Questions tagged [spectra]

Questions about the observed frequency range of the electromagnetic radiation of a celestial object.

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

So, I know the sun is getting brighter over it's lifespan and I'm wondering how that affects its emission spectrum. The reason I'm asking this is because I find it weird that plants reflect green ...
Elhammo's user avatar
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22 votes
2 answers
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Why are wavelengths shorter than visible light neglected by new telescopes?

The diagram below, which I stole from this post by @HDE226868, shows that angular resolution as a function of wavelength suddenly drops by three orders of magnitudes from visible to UV-light. The ...
LocalFluff's user avatar
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15 votes
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Formation of elements in the Sun other than helium

I just learned that the Fraunhofer lines of the Sun's spectrum indicate that the Sun contains various elements other than just hydrogen and helium (for example, Na and Fe) but don't the Sun's p-p ...
Jack the Ranger's user avatar
14 votes
1 answer
898 views

What happened to the reemitted photons during recombination?

To my understanding, the Cosmic Microwave Background Radiation (CMBR) is light released during the recombination epoch where the formation of neutral hydrogen atoms allowed for a sudden drop in the ...
YiFan's user avatar
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13 votes
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How to detect emission lines in optical spectra?

Is there any handy module to detect emission lines in a spectrum like one we get from the Sloan Digital Sky Survey (SDSS)? You can see there are many emission lines like Ha,OI in the spectrum below. ...
questionhang's user avatar
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13 votes
1 answer
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What is the Lyman Alpha forest Used For?

The Lyman-alpha forest is an interesting feature found in the spectra of sufficiently distant objects. This series of absorption lines extends over a range of frequencies, and are a result of the ...
astromax's user avatar
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10 votes
1 answer
939 views

Recording Spectral Lines at Home

I was wondering if it would be possible to record the emission/absorption spectra of stars without expensive spectroscopy equipment. Would it be possible to somehow utilize diffraction grating? I own ...
N. Bar's user avatar
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9 votes
1 answer
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Why does the Sun deviate from a typical blackbody spectrum in the S band?

This is sort of a follow-up to this question, and my answer to it. The graph I see here details the radio (and other frequencies) emission of the sun. What's most notable and interesting to me is the ...
Calc-You-Later's user avatar
9 votes
2 answers
674 views

Typical wavelength of solar flare

I read that solar flares are customarily viewed in H-alpha light, as a temporary brightening of a small portion of chromosphere. What all can be interpreted from this? Is it because, energy of the ...
seeking_infinity's user avatar
8 votes
2 answers
789 views

How exactly will DESI simultaneously capture individual spectra from 5,000 galaxies using optical fibers?

The BBC News article Telescope tracks 35 million galaxies in Dark Energy hunt says: The aim of the five-year programme is to shed light on Dark Energy - the mysterious force thought to drive an ...
uhoh's user avatar
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7 votes
4 answers
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Why doesn't the Sun produce an emission spectrum?

I have read that the reason why the Sun produces an absorption spectrum is because the temperature drops as you go away from the center, such that as the various layers of the atmosphere of the sun ...
Physics2718's user avatar
7 votes
1 answer
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Why does higher surface gravity broaden spectral lines?

It's always made intuitive sense to me that a higher surface gravity leads to broader spectral lines from a star, but yesterday I realized that I don't have a physical explanation for why this is so. ...
NeutronStar's user avatar
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7 votes
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Converting from $\mathrm{W \: m^{-2}}$ to $\mathrm{Jy \: km \: s^{-1}}$

Suppose I observe a spectral line with rest frequency $\nu_0$ and integrated flux density $F = 10^{-26} \mathrm{W/m^2}$. Is the following line of reasoning correct? $1 \: \mathrm{Jy} = 10^{-26} \: \...
Framazu's user avatar
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7 votes
1 answer
138 views

Have we detected spectra of exotic atoms in stars?

I was reading this wikipedia article on positronium (a type of exotic atom) and noticed it mentioned that positronium has a spectra (of course). So naturally this makes me wonder, have we looked at ...
Sidharth Ghoshal's user avatar
7 votes
1 answer
436 views

Strong orange line in wood fire spectrum?

I just built a DIY spectroscope using a CD and after making some tests, I noticed a really strong emission line located in the orange-yellowish zone of the fire spectrum (specifically, burning wood). ...
Jotarata's user avatar
7 votes
1 answer
4k views

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?

Looking at spectra of emission nebulae like the Lagoon Nebula, the $[\text{O III}]$ lines are prominent in intensity. However, the abundance of oxygen is minuscule compared to hydrogen. How then are ...
Arvind H's user avatar
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7 votes
1 answer
326 views

How do amateur astronomers do stellar spectroscopy?

