Early-type star | Wikipedia audio article
Channel: wikipedia tts
Date: 04/10/2019

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Stellar_classification


00:02:09 1 Conventional color description
00:03:04 2 Modern classification
00:03:55 2.1 Harvard spectral classification
00:06:59 2.2 Yerkes spectral classification
00:09:54 2.3 Spectral peculiarities
00:10:28 3 History
00:10:49 3.1 Secchi classes
00:11:34 3.2 Draper system
00:12:18 3.3 Harvard system
00:13:39 3.4 Mount Wilson classes
00:14:01 4 Spectral types
00:14:28 4.1 "Early" and "late" nomenclature
00:16:24 4.2 Class O
00:18:45 4.3 Class B
00:21:55 4.4 Class A
00:22:58 4.5 Class F
00:23:43 4.6 Class G
00:25:21 4.7 Class K
00:26:44 4.8 Class M
00:28:33 5 Extended spectral types
00:28:50 5.1 Hot blue emission star classes
00:29:09 5.1.1 Class W: Wolf–Rayet
00:31:31 5.1.2 The "Slash" stars
00:32:31 5.1.3 The magnetic O stars
00:32:46 5.2 Cool red and brown dwarf classes
00:33:43 5.2.1 Class L
00:34:44 5.2.2 Class T: methane dwarfs
00:36:13 5.2.3 Class Y
00:38:16 5.3 Late giant carbon-star classes
00:39:07 5.3.1 Class C: carbon stars
00:40:40 5.3.2 Class S
00:42:35 5.3.3 Classes MS and SC: intermediary carbon-related classes
00:43:09 5.4 White dwarf classifications
00:45:43 5.5 Non-stellar spectral types: Classes P and Q
00:46:10 6 Stellar remnants
00:47:13 7 Replaced spectral classes
00:47:43 8 Stellar classification, habitability, and the search for life
00:49:33 9 See also



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SUMMARY
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In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature.
Most stars are currently classified under the Morgan-Keenan (MK) system using the letters O, B, A, F, G, K, and M, a sequence from the hottest (O type) to the coolest (M type). Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g. A8, A9, F0, and F1 form a sequence from hotter to cooler). The sequence has been expanded with classes for other stars and star-like objects that do not fit in the classical system, such as class D for white dwarfs and classes S and C for carbon stars.
In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star's spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class 0 or Ia+ is used for hypergiants, class I for supergiants, class II for bright giants, class III for regular giants, class IV for sub-giants, class V for main-sequence stars, class sd (or VI) for sub-dwarfs, and class D (or VII) for white dwarfs. The full spectral class for the Sun is then G2V, indicating a main-sequence star with a temperature around 5,800 K.