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1,113 questions with no upvoted or accepted answers
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17
votes
1answer
428 views

How small can a spiral galaxy be?

The smallest observed spiral galaxies I can find are NGC 2976 and NGC 4605, both with a diameter of 20 kly, but I don't have anything like an exhaustive source to search. I've also found a mention ...
13
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0answers
524 views

How to determine scalar-to-tensor ratio r from CMB polarization spectrum?

CMB polarization spectrum can tell us about the primordial scalar and tensor perturbation. By analyze B and E mode angular spectrum power spectrum and temperature power spectrum we can determine the ...
12
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0answers
313 views

What fraction of a star's hydrogen store will be fused over its lifespan?

A main sequence star will fuse some of its hydrogen, but not all. In massive stars ($>1.5M_\odot$) the core is convective but the rest of the atmosphere radiative and hence does not mix much: as it ...
11
votes
0answers
240 views

What is the limiting abundances of elements at the end of the stelliferous era?

Is there any reputable published source on expected elemental abundances at the end of the era of stellar fusion? I am here interested in the contents of galaxies; much of intergalactic gas will be ...
10
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0answers
235 views

Planning to revisit Arthur Eddington's experiment from 1919

As the fateful day draws closer, the United States will host a celestial event that comes once in three generations. I plan to witness this first hand at the exact center of greatest eclipse. In the ...
10
votes
0answers
141 views

Estimating the tangential and cross component of the galaxy's shear using Gnomonic projection

I would like to know how I can estimate the tangential and cross component of the galaxy's shear using Gnomonic projection of the right ascension and declination the galaxies relate to the center of ...
9
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0answers
88 views

How can maser emission be unpolarized?

I was reading that: However, unlike Galactic sources such as W3(OH), the emission is unpolarized and the 1667 MHz line is stronger than the 1665 MHz line. but how is this possible? Does not the ...
8
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0answers
117 views

Incompleteness in HIPPARCOS data?

I made a small script to plot HIPPARCOS stars, and I realize there are sections of the sky with more completeness than others, as the following image shows. Has this “boxiness” been documented? Why ...
8
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0answers
91 views

Determining wind speed distribution on Mars using dune shapes?

As a fan of exometeorology (the study of atmospheres of other planets), I scanned through a whitepaper Measuring Mars Atmospheric Winds from Orbit which says Measurements of Mars atmospheric winds ...
8
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0answers
179 views

How many meteorites have been found some place other than Earth? Where is an authoritative list maintained?

Backgound: After seeing this tweet by astronomer Kacper Wierzchoś about our not-so-new but at least newly-discovered "mini-moon" I scrolled down and saw the tweeted image below. The object ...
8
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0answers
146 views

What alternative facilities would be available in the event of JWST being destroyed?

Unfortunately, space launches can and do go wrong. Suppose that after all the delays and budget overruns, the launch of the James Webb Space Telescope fails and the telescope becomes a cloud of very ...
8
votes
1answer
141 views

Error propagation methods for orbit parameters

Recently I've encountered an article in our local astronomical popularization magazine. It is about a well known task of Sgr A*-black hole's mass estimation. The article is written as a step by step ...
7
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0answers
177 views

Explanation of an imaginary transformation occurring in the determination of trigonometric series for the elliptical equation of the center

One of the oldest problems in astronomy, which dates back to to the time of Kepler, is the problem of development in infinite trigonometric series of the "equation of the center" - to ...
7
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0answers
115 views

How do radio astronomers avoid having their receivers burned out by ground-imaging radar from satellites?

After about 34:00 in the 9th press conference of AAS 235, radio astronomer and NRAO's spectrum manager Harvey Liszt talks about Radio Astronomy in a New Era of ...
7
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0answers
136 views

Why would a black hole have a disk, but not emit x-rays?

There's a recent paper in Nature about LB-1, a B-class star orbiting a massive black hole. I don't understand how these two parts of the paper can be reconciled. On page 2, the authors argue that the ...
7
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0answers
111 views

Water vapour in space

This question is inspired by, but different from, What happens if an ice cube is left in space? Mark's accepted answer says "…if you stick your ice cube out in the Oort Cloud, it'll grow: the mean ...
7
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0answers
82 views

Is the Ordovician meteor event detectable in the lunar cratering record?

