# Tag Info

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Note You should clarify your statement from "...a charged particle cannot gain energy from a magnetic field..." to "...a charged particle cannot gain energy from a static magnetic field..." There is nothing wrong with energy transfer from time-varying magnetic fields. Background If the spatial gradient in the magnetic field is slow enough such that the ...

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The surface temperature of the star has no direct bearing on its metal content. Most stars in the immediate vicinity of the Sun have a very similar metal content. What you are talking about is how this metal content affects the observed spectrum of the star. If the star's photosphere is very hot then the metals become ionised and you don't see the (for ...

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I'll add a few more options for getting the ages of stars, beyond the HR diagram technique mentioned in Chris White's answer. If you can get a R=50,000 optical spectrum of a star with decent signal to noise ratio will quite easily give you the temperature (to 100K), surface gravity (to 0.1 dex) and metallicity (to 0.05 dex), plus a host of other elemental ...

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When calculating redshifts, we usually look for signature features in astronomical spectra, usually emission or absorption lines. For example, the universe contains lots of hydrogen. From quantum mechanics, we know that hydrogen has many different energy states which are fixed. This means it can only emit photons with a particular set of wavelengths (these ...

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No. If you go to a random spot in the visible universe, you will usually be far from any galaxies because the separation between galaxies is large compared to the size of the galaxies themselves. Since distant galaxies are so dim that we can't even see them, you certainly cannot see your reflection by them.

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Many spectral lines are very sensitive to the surface gravity of the star - which enables a distinction between dwarfs and giants, because a giant's surface gravity is factors of $\sim 100$ lower than that of a dwarf of the same temperature. The reason that surface gravity plays a role is via hydrostatic equilibrium; the densities and pressures in a gas ...

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While cnosam's answer is completely correct, I don't know if it really solves your confusion. The key point is that, when a photon is emitted, it knows nothing about the current size of the Universe. It is emitted at a very specific wavelength given by quantum mechanics, not by cosmology. Traveling through expanding space subsequently increases its ...

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In the case of the second order acceleration, two clouds are approaching, therefore the energy the charged particle gains comes from the energy of the clouds. In the case of the first order acceleration, the charged particle gains energy as it moves repeatedly through the shock front. The region before the shock front (upstream) moves at higher speed than ...

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Yes. This can be done (and is done typically) using systems of pulsars, especially in 'Pulsar Timing Arrays'. See for example https://en.wikibooks.org/wiki/Pulsars_and_neutron_stars/Using_pulsar_timing_to_study_(and_navigate)_the_solar_system. Pulsars (specifically millisecond pulsars, MSP) can be incredibly accurate clocks. Relative motion between the ...

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The key word, to answer your question, is wavelength, as in: which wavelengths are you interested in? So far, GRBs have been seen in all wavebands, from TeV down to radio frequencies (of course, not all GRBs have been observed at all frequencies). The waveband in which GRBs release most of their energy is, unsurprisingly, that of $\gamma$ rays, with hard ...

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