Unanswered Questions
192 questions with no upvoted or accepted answers
10
votes
0
answers
214
views
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 ...
8
votes
1
answer
622
views
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
votes
1
answer
187
views
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 ...
7
votes
0
answers
256
views
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 ...
6
votes
0
answers
52
views
Historically, when were the terrestrial planets first called terrestrial planets?
When did we start using the phrase "terrestrial planets" to refer to the inner planets in English scientific writing?
6
votes
0
answers
153
views
How was the axial tilt of planets measured?
https://en.wikipedia.org/wiki/Axial_tilt#Solar_System_bodies gives the axial tilt of all planets with two decimal precision, but how and when were they measured so precisely ?
I guess it's "easy&...
6
votes
0
answers
173
views
How quickly do planetary rings form?
Just a very general question, but I haven't seen this discussed elsewhere. If a moon gets busted up for some reason, say a collision with another moon, and is at the right orbital distance from its ...
6
votes
0
answers
219
views
Kepler - Creating the Ellipse (Astronomia Nova)
In Chapter 58 in Astronomia Nova, Kepler made his final step to finally create the ellipse (for the orbit of planets)
http://science.larouchepac.com/kepler/newastronomy/part4/58/index.html
In the ...
5
votes
0
answers
35
views
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 ...
5
votes
0
answers
88
views
Is there a noob-friendly website/app for tracking a astronomical body's apparent movement over time?
As I walk home along my road most nights in winter, I see the Moon and one-or-more planets.
Unsurprisingly, over the last 2 months, if it's been the same planet and it (and the Moon) has been in ...
5
votes
0
answers
70
views
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?
...
5
votes
0
answers
289
views
Why aren't there sulfuric acid seas on Venus?
It's commonly known that sulfuric acid rain doesn't reach Venus' surface. It evaporates instead because the surface it too hot.
But considering how high the pressure at the surface (9.3 MPa), shouldn'...
5
votes
0
answers
86
views
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 ...
5
votes
0
answers
98
views
Why do degenerate objects get hotter as more mass is added?
After reading this question, I decided to post a question about degeneracy. I've seen simulations on large, $15\text{+ }M_J$ objects that are accreting mass. They do not grow in radius, instead they ...
5
votes
0
answers
186
views
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 ...