29
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 ...
- 146k
18
votes
Accepted
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 ...
- 146k
17
votes
Accepted
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 ...
- 146k
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 ...
- 146k
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 ...
- 37k
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 ...
- 1,600
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 ...
- 146k
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 ...
- 4,864
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) ...
- 2,867
12
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 ...
- 336
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 ...
- 146k
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 ...
- 1,565
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 ...
- 146k
10
votes
Accepted
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 ...
- 146k
10
votes
Accepted
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 $R^2 T^...
- 146k
10
votes
How has the resolution of astronomical spectrographs improved over time?
There are probably two aspects to this. First, is there a progression in the technological capability to produce spectrographs that are of higher and higher resolution - almost certainly. Second, is ...
- 146k
9
votes
Accepted
Was the discovery of six exoplanets around one star as "easy" as counting six peaks in the FT?
I suspect that the record holder (as of 14/2/2017) is HD 10180 which has at least 7 planets and possible evidence for as many as 9.
Lovis et al. (2011) announced the initial discovery based on 190 ...
- 146k
9
votes
Accepted
Natural line width from absorption lines
The natural linewidth also causes absorption lines to be broadened in exactly the same way.
Usually, the natural linewidth is far narrower than the width caused by (i) Doppler broadening by thermal ...
- 146k
9
votes
Star surface temperature?
Yes, there are different relationships between effective temperatures and different colours. That is because the various filters sample different wavelength regions of the stellar spectrum.
You can ...
- 146k
8
votes
Why N$_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 ...
- 4,864
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 ...
- 146k
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-...
- 36k
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 ...
- 5,966
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 (...
- 33.5k
7
votes
Solar visible light spectrum
What you're missing is that the resolution of a prism isn't high enough to resolve the relatively narrow spectral lines. What's more, the light that gets generated by fusion reactions doesn't reach ...
- 2,946
7
votes
What is the difference between emission line and recombination line?
A recombination line is a special case of an emission line.
Emission lines
An emission line is any spectral feature that rises above the continuum — i.e. the average amplitude of the spectrum (in ...
- 37k
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, ...
- 146k
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