45 votes
Accepted

Do we know a star that is similar to the Sun when it would be a red giant?

Models for the future behaviour of the Sun do vary, mainly as a result of uncertainty of mass loss during the red giant (H shell burning) and asymptotic red giant (H+He shell burning) phases. A ...
ProfRob's user avatar
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18 votes
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Are main-sequence G9 stars habitable?

Stars themselves are not "habitable", but any star could have a "habitable zone". Generally the term "habitable zone" refers to the zone around a star in which water ...
James K's user avatar
  • 121k
16 votes

Do we know a star that is similar to the Sun when it would be a red giant?

Arcturus is a RGB star, probably fairly similar how the Sun will look when it becomes a red giant. Arcturus is slightly more massive than the Sun ($m_{\rm Arc}=1.08 m_{\odot}$), but the main ...
AtmosphericPrisonEscape's user avatar
16 votes

Spectral class and luminosity of hydrogen bomb explosions?

Hydrogen bombs aren't like little stars. The process of fusion in stars is slow, releasing very little energy per cubic metre. As a result of this, and their large scale, stars are close to ...
ProfRob's user avatar
  • 152k
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
  • 1,256
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
  • 2,659
11 votes
Accepted

Can someone explain this diagram showing the spectral type distribution of bright stars

It's all to do with the relationships between mass, spectral-type and luminosity and the initial mass function of stars. I think your explanation of points 1 and 2 are completely correct. O and B ...
ProfRob's user avatar
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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^...
ProfRob's user avatar
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9 votes
Accepted

What spectral type of star has an absolute magnitude of exactly 0?

There isn't a one-to-one relationship between spectral type and absolute magnitude. Instead, there is a mean relationship with a fair bit of scatter around it. The reason is that the luminosity of a ...
ProfRob's user avatar
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9 votes
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How does a star's rotation affect a star on the main sequence?

This is a well-studied problem. The effect of rotation on the structure of a low-ish mass star (like the Sun) is summarised by Eggenberger (2013). Such stars are never observed to rotate so fast that ...
ProfRob's user avatar
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9 votes
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How do I say the luminosity class aloud?

The luminosity classes are indicated by Roman numbers. So you pronounce them as numbers if you don't spell out the actual name of the luminosity class you are referring to. Pronouncing them as letters ...
planetmaker's user avatar
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9 votes
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Convert from spectral type to RGB color?

Below is a model taken from Mitchel Charity's page, What color are the stars? Other points, if required, may be obtained by interpolation. There are plenty of caveats with this and you should ...
James K's user avatar
  • 121k
8 votes
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Would a red dwarf star resemble our own Sun at sunset to an observer on a nearby planet?

Your question may ulitmately be about the physiology of the eye, which is off-topic here. The spectrum of the Sun seen low on the horizon is quite different to the spectrum of an M-type red dwarf. The ...
ProfRob's user avatar
  • 152k
8 votes

How do I say the luminosity class aloud?

Usually when spoken aloud, you say the actual description of the class, e.g. "main sequence", "giant", "sub-giant", and so on. In this case you would say "Em four ...
Kyle's user avatar
  • 421
7 votes

What spectral type of star has an absolute magnitude of exactly 0?

A star with magnitude 0 would be 85 times brighter than the sun (since Magnitude=-2.5 log(Luminiosity)) Referring to the H-R diagram on Wikipedia shows that there is quite a range of spectral types ...
James K's user avatar
  • 121k
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
6 votes
Accepted

Is there an O1 or O0 star?

This is what Wikipedia says about it: When the MKK classification scheme was first described in 1943, the only subtypes of class O used were O5 to O9.5. The MKK scheme was extended to O9.7 in 1971 ...
Glorfindel's user avatar
  • 4,790
6 votes

Reason for different surface temperatures of Tau Ceti and Epsilon Indi at similar properties

Metallicity (or the fraction of things other than Hydrogen or helium) If you look on the Wikipedia page it points out that Tau ceti is metal deficient ([Fe/H] = -0.55) and Epsilon Indi has [Fe/H] = -0....
Rob's user avatar
  • 2,035
6 votes

Why the Sun is white if it is G2?

Although the emission peak of light in the solar spectrum is more or less in the yellow-green part of the visible spectrum, it also emits a lot of red and blue light, and about the same quantity. ...
JOAQUÍN HERNÁNDEZ's user avatar
5 votes

How would the characteristics of a habitable planet change with stars of different spectral types?

The following table gives the mass, radius, temperature, and luminosity of an average star of several selected spectral types: $$\begin{array} {d|c|c|} \text{Spectral Type} & \text{Mass} (\odot) &...
user177107's user avatar
  • 2,689
5 votes

Is WASP-12 a F-type star or a G-type star?

There is actual variation in the literature. The WASP team announcement of the discovery of a planet states "the host star is a supersolar metallicity ([M/H] = 0.3+0.05–0.15), late-F (Teff= 6300+...
James K's user avatar
  • 121k
4 votes
Accepted

Are the sub-spectral types (1,...9) based on temperature or spectral lines?

The spectral classes (O, B, A, F, G, K, M) and their 10 subtypes (0 to 9) were initially meant only as differentiators of spectral type. Annie Jump Cannon was the creator of this system. Through her ...
Calc-You-Later's user avatar
4 votes
Accepted

Why is the Sun less massive than other G2V stars?

It isn't. You've just got dodgy table from wikipedia. A more modern (and well-used) version is here. It lists G1V 1.07 5880 G2V 1.02 5770 G3V 1.00 5720 This is an average relationship. The closest ...
ProfRob's user avatar
  • 152k
4 votes
Accepted

Strange spectral types in star catalogs

Wikipedia has a pretty comprehensive list of all these peculiarities and their meaning. Spectral classification also is not always unique or unambiguous. "/" denotes stars which could be ...
planetmaker's user avatar
  • 19.4k
4 votes

Stellar classification spectral lines: chemical abundance vs temperature

Both explanations are right. The strength of an absorption line does depend on the abundance of a chemical element in the photosphere. But it also does depend on the temperature of the photosphere. ...
ProfRob's user avatar
  • 152k
4 votes

Are main-sequence G9 stars habitable?

Another way to find the limits of the habitable zone of a star is to find the ratio between the star's luminosity and that of the Sun. Some sources give the luminosity of a star in units of solar ...
M. A. Golding's user avatar
3 votes
Accepted

What does the "a" at the end of a spectral type mean?

If present, an a (or b or ab) do not refer to spectral peculiarities but are part of the luminosity class definition explained further up on the page. Occasionally, letters a and b are applied to ...
planetmaker's user avatar
  • 19.4k
3 votes
Accepted

Determine spectral type of star from its properties

There are no exact boundaries in temperature, luminosity, surface gravity etc. for spectral classes because the classification system works in a different way - it is fundamentally an empirical system,...
Eric Jensen's user avatar
  • 4,864

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