All Questions
2,115 questions
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In general relativity, how do we know when the coordinates we compute are physical observables?
(One of) the whole point of general relativity, is that the coordinates we mathematically use are just "labels", that can change and live on a curved surface. But at some point we have to ...
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19
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Finding the Flux Ratios of Two Stars in the V-Band [closed]
I am hoping to verify my approach / answer as I study for a final exam! I am given the V magnitudes for star A = 7.0 and star B = 8.5.
$$ \frac{F_B}{F_A} = 10^{-0.4(V_B - V_A)} $$
$$ \frac{F_B}{F_A} = ...
3
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1
answer
139
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What are these circular objects on the JWST image?
While admiring this beautiful image (Spiderweb protocluster field) https://esawebb.org/news/weic2428/ captured by the James Webb Space Telescope (JWST), I noticed several (more than five) circular ...
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Auroral Kilometric Radiation (AKR) Peak Frequency Calculation
Auroral Kilometric Radiation (AKR) occurs due to emission from charged particles moving in helical paths around planetary magnetic field lines at or around the electron gyro frequency and/or its lower ...
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24
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Astronomical Horizon VS Apparent/Visible Horizon VS Geometric Horizon
The definition I got for the astronomical horizon is this:
The astronomical horizon is the imaginary horizontal plane always at a 90-degree angle from the observer's zenith (the point directly above ...
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28
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Relativistic time effects or gravitational lensing in solar observations made by observatories and satellites?
As mentioned, I was wondering about whether there are any phenomena affecting the measurement made in Earths time-scale after a physics seminar at IISERTVM. Any discussions and answers from specific ...
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7
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3
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2k
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How do we detect a black hole?
If light cannot escape from a black hole, how do we detect its presence? I mean there is nothing that can be faster than light so if light can not escape from the black hole there should be nothing ...
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CMB map construction
On wiki, it has the individual band maps of CMB, which I understand has emission from the galactic plane as shown below.
But the mostly used map is the smooth one like this. How to go from the maps ...
- 191
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3
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Do bigger telescopes see more objects primarily because they collect more light, or because they resolve things better?
I encountered this question in an exam recently (which I have simplified to focus on the core question). After describing two modern astronomy telescopes, one big and one small, the question asks why ...
- 22.1k
27
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3k
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Why are the northern lights so much less visible to the naked eye than to smartphone cameras?
The northern lights have been visible where I live recently, but I've found them to be practically impossible to see with the naked eye. Phone cameras, however, show them quite brilliantly. How is ...
- 1,289
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I'm trying to replicate Rømer's experiment but can't seem to get even close to the correct value for the speed of light
I am trying to replicate Rømer's experiment where he determined the speed of light by observing and measuring the eclipse timings of Io by Jupiter. I'm using Stellarium for this experiment and no ...
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Evidence for Dark Energy that *distinguishes* between a CDM model with a non-homogeneous universe from the standard $\Lambda$CDM Model
Has any evidence been found that distinguishes between a CDM model with a non-homogeneous universe and the standard $\Lambda$CDM Model ?
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25
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3k
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Is it possible to know where the Sun is just by looking at the Moon?
A nine year old child asked me if it is possible to know where the Sun is located just by looking at the Moon from the Earth.
I said I don't know, that I only know that the lunar surface reflects the ...
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3
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2
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810
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Wondering about ancient methods of estimating the relative planetary distances
Regarding https://physics.stackexchange.com/a/156155/349202 and estimating with geometry the relative distance of Venus to the sun prior to the Venus transit of 1769, I follow the logic of @viktor-...
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115
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What is the reason that the unstable Lagrange point $L_2$ is used for the JWST instead of the stable $L_4$ or $L_5$ points?
I understand how the Lagrange points work in the two-body problem. I can do that math. I understand that for L1, L2, or L3, if the object is perturbed to deviate away from that point, the ...
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answer
67
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Problem understanding the bending of space-time curve as gravitational force! [duplicate]
I got the point of considering gravitational force as curvature on space-time fabric for bigger objects like stars, planets, blackholes. But my doubt is over the objects like us, what keeps us on this ...
