44 votes
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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 ...
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17 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 ...
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17 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 ...
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11 votes
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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 ...
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9 votes
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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8 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 ...
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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 ...
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6 votes
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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 ...
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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....
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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) &...
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4 votes
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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 ...
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4 votes
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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 ...
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4 votes
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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 ...
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3 votes
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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 ...
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3 votes
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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,...
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3 votes

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

I'd say there are fewer M stars on list because they are least bright. they may outnumber other star types but only nearest ones would make list of brightest stars. Type O stars are rare hence the ...
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  • 4,336
3 votes

B-V to U-B colour index

Both $B-V$ and $U-B$ are a reflection of how hot the surface of a star is. To first order (inhomogeneous surface temperatures do exist) this has a single value for a given stellar photosphere and so ...
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3 votes
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Stellar electromagnetic signatures

The spectrum of a star is almost certainly a unique fingerprint. Even though stars are born in clusters, formed from the reasonably chemically homogeneous environment of a giant molecular cloud, there ...
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2 votes

Compare this planet to Earth and determined its habitability (can humans live in this environment?)

A very low mass M-dwarf (what you have there is something like an M5-M6 dwarf) will remain a highly magnetically active star for several billion years. As such, the spectrum of light from such an ...
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2 votes

Stellar electromagnetic signatures

Even the optical spectrum alone has lots of goodies. In addition to chemical abundance, size, and other outer properties from emission and absorption lines you can get the rotational rate from a ...
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2 votes
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Why is TiO special?

TiO is used as a sunscreen, it has high absorption and emittance rates and a high radiation potential. SiO2 is used for fiber optic cables and probably deflects and transmits photons a lot more, and ...
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2 votes

Is there a relationship between stars' absolute magnitude, spectral class and relative location in a cluster?

Stars born together in clusters have more-or-less the same age. As a rule of thumb, any spread in age, measured in millions of years, is smaller than the extent of the cluster in parsecs. For most ...
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