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Hot answers tagged spectra

28 votes
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Formation of elements in the Sun other than helium

The Sun is currently turning hydrogen into helium. There are no other nuclear reactions taking place at any significant rate in the Sun. The Sun will not start to make heavier elements until it ...
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16 votes

Why are wavelengths shorter than visible light neglected by new telescopes?

There are some technological issues to solve with putting any large telescope into space - and a space telescope is required at UV wavelengths. It is not possible to optimise such an instrument to ...
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15 votes

Why are wavelengths shorter than visible light neglected by new telescopes?

You're correct in that the sharp dropoff is simply because there are very few planned major telescopes operating in the UV range, whereas there are a substantial number planned in the infrared range. ...
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15 votes
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What happened to the reemitted photons during recombination?

There should indeed be emission lines at the appropriately redshifted frequencies. However, they are going to be incredibly faint and diluted because the ratio of photons to baryons at the epoch of ...
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13 votes
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Why does the Sun deviate from a typical blackbody spectrum in the S band?

There are other ways of getting emissions than just direct thermal radiation. Most of it happens through plasma interactions in the solar corona and atmosphere than in the chromosphere. This review ...
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12 votes

Why doesn't the Sun produce an emission spectrum?

The photosphere of the sun does produce an emission spectrum (a Planck spectrum according to its temperature of about 6000K). It is only that the atmosphere above the photosphere (the chromosphere) ...
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11 votes

Why does higher surface gravity broaden spectral lines?

In order to be in hydrostatic equilibrium, high surface gravity atmospheres have higher pressures at the same sort of temperatures. That means the density of atoms and ions is higher. If the particle ...
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11 votes
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Recording Spectral Lines at Home

Here is a link to a diffraction grating that can do what you want. It is mounted in a 1.25" filter ring that attaches to an eyepiece, or to most astro cameras. I believe they also sell adapters for ...
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10 votes
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Where can I find a database of galactic spectra?

The Sloan Digital Sky Survey Data Release 15 contains over 4 million spectra of both galactic and extra-galactic origin from the multi-fiber spectrographs. Of these spectra, 0.7 million came from the ...
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9 votes
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Why is the flux density and amplitude different for galaxies than stars?

A galaxy is obviously going to be much more distant than the stars. On the other hand the galaxy contains a lot of stars which will contribute to the overall spectrum. Whether the galaxy or a star ...
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8 votes

Which measurements have shown that 2014 MU69 is red? (New Horizons' next target)

This was a hard one to answer, primarily because of the difficulty in tracking down information. The Observations of MU69 The extended mission for New Horizons involved adjusting its orbit to do a ...
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8 votes

Clarification of radio spectrum terminology

Terminology The terminology of thermal and non-thermal emission is somewhat unfortunate. Formally, non-thermal emission is continuum radiation from particles with non-Maxwellian energy spectra. ...
7 votes

Is there evidence of super-heavy elements in the x-ray and gamma-ray spectrums of neutron stars?

The crusts of neutron stars will contain "super-heavy", neutron-rich nuclei. This is an inevitable consequence of the high density material, the accompanying degenerate electrons (that block $\beta$-...
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7 votes
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Identifying common galaxy spectral lines

You need to compare it with the spectrum of a similar galaxy at a known redshift, that would probably enable you to identify features with known rest wavelengths. If you can find such a template, ...
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7 votes
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Converting from $\mathrm{W \: m^{-2}}$ to $\mathrm{Jy \: km \: s^{-1}}$

You are essentially correct, but here's a more in-depth explanation: Both units are a measure of the total flux $F$ of a light source in some interval, e.g. a spectral line or a broader region given ...
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7 votes
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Why doesn't the Sun produce an emission spectrum?

The hotter layers above the solar photosphere do have an emission spectrum. The emission spectrum is much fainter than the visible photosphere and so is not easily seen through broadband filters in ...
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7 votes
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How to find the resolution of a spectrum?

You really need to find the resolution that the synthetic spectra were generated at. This isn't something you should be trying to find from the spectra themselves. From the Table you have shown, you ...
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6 votes

How do we know which elements are in a galaxy spectra?

Because the wavelength ratio of the lines remains constant despite any cosmological red shift. For example, if the redshift is $z$, all the lines are shifted redward in wavelength by a factor $(1+z)$....
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6 votes
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How do I understand a brown dwarf with a M-type spectrum?

The spectral type of an object is almost entirely determined by the temperature of its photosphere. ie Saying something is type M3.5 is just a measure of its surface temperature. An M3.5 brown dwarf ...
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6 votes

How to model and subtract nebular emission lines from stellar spectrum

In general, you can't. If obtaining spectra in regions where there is expected to be a spatially varying background then you either need to do long-slit spectroscopy so that you have a good ...
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6 votes
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How exactly will DESI simultaneously capture individual spectra from 5,000 galaxies using optical fibers?

You can probably get most if not all of your questions answered by perusing the main DESI web site, which I encourage you to check out. There is, for example, a nice video describing the assembly of ...
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6 votes
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What is the best database for identification of spectral lines?

There is the NIST Atomic Spectra Database where you could browse by elements. This the reverse approach, meaning that you have to first query element by element and then see which of the lines you ...
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6 votes
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Why are the wings of many strong lines, including hydrogen lines and most metal lines, stronger in Dwarfs than in Supergiants?

Collisional broadening - which includes van der Waals and Stark broadening - is more important in the higher gravity, higher pressure/density atmospheres of dwarf stars (a factor of 100-1000 higher ...
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What is an "arc" spectrum ?

An arc spectrum is one produced by a discharge lamp where the discharge is through ionised gas, in the case of He-Ar a mixture of Helium and Argon, which produces a predictable line emission spectrum. ...
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What is this graph showing?

This is a spectral energy distribution (SED). Since astronomical objects don't emit light a single frequency an SED tells you how much emission you're getting across a range of frequencies. "log" ...
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How to disentangle a very distant star's relative velocity vs. redshift distance

Conrad is almost right. It is true generally that if a Galaxy is close enough to take spectra of individual stars (e.g. luminous supergiants) then it is not far enough away to be regarded as part of ...
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5 votes
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Why are O III lines so prominent in the spectra of emission nebulae when the amount of oxygen relative to hydrogen is a million times smaller?

This is an excellent question. Think about the way in which emission happens. $\text{H}\alpha$ emission happens when an electron makes a transition from the third energy level to the second, emitting ...
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5 votes
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Can you identify a star's 'signature' from its spectroscopy?

Realistically, no - there are too many stars with the same spectrum. The pulsar idea is a good one, though. There is a reason our location relative to some bright pulsars was sent out on the Voyager ...
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Is there a far away probe that has recorded the light spectrum from Earth as if it were an exoplanet?

TL;DR: (1) we don't need to go very far to measure the spectrum of Earth's reflected light: a satellite in orbit around the Earth could easily do that; however, (2) detecting the reflected light of an ...
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How to differentiate elements that have same spectral lines in a star?

If you only had that single line, you would be unable to differentiate them. This is especially true of redshifted objects where we couldn't tell the actual wavelength of an isolated peak. But a ...
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