Approximately 468 million years ago there were a large number of L-chondrite meteorites falling to Earth. This is called the Ordovician meteor event and was probably the result of a large collision in ...
7
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0answers
119 views

Has the Penrose process ever been linked to an observed phenomenon in some way?

This answer to What defines the plane of an accretion disk around a black hole? mentions the Penrose process as a potential mechanism that could change the axis of the orbital angular momentum of an ...
7
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0answers
442 views

What are the analysis steps in taking raw data from Kepler to a planetary system determination

I wish to get a concise list of the analysis steps required to take raw light data from a Kepler data set of a star through the steps needed to get to an analytical determination of the existence of a ...
7
votes
1answer
208 views

What if there was an asteroid belt with the mass of a planet?

In the past, the asteroid belt was thought to be the remains of a shattered planet. Of course, that was all pseudoscience, the mass of the asteroid belt being 4% of the moon. I've been wondering, what ...
6
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0answers
49 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 ...
6
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0answers
138 views

Are there any planetary ring system other than “Phoebe ring” not aligned to the equatorial plane?

Continuation of: Is it possible for planetary rings to be perpendicular (or near perpendicular) to the planet's orbit around the host star? The answers discussed about Uranian ring system (how ...
6
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0answers
90 views

Is there work underway to push the long baseline capabilities of the Event Horizon Telescope to sub-millimeter wavelengths?

The Max Planck Institute for Radio Astronomy's press release Something is Lurking in the Heart of Quasar 3C 279; First Event Horizon Telescope Images of a Black-Hole Powered Jet shows a stunning ...
6
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0answers
76 views

Color index B-V of the dimming Betelgeuse

Using AAVSO light curve generator I have plotted V and B magnitudes of Betelgeuse in the past 150 days to see trend of B-V color index. If dust would be the cause of the recent drop in the star ...
6
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0answers
176 views

Could a star have a Saturn-like ring?

Saturn's rings will never clump together, because they are within the Roche limit. Which makes me wonder if a star could have rings that are kept from clumping together due to tidal forces. Have any ...
6
votes
1answer
185 views

Can someone calculate the age of the KOI-4878 star?

The star’s low metallicity and fairly high space velocity suggest that KOI-4878 is older than the Sun. But I don't know how to calculate an estimation for the age. KOI-4878 data on Simbad
6
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0answers
192 views

Formation of the First Stars

I've got a few questions about the first stars to form in the universe. First off how might metalicity have impacted the formation of the first stars and also what effect would the absence of metals ...
6
votes
1answer
135 views

What are realistic and unrealistic values for the high energy gamma ray spectral indices of pulsar wind nebulae?

This summer, I was working on a project fitting very high energy gamma ray spectra of the Crab Nebula, a pulsar wind nebula. At energies about $\sim$1 TeV, a simple power law suffices, i.e. $\phi(E)\...
6
votes
0answers
173 views

Is Spherical Astronomy by W. M. Smart a good book on positional/spherical astronomy?

I'm a math undergrad, but I'm really interested in learning positional astronomy; However, the only well-referenced textbook I've come up with is Spherical Astronomy by W. M. Smart. I would like to ...
6
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0answers
1k views

What is the highest resolution image of the moon taken from Earth's surface?

According to this article: https://www.theguardian.com/science/2018/jul/26/star-spotted-speeding-near-milky-way-black-hole-for-first-time the Very Large Telescope is "powerful enough to see a tennis ...
6
votes
0answers
83 views

How often do partial solar eclipses of 90% of totality occur in same place?

I know that the mean interval between total eclipses in a single place is about 375 years, which is not surprising given the small band of area of the totality. However, the penumbra of the eclipse ...
6
votes
0answers
117 views

Do mixed type remnant collisions produce anything interesting?

The recent detection of a binary neutron star inspiraling and colliding raises an interesting question in my mind. Type Ia supernovae are believed to be caused by white dwarf/regular star pairs and/or ...
6
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0answers
264 views

What is a radio “homology telescope” and is the 500m dish in China one?

