Questions tagged [astronomy]

The science dealing with objects and phenomena located beyond Earth. In particular, this applies to observations and data. At its core, astronomy is the physically informed cataloging and classifying of the contents of the universe in order to better understand what is out there.

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Estimating the radius of saturn [closed]

I have a question on how to approach such a problem. In this task, we'll focus on the Saturn mission Cassini. The spacecraft reached its final orbit through a fly-by at Titan and captured one of its ...
Enkt Enktson's user avatar
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1 answer
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How is the trajectory of a star found relative to the Sun?

So i know we can get radial velocity by measuring blue shift and then we can use the distance to the star and its proper motion to get its tangential velocity. In the case of Bernards star, its ...
user2279603's user avatar
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Determine the equation of earth's orbit

I am trying to find the the equation earth's orbit using Kepler's Scheme. After every 1.88 years Mars returns to its initial position in the sky. With reference to the diagram and data below find the ...
sameed hussain's user avatar
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Is there a galactic "goldilocks" region in the galaxy

I'm wondering if there's a region where the star density in the galaxy create the conditions in outer space where the galactic temperature is between 0 and 200°F. This may cause a ring shaped where ...
Matt Staab's user avatar
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Estimate Saturn's mass [closed]

How can you estimate Saturn's mass using data from Cassini's final moments in September 2017 (apoapsis on September 12 at 1:27 a.m. EDT Saturn time at a distance of about $1.3*10^6$ km from Saturn, ...
Enkt Enktson's user avatar
2 votes
1 answer
74 views

Einstein's derivation of stellar aberration formula: replacing the direction of the ray with a difference in angles justified?

I was going through the translation of Einstein's 1905 paper "On the Electrodynamics of Moving Bodies"(See https://einsteinpapers.press.princeton.edu/vol2-trans/175). In deriving the stellar ...
JKrsl's user avatar
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Do the colder and warmer poles of the CMB's Axis of Evil corresponds to the terrestrial poles?

Does the terrestrial North or South Pole correspond to the colder and warmer poles in the CMB, as differentiated by the 'axis of evil'? If so, which to which?
Svenn's user avatar
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Observing an event horizon while approaching one

A thought crossed my mind that I realized was hard to conceptualize so I decided to simplify the question by putting it in terms of event horizons. If I am an observer approaching black hole "A&...
Diniden's user avatar
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Is there any tools for observing magnetic fields and forces of black holes and galaxies?

I want to know about how we can find magnetic forces and fields in space around stars, planets, galaxies, pulsars especially pulsars. How (by what means) did determine magnetic fields around a pulsar?
QQQ's user avatar
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2 answers
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Is cosmological redshift associated with recession velocity when the light left or when it arrived?

Is the cosmological redshift $z$ associated with the recession velocity when the light left, when it arrived, or something in-between?
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Why is $G*M_{sun}=4\pi^2$ when using AU/year units?

So, when using AU/year units, it turns out that 3rd Kepler Law: $\frac{r^3}{T^2}=\frac{G*M_{sun}}{4\pi^2}=1$, meaning $G*M_{sun}=4\pi^2$, any easy explanation for this? Cheers.
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Derivation of the coherence length of the light coming from a star

Consider a star perceived under an angle $\alpha$ from the earth. In the Hanbury Brown Twiss experiment, they say that the coherence length $L_{coh}$ of this light is given by $$ L_{coh}= \frac{\...
Nicolas Schmid's user avatar
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What is the reason for slanting of (Solar) analemma?

Why is a (solar) analemma, photographed (Multiple exposure imagery)in the morning or afternoon at latitudes other than geographical poles or the equator, slanted? (For further examples of slanting ...
Jacob Miller's user avatar
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How do you find the extinction coefficient for Gaia photometry?

I have Gaia photometry g, bp, and rp. My final goal is to find the photometric temperature but first I need to account for reddening by finding the extinction coefficient. I’m really stumped on how to ...
Snav's user avatar
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Is the speed of Earth's spinning constant over a given 24 hours?

Is the speed that the Earth spins on its axis constant over the course of 24 hours? As opposed to does it turn faster and slower during different hours over any given day even by a very small ...
JohnTrainor's user avatar
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Does the Earth's magnetic field lag behind the Earth as Earth orbits the sun?

I imagine that when the earth orbits the sun, the earth's magnetic field is also subject to the sun's gravity, since photons and light are subject to gravity. As a result, the magnetic field does not ...
garmichaels's user avatar
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Measured Value of Hubble's Constant [duplicate]

As we know, Hubble's Constant is not exactly a constant, but its value varies with time. However, we also speak of measuring its present-day value. The measurements by cosmic distance ladder would ...
V Govind's user avatar
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How fast do I have to fly vertically up to pause sunset?

