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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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18 votes
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Problem regarding the absorption lines of the Sun

Possibly you are under the misapprehension that the number of photons is a conserved quantity? That isn't true, there are more photons at any given wavelength when you are deeper into the star because ...
ProfRob's user avatar
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18 votes
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How would a person know if a planet is orbiting a binary star?

The light from the two stars would be Doppler shifted in a sinusoidal pattern (for a circular orbit). The signals from the two stars would be in anti-phase and would oscillate at the orbital period of ...
ProfRob'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

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
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13 votes
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What does "Effective radius of [CII] line is 1.4 kpc" mean?

Defining the radius As the surface brightness (SB) of extended objects does not reach zero at some well-defined radius, we need a measure to be able to compare various objects. Probably the most used ...
pela's user avatar
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13 votes

How accurate is astronomical spectroscopy?

We all know that green is a mixture of blue and yellow, and that purple is a mixture of red and blue. Only humans (and other animals with human-like color perception) know that. For a spectrometer a ...
jpa's user avatar
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12 votes
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Why is $H_\delta$ prominent in type A stars?

H$\delta$ absorption is formed when hydrogen in the level $n=2$ is excited to $n=6$. To get strong H$\delta$ absorption lines you need large amounts of hydrogen in the first excited state $n=2$ and a ...
ProfRob's user avatar
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12 votes
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Blue color of ion (plasma) comet tails

Close, but not quite right - the blue light is indeed emission from CO$^+$, but it's from the CO$^+$ ions themselves, with no need for recombination to CO; that (ionized) molecule has a strong set of ...
Eric Jensen's user avatar
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12 votes
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Using optical fibers in astronomy

There is already a good answer that has been upvoted and accepted. I also upvoted that answer right after I posted. But maybe I can make a helpful contribution. In an answer I posted here, I showed ...
Ed V's user avatar
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11 votes
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Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

The Ca triplet in the near infrared are extremely strong resonance absorption lines. They are by far the strongest features in the near infrared spectra of cool G,K,M type dwarfs and giants, which ...
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
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10 votes
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What is the temperature of the solar atmosphere (the corona) and how is it measured?

This is a rather broad question and this will not be a fully comprehensive answer. There is no single temperature to the solar corona. The coronal temperature varies by an order of magnitude from ...
ProfRob's user avatar
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10 votes
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How do astronomers calibrate the intensity scale of their spectrometers?

This can be done in a number of ways. There is a "theoretical" approach, where the transmission and reflection characteristics of all the components are measured in the lab and put together ...
ProfRob's user avatar
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10 votes
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Does the luminosity of a star have the form of a Planck curve?

Radiant intensity depends on both the the (effective) temperature and emitting area of the star. If the spectrum can be represented as a blackbody, then the radiant intensity is proportional to $R^2 T^...
ProfRob's user avatar
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10 votes

How has the resolution of astronomical spectrographs improved over time?

There are probably two aspects to this. First, is there a progression in the technological capability to produce spectrographs that are of higher and higher resolution - almost certainly. Second, is ...
ProfRob's user avatar
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10 votes
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Does the expansion and contraction of a variable star affect the measured radial velocity?

The radial velocity variations of beta Cep were discovered by Frost (1902) using a spectrograph with photographic plates. The amplitude of the variations was approximately what you have measured. ...
ProfRob's user avatar
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10 votes

Where in a star are the spectral absorption lines formed?

It depends on the size of the star's subphotospheric convection zone and the speed of other (non-convective) mixing processes. Absorption lines are formed in the photosphere, a thin (few hundred km) ...
ProfRob's user avatar
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9 votes
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Was the discovery of six exoplanets around one star as "easy" as counting six peaks in the FT?

I suspect that the record holder (as of 14/2/2017) is HD 10180 which has at least 7 planets and possible evidence for as many as 9. Lovis et al. (2011) announced the initial discovery based on 190 ...
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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9 votes

Star surface temperature?

Yes, there are different relationships between effective temperatures and different colours. That is because the various filters sample different wavelength regions of the stellar spectrum. You can ...
ProfRob's user avatar
  • 153k
8 votes

Why N$_2$ is a non-absorbing species in the spectrum of the Earth?

As your question is based on the plot you posted, I suggest you to look for a lower wavelength range of the atmospheric electromagnetic absorption. A quick search in google gave me this paper, which ...
SebaGM's user avatar
  • 81
8 votes
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How do astronomers detect the 'metals' in a star? If the atoms are presumably completely ionized?

You are correct that the characteristic emission and absorption lines we see in stars' spectra are from electrons that are bound to atoms making transitions between different energy levels. That is ...
Eric Jensen's user avatar
  • 4,894
8 votes

Phosphine on Venus?

Essentially what they did was assume that normally when observing with their telescope the spectral absorptions they see are due to the Earth's atmosphere. Which is a pretty good assumption. They then ...
Patrick's user avatar
  • 528
8 votes
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How can I calculate the luminosity and mass of a star only knowing it's peak wavelength and it's subtended angle?

The only star subtending an angle of 32 arcminutes at the Earth is the Sun! The angular size combined with the orbital separation of the Earth from the Sun gives its radius. The peak wavelength gives ...
ProfRob's user avatar
  • 153k
8 votes

Where in a star are the spectral absorption lines formed?

In principle, assuming that there are not already substantial amounts of an element present, there is actually only a relatively small amount of mass required to produce an absorption line. Absorption ...
Thomas's user avatar
  • 3,494
7 votes

Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

The ESA states it pretty clearly (although their figure of 855.2 nm is incorrect; it should be 866.2 nm): The RVSĀ wavelength range, 847-874 nm, has been selected to coincide with the energy-...
HDE 226868's user avatar
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7 votes

Can some stars not emit any energy in the visible spectrum?

Light that is not light That's meaningless. All light is electromagnetic radiation. A finite part of the infinitely large range of the electromagnetic spectrum is visible light. So you should talk ...
StephenG - Help Ukraine's user avatar
7 votes
Accepted

What forces expelled these huge clouds, then blocked further progress, yet allowed it to maintain its threads?

This was a coronal mass ejection. Those 1973 astronomers weren't looking at the picture correctly. They didn't have the tools at that time to look at the picture correctly. Coronal mass ejections (...
David Hammen's user avatar
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