8

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 reason that a red dwarf is red, is not just that it is cool, but that there are great chunks of the spectrum that are absorbed by molecules in the photosphere ...


8

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 star of a given effective temperature depends on its composition/metallicity and how far along in its main sequence lifetime it is. Basically, late B-type main ...


6

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 and O4 in 1978, and new classification schemes that add types O2, O3, and O3.5 have subsequently been introduced. It references the paper A New Spectral ...


6

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 possible with this luminosity: from B type main sequence stars, and A type sub-giants, such as 4 Sco There are also G and K and M type Giant stars with this ...


4

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) & \text{Radius} (\odot) & \text{Temperature (K)} & \text{Luminosity} {(\odot)} \\ \hline \text{M8V} & \text{0.082} & \text{0.111} & \...


4

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 and most consistent relationship will be between spectral type and effective temperature and indeed the Sun is normally attributed a spectral class of G2V and $...


3

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 luminosity classes other than supergiants; for example, a giant star slightly less luminous than typical may be given a luminosity class of IIIb, while a ...


3

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 work for/with Edward Pickering, she ended up classifying nearly a third of a million stars over a few decades. She (and many others) did not realize that this ...


3

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, with classification based only on the appearance of features in the spectra. The Yerkes or Morgan-Keenan (MK) system is based only on a set of standard stars ...


2

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 stellar clusters, smaller than a few pc, the only chance of measuring age differences occurs in the first 10 million years of life. There is no evidence for age ...


1

Just to add an example to what has already been said by eshaya and Larz.Astro. Here is the spectrum of the Black Hole binary Cygnus X-1 in its hard and its soft state. The plot is taken from Gierlinski et al. 1999 . You see that the soft state consist of mostly thermal emission below 10 keV, while the hard state is dominated by non-thermal (comtonized) ...


1

Not only in X-ray astronomy (chemistry also and pretty much everything related to X-rays). If you have an X-ray spectrum, the region with photon energy > 5-10 Kev is called "hard" X-rays, less than that it is called "soft" X-rays. Wiki has a nice explanation for that (Energy Ranges): https://en.wikipedia.org/wiki/X-ray However, I find ...


1

Active galaxies are known to change state as seen by a change in slope of their X-ray and gamma-ray spectra. We say that a spectrum has become harder (or changed to its hard state) when the slope changes so that there are relatively more high energy photons, and it becomes softer when the ratio of low energy photons to high energy photons increases. The ...


1

The orbital periods, and thus years, of planets in the habitable zones of stars of different types may vary a lot, depending on how wide or narrow a star's habitable zone is and which types of stars can have habitable planets. Thus it may be possible for some habitable planets to have years tens times as long as others, possibly even hundreds of times as ...


1

The main effect would be the radiation environment. A planet in the habitable zone of an M-dwarf would likely be subject to far more ultra-violet and X-ray observation for longer than a planet orbiting a G-dwarf of similar overall age. The reason for this lies in the physics of stellar dynamos that power the magnetism of cool stars. Fast rotating cool stars ...


1

The absolute magnitude quantifies the luminosity of an object at a standard distance of $10\ \mathrm{pc}$ from Earth. For example, in the case you mentioned, Vega becomes dimmer than at its actual distance (about $7\ \mathrm{pc}$). To answer your question, I don't think there is an actual star with exactly 0 absolute magnitude. If there is then, following ...


1

I don't believe that O0 is a real classification(see this chart), but if it were following the temperature steps it would probably be around 80,000-90,000 degrees Kelvin. The hottest star we know of is WR 102, which is 210,000 degrees Kelvin, and that is much, much hotter than my predicted O0 temperature. So the short answer is yes, O0 temperature stars ...


1

Yes, the spectral type changes with age. The spectral type is a function of temperature, gravity and chemical composition at the photosphere. All of these can change during a star's life. A star spends most of its life on the main sequence and changes in temperature and gravity are relatively slow. But thereafter there are comparatively rapid changes. For ...


1

Usually, the spectral classification is done analyzing the spectra of the star, we measure the depths of several key lines and compare them, each spectral type has his own characteristic relative intensities etc. Is not a perfect boundary and some times the stars bounce from type to type depending on who classified it and what data is available (is not the ...


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