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Apr
22
comment Is there any way a meteor can hit at less than escape velocity?
Indeed, you didn't clearly state what you meant.
Mar
26
comment Is the motion of the Sun around the Galaxy a result of gravitational pull?
@RobJeffries I haven't followed this much recently, but 1/3 is significant, though perhaps not 'huge'. The details are still very much model dependent. The vertical motion is definitely anharmonic, though (because the density is not constant with z over the orbit of the Sun).
Mar
25
comment Would being ejected from the Milky Way Galaxy have any major impact on life on Earth?
The only realistic way to eject stars from a galaxy is by close encounters with a massive object (ideally a supermassive black hole - SMBH), which would certainly destroy the Solar system (unbind most planets) if this happens to the Sun (when it collides with M31s' SMBH in the merger).
Mar
25
comment Is the motion of the Sun around the Galaxy a result of gravitational pull?
@RobJeffries "There isn't thought to be a huge amount of dark matter interior to the Sun's orbit [...]" I'd thought that about half the mass interior to the orbit of the Sun is dark (that's not much as dark matter goes, but relative to the baryonic component it's certainly significant). For an exponential disc (as the baryonic parts of disc galaxies are observed to be), the rotation velocity peaks at 2.1 scale radii and drops thereafter. For the Milky Way that's interior to the Sun and there is no indication of a drop.
Mar
25
comment Initially non-flat space-time makes dark matter obsolete$\dots$
You may be able to explain away dark energy with inhomogeneities of space-time (which we know is reality, since matter is inhomogeneous, but this is usually ignored in cosmological models).
Oct
19
comment What were the 2 satellites I saw this morning?
I'm voting to close this question as off-topic because not about astronomy
Oct
19
comment What were the 2 satellites I saw this morning?
Almost certainly not astronomical objects.
Oct
19
comment Is the time lapse considered when estimating the age of the universe?
Which time-lapse are you referring to?
Oct
16
comment Two species of dark matter?
@RobJeffries I'm particularly concerned about the waste of brain, of which comparatively little is spend in the dark-matter 'industry'.
Oct
16
comment Two species of dark matter?
@RobJeffries thanks for your comment. I'm fully aware that dark matter is only still a hypothesis and hinges on the correctness of GR, which in turn is not experimentally verified on the relevant field strengths (or shall I say 'weakness'). The cuspiness issue is not a fundamental problem, as its prediction ignores baryonic effects, which must play a role on small scales. Moreover, on galaxy-cluster scales, the cusps are there (the mass profile in the outer parts of central-cluster galaxies is what we expect for the inner parts of the cluster halo).
Oct
15
comment Two species of dark matter?
@AlexeyBobrick There is zero evidence for supersymmetry. AFAIK, supersymmetry has not made a single falsifiable prediction that was later verified. Supersymmetry is a classiacal WOMBAT (= Waste Of (tax payer's) Money, Brain, And Time).
Oct
14
comment Two species of dark matter?
Would the downvoters please indicate what I could improve with this answer and/or why it's not useful?
Oct
8
comment Could there be dark matter black holes?
@questionhang As I've said 'since DM cannot lose its excess energy and angular momentum as easily as gas'. It can only lose it via gravitational interactions (with anything), but that is very inefficient.
Oct
6
comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?
I was not asking for a comment, but for improvement to your answer, and I was not asking because I doubted it, but to give you a chance to improve your answer (though I was a bit surprised at the time scale of only 1Gyr).
Oct
5
comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?
The only remotely sensible answer here.
Oct
5
comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?
You should provide evidence (via links to respectable sources) for your claims that in 1-2 billion years water on Earth will be evaporated.
Oct
5
comment What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?
Why do you assume that any humans or even any observing life forms will be around on Earth in 4billion years?
Oct
5
comment When will all eight planets in our solar system align?
Ignoring [...] interference from any bodies [...] interfering with their orbits -- this obviously includes the Sun, and without the Sun, the planets orbits are not well defined. Hence your question is unclear.
Oct
5
comment When will all eight planets in our solar system align?
There are several blunders in this answer. First, using all digits in your tables (which implies converting to centidgrees and centidays) I actually get $x\approx1.698\times10^{42}$ (from the same online tool), which amounts to $1.29\times10^{33}$yr. I don't know how you obtained the lower value, but I strongly suspect you omited some digits. Secondly this shows that when adding more digits the solution tends to infinity: the correct answer is: radial alignment never occurs. Finally, assuming that the planets' orbits are following this simple motion is just wrong.
Oct
5
comment When will all eight planets in our solar system align?
Never even if they were co-planar.