2
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1
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339
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Issue with the roots of the Equation of Time
Regarding the famous derivation of the Equation of Time available here that i'm trying to rewrite a modern version with much more detailed steps:
http://info.ifpan.edu.pl/firststep/aw-works/fsII/mul/...
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2
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2k
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Has any astronomer ever observed that after a specific star going supernova it became a Black Hole?
Do we have any observational direct verification and historic record of a star after going supernova was turned into a Black hole?
- 4,376
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1
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AStronomic nova or supernova (Ia), what peak intensity and wavelength to expect in the UV, extinction coefficient of ozone layer?
see https://www.nasa.gov/centers-and-facilities/marshall/nasa-global-astronomers-await-rare-nova-explosion/. T Coronae Borealis is expected to go nova. Distance 2630 light-years. Its magnitude is ...
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33
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Kepler's measurements in solar system
I am interested in knowing that does Kepler measured distances in solar system or only relative distances to a astronomical unit which he doesn't know how long is it in our meters.
- 1,419
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37
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Do magnetar stars relatively produce stronger gravitational waves than neutron stars? [closed]
According to Reissner-Nordstrom solution to Einstein's gravitational field equations in astronomy the electric or magnetic or both, field of a charged body of mass generates its own gravitational ...
- 4,376
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33
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Converting Multiple FITS files into one dataset?
I am doing a project involving data from LASCO C2 on the SOHO spacecraft. I tried to download the data from the SOHO science archive and it comes out as multiple FITS files. Is there a way to convert ...
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1
answer
51
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Centrepetal force at the north or south pole
If you're, for example, 5 m away from the geographic north or south pole, gravitational force points inward, but centrepetal force points almost directly perpendicular, out into space. In that case, ...
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1
answer
72
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Continuous $4\pi$ steradian monitoring of space
What would it take to constantly survey space at a selection of frequencies? I'm imagining a set of satellites pointing away from the Earth and scanning all sectors of space. Can anyone point me to ...
3
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1
answer
52
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Is any planets angular speed roughly constant?
The duration of a sidereal day stays pretty much constant on Earth as far as I know. But I was wondering if that is typical or even always the case. For example, can moons influence it? Or can ...
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What is the velocity anisotropy in galaxies?
I came across this term recenlty, and it seems that there aren't many sites explaining it well.
What is galaxy anisotropy velocity?
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463
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Astronomy Without Fusion
Let us begin with diffuse clouds of atomic hydrogen as we believe was the case in the early universe, but assume that nuclear fusion is not an existing mechanism.
What would happen under the influence ...
- 11.2k
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1
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37
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What is the relative density contrast?
I was reading a paper talking about the KBC Void, a local underdensity in the Universe which we are also part of.
The authors calculated: "[...] the observed relative density contrast δ ≡ 1 − ρ/...
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84
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Will the new atronomy, big data and AI generated algorithms, be able to extend the red shift - distance graph to double digit red shifts anytime soon? [closed]
So far, distances in the universe, using standard candles, have been measured out to a red shift of around 3, at a co-moving distance of around 20 billion light years. It was these measurements that ...
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Drake Equation with Random Walks
Goal
I'd like to use the Drake Equation with random walk theory to estimate the probability of aliens reaching Earth.
Drake Equation
The Drake Equation estimates the number of advanced civilizations ...
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70
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Discovery of a Formula for Geostationary Orbit Distance: Seeking Expert Feedback [closed]
I’m an amateur enthusiast without a formal academic background in mathematics or science. Recently, I stumbled upon an idea and derived a formula that I believe calculates the distance traveled along ...
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79
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Is there a reason why in the astronomic pictures of galaxies and nebulosas there is so little green color?
From a quantum physics standpoint, why do astronomical images of galaxies and nebulae exhibit so little green color in their spectral composition?
When we look at the pictures of galaxies provided by ...
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About redshift and distant objects observation
I did a few Time&Length dilation factor calculations. This is for a distant clock away from any field and a clock on Earth on the equator with the moon passing over clock coordinates, the factors ...
