All Questions
1,756
questions with no upvoted or accepted answers
6
votes
0
answers
504
views
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 ...
6
votes
0
answers
199
views
How far have stars been seen beyond the center of the Milky Way?
What lies near the center of the galaxy is of great interest and in recent times the motion of dozen(s) of stars at the center of our galaxy orbiting around Sgr A* have been measured in great detail. ...
6
votes
0
answers
103
views
What's the number density of `Oumuamua like objects?
Recently, the fly-through the Solar system of the inter-stellar object (ISO) `Oumuamua caused quite a stir in the astronomy community. I wonder whether there are reliable estimates for the (local) ...
6
votes
0
answers
69
views
Recreating Observer Ecliptic Lat/Lon from JPL Horizons using SPICE toolkit
I apologise if this is the wrong place to ask. I am trying to recreate part of the calculations by the JPL Horizons system using SPICE. Specifically the Observer Ecliptic Latitude and Longitudes.
I'd ...
6
votes
0
answers
109
views
What is the relation between the saros (18 years, 11 days, 8 hours) and the period of lunar nodal precession (18.6 years)?
I am wondering. I am sure that they are related. How can we derive one from the other?
6
votes
0
answers
331
views
What would go into the design of a simple sky quality meter, used to measure night sky brightness?
@MCG's answer mentions several methods to classify night sky quality or brightness, and goes on to say:
Additionally, you could always purchase a SQM (Sky quality meter) which is a small, portable ...
6
votes
0
answers
102
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
0
answers
118
views
Need help understanding stellar spectroscopy data from ESO
The European Southern Observatory webpage has a web page that has tabular spectrogram data from A. J. Pickles, University of Hawaii. There are over 130 .dat files there. Each one represents a ...
6
votes
0
answers
239
views
Viewing "Diamond Fuji"
Diamond Fuji is a phenomenon in which the (typically) setting sun is positioned directly atop Mt Fuji. Some relatively detailed predictions for viewing times at a nearby park are available here.
I ...
6
votes
0
answers
216
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 ...
6
votes
0
answers
62
views
Did the Juno mission locate Jupiter at the same precision as Saturn (4 km)?
Juno's low perijove should be great for measuring Jupiter's gravitational effect on Juno's orbit. Cassini together with VLBI has measured Saturn's location to within 4 km.
Will Was Juno be able to ...
6
votes
0
answers
479
views
Linear limb darkening coefficient, u
I was wondering if anyone knew of any resources to understand the linear limb darkening coefficient, $u$. That is to say, how the $\theta$-dependent coefficient $u$ (or sometimes $b_{\nu}$) varies ...
6
votes
0
answers
148
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
votes
0
answers
68
views
What is the reason for the dispute over the variation of core mass with heavy metal abundance?
In Metal-Poor Stars IV: The Evolution of Red Giants, Rood writes
The differences in the results of these papers are large enough to introduce appreciable uncertainties into the study of the ...
6
votes
1
answer
187
views
Do narrow lines in the spectra of O- and B- type stars always indicate magnetic fields?
I was reading a paper on the differential emission measures of a set of hot O- and B- type stars. As the authors discuss in Section 3 (page 959), two stars, $\tau$ Sco and $\theta^1$ Ori C, have ...
6
votes
1
answer
475
views
Could non-supernova carbon, oxygen, or silicon flashes be observed?
I was reading about the helium flash, the short but sudden onset of helium fusion in certain red giant stars. As I understand, the upper (nondegenerate) layers of the star absorb the energy as they ...
6
votes
1
answer
292
views
Why did the Event Horizon Telescope take so long to take a photo of a black hole?
The Event Horizon Telescope is in the news now because they are about to release the first ever picture of a black hole. They have been working on this since 2006. Why did it take 13 years to produce ...
6
votes
1
answer
216
views
Could an ultra-hot Jupiter flare?
Some of the ultra-hot Jupiters (WASP-33b, KELT-9b) have dayside surface temperatures similar to low-mass stars. Would they be capable of producing flares? To be specific, I am asking about the ...
5
votes
0
answers
26
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
125
views
Why do double neutron stars remain bounded?
I read that in principle, the formation of a double neutron star requires that at the time of the second supernova explosion the binary consists of a $\sim$ 1.4 solar mass neutron star, and a second ...
5
votes
0
answers
61
views
Is gravitational lensing "additive" in a line of sight?
As usually depicted, gravitational lensing implies, at least, three objects: a distant source, an observer, and a "massive enough" object in the middle, where enough is the mass needed to ...
5
votes
0
answers
86
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
1
answer
238
views
Will Lunar Months be the same length Millions of Years in the Future?
If I remember correctly, the amount of time it takes for the moon to rotate around Earth is getting longer over time. Is this true, and if so or the opposite is true and a lunar month is getting ...
5
votes
0
answers
153
views
If a Milky Way supernova were to happen, how long would it take for astronomers to be notified?
If a Supernova were to happen in the Milky Way, how long would it take for astronomers to be notified?
How long would it take for the people running the gravitational wave and neutrino detectors to ...
5
votes
0
answers
90
views
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 ...
5
votes
0
answers
174
views
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 ...
