Unanswered Questions
175 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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7
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256
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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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How do I calculate the Hill radius of a star in a binary system?
Is there an easy way to calculate the Hill radius of a star in a binary system at different orbital radii where both stars are of the same mass and in circular orbit around one another’s centre of ...
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6
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129
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Kepler ellipse orbit fit issues
I am helping my high schooler with a research paper that uses PyAstronomy to fit the orbit of stars around Sag A. It isn't working because the angles (parameters Omega, omega, and i) seem to have a ...
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Did Aliens make Oumuamua?
Dr. Avi Loeb, the distinguished astrophysicist and chair of Harvard's Astronomy Program, just published a book called Extraterrestrial: The First Sign of Intelligent Life Beyond Earth.
In the book, Dr....
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6
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101
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Callisto's orbit: circular vs JPL is periodic 4 degree error, why?
I am approximating the azimuthal angle of Callisto from Jupiter or the Jupiter+moons barycenter using a constant angular speed circular orbit. This differs from the JPL ephemerides by only about 4 ...
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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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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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5
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203
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Different techniques for calculation of celestial bodies dynamics with different time-scales
Differential equations describing the dynamics of celestial bodies (rotation, nutation, precession and other effects) can be solved numerically, which makes it possible to study their general non-...
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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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5
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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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185
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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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100
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How does the orbit of a 2-body system evolve as it orbits a more massive 3rd body?
I have been reading up on how multiplicity of star systems decline with star mass, which implies a relatively common occurrence of binary star systems orbiting more massive stars. I would imagine this ...
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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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4
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144
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Just how resonant is the "resonant sextuplet of sub-Neptunes transiting the bright star HD 110067"?
The November 29, 2023 arXiv preprint A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067 constructs a resonant chain of orbital periods based on mean motion resonances (MMRs) and ...
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