Astronomy - Ch. 17: The Nature of Stars (21 of 37) Stellar Classification: Spectral Class

[@Jenab7]

Detailed Luminosity Function (number density) for Stars in the Solar Neighborhood *Main Sequence* • 0.003674 main sequence stars per cubic light year. *Main Sequence, by spectral type* • 1.345e-9 main sequence O stars per cubic light year. • 4.573e-6 main sequence B stars per cubic light year. • 2.286e-5 main sequence A stars per cubic light year. • 1.103e-4 main sequence F stars per cubic light year. • 2.744e-4 main sequence G stars per cubic light year. • 4.371e-4 main sequence K stars per cubic light year. • 0.002824 main sequence M stars per cubic light year. *Main Sequence, by groups of spectral type* • 1.377e-4 stars of types B,A,F per cubic light year. • 7.115e-4 stars of types G,K per cubic light year. • 0.003536 stars of types G,K,M per cubic light year. *Other Stars and Substellar Objects* • 0.001076 brown dwarfs (L,T,Y) per cubic light year. • 1.479e-4 white dwarfs per cubic light year. • 5.111e-5 subgiant stars per cubic light year. • 8.070e-6 giant stars per cubic light year. • 1.345e-9 supergiant stars per cubic light year. *All of the above, combined* • 0.004957 objects per cubic light year.

[@ekaterinastrieby6432]

What an excellent video! Such are rare on youtube.

[@Physics-Learner-fs8xd]

michel why is the o class part blue and part violet?

[@MichelvanBiezen]

In astronomy we don't make a distinction between blue and purple. We just call it blue.

[@ElitheScienceGuy416]

why even though you mentiond red giants did you not mention red & blue supergiants

[@MichelvanBiezen]

The general class is "red giants". They are however sub-divided into sub-giants, red giants, and red supergiants. (Covered in other videos)

[@tgchris2222]

I realize this is all based on surface temp, but with such high internal temps why isn’t there more X and Gamma rays off stars?

[@MichelvanBiezen]

The radiation from any object comes from the surface. The high energy photons generated in the interior, lose their energy before thy make it to the surface.

[@humanitySL]

Very clear. Thanks

[@taleof2kitties]

Isn't our sun a white star?

[@MichelvanBiezen]

Anna, No it is not. For the Sun to be a white star the surface temperature needs to be close to 10,000K Since the surface temperature of the Sun is about 5800K it is a yellow star. One way to think about it is this way: When you look at a picture of the Sun, or when you quickly glance at it during the daytime, what color do you see?

[@taleof2kitties]

Oh! Ok, why is it then that most articles online say that it is white and even my professor says that it is white? Are they talking about a different property of the sun?

[@MichelvanBiezen]

Anna Lebedeva No one should claim the Sun is a white star. The surface temperature is not hot enough. Sirius for example is a white star with a surface temperature near 9000K They may be referencing sending sunlight through a prism and getting all the colors of the rainbow when it is refracted.

[@taleof2kitties]

Got it! Thank you for clearing that up!

[@ElitheScienceGuy416]

well it is a g class star so it mostly emits yellow light but it is slighty whiteish

[@Jenab7]

Naw! It's LUMINOSITY *CLASS* (I,II,III,IV,V), and SPECTRAL *TYPE* (O,B,A,F,G,K,M).