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48
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Is there a database or catalog of all black hole candidates?
I am searching for a catalog, list, database, etc. That should show astronomical observations of known black hole candidates. I am primarily interested in knowing the mass of these candidates.
I have ...
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2
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126
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Is the information or energy in a black hole converted to another form of energy during decay of Hawking radiation?
The Hawking temperature equation states that the temperature of a black hole is inversely proportional to it's mass, and and the black hole loses mass when it emits particles in the form of radiation, ...
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Geocentrism and annual tide variation
I have read that in the before common era, Seleucus of Seleucia have studied tides and probably used annual variation as an evidence of heliocentric. However, tides are known to be affected by ...
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1
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50
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What is emission line ratio?
As the header stated, what exactly is the 'emission line ratio'? Like, [O III]/Hβ or [Ne V]/[Ne II]. Recently I've been reading some research papers in astronomy and astrophysics pertaining to ...
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1
answer
53
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Assessing the quality of wavefront correction in adaptive optics systems: the case of single and multiple radiation sources
Generalized diagram of an adaptive optical system is as follows:
Wavefront from the observation object passes through the atmosphere and is distorted. It is then reflected from the deformable mirror ...
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2
answers
49
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Stars that have fairly high gravitational redshift and calculation of their surface temperature by Planck emition spectra?
How high can the ratio between gravitational redshift and planck emition spectra be depending on the mass of the star so by how much this gravitational redshift could elongate the Planck spectra of ...
- 2,275
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1
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67
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What is the function that demonstrates a planetary transit light curve given a planet's projected distance from its star?
Last night I was measuring the brightness of a Hot-Jupiter parent star to try and isolate the transit light curve (specifically Tres-2b). I have been wondering how to obtain the function that ...
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1
answer
78
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Using helioseismology what are the equations astrophysicists use to determine the age of the Sun?
Astrophysicists talk about solar models when determining parameters of the Sun. But these models must be built from equations. When explaining to the general public what these equations are would be ...
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113
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Does the Kardashev Scale have any practical application?
As the question states: are there any practical applications of the Kardashev Scale?
- 1,068
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Is it possible to predict the appearance of auroras?
Yesterday I saw online a lot of people seeing auroras both in the North and in the South of the globe. Unfortunately, I wasn't one of these people, and this got me curious about how much we can ...
- 23k
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46
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Trajectory of supergiants on HR diagrams
I am a secondary school student currently studying cosmology. My A Level textbook supplies the following HR diagram with regards to what trajectories different stars follow:
I found myself unable to ...
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36
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Magnetic tubes or magnetic field lines around a black hole?
A picture is worth thousand words:
Magnetic field lines, unlike magnetic tubes, have a continuous distribution. Recent pictures of black hole magnetic structure show tubes. Is there a model that ...
- 1,980
2
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Which of the blocked radiation windows will (mostly) open if one where to observe from the surface of Mars, instead of the Earth?
Earth’s atmosphere is composed of about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.1 percent other gases. Trace amounts of carbon dioxide, methane, water vapor, and neon are some ...
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Galaxy harassment; flyby encounter (tidal interaction)
This following image is from the paper https://adsabs.harvard.edu/pdf/1978AJ.....83..219R#page=4
It shows the path of a flyby encounter of NGC 3627 (M66) with the galaxy NGC 3628 (the Hamburger galaxy)...
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144
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How can I see Orion's Belt in winter and summer?
How can the 23 degree tilt of the Earth enable someone in Argentina to see the same constellation (Orion's Belt) in winter as someone in Britain in summer?
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The astonomer's method of color differencing as applied to proving Einsteinian relativity during a total solar eclipse
I'm looking to see if the astonomers' method of color differencing was ever applied to the stars near the Sun during a total solar eclipse, for example, to demonstrate Einsteinian relativity visually ...
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3
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1
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281
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Speed at which the Moon moves past a point on Earth's surface?
I'm trying to calculate how fast a point on the surface of the Moon is moving past a point on the surface of the Earth (I assume a point on the equator of each for simplicity).
I know the Earth is ...
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