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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What definition of now is used in our stellar neighbourhood?

Within General Relativity the idea of simultaneity is fairly arbitrary, every coordinate system has one. Which one corresponds to my personal local sense of now appears indefinable in any objective ...
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1 answer
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Are all Astronomers also technically physicists? [closed]

There is a website many schools will use to show their students job descriptions to give them inspiration and know what they wish to be when they grow up, show them some options, you know? Well, I was ...
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Length of Lunar Month

The time it takes the Moon to return to a given position as seen against the background of fixed stars, $27.3$ days, is called sidereal month. The time interval between identical phases of the Moon is ...
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Is the diameter of earth's north pole similar to the south? (Think axis of rotation+ axis of precession)

Earth is an oblate spheroid, not a sphere, since it's rotation around the axis causes it to bulge along the equator. Is it teally a symetric oblate spheroid though, or also not even that? To explain: ...
5 votes
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Thermodynamic ensemble of Stars instead of molecules

If we take an enormous amount of molecules (an ensemble), the laws of statistical thermodynamics become valid: we can use them to make predictions of the macroscopic behavior of the ensemble. I was ...
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Solid angle of celestial bodies

I found online that by using the definition of angular diameter, the formula for the solid angle of a celestial object can be defined in terms of the radius of the object, $R$, and the distance from ...
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1 answer
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Why is the time difference of equal tide states not 50 minute if one lunar day is 24 hour and 50 minutes?

I do understand that tidal forces are caused by de difference of gravitational force between both opposite points of the earth where a bulge is formed. I do understand that a lunar day is ruffle 24 ...
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2 answers
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Justification for proportionality in Hubble's law

I just read about the Hubble's law which states that the speed $v$ (related to a point $A$, let's say the center of Earth) of a galaxy and its distance D (to the same point $A$) are proportional: $v = ...
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Can strong magnetic fields exist in a large scale?

there. Can strong magnetic fields with strength about $1$ T to $10^{3}$ T exist in a large scale, e.g., about several light years? I searched on Google Scholar, but I could not find related papers.
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How loud is the Perseus cluster?

The gas near the center of the Perseus cluster exhibits quasiperiodic pressure oscillations that can be interpreted as sound. I found a paper that says that these pressure waves have a wavelength of ...
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Difference between Earth's surface area seen from ISS and the theoretical area if light refraction is neglected

What is the difference between Earth's surface area seen from ISS and the theoretical area if light refraction is neglected? I watched a video telling that it is not possible to know why a great ...
1 vote
2 answers
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Too many low redshift galaxies in NED database

When using the NED database I found there are too many galaxies with very low redshift (Near zero). I used NEDs search by parameters function to find all galaxies within Z=0 to Z=.03 redshift. I did ...
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Does the RA and DEC of the sun change with time?

I'm almost certainly misreading this, but it's said that "one of the great advantages of the equatorial system is that the RA and Dec of a star do not change with time, at least over short ...
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By analytic geometry, how to figure out if a given point is in shadow of a planet?

I have a spherical star with known position (in 3D space) and radius. I also have a spherical planet with known position and radius. Given a point that is more distant to the star than the planet is, ...
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Is there a naturally occurring siderostat (fixed orientation, absolutely nonrotating object as if locked to the distant galaxies or the universe)?

Often, a telescope is attached to an equatorial mount with a motor that counteracts the earth's rotation so that the telescope has no net rotation. It may be designed to counteract the known rotation ...
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Showing that flux fluctuation is $q^2 P_n(q)/2\pi$

In the context of spectral analysis of a sufficiently small section of the sky, 1 states that the flux fluctuation is given by $q^2 P_n(q)/2\pi$ on the angular scale of wavelength $2\pi/q$, where $P_n(...
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How does the echo of a radio wave from Venus depend on the rotation speed and direction of the planet?

In this paper from around 1960 scientist used echos of radio waves from the Venus' surface to determine its rotational speed and direction. How can the rotation of Venus affects the echo of the radio ...
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4 votes
1 answer
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What are the farthest distances JWST can see?