5
votes
0
answers
513
views
How far away must galaxies be before current telescopes can no longer measure how quickly they are rotating around one another or internally?
What is the distance limit and does it depend on the size of the galaxy and on noise and interference from gas clouds and our own Milky Way?
5
votes
0
answers
202
views
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-...
5
votes
0
answers
113
views
There is a decibel limit to sound based on the medium, what is the decibel limit in neutronium?
I've been participating in many discussions online about the classic thought experiment on pressing a button a light year away with a light year long rod. The solution boils down to the speed of ...
5
votes
0
answers
68
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
83
views
A couple of questions about Earth's hypothetical planetary rings
From what little I know of this subject, It should be possible for Earth (Or a planet the size of Earth) to keep a system of Planetary Rings. However, looking around the internet only gives me info ...
5
votes
0
answers
133
views
Positional astronomy - Speed of the sun in sky
Let $\vec{r}$ be the position of the Sun in the sky, from Earth. How could I estimate the magnitude of $d\vec{r}/dt$, to measure the rate of change in time of the arc it traces? I suppose it would be ...
5
votes
0
answers
105
views
Beginners question about time scales
I'm using https://github.com/Bill-Gray/jpl_eph for a personal project to read JPL DE files, namely DE430 and the more recent DE440. This generally works great and when tested against a reference ...
5
votes
0
answers
134
views
What is this cluster of light trails captured on long exposure images?
I was taking photos of the Perseids meteor shower on 13/08/2022 in Peak District in the UK. The camera was fixed stably on a tripod, set on manual mode, taking 8-second exposures continuously.
When I ...
5
votes
0
answers
70
views
"Quarter root of intensity" in coronographic plots
In excitement regarding the JWST release, I came across Krist et al, The JWST/NIRCam coronagraph: mask design and fabrication, within which there is the following plot:
Fig. 9. Focal plane images ...
5
votes
0
answers
121
views
When's the most recent time that we could have missed a supernova?
I know that if a supernova were to happen in the galactic Core, the dust there would prevent the visible light from it from reaching us, so if one were to have occurred there in say 1900, we wouldn't ...
5
votes
0
answers
89
views
Time dilation if an asteroid and a small black hole entered a larger black hole?
For an outside observer, everything moves slower the closer it is to a black hole's event horizon, even photons, due to the black hole's time dilation.
We also know that when two black holes collide, ...
5
votes
0
answers
266
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
49
views
Extract surface density profile from a temperature profile?
I have a protoplanetary disk model which outputs a temperature vs. radius profile, based on radiative transfer. Looks something like this...
One of the inputs to the model is the surface density ...
5
votes
0
answers
207
views
Spectrum features of main sequence and giant stars with the same spectral type
Hence, the spectral features of the supergiant are different from those of the Sun-in accordance with the Saha equation- even though both stars are essentially at the same temperature. The pressure ...
5
votes
0
answers
42
views
HR 6819 "Vampire" star - mass disparity in binary star system
Regarding the two B-type stars of the HR 6819 system, a recent news item (2 March 2022), European Southern Observatory researchers find 'vampire' star sucking outer layers of companion star states,
...
5
votes
0
answers
36
views
How to model the kinematics of gases expelled from comets and planetary atmospheres?
Once the ices of comets sublimate, where do they move to, and with which equations do you describe their motion in the interplanetary medium? Similarly, where do the gases that are stripped from the ...
5
votes
0
answers
149
views
Is it possible to narrow down possible dates for the following eclipse pattern?
I am searching for an year which satisfies the following criteria.
Dates are in Gregorian calendar.
Criteria
Year range 3800 BC to 500 BC
Solar Eclipse of any kind between October 14 and October 22 ...
5
votes
0
answers
98
views
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 ...
5
votes
0
answers
64
views
Type Ia supernova by fallback?
Is it possible for a massive star of more than 1.4 solar masses (probably around 3 or more but below the threshold for type II) to collapse into a white dwarf and a planetary nebula, then go supernova ...
5
votes
0
answers
77
views
Obtaining the derived period of $\omega$ Canis Majoris
I have read these two papers:
On the nature of the Be phenomenon I. The case of ω Canis Majoris
Stellar and circumstellar activity of the Be star ω CMa
II. Periodic line-profile variability
In the ...
5
votes
0
answers
73
views
Is there a mass-vs-radius chart for neutron stars?
I'm aware that we currently don't have an equation of state for the radius of a neutron star, because we don't know what happens to neutrons at their cores, and because the equations involved with ...
5
votes
0
answers
104
views
Comparing Observing Techniques to Quantify the Effects of Starlink Satellites on Astronomical Observations
To take pictures of satellites I think I could use these methods listed below (are there more?)
Method 1
The satellites are tracked and their positions predicted. By utilising software tools and code ...
5
votes
0
answers
79
views
What limits can we set about life beneath the ice of Europa?
Do we know enough about the conditions beneath the ice of Europa to say anything about the complexity of life that may live there? Can we rule out macroscopic life?
5
votes
0
answers
79
views
A new (radio) neutrino telescope in Greenland?
I just stumbled upon ScienceMag news from July 14th, 2021 which says:
By placing hundreds of radio antennas on the ice surface and dozens of meters below it, they hope to trap elusive particles known ...