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 did the ancient Greeks know about the solar system, and how? [closed]

I'm aware that it was known to the ancient Greeks that the planets were somehow different from the stars. But in what depth did they know the solar system? In particular, did they know: that the sun ...
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So what actual physical event would allow us to observe the speed of gravity?

I have read, if the sun disappeared it would take 8 minutes before this could be detected on Earth due to speed of gravity being $c$. Of course, the sun can't disappear. Perhaps realizing this ...
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Can a detector fail to detect a wave of electromagnetic radiation because the wave's amplitude is at or near its minimum?

If a very brief wave (perhaps a single photon, or maybe a soliton?) is at its minimum (a 'node') when it encounters a detector, would it still be detected?
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How do astronomers detect the spin of the black holes?

There are various theoretical models for accretion disks and relativistic jets from black holes that considers the black hole to be either rotating (Kerr geometry) or non-rotating (Schwarzschild ...
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Should we easely measure the Hubble parameter as it was e.g. 5 billion years ago?

We see very distant stars and galaxies as it were unbilievebly long time ago.If we can measure the receding velocities as a Hubble flow by measuring the Doppler effect for the wavelength and increase ...
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Frequency of single star systems versus multi star systems

What, as of now (2020), is the estimated frequency of single star systems versus multi star systems? While searching for planets (some decades ago the dogma was "rare earth", but now quite a ...
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Problem regarding the absorption spectrum of the sun

Some of the wavelengths of light that are emitted from the sun will be absorbed by atoms in the outer layer of the sun and also the atmosphere of the sun, and we see this as absorption lines in the ...
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Calculating pressure and flux tensors in radiative astrophysics

I need to calculate the components of the radiative flux tensor and the pressure tensor, but I am having a little trouble figuring out what the integral should be. The flux is defined as $$F_v = 4{\pi}...
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Empirical relation between O[III] and H$\alpha$ line fluxes

I have the H$\alpha$ line flux ($L_{H\alpha}$) of an extragalactic source. To calculate the bolometric luminosity, is there an empirical relation between $L_{H\alpha}$ and $L_{O[III]}$, akin to $L_{O[...
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Cassegrain telescope design

How are the dimensions of a cassegrain telescope configured? In particular the distance of the secondary hyperbolic mirror from the primary mirror and also the diameter of the secondary mirror. Any ...
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What is the logic behind the Eddington expedition that proved Einstein's general theory of relativity?

The Eddington expedition in 1919 proved Einstein's general theory of relativity. [Eddington] argued that the deflection, or bending, of light by the Sun’s gravity could be measured... because ...
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Can Hawking radiation be observed from the radiation (spectrum) of M87*?

Using $M87^*$ data from EHT observation (mass, temp of the surrounding accreting disk) and approximating area of EH by euclidean geometry $4\pi r^2)$, error comes around of order one or two. One gets ...
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How do they calculate the distance merging massive bodies are away from earth using just the gravitational waves? [duplicate]

I guess the title sums up my question nicely. So, how do physicists/cosmologists/scientists determine the distance two or more merging bodies are away from earth given just their emitted gravitational ...
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If an object falls from a great height, such that the force of gravity is nonuniform, how much energy is dissipated by air resistance during the fall?

We are also to assume that air resistance provides a small perturbation to the motion, which is largely determined by the force of gravity. Suppose that air resistance is proportional to the square of ...
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What determines if light rays will be parallel to each other after refraction through a lens?

This is an example of a refracting telescope: As you can see, when passing through the eyepiece (second lens), the rays are refracted parallel to each other. Why are they refracted parallel relative ...
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Length measure in Astronomy

In cosmology, we have a couple of different length measures. Among them, comoving and proper distnlances seem to be good fit to real world use cases in astronomy. So my quesion is which length measure ...
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How far is Hill's sphere applicable? What's the maximum mass?

Hill's sphere is the assumed sphere that a smaller body -rotating around a bigger one- attracts other objects to rotate around it. For example, in the case of Earth, the radius of its Hill's sphere is ...
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Astronomical objects that should have magnetic bubbles similar to those found by the Voyager probe at the edge of our solar system

I've known about the existence of magnetic bubbles at Solar System's edge from a video edited by NASA from an official channel of YouTube, I refer [1] (as explicitly stated in the title, it was a ...
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Relative speed of galaxies in deep space

Let say we observe two galaxies, one little bit closer to us than the other one. If we calculate the speed of the farther one does it mean that according to the Hubble law when the closer one reaches ...
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Is the cosmic event horizon viewed from Andromeda different from the one viewed from Earth?

If the most distant galaxies we see in deep space are in proximity of our cosmic event horizon does it mean that if we were on Andromeda galaxy and looking in the same direction we would see objects ...
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Will Milky way and Andromeda collide for sure?

Is it sure that Milky way and Andromeda will collide or might they just start a rotation around their center of masses?
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Pinhole camera as a device to develope photos of distant stars? [closed]

Could a transparent slab coated with photosensitive film be placed inside a pinhole camera nearly paralel to the path of the light emitted by a source of light(star) to produce a picture wich due to ...
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How are the units (seconds) of the dispersion constant determined?

The following is taken from Cordes [1] on pulsar astronomy. The dispersive time delay [is] $$t_\mathrm{DM}=\frac{e^2}{2\pi m_e c} \frac {\int_0^Dds \text{ } n_e}{\nu^2} = 4.15\text{ms} \text{ DM } \...
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What difference does the wavelength and/or frequency of a gravitational wave make? On the detector, for instance?