I was just wondering a simple question: what is the farthest distance (equivalently the least time after the Big Bang) that the JWST could theorically see? Can it be estimated somehow WITH SOME ...
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Can we measure the black-body radiation/ electromagnetic radiation that pass through some point P in space?

I was wondering if we can measure the black-body/electromagnetic radiation energy of a point in space without actually knowing the source of this energy. Let us say 2 stars emit black-body radiation/...
7 votes
1 answer
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Why does the light from stars / satellites tremble? [duplicate]

Clear Sky. 1 ---> Light from stars visible. 2 ---> Light from satellites visible. 3 ---> Light from airplanes (passing by) visible. Apart from the change in color, the light from 1 and ...
0 votes
1 answer
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What would happen when two wave functions intersect in a Fourier series representation of periodic signals? [closed]

I saw a piece of code on github which transforms the planetary movement into the fourier wave function. These circles are given by the x and y ordinates: x=cos(ωt) y=sin(ωt), which are periodic. ...
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1 answer
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How is perspective compensated when analyzing the rotation of distant galaxies?

I can't find any information about that, but I always wondered: When analyzing a distant galaxy, how is the perspective taken in account when analyzing both its movement and the apparent density ...
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How to obtain exoplanets transmission spectra from JWST's NIRISS data of WASP96?

I was having a look at JWST's NIRISS data of WASP96 (specifically at the x1dints fits file which should be already calibrated). From this, I would like to obtain a result in a fashion similar to the ...
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If barycenter true, then how general relativity explain it?

I found that earth actually doesn't orbit sun. Sun and other planets both orbit the barycenter(Their central of mass).Then, what about Einstein's theory ? That heavy mass(sun) wrap space-time, thus ...
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1 answer
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In what sense is the JWST image of Jupiter an improvement over prior telescopes?

JWST photographed Jupiter: The data includes images of Jupiter and images and spectra of several asteroids... The data demonstrates Webb’s to track solar system targets and produce images and spectra ...
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1 answer
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In VLBI astronomy measurements, does one measure the same photon using both instruments?

Most professional astonomy (that I heard of) at visible or radio frequencies is done with instruments that try to collect EM waves such that signals stay coherent. But I wonder why the light from ...
2 votes
1 answer
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Why can we see all the way back to 600 million years after the Big Bang?

I apologise that what I'm about to ask has probably in some format been discussed before on the site. Like many recent questions here, this is motivated by the James Webb telescope: a relative of mine ...
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"Now" in galaxies billions of light years away

Lets say we see a red giant that has 10 million years left before going supernova, and it is 100 million light years away from Earth. Would it be incorrect to say that now, that star has long since ...
62 votes
7 answers
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Why do some lights captured by the Webb telescope have rays and others don't?

On the images captured by Webb telescope one can see some lights with 6 rays, but most others don't have any. One would expect the optics to transform all light sources at infinity in the same manner. ...
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16 votes
4 answers
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Does dusk really remain for a shorter period of time at the equator?

It is said that the dusk remains for shorter time at equator than the poles. Because, the equator rotates faster than poles. But it is also true that time is the same in every latitude, and if it's ...
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1 answer
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Is this how we get the stellar parallax angle?

I know this question has been asked before, but for me, something is missing in the answers. I think I might have it figured out though. So the parallax is usually explained with an illustration ...
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Satellite’s Position and Path on 2D Map [closed]

When the ISS orbit the Earth, its path traced on a 2D Mercator Earth Map is similar to a sinusoidal wave. I am wondering is there any way to determine the trig function of the wave, knowing the ...
-1 votes
2 answers
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Why the outer rim of our observable Universe is the oldest in age?

I don't get it. They telling us that the Webb space telescope will look far away from our home position deep into our observable Universe towards its outer rim about 13 Billion lyrs away where the ...
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If there was an infinite amount of matter at big bang to form an infinite universe how it was possible for a so huge amount of matter to expand?

