Unanswered Questions
177 questions with no upvoted or accepted answers
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What am I misunderstanding about the scale factor-redshift relation?
If the scale factor as a function of time represents or is equal to the average distance between the galaxies, then it increases altogether with the CMB redshift $z$, but it also must be equal to the ...
- 37.3k
2
votes
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47
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Do there exist open-source implementations of non-SGP4 propagators?
I'm well familiar with SGP4 and its implementations in various languages. I am curious if there are open-source implementations of J2Mean, J2, J3, J4, etc propagation techniques.
If my terminology is ...
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1
vote
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16
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cross-matched SDSS-WISE catalog
Please where can I find cross-matched SDSS and WISE dataset for a machine learning project?
(Galaxy-star-qso classification task)
2
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84
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Would we know if the universe was rotating?
I was wondering what we would observe if the universe had a small rotation. My conclusion was that galaxies on the equatorial plane of the universe would be slightly more redshifted than galaxies than ...
- 373
3
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41
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Why MIT's Benjamin Rackham says "nearby ultracool dwarf SPECULOOS-3" would look "purplish-red, spotted, and flaring" from an airless orbiting planet?
May 15, 2024 MIT News article Newly discovered Earth-sized planet may lack an atmosphere includes the following:
“We can say from our spectra and other observations that the star has a temperature of ...
- 30.7k
0
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35
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Project Analog Hypothetical Planet
For my story Project Analog, I was wondering if a hypothetical planet (Let's call it Suria). It has the same size and conditions as Earth with the same axis, tilt, and rotation, as well as one moon. ...
CommunityBot
- 1
2
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answers
25
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Relative translational dynamics of two spacecraft in Keplerian orbit
I need your help understanding some equations in a paper about autonomous rendezvous and proximity operation. The paper is available at this link, but I will summarize the main point in the following.
...
- 33
2
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answers
102
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What would the Big Crunch theoretically look/feel like?
In the Big Crunch theory, the expansion of the universe reverses, resulting in all matter contracting into a single point. Imagine you are alive at the time of this event. What would the sky look like?...
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51
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Has anyone attributed a specific Baily's bead to a specific feature on the Moon? If so, when was this first done?
From Wikipedia's Baily's beads:
Lunar topography has considerable relief because of the presence of mountains, craters, valleys and other topographical features. The irregularities of the lunar limb ...
- 30.7k
2
votes
0
answers
38
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Finding the cartesian position of the lunar ascending node
What I'm trying to derive
The cartesian position of the lunar ascending node relative to the true equator and equinox of date reference frame. My issue is I'm getting a bit tripped up with reference ...
- 321
2
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0
answers
34
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Local anisotropies in the expansion of the universe and tidal forces...?
In the context of the large-scale structure of the universe, there can be local anisotropies (https://www.aanda.org/articles/aa/full_html/2021/05/aa40296-21/aa40296-21.html).
I understand from this ...
- 1,017
0
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19
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Converting equatorial coordinates of a comet's pole into cometocentric orbital coordinates I and Phi
The comet's spin axis orientation is usually reported in equatorial coordinates RA, Dec; however sometimes these are shown in form of the Eulerian angles equatorial obliquity (I), i.e. the angle ...
VIRGINIO OLDANI
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25
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Deriving Faber-Jackson Relation from Milgrom's Law
I am reading Famaey & McGaugh 2011, a review paper on Modified Newtonian Dynamics. My question concerns bullet 3 in Sec 5.2, where the authors try to explain how Faber-Jackson Relation can be ...
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1
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0
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65
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Is this description of ecliptic times correct?
I did a brief write-up as a pet research project to explore astro-geological calculation and visualisation for
Muslim prayer times. It's not meant to be authoritative (either scientifically
or ...
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3
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0
answers
110
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How well are planetary formation models (e.g., determining $\mathrm{\dot{M}_{planet}}$) understood in 2024?
I know that planets can form through accretion, bulging up from $0$ to their final mass $\mathrm{M_{planet}}$ at $\mathrm{M}(t_f)$. I know that when studying Planetary formation and migration theories,...
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