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29 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 ...
ProfRob's user avatar
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17 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 ...
ProfRob's user avatar
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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. ...
HDE 226868's user avatar
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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 ...
ProfRob's user avatar
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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 ...
Anders Sandberg's user avatar
13 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) ...
Thomas's user avatar
  • 3,504
13 votes

Did the Sun's light always peak in the green wavelengths?

Nice question! Sun's spectral peak wavelength is currently 483 nm which falls under the category of green. Sun's wavelength changing In it's early days, the Sun was a lot cooler than it is today. So ...
Arjun's user avatar
  • 1,474
12 votes

Did the Sun's light always peak in the green wavelengths?

No, but that's not why plants reflect green light The Sun, as well as the light of nearly all stars in the universe, had their peak wavelengths shift at some point during their life. In the case of ...
Alastor's user avatar
  • 2,668
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 ...
ProfRob's user avatar
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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 ...
amateurAstro's user avatar
  • 1,780
11 votes

What is the meaning or information given by the solar image at 4500Å?

The 4500Å images (in the blue part of the visible light spectrum) are designed to show the Sun's visible "surface" or photosphere. I'm not 100% sure, but by the looks of it, the banding and ...
Matt Pitkin's user avatar
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 ...
astrosnapper's user avatar
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10 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 ...
pela's user avatar
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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 ...
ProfRob's user avatar
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9 votes
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Natural line width from absorption lines

The natural linewidth also causes absorption lines to be broadened in exactly the same way. Usually, the natural linewidth is far narrower than the width caused by (i) Doppler broadening by thermal ...
ProfRob's user avatar
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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 ...
zephyr's user avatar
  • 15k
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. ...
William Miller's user avatar
8 votes
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What objects in the night sky have the narrowest range of visible light

...the narrowest spectrum of visible light... is tough because most process that make electromagnetic radiation either result in broad continua or multiple emission lines. I originally wanted to ...
uhoh's user avatar
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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 $\beta$-...
ProfRob's user avatar
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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, ...
ProfRob's user avatar
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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 ...
ProfRob's user avatar
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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 ...
ProfRob's user avatar
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7 votes
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Supernova remnant spectral lines

I would go to the AtomDB and then look for lines with high emissivity in a specific wavelength region. So under "List lines in wavelength region:" select a not too wide energy band and play ...
SpaceCore's user avatar
  • 3,441
7 votes

Did the Sun's light always peak in the green wavelengths?

One more reference for why plants are green is Quieting a noisy antenna reproduces photosynthetic light harvesting spectra (2020). They compute the optimal absorption frequencies for a noise-...
Daniel Darabos's user avatar
7 votes

Is it practical to build a DIY spectroscope that can clearly show absorption lines in a spectra of the Sun?

Yes, you can make a spectrograph using little more than an unwanted DVD disc and a cereal box. If you are careful enough and look at the second order diffracted spectrum then the Fraunhofer lines can ...
ProfRob's user avatar
  • 155k
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 ...
ProfRob's user avatar
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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 ...
ProfRob's user avatar
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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 ...
Peter Erwin's user avatar
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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 ...
B--rian's user avatar
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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 ...
ProfRob's user avatar
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