If there was an infinite amount of matter at big bang to form an infinite universe how it was possible for a so huge amount of matter to expand? Is it better to think that the universe is spatially ...
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1 answer
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Hardness ratio of gamma-ray busrts

As we know there are two types of GRB (gamma-ray bursts) classes based on their time duration (t90). The presence of bimodality in histograms also verifies it. Also, I have read many papers in which ...
4 votes
1 answer
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Calculating the time interval between sunrises with and without the atmosphere

I have developed a method to calculate the time of sunrise, sun noon and sunset, but it does not take the atmosphere into account. Therefore, in order for my results to be useful in practice, I need ...
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1 answer
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Does the index of refraction of the sun's corona and solar wind contribute to the bending of light

It's not hard to imagine that the sun's corona and surrounding solar winds have an optical density that can affect the index of refraction near the surface of the sun and bend light in these regions. ...
11 votes
6 answers
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How could Tycho Brahe determine positions without accurate clocks?

Tycho Brahe determined the positions of stars and planets to an accuracy of 2 minutes of angle. Pendulum clocks hadn't been invented yet so he couldn't have known the time to better than 15 minutes. ...
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How much energy does a cosmic ray lose before it hits a detector?

The origin of extremely high energy cosmic rays is still unclear, by my understanding. But say that they are produced by whatever local source does it: how much energy is lost to environmental effects ...
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6 votes
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Why are radio telescopes in orbit radio telescopes?

We use radio telescopes on Earth because of the atmosphere, right? It blocks the more energetic wavelengths but not radio waves and microwaves. So, since radiation like x-ray and gamma radiation are ...
4 votes
2 answers
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About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

What is this all about?: At 12 May 2022 at the ESO official announcement live streaming event the EHT representatives claimed that the Sgr A* BH accretion disc spin axis is sort of facing Earth's ...
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What are the three bright spots in the Sagittarius A black hole picture? [duplicate]

Today the first picture of the Sagittarius A black hole was released. Although somewhat similar to the first picture of the M87 black hole released three years ago, to my eye there's a notable ...
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The Event Horizon Telescope collaboration will announce groundbreaking observations of our galaxy at 12 May 2022, what this announcement could be? [closed]

"Live webcasting for the ESO-hosted EHT 2022 event On 12 May 2022 at 15:00 CEST, the European Southern Observatory (ESO) will host a press conference on groundbreaking new Milky Way results from ...
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4 votes
2 answers
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How can we extract the Doppler shift of supernovae?

My understanding is that supernovae are used as standard candles, whose spectral lines indicate the recession velocity of the host galaxy. But the material from the supernova is ejected at a ...
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Wouldn't our own EM emissions be good the places to look for signs of intelligent life?

I read that only a narrow band of radio waves are reserved for astronomical observation, and humans emit all sorts of electromagnetic waves, which leads to my question: Could there be signals of ...
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Based on structure formation and the lifetime of the universe why is there an upper bound on the cosmological constant?

I understand that significantly greater values than the cosmological constant would result in difficulty for the formation of large gravitationally bound structures within the lifetime of the universe....
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How does one generate a formula(s) for an artificial satellite's location at time $t$ given a set of known locations at discrete times?

Given a set of spatio-temporal points in space {(Lat_1, Lon_1, Alt_1, Time_1), ... (Lat_n, Lon_n, Alt_n, Time_n)}, I need a function (i.e. a formula) that takes these points (or subset of points) as ...
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Continuity equation for the estimation of cosmological dimensionless parameters

I want to set up a system of equations to find the dimensionless density parameters $\Omega_i$ as a function of $N=\ln(a)$, from the continuity equation: $$\dot{\rho_i}+3H(p_i+\rho_i)=0$$ where the ...
1 vote
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Would the collision of a neutron star and an anti-neutron star destroy the galaxy it happens in?

My question is a follow up to this one: Does the collision of a neutron and anti-neutron produce energy?. Quoting from the accepted answer: "The collision of a neutron and antineutron star would ...
49 votes
4 answers
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Could I, within my lifetime, reach any star I wanted if I went fast enough?

Disclamer: I'm not talking about FTL travel here. I'm also not talking about any weird space warping mechanics like wormholes and such. I've always thought that if a star was 4 light years away, then ...
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