28 votes
Accepted

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 ...
  • 120k
18 votes
Accepted

Is any consensus forming on the solution to the "Lithium Problem"?

There is no absolute consensus and nothing proven beyond doubt, but there are favourite explanations. The discrepancy between the predicted big bang nucleosynthetic abundance of Lithium 7 and the ...
  • 120k
17 votes
Accepted

Problem regarding the absorption lines of the sun

Possibly you are labouring under the misapprehension that the number of photons is somehow a conserved quantity? That isn't true, there are more photons at any given wavelength when you are deeper ...
  • 120k
15 votes
Accepted

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 ...
  • 120k
13 votes
Accepted

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 ...
  • 34.2k
12 votes
Accepted

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 ...
  • 120k
12 votes
Accepted

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 ...
  • 4,754
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) ...
  • 2,328
11 votes
Accepted

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 ...
  • 120k
11 votes
Accepted

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 ...
  • 1,450
11 votes
Accepted

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 ...
  • 326
10 votes
Accepted

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 ...
  • 120k
9 votes
Accepted

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 ...
  • 120k
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 ...
  • 81
8 votes
Accepted

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 ...
  • 4,754
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 ...
  • 528
8 votes
Accepted

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 ...
  • 120k
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 RVS wavelength range, 847-874 nm, has been selected to coincide with the energy-...
  • 34.2k
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 ...
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 (...
  • 28.7k
7 votes
Accepted

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, ...
  • 120k
7 votes
Accepted

Why does Earth have a dip in the CO2 absortion spectrum from 14 to 16 micron?

Eric Jensen has already provided a nice link to a description of the basic structure of the ${\rm CO}_{2}$ spectrum, so I'll focus on the question of why there's a "spike" at 15.0 microns in ...
  • 14.9k
7 votes
Accepted

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 ...
  • 120k
7 votes
Accepted

Why would someone choose a lower resolution grating over a higher one when performing spectroscopy?

You are correct that using a more dispersive grating will spread your signal out more on the detector. Thus if you have a source with a set flux per unit wavelength interval, then a more dispersive ...
  • 120k
7 votes
Accepted

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 ...
  • 120k
6 votes
Accepted

Why do linear velocity redshifts correspond to linear pixel shifts when the spectra are binned in constant log wavelength?

All this means is that you need to bin your spectra in equal intervals of log wavelength for each pixel to be a constant interval in velocity. First consider the case whereeachpixel is worth a ...
  • 120k
6 votes

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

According to Cropper and Katz 2011 part 2.2, the RVS working group considered other bands, but the ~850 nm band is relatively unaffected by absorption in the Earth's atmosphere, facilitating ground-...
  • 16.9k
6 votes
Accepted

Are blue and red shift visible?

No, the blue and red shift of stars is not possible to detect with the naked eye. There are a couple of reasons for this. First the effect is slight: even for an object moving at thousands of km/s (...
  • 94.2k
6 votes

Solar visible light spectrum

When we look at spectral lines in a star's spectrum, we're actually looking for absorption lines, not emission lines. A star's spectrum usually resembles that of a black body, continuous and smooth. ...
  • 34.2k

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