This question consists of 2 parts: How can amateur astronomers measure the spectrum of stars? In addition to diffraction gratings, what equipment do they use (like telescopes, and the focal length ...
user avatar
6 votes
3 answers
1k views

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

On the latest solar images from NASA, there is one picture lablled "continuum 4500 Å". There are bands diagonally in the picture as well. What is the ...
not2qubit's user avatar
  • 225
6 votes
2 answers
1k views

What is the best database for identification of spectral lines?

What is the best database for the identification of spectral lines? For instance, I have a red spectrum of A0 star and I would like to recognize the most prominent lines, where to find them? Many ...
Elena Greg's user avatar
6 votes
1 answer
821 views

Where can I find a database of galactic spectra?

I was wondering where spectra of galaxies at various redshifts are to be found. I'm looking for ones that can be used to find the recessional velocity of the galaxy and eventually the Hubble Constant. ...
Pedro de Oliveira's user avatar
6 votes
1 answer
374 views

Natural line width from absorption lines

Emission lines have a certain natural width. Due to the uncertainty principle systems that spontaneously decay or produce radiation have a fundamental energy blur, and their radiation has a ...
trynerror's user avatar
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6 votes
3 answers
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Is it practical to build a DIY spectroscope that can clearly show absorption lines in a spectra of the Sun?

Is it practical to build a DIY spectroscope that can clearly show absorption lines from the Sun? "Practical" means that the kit can be made at home or relatively cheaply bought (less than £...
Slarty's user avatar
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6 votes
1 answer
183 views

Clarification of radio spectrum terminology

For a radio spectrum, when is it called thermal emission, synchrotron emission, self-absorbed synchrotron emission and inverted spectrum? They are all power-law and their difference is power-law index?...
questionhang's user avatar
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6 votes
2 answers
873 views

Temperature gradient in stars

It is a well known fact that in stars, there exists a temperature gradiënt. The observational reason is because we perceived spectral lines in the otherwise continuous spectrum of a star. If this ...
Einsteinwasmyfather's user avatar
6 votes
1 answer
304 views

How does the black hole at the center of M87 look like in the visible spectrum?

I learned here that the picture of the black hole we saw all over the news was a false color image, based on the radio spectrum emissions. How would the black hole at the center of M87 look like when ...
asmani's user avatar
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6 votes
1 answer
187 views

Do narrow lines in the spectra of O- and B- type stars always indicate magnetic fields?

I was reading a paper on the differential emission measures of a set of hot O- and B- type stars. As the authors discuss in Section 3 (page 959), two stars, $\tau$ Sco and $\theta^1$ Ori C, have ...
HDE 226868's user avatar
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5 votes
2 answers
314 views

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

The recent NASA feature article New Horizons: Possible Clouds on Pluto, Next Target is Reddish MU69 is actually the smallest KBO to have its color measured – and scientists have used that data to ...
uhoh's user avatar
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5 votes
1 answer
494 views

Why is the flux density and amplitude different for galaxies than stars?

This might be a simple question, but I'm having a hard time answering it myself - or at least answer it correctly, I think. I'm sitting with different spectrals; many for stars and one for a galaxy. ...
JohnGoodWill's user avatar
5 votes
2 answers
656 views

How to find the resolution of a spectrum?

I have been tasked to find the spectral resolution of some synthetic spectra (wavelength in Angstroms vs. flux) of different stars and degrade them to the resolution of observed spectra. But I am not ...
SaptarshiS's user avatar
5 votes
1 answer
108 views

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

It occurs to me, that between the surface and interior of neutron stars, gravitational pressure might produce super-heavy elements and that signatures of such elements might be detectable in the star'...
Ronald Swager's user avatar
5 votes
1 answer
314 views

How to extract galaxy spectra for different radii in Python for spectra taken by long slit spectrograph?

I am trying to extract the kinematics from the elliptical galaxy NGC 4697 using the Fourier Correlation Quotient (FCQ) algorithm described by Bender (http://adsabs.harvard.edu/full/1990A%26A...229.....
trynerror's user avatar
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5 votes
1 answer
459 views

Why are the wings of many strong lines, including hydrogen lines and most metal lines, stronger in Dwarfs than in Supergiants?

What is the reason? Is it because Dwarfs have higher surface gravity (log g), in turn related to pressure, than Supergiants so there is more contribution from van der Waals and Stark broadening?
Jay D's user avatar
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5 votes
1 answer
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What is an "arc" spectrum ?

I sometimes hear about astronomers using an arc spectrum to calibrate observations. For example a "He-Ar arc spectrum". What is an "arc" in this context? I assume it's nothing got to do with angles (...
Realta's user avatar
  • 51
5 votes
1 answer
107 views

What is the physical interpretation of the derivative of the emitted and observed wavelength?

The flux F of an event at redshift $z$ is related to its luminosity L as $$F=\dfrac{L}{4\pi d_L^2}\,,$$ where $d_L\equiv d_L(z)$ is the luminosity distance between us (the observer) and the event (...
Catarina Alves's user avatar
5 votes
1 answer
148 views

What leads an observer to choose a narrow slit over a wide one (and vice-versa) when observing?

