Questions tagged [electromagnetic-spectrum]

Questions about a certain range of frequencies of electromagnetic radiation, given e.g. as wavelengths or wavenumbers. Consider using the tag "wavelength" as well.

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How are absorption cross sections calculated?

I would like to develop a more intuitive understanding of cross sections, in the context of radiative transfer. I understand that a cross section, $\sigma_\nu$, is a measure of a given atom/molecule's ...
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How luminous does a brown dwarf have to be to illuminate an Earth-sized planet with 0.5 lux at 2,000,000 kilometers away?

A brown dwarf is a deuterium-fusing substellar object, and, in the cases of the larger ones, a lithium-fusing one. They often emit electromagnetic radiation in frequencies that humans cannot see. ...
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color of stars and temperature

I recently got questioned on why stars are the color they are. I know the color of a star depends on its surface temperature where hotter stars produce more light towards the blue side of the spectrum ...
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What would it take to view "the whole EM spectrum"?

I know the EM spectrum goes off both ends, but nearly everything anyone has bothered to use it for has wavelengths between $10^8$m (ELF) and $10^{-12}$m or so (gamma rays). So for the purposes of this ...
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How is the H II 'region' directly detectable? By Compton or Thomson free-particle scattering? At what wavelengths?

The Wikipedia page on H II regions says that they are 'indirectly' detectable by the detection of doubly-ionized oxygen atoms mixed in.... (I am presuming atoms, not diatomic molecules...) But are ...
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What would be the effects of a -400 nanotesla geomagnetic storm on modern electronics? [closed]

After reading the Wikipedia article on geomagnetic storms, I'm curious about what the effects of a -400-nanotesla-minimum geomagnetic storm would be on modern military and consumer electronics. The ...
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What would be the electric potential and the energy produced in a cable connecting two electronic devices on the magnetic poles of the earth? [closed]

The earth is a large magnet moving in the magnetic field of another large magnet the sun. And if we connect the two poles of the earth by a cable there would be energy and an electric potential in ...
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If my eyes were really big, would I see radio waves?

Considering an assertion that the fundamental difference between different ‘types’ of electromagnetic waves is frequency/wavelength, and larger antennas are needed for longer wavelengths, if my eyes ...
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Why do some electromagnetic waves continue travelling while others disappear?

Cosmic background radiation emitted when the Universe was very young still exists. But my wifi signal seems to disappear a short distance from my apartment. Why?
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What are the typical emissions of Jupiter's Aurorae?

I'm looking for some solid measurements of the full range of emissions from the Aurorae on Jupiter. I've found partial sets of data in the past which are most easily summarized here. As you can see, ...
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Why isn't most hydrogen in the universe molecular (diatomic), instead of atomic (monoatomic)?

Similar questions have been asked before; but, why? Is the monoatomic hydrogen left over from the Big Bang? And hasn't had the opportunity to collide with other hydrogen atoms yet? Or are hydrogen ...
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Spectrum of stars

If some specific metal is shown in a star's spectrum, does it indicate that the star has that specific metal? For example, the Sun, a G2 star, shows medium strength of Ionised Calcium in its spectrum, ...
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Does a photon need to have EXACTLY the right energy to be absorbed by a gas molecule?

From an answer to this question, https://physics.stackexchange.com/questions/281660/how-does-an-electron-absorb-or-emit-light, Absorption of a photon will occur only when the quantum energy of the ...
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If the Earth circled a red dwarf/giant or a brown dwarf, would its sky still look blue? [duplicate]

I have the impression that in brown dwarf and weak red dwarf systems, everything looks more reddish on a planet, including its atmosphere regardless of composition. Suppose there's a planet having an ...
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Missing line in solar spectrum

Referring to this answer to What's the rationale behind the false colours in solar observation photographs? which includes the table from Wikipedia's Fraunhofer lines: In the Table of wavelengths ...
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How to calculate the redshift of a line in a bunch of line spectra?

If in a spectra, there are many lines, mixed with gravitational redshift and non-redshift lines. For example, in this paper, they identify lines both redshifted and no-redshifted. Then how can i ...
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Do free protons and neutrons absorb much radiation? To affect astronomers' observations? If so, at what wavelength(s)?

In a plasma, or wherever, do the completely ionized nuclei commonly absorb much EM radiation? Or any free neutrons or protons? Can astronomers detect this? Enough so that astronomers take it into ...
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Would a red dwarf star resemble our own Sun at sunset to an observer on a nearby planet?

Suppose you're observing a red dwarf star at Noon from the surface of an Earth-like planet orbiting in the red dwarf's habitable zone, so that the red dwarf's luminosity is equal to our own Sun. Aside ...
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Why is blue light extincted more strongly than red?

We know that blue light suffers extinction more strongly than red (examples include ISM, atmosphere etc.), but why? Is it a property of the shorter wavelength itself? Can someone provide a conceptual ...
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Why is Ganymede's aurora only visible in ultraviolet while Earth's is bright green and red?

GANYMEDE AURORAE NASA's Hubble Space Telescope observed a pair of auroral belts encircling the Jovian moon Ganymede. The belts were observed in ultraviolet light by the Space Telescope Imaging ...
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Why do pulsars turn "off" from rotation?

I was looking at the Pulsar wikipedia article and I came across an interesting aspect that said pulsars turn off from rotation: When a pulsar's spin period slows down sufficiently, the radio pulsar ...
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