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Dec
20
comment Stable polar solar orbit with the Earth continuously observable
@Neomada: Noordung's edit makes your question more appealing to snobs like me who are more likely to read a question that is properly formatted than one which isn't. You should be thanking him, not insinuating that his motives were cynical.
Dec
20
comment If the moon wasn't receding from Earth, what would be the impact on the weather and tides?
The energy of the sound of waves crashing comes from the moon. I am going to mention this to my daughters next time we are at the beach with the moon visible. Thank you for this wonderful insight.
Dec
13
comment Why, in the Solar System, all the mass seems to be concentrated at the centre?
@RobJeffries: Thank you for mentioning the situation with Vega. I do believe that a few years ago it was thought that the disk is protoplanetary. I should read more, science progresses!
Dec
13
comment Why, in the Solar System, all the mass seems to be concentrated at the centre?
I mentioned that "Not much matter can form a stable orbit there" and you might notice that 97% of the mass of the solar system is not found there!
Dec
13
comment Why, in the Solar System, all the mass seems to be concentrated at the centre?
I don't have any idea, but I should imagine (warning: speculation following) that there is more of a continuum than a cutoff point. A dust particle may be perturbed by a passing Theia and thus be ejected by gravitational slingshot. However, two fist-sized objects would interact in a more uniform fashion and neither would have enough momentum to eject the other. I don't believe that we have the technology to observed this in nature yet, nor do we have the technology to perform Monte Carlo planet-formation experiments just yet.
Dec
13
comment Why, in the Solar System, all the mass seems to be concentrated at the centre?
@HDE226868: From what I understand, during the early stages of planetary formation (such as that which Vega is undergoing right now) things are too chaotic (i.e. too many random gravitational encounters and collisions) to really have a stable orbit for any accretions of matter without significant mass. I'm not sure how long this stage lasts, but I do believe that we can observe it for quite a few stars (such as the afore-mentioned Vega). So the accretions of matter which have not-significant mass are constantly having their orbits perturbed.
Dec
13
comment Why, in the Solar System, all the mass seems to be concentrated at the centre?
Nice answer, but I feel that you stop right where it gets interesting! I pick up where you left off in another answer. If you feel that this should be a single answer you can edit my answer into yours.
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
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.
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
23
comment What should I look for in an astronomy tripod?
I need to take that picture for you!
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.
Oct
19
comment Might Oort cloud comets be exchanged between solar systems?
Thank you for this terrific analysis.
Oct
19
comment Do all stars have an oort cloud or is it a rare occurance?
Concerning the assertion that passing stars may disturb Oort cloud objects, this question is in need of elucidation!
Oct
19
comment Might Oort cloud comets be exchanged between solar systems?
Note that this answer supports the assertion that passing stars can influence Oort cloud objects.