to support its own weight. Becoming actually round under the influence of its own gravity takes on the order of 10^18 KG or so for rock I believe was what we came up with.
Dec
11
comment Could Venus be a source of Earth's water?
Considering that the particles of Venus's "tail" would be in orbit around the Sun confined more or less to the ecliptic plane, it actually is feasible that they were collected by the Earth after a few rotations.
Dec
11
comment What is the most oblate astronomical object known?
@ThePopMachine: Then you mean a baryonic or rigid object, as in astronomy many structures (think planetary nebulae) are considered objects. Though as an Earth dweller I understand why you are interested in rigid objects, but as you learn more about astronomy you will find that the difference is negligible. For instance, even rocky asteroids are fluid on the scales of their diameters, that is why e.g. Vesta is differentiated. The rock 'flows' at astronomical scales.
Dec
8
answered Why is there a black stripe in the Hubble images of Pluto?
Dec
4
comment How can astronomers determine the difference between “hydrostatic equilibruim” and “just happens to be spherical”?
Earth and Mars are very much in hydrostatic equilibruim. Please don't post speculation or opinions as if they are fact, this is not Yahoo Answers. If you don't know much about a topic, then let somebody else who does know come along and answer it. I would have expected better from a user with over 3000 reputation on the site.
Dec
4
awarded  Critic
Nov
30
answered What are the last images from the Galileo orbiter before impacting Jupiter?
Nov
24
comment Roche Limit for Earth-like body around Earth-like body
Nice answer. Consider our own moon's effect on the oceans.
Nov
24
comment moonless night and lunar phase
@questionhang: Correct. The Moon is in the direction of "up" during the night when it is full. So far as the Moon never appearing during the whole night, there may be up to about an hour of a very small sliver of moon slightly after sunset or slightly before sunrise. Any more than that and I wouldn't call it a 'moonless night'.
Nov
24
comment moonless night and lunar phase
@Jeremy: By "once per month" I mean "once per lunar phase cycle the Moon passes close by the Sun".
Nov
24
revised moonless night and lunar phase
Proper capitalisation
Nov
24
answered moonless night and lunar phase
Nov
23
answered Why does a particle feel no force at radii greater than itself?
Nov
23
comment What should I look for in an astronomy tripod?
I need to take that picture for you!
Nov
9
answered What should I look for in an astronomy tripod?
Nov
3
comment I'd like to become an astronomer. What experience do I need?
I think that closing the question rather than asking for clarification is plain wrong. You could simply point the OP to Swinburne Astronomy Online or even Galaxy Zoo and answer their question. In fact, almost every single "star tour" that I give people ask "How can I become an astronomer". The field is so broad, and there is so much work for amateurs to do, that you are doing the OP and the community a disservice by closing this common, valid question.
Nov
3
comment How would Special relativity explain past-present-future if thinking about 13-billion-light-years distanced objects
Considering your example of the gravitational lensing, I'm removing my former comment. When I get some time I'll research the issue and get back to you. It won't be this week, though! Thank you.
Nov
3
awarded  Enlightened
Nov
3
awarded  Nice Answer