This question is about design aspects of large radio telescope dishes which allow them to flex under the influence of gravity as they change elevation angle, and still maintain good optical ...
6
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0answers
124 views

Semimajor axis variations in co-orbital moons

I've been playing with simulations of co-orbital bodies similar to Saturn's moons Janus & Epimetheus- horseshoe orbits where the two bodies are of comparable mass- and I'm seeing some very odd ...
6
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0answers
101 views

Why can primordial tensor perturbations of the CMB be ascribed to gravitational waves?

Why can primordial tensor perturbations of the CMB be ascribed to gravitational waves? Is this attribution unique, or are there other mechanisms that could lead to the excitation of tensor modes? In ...
6
votes
1answer
173 views

Can Jupiter's nightside be classified as spectral type Y?

As far as I am aware, the latest spectral types that have been assigned are around Y2, for objects like WISE 0855-0714 that have temperatures around 250 K or so. I've also seen several directly-imaged ...
5
votes
0answers
64 views

Where can I find Arecibo's data archive?

Does anyone know where I can find Arecibo's historical data? After much searching, I can find neither hide nor hair of it. It doesn't help that the search results are completely dominated by the news ...
5
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0answers
45 views

Is the discovery of a “mass gap” black hole by this tiny telescope just plain luck/serendipity or could it be the first of many similar discoveries?

The Kilodegree Extremely Little Telescope is a pair of modest lenses with high quality medium format CCDs attached sitting on oversized mounts in Arizona and Sutherland. These very modest instruments ...
5
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0answers
60 views

Reproduce and plot myself from a paper with appropriate scripts and Fisher/Covariance matrixes

I would like to reproduce and plot myself the figure below. This plot, even it begins to date, is full of informations for me. The paper is located here : paper Suzuki et al. 2011 I have contacted ...
5
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0answers
38 views

What fraction of matter is not bound to the galaxies, groups and clusters that we see?

We know that most of the matter in the universe has collapsed into galaxies and galaxies into groups and clusters and that a lot of matter is presently in clusters between the galaxies. But, what ...
5
votes
0answers
313 views

Black spot in Mars' sky

There is a sequence of three raw images by Mars Curiosity Rover taken during Sol 3066 (22/03/2022, roughly) that show the same features of Mars' landscape and sky. They are separated by 38 seconds' ...
5
votes
0answers
87 views

Recommend a radio calibration target for amateur radio telescope

I have a small antenna and radio system that can receive frequencies between 1MHz and 1GHz. The system has a discone antenna. I plan to do some aperture synthesis based on the daily rotation of the ...
5
votes
0answers
56 views

What is the birth of a star like?

Here's what I'm curious about. So this hydrogen gas collects and at some point, it eventually becomes a star. What does that process look like? If you were there as a witness to the formation of a ...
5
votes
0answers
174 views

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....
5
votes
0answers
122 views

Extraterrestrial snow?

What do we know about extraterrestrial snow? On which (exo)planets or (exo)moons do we have direct hints for its existance? This is indeed a children's question, but I struggle to answer it ...
5
votes
0answers
56 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 ...
5
votes
2answers
98 views

Kepler's Law, focal points - Heliocentric or Barycentric?

It is known that all the mass in the Solar system moves around the Barycenter. For the two focal points in Kepler's law; is the first focal point $F_1$ a Heliocenter? Or is it actually a Barycenter? ...
5
votes
1answer
163 views

Why are these telescope mirror makers not upside down? (Daniel K. Inouye Solar Telescope)

The new open access Solar Physics article The Daniel K. Inouye Solar Telescope – Observatory Overview is the first of several papers about the new state-of-the-art solar observatory. For more info see ...
5
votes
0answers
78 views

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 ...
5
votes
0answers
80 views

How long would it take to first detect a new object in the night sky given its apparent magnitude?

If an object as bright as the star Polaris (Apparent Magnitude +1.8) showed up in the night sky, it would be detected almost instantly by stargazers. If an object as bright as Pluto (Apparent ...

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