I'm standing on the famous Laguna Beach in southern Los Angeles to watch the sunset on December 18th (33.541679°N 117.777214°W, 0m elevation, 16:44 PST). Now, from my perspective at the shore, the sun'...
Richard Zhu's user avatar
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What math predicted the eclipse of Betelgeuse?

It's amazing that scientists can predict something as small as last weeks eclipse of Betelgeuse. The general relativity aspects are quite specialized. Can someone point me to the math involved in ...
foolishmuse's user avatar
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Advantage of a single large telescope over many small ones for optical/infrared spectroscopy?

In a thought experiment where we would like to do optical/infrared spectroscopy on distant galaxies, and in which we would like to increase as much as possible the resolution of the spectroscopy (...
Vincent's user avatar
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Does average length of sidereal day change if earths axis is tilted in different way

Can precession of axis of rotation of earth cause change in average sidereal day length?
MultiUniverseExplorer's user avatar
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Is differential number density the same as flux density?

I'm trying to convert the differential number density of photons to luminosity (using slide 17 of https://www.astro.rug.nl/~sctrager/teaching/OA/Photons.pdf) and ...
John's user avatar
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How do I approximately calculate the sidereal time at an specific location in a specific time and month (no year)?

How do I approximately calculate the sidereal time at an specific location in a specific time and month ? Most formulas required to input a year too, and then they want you to deal with Julian day, ...
darkside's user avatar
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2 answers
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Why is the time from vernal and autumnal equinox different than from the autumnal to the vernal one?

In my lecture the professor stated that the time from vernal to autumnal equinox is about 186 days , while that from autumnal to vernal equinox is about 179 days. I was wondering why are these time ...
darkside's user avatar
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2 votes
2 answers
216 views

How to measure the ratio of a planet's radius to a star?

I was reading a physics problem related to astronomy, and upon re-reading it, I realized that it could be really indicated to extrapolate some really interesting physics-related information. One of ...
Bml's user avatar
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17 votes
3 answers
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Paradox about white dwarfs and ionization

I am facing a dilemma. The fact that matter is ionized allows ions and electrons to be much closer together than they are in atoms (Bohr radius $a = 0.5 \cdot 10^{− 10} \mathrm{m}$), and the result is ...
Bml's user avatar
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7 votes
1 answer
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What is the smallest known gravitationally bound system?

Recent discovery of a satellite orbiting Dinkinesh made me wonder how fragile that system must be. Based on the numbers and photos given by NASA, I estimate that binding energy of the two bodies is of ...
user1079505's user avatar
1 vote
1 answer
53 views

Andromeda Galaxy and Hubble

When Hubble determined the distance to Andromeda he based his estimation on Cepheids. However, the result was less than half the current value. What was the cause of this error and could another ...
Christian Speth's user avatar
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32 views

Can dark matter be isolated from baryonic matter?

The above is an image to test Verlinde's emergent gravity theory (2016, https://arxiv.org/abs/1611.02269). The research team observered galaxies and masses beyond, used gravitational lensing (y-axis) ...
Koen de Jong's user avatar
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Orbital obliquity of the Earth

Consider that we have all the orbital parameters that characterize the Earth. How would one calculate the orbital obliquity of Earth? One could argue that since the rotation of Earth doesn't change ...
RKerr's user avatar
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How can I find the expected value of the number of particles in a region?

The actual problem asks to find the expected value of number of molecular clouds between Earth and the gallactic center, these clouds are distributed through the gallactic disk approching it as a ...
MJ_'s user avatar
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0 answers
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Pattern of source-tracking two-element radio interferometer

In a two-element adding Interferometer, the phase difference comes about as EM-waves from a source at an angle $\theta$ to the baseline-normal generally cover different path lengths when travelling to ...
Merkel_Bot's user avatar
1 vote
1 answer
60 views

Have we independently verified Leavitt’s luminosity-period relationship?

After Henrietta Leavitt discovered the relationship between luminosity period amongst cephids in the Magellanic Clouds, how was she so sure that you can extend this relationship to other Cepheids ...
Justin 's user avatar
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Can gravitational waves be compared with a sinking water phenomena?

Let's say we have some water in the sink and open the closure. The water starts to move towards it in a whirlpool-like manner. If we have a table tennis ball and leave it near the hole of the sink it ...
Krešimir Bradvica's user avatar
4 votes
2 answers
291 views

How do we know when the earth completes an orbit?

