Unanswered Questions
191 questions with no upvoted or accepted answers
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How well conserved is etendue in extreme gravitational lensing scenarios?
This excellent answer to Could dark matter exist in the Universe in the form of sufficiently dense objects? includes the following image and description:
Light from the background galaxy circles a ...
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8
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1
answer
622
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Why do the Sun and gas planets rotate faster at equator than at poles?
From this site, it states that:
The Sun spins faster at its equator than at its poles.
I have also read somewhere that the gas giants (gaseous planets like Jupiter, Saturn, Uranus, and Neptune) also ...
8
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What is the history of the average pressure, density, and temperature of the matter in the universe over time?
This question is inspired by this more specific question where Cerelic wanted to know if conditions were suitable for liquid water to exist during an epoch when the characteristic temperature of the ...
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Get the expression of probed volume between 2 redshifts
1) I can't manage to find/justify the relation (1) below, from the common relation (2) of a volume.
2) It seems the variable r is actually the comoving distance and not comoving coordinates (with ...
CommunityBot
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265
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RA/Dec of a meteor shower's radiant point based on its associated comet's orbit; simple set of equations? "Classic" early reference to cite?
Below this answer to Why are Delta Aquariids “for the southern hemisphere” while the Perseids are “for the north”? I wrote the comment:
+1 To make this complete, ...
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5
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Newtonian theory of small perturbations: Continuity equation
Starting with the continuity equation
$$\frac{\partial \rho}{\partial t} + \nabla_r(\rho \vec{u}) = 0$$
making those substitutions.
$$\nabla_r = \frac{\nabla_x}{a}$$
$$\rho(\vec{x},t) = \bar \rho(t)[1 ...
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95
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Are dust-dust collisions necessary to explain Kordylewski clouds at Earth-Moon L4/5? Aren't the cross-sections, number density timescales too small?
The recent question Can dark matter accumulate at Lagrange points? mentions Kordylewski clouds and that article begins:
Kordylewski clouds are large concentrations of dust that exist at the L4 and L5 ...
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Why does the tropical year have a ~161 years cycle?
Using PyEphem, I calculated the time difference between consecutive summer solstices in the south hemisphere for the last 4000 years, and plotted them in a graph. It seems like random noise around the ...
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Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow?
Do all the accretion disks around a compact object (black hole or neutron star) emit astrophysical jet outflow? I mean is it mandatory for a jet to be emitted from an accretion disk?
If so, then why?
...
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Why does the axis tilt (obliquity) of Earth change over time?
I have recently learned that the polar axis of Earth moves in a complex fashion. There are both precession and nutation. I have learned that Earth's obliquity varies between 22.1 and 24.5 degrees on a ...
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How do the giant planets excite the orbits of asteroids?
The giant planets, particularly Jupiter, are notorious for bringing about changes in eccentricities and inclinations of smaller bodies(asteroids and KBOs). Jupiter, in fact, throws almost all the ...
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Did the density wave theory for spiral arms take account of this phenomenon?
I came across this link. In it the author speculates that in the outer region of a galaxy, the spiral arms overtake the stars, and vice versa for the inner region. That means there must be a middle ...
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186
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What are some good books/online resources for astronomy problem sets?
I am currently studying for the international olympiad for astronomy and astrophysics (the syllabus can be found here: https://www.ioaastrophysics.org/syllabus/). I am currently using Carroll Ostlie's ...
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62
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Strength of core-envelope coupling in stars
For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope?
I understand that the core-envelope boundary is only (...
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Would the existence of Planet Nine rule out the possibility of a sixth giant planet?
I'm aware that there have been attempts to simulate the evolution of the Solar System with six giant planets1, as opposed to the traditional four or five. The recent proposed Planet Nine would ...
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