When they talk about the arms of LIGO or Virgo stretching by a thousandth of the width of a proton, they always emphasize that this is the wave's amplitude, not wavelength... The wavelengths are ...
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Why is there so few Helium on (inside) Earth?

According to this article, there is a large quantity of Helium in space (stars), but very little is accessible to us on Earth: Helium is abundant in space, where it's produced as a product of the ...
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What is a “strong line”?

What is a “strong line” in an FFT (Fourier Transform) waveform? How does one identify a “strong line” in an FFT trace?
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Non-linear regime of matter power spectrum

Question 1 I was trying to understand why cosmologist calculate the matter fluctuations in spheres of $8 h^{-1} Mpc$. I look for information and I find that in this scale the fluctuations become ...
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Perspective confusion in Sky Map mobile app

I have recently ran into an observation which broke my mental schemes, using the Sky Map mobile application. For an introduction before my actual issue, I should state my understanding that, since the ...
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What is “spectral turnover”?

In a paper which deals with the spectra of radio frequency cosmic events, the word “spectral turnover” is used. What is “spectral turnover”?
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Is the parallax of NEOWISE primarily caused by the earth's or the comet's motion?

The Comet C/2020 F3 (also known as "NEOWISE") appears to move compared to stars in the background: (Screenshots from Stellarium) Those images are one hour apart as seen from Germany. Is ...
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Vectorize altazimuth coordinates?

Is there a way to convert a pair of altazimuth coordinates (one for each of two observers) into vectors so as to compute the difference between them (i.e. both altazimuth coordinates point at the same ...
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How do we experimentally estimate the luminosity of a distant star?

While calculating the matter density of the universe, we need to find luminosity. How do we experimentally estimate the luminosity of a star?
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Converting altazimuth coordinates to a vector to determine a baseline vector?

I know the equatorial coordinates of a “beam” pointing from an Earth-based observer toward some distant star. I have converted those coordinates to altazimuth coordinates for that observer and a ...
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Is the sound of pulsars converted radio waves, or actual sound that's has been put into a loudspeaker?

Do neutron stars produce sound? In the answer to the above question, it has been mentioned that: 'The pulsar signal is often transformed directly into an audible signal by simply feeding it to a ...
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Where can I hear the trapped sounds inside a pulsar?

I have been searching for an audible track of stellar oscillations inside a pulsar, but I don't seem to find what I want. No, I am not asking about the radio waves emitted that have been converted ...
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Definition of eclipsing binaries?

In the second minimum (the 3rd step) there is a smaller decrease in light intensity. For this to happen, wouldn't you need to be looking at the plane of orbit from above rather than directly along the ...
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How is VLBI delay calculated, practically?

I’m working on a research project wherein we are trying to solve a problem very similar to VLBI delay. We have two radio receivers, and we know their locations. We also know at what time one receiver ...
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How are solar oscillations detected?

While reading through a page on beginner Helioseismology, I occasionally came across the terms p-modes or g-modes, which I know are caused by pressure and gravity. I wanted to know how do satellites ...
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What's the reference/original wavelength while calculating redshift?

Measuring redshift is one of the ways of analyzing distance in astronomy, since the redshift of an object is caused by the expansion of space between us and the object, the more space there is between ...
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How can I calculate “temporal parallax”?

A radio transient was observed by an observatory. I know the observatory’s location, the pointing center of the beam in galactic coordinates and right ascension/declination, and the exact time the ...
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What is the “single pulse radiometer equation”?

This document https://arxiv.org/pdf/1601.03547.pdf refers to the “single pulse radiometer equation”. Apparently, it’s used to calculate the flux of radio transients. What is the “single pulse ...
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Is there a way to measure flux indirectly?

Is it possible to calculate the flux of some electromagnetic radiation (say, a radio wave) using other parameters?
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Why are low-frequency radio transients so rare?

Why are low-frequency radio transient (fast radio bursts, etc) so rare? Is it due to our observational equipment, or something intrinsic to transient phenomena?
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Does Hawking radiation can have any observable effect on Black hole shadow

Last year we captured shadow of black hole at the centre of M87 by Event Horizon telescope. I am wondering if Hawking radiation can have any effect on the black hole shadow. The more I think about ...
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How is the “intensity” of a fast radio burst measured?

I’ve read that Fast Radio Bursts are very “intense”, but how is intensity measured?
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Why don't ionic liquids evaporate in a vacuum?

Proposals exist for a rotating liquid mercury telescope on the Moon, using ionic mercury. Pure mercury has a triple point at 312 K and 0.2 mPa, but the Moon's surface pressure is far lower than this. ...
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What’s the difference between FoV and IFoV?

I read that radio telescopes have “huge fields of view (FoV)”, but are unable to precisely localized objects due to their “small instantaneous field of view (IFoV)”. Apparently, somehow the size of ...
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Which parameters can be used to differentiate between bulge and bulgeless galaxies?

I started doing a project which needs a set of bulgeless galaxies, but I don't how to differentiate between bulge and bulgeless galaxy. It would be useful if you could specify which parameters can be ...
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How astronomers estimate the redshift of galaxies clusters?

I don't understand how astronomers estimate the redsfhit of a cluster. As far as I understand a cluster of galaxies is something really "big", so I expect that different galaxies in the ...
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Which one of the two does Gamma-Ray Astronomy most relate to: Physics or Chemistry?

So when I talk about Gamma-Ray astronomy, more specifically the following things: Sources of Gamma Rays in the Universe and how they originate Detection of Gamma Rays Gamma Ray Bursts or GRBs ...

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