In spectroscopy, a wide slit will lead to lower spectral resolution while too narrow of a slit will reduce incoming flux from the object. From what I read, it appears as though there is always a ...
Astroturf's user avatar
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5 votes
1 answer
465 views

Understanding better the factors on $C_l$ in Angular power spectrum and Relation with Matter power spectrum

I am looking for an explanation on the angular power spectrum. I found this extract that is interesting but not fully understood for me (I will cite the step that I didn't understand) "what is ...
user avatar
5 votes
1 answer
338 views

How to remove redshift from galaxy spectra in Python?

Hello I extracted a spectrum from the central region of the 2D spectrum of the major axis from NGC 4697 (I just took a central row in the 2D data set, see this question for more information: How to ...
trynerror's user avatar
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5 votes
1 answer
1k views

How do you estimate the error on the height/width of a Gaussian?

I'm trying to fit Gaussians to several lines in a spectrum that I have. Some of them overlap with one another, causing the fitting program that I'm using to not be able to give reasonable estimates ...
Sam V's user avatar
  • 151
4 votes
3 answers
353 views

Spectrum of stars

If some specific metal is shown in a star's spectrum, does it indicate that the star has that specific metal? For example, the Sun, a G2 star, shows medium strength of Ionised Calcium in its spectrum, ...
Jack the Ranger's user avatar
4 votes
1 answer
369 views

Identifying common galaxy spectral lines

How does one identify the common galaxy absorption lines (e.g. Na, Mg, K, etc.) and emission lines (H-alpha, O III, S II, etc.) by just looking at a galaxy spectrum (like the one below)? I need to ...
RUNN's user avatar
  • 165
4 votes
2 answers
287 views

How to disentangle a very distant star's relative velocity vs. redshift distance

We measure a star's relative velocity towards or away from us via its Doppler-shifted spectrum. This is also how we measure the distance of very distant stars: measuring the shifts in the spectrum ...
jvriesem's user avatar
  • 652
4 votes
1 answer
509 views

Has the new type II supernova SN 2023ixf's subtype been determined yet, and is a tentative light curve possible? Is it still getting brighter?

Wikipedia's article on SN 2023ixf begins: SN 2023ixf is a type II (core collapse) supernova located in the Pinwheel Galaxy (M101). It was first observed on May 19, 2023 by Koichi Itagaki and ...
uhoh's user avatar
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4 votes
1 answer
103 views

How to model and subtract nebular emission lines from stellar spectrum

I have optical stellar spectra from a star forming region with spatially varying nebular background. I want to subtract the nebular lines from the stellar spectra (which are varying in intensity from ...
pziphi's user avatar
  • 71
4 votes
2 answers
2k views

Why don't we see purple stars

I know that we don't see green stars because in blackbody radiation star doesn't produce one spectrum. The stars that have peaks in the green spectrum produce other spectrum in nearly same amout. ...
Ro Theory's user avatar
  • 169
4 votes
2 answers
712 views

What causes the Balmer Jump?

To quote Wikipedia: Balmer Jump is caused by electrons being completely ionized directly from the second energy level of a hydrogen atom (bound-free absorption), which creates a continuum absorption ...
Hika's user avatar
  • 43
4 votes
2 answers
1k views

When examining an exoplanet's atmosphere is the star's emission spectra or planet's light used?

My understanding of the main method we use to figure out an exoplanet atmosphere composition is that when a exoplanet transits their sun, visible light passes through the planet's atmosphere, and ...
Hash's user avatar
  • 503
4 votes
1 answer
2k views

How to correct observed flux densities for redshift

Say I have a spectrum of a galaxy at a redshift $z$, in flux density units of erg/s/cm^2/Angstrom. I'd like to recover the spectrum (in the same flux density units) at z=0, i.e. at its rest ...
curious_cosmo's user avatar
4 votes
1 answer
1k views

In galaxy optical spectra, why are Hbeta and Hdelta sometimes absorption lines?

I've heard that $\mathrm{H\beta}$ and $\mathrm{H\delta}$ lines in galaxy spectra might be either emission lines or absorption lines, is that correct? From Wikipedia, Balmer lines are usually emission ...
Chris's user avatar
  • 161
4 votes
1 answer
208 views

How long do hot X-ray sources last?

Some X-ray sources in nebulae are caused by hot materials in the millions of degrees that formed in supernovae. What's the cooling rate of this stuff? How long does it stay this hot? If we would take ...
Gimelist's user avatar
  • 183
4 votes
0 answers
58 views

How are plage regions related to the density of medium and velocity FeII ions?

During a literature review (abstract), I found that the intensity of FeII (298.5 nm) ions in the last solar minimum was higher than the two previous solar minima 21 & 22. The velocity of FeII ions ...
Autodidact's user avatar