Two bodies in space always orbit their center of mass. So the relative motion of the Sun and the Earth happen in the same line, save for the rotation of the Sun. So, how do we measure The time taken ...
Jyothish Kumar's user avatar
2 votes
1 answer
45 views

Is this already an established functional relationship or have I created hodgepodge?

Last winter I started toying with the galaxy gravitational rotation curve graphs. I started modifying the exponent of $r$ that in effect change the $1/r^2$ law and therefore correct the mismatch, ...
Sandman's user avatar
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1 vote
1 answer
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Does NFW profile work for any galaxy?

We use Navarro–Frenk–White (NFW) to calculate Dark Matter (DM) density. Can we use it for DM halo in any galaxy or is it used only for Milky Way (MW)?
Peyman's user avatar
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1 vote
1 answer
34 views

Bolzmann Distribution question

I am busy working through an Astronomy textbook. I am presently working in the formation of spectral lines section. I'm struggling with the statistical weights of the Boltzmann Distribution ...
johann's user avatar
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16 votes
3 answers
4k views

What does the sky look like from the moon?

From pictures taken on the moon, it appears that there are no stars visible in the sky, but I do not know if this is an effect due to cameras. What is the actual appearance of the sky on the moon? ...
Aelion's user avatar
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5 votes
2 answers
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What is the Metric of the Gravitational Field of the Sun?

What metric determines the "geometry" of the gravitational field generated by the mass of the sun? Is there a general metric that incorporates arbitrary mass and devolves into the ...
Mathipulator's user avatar
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0 answers
16 views

Luminosity effect in stellar spectral classification

“Atoms with small ionization energy,Ir,will have a higher ionization in the atmospheres of giants than in those of dwarfs, and the atoms with large Ir will behave in the opposite way. This ...
teacher's user avatar
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1 vote
1 answer
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Basic: calculating a satellites height from its angular speed

A few days ago, while loooking at the night sky, I saw a satellite and I wondered if it would be possible to tell how far it is just by looking at it. The only possible naked-eye measurement that I ...
Pablo's user avatar
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0 votes
1 answer
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How can we conclusively say that there is no Blackhole in the Solar System?

With the Gravitational perturbations among Neptune, Uranus & pluto, Is there anyway to know conclusively that there is no rogue Blackhole roaming the solar system? The Event Horizon may be very ...
Gopal Anantharaman's user avatar
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1 answer
144 views

What if dark matter/energy did not exist?

What if dark matter and dark energy did not exist and were only due to a misinterpretation of the red shift of light or a measurement bias? What would be the implications/consequences?
Olandelie's user avatar
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Earth's motion in the universe

In the context of working with atomic clocks I have to obtain the orientation of the Earth for every given Julian date. I am trying to obtain a 3d vector summing up all of earth's motions in the ...
joséphine's user avatar
-2 votes
1 answer
69 views

Why do sun emit light of different frequencies? [duplicate]

The sun emits white light, which is a mixture of light from all frequencies. Instead, it should have emitted a beam of light of the same frequency, as the source is the same? So, can you please ...
Shubharth Chaudhary's user avatar
1 vote
1 answer
33 views

Seyfert Galaxies: How does this statistical deduction about the age of their nucleus make sense?

As per this book, An Introduction to Active Galactic Nuclei by Bradley Peterson: The nuclear emission must last more than $10^8$ years, because Seyfert galaxies constitute about 1 in 100 spiral ...
Arihant's user avatar
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3 votes
1 answer
93 views

What happens to objects along spiral galaxy arms over long periods of time?

Observations of spiral galaxies reveal that objects within the same arm of a spiral galaxy move at around the same speeds, regardless of their distance from the center of the galaxy. Conversely, the ...
geoscience123's user avatar
1 vote
1 answer
69 views

In the future, can advanced telescopes be used to observe different laws of physics at the time of the big bang?

I've heard that because light takes time to travel from one place to another, we see objects in distant galaxies as they were when they released the light. new and advanced telescopes are able to see ...
Hannah's user avatar
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3 votes
1 answer
60 views

Modelling a fully relativistic White Dwarf Star

I am trying to model a fully relativistic white dwarf using different central densities. Using the below equations: $\frac{dP}{dm} = -\frac{Gm}{4\pi r^4}$ $\frac{dr}{dm} = -\frac{1}{4\pi\rho r^2}$ and ...
A.M's user avatar
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