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programming numerical algorithms for astrophysical applications.


Dec
27
comment What was the length of year 1 million years back?
@AlexeyBobrick I got relative escape velocity for MW and M31 of 100−150km/s where/how did you get this number? It sounds much too small.
Dec
27
awarded  Nice Answer
Dec
26
comment What was the length of year 1 million years back?
@AlexeyBobrick (1) the difference here is that M31 and the Milky Way (MW) dominate the total mass of the local group, so you should not compare to a star cluster, but a binary star plus some planets. (2) In this case, if the relative velocity of M31 wrt MW is receding, gravitational forces will eventually overcome it and result in the observed approaching velocity. Note also that recent determinations of M31s proper motion (and hence transverse velocity) yielded a value much smaller than the radial velocity). There is some research literature on this (search for "local group timing argument").
Dec
25
awarded  Critic
Dec
25
comment If we were to see the Sun with our naked eyes from the Orion belt, would all planets be encompassed inside the star? Is this calculable?
The observed image of a star is not a sharp edged circle. There are two effects which prevent us from seeing the actual stellar edge (which can be seen for the Sun). First, atmospheric seeing and second diffraction. The first jiggles the image on very short time scales (causing a sparkling appearance) and is caused by turbulence in the upper atmosphere. This effect may be quantitatively and/or qualitative different when observing from any other planet, say in Orion.
Dec
25
comment How would the night sky look from inside a globular cluster?
I'm not sure, but I would think that there is no stable habitable zone within a globular cluster (GC), except perhaps in its outer parts. The stellar density is so high that Solar-system-like objects will be destroyed/destablised by stellar encounters. Hence life as we know it may never form there. Moreover, the fraction $Z$ of non-primordial elements ("metals" in astronomy slang) is very low, at least in the old GCs of the Milky Way. Low $Z$ stars are much less likely to host planets. Thus, there may be nobody so observe the GC night sky.
Dec
25
comment What was the length of year 1 million years back?
@AlexeyBobrick I disagree regarding M31. Very likely the local group of galaxies (of which the Milky Way and M31 are the main masses) is gravitationally bound. Hence their velocities are not random. M31 and the Milky Way are likely to merge (and form an elliptical galaxy) in a few $10^9$ years.
Dec
25
revised What was the length of year 1 million years back?
added 153 characters in body
Dec
18
awarded  Teacher
Dec
18
comment What was the length of year 1 million years back?
@JqueryLearner The number of days in a year and the length of the year are two completely different things (because the length of a day changes with time).
Dec
18
awarded  Editor
Dec
18
revised What was the length of year 1 million years back?
added 235 characters in body
Dec
18
answered What was the length of year 1 million years back?