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INI

Stellar Spectral Classification - INI

The Stellar Spectral Classification is a classification system developed by Annie Jump Cannon and colleagues at Harvard College Observatory between 1918 and 1924. It categorizes stars into ten types (O, B, A, F, G, K, M, L, T, Y) based on surface temperature, systematically organizing everything from the hottest blue giants to the coolest brown dwarfs. This classification was formally adopted by the precursor to the International Astronomical Union in 1922 and remains the standard classification system used worldwide in astronomy today.

astronomy stars spectral classification Harvard classification surface temperature brown dwarfs 
[item.o-type]
code=O
slug=o-type
name=O-type Star
description=The hottest and most massive blue giant stars.
abundance_percent=<1
color=Blue
example_stars=["Zeta Ophiuchi","Lambda Orionis","Theta1 Orionis C"]
lifespan=5-6 million years
mass_solar_max=150
mass_solar_min=16
mass_solar_typical=30
temperature_max_kelvin=50000
temperature_min_kelvin=28000
temperature_note=Some subdwarfs can exceed 100,000K
temperature_typical_kelvin=
mass_jupiter_max=
mass_jupiter_min=
mass_jupiter_typical=
object_type=

[item.b-type]
code=B
slug=b-type
name=B-type Star
description=Hot blue-white massive stars.
abundance_percent=0.13
color=Blue-white
example_stars=["Rigel","Spica","Regulus"]
lifespan=~300 million years
mass_solar_max=16
mass_solar_min=2.1
mass_solar_typical=7
temperature_max_kelvin=30000
temperature_min_kelvin=10000
temperature_note=
temperature_typical_kelvin=15000
mass_jupiter_max=
mass_jupiter_min=
mass_jupiter_typical=
object_type=

[item.a-type]
code=A
slug=a-type
name=A-type Star
description=White stars with the strongest hydrogen lines.
abundance_percent=0.625
color=White
example_stars=["Sirius A","Vega","Altair","Fomalhaut"]
lifespan=1-2 billion years
mass_solar_max=2.1
mass_solar_min=1.4
mass_solar_typical=1.7
temperature_max_kelvin=10000
temperature_min_kelvin=7400
temperature_note=
temperature_typical_kelvin=8500
mass_jupiter_max=
mass_jupiter_min=
mass_jupiter_typical=
object_type=

[item.f-type]
code=F
slug=f-type
name=F-type Star
description=Yellow-white stars with intermediate temperature.
abundance_percent=3
color=Yellow-white
example_stars=["Procyon A","Polaris Aa","Canopus"]
lifespan=4-8 billion years
mass_solar_max=1.4
mass_solar_min=1
mass_solar_typical=1.2
temperature_max_kelvin=7500
temperature_min_kelvin=6000
temperature_note=
temperature_typical_kelvin=6700
mass_jupiter_max=
mass_jupiter_min=
mass_jupiter_typical=
object_type=

[item.g-type]
code=G
slug=g-type
name=G-type Star (Yellow Dwarf)
description=Yellow main-sequence stars like our Sun.
abundance_percent=7.5
color=Yellow
example_stars=["Sun","Alpha Centauri A","Tau Ceti","51 Pegasi"]
lifespan=~10 billion years (for solar mass)
mass_solar_max=1.15
mass_solar_min=0.8
mass_solar_typical=1
temperature_max_kelvin=6000
temperature_min_kelvin=5200
temperature_note=
temperature_typical_kelvin=5778
mass_jupiter_max=
mass_jupiter_min=
mass_jupiter_typical=
object_type=

[item.k-type]
code=K
slug=k-type
name=K-type Star (Orange Dwarf)
description=Orange main-sequence stars cooler than the Sun.
abundance_percent=12
color=Orange
example_stars=["Epsilon Eridani","Alpha Centauri B","61 Cygni A"]
lifespan=17-70 billion years
mass_solar_max=0.8
mass_solar_min=0.5
mass_solar_typical=0.65
temperature_max_kelvin=5200
temperature_min_kelvin=3900
temperature_note=
temperature_typical_kelvin=4500
mass_jupiter_max=
mass_jupiter_min=
mass_jupiter_typical=
object_type=

[item.m-type]
code=M
slug=m-type
name=M-type Star (Red Dwarf)
description=The most common and longest-lived red main-sequence stars.
abundance_percent=75
color=Red
example_stars=["Proxima Centauri","Barnard's Star","TRAPPIST-1","Wolf 359"]
lifespan=1-10 trillion years
mass_solar_max=0.5
mass_solar_min=0.08
mass_solar_typical=0.3
temperature_max_kelvin=3900
temperature_min_kelvin=2400
temperature_note=
temperature_typical_kelvin=3200
mass_jupiter_max=
mass_jupiter_min=
mass_jupiter_typical=
object_type=

[item.l-type]
code=L
slug=l-type
name=L-type Dwarf
description=Cool brown dwarfs with water and metal hydride absorption.
abundance_percent=
color=Dark red
example_stars=["2MASS J0523-1403","DENIS-P J1228.2-1547"]
lifespan=
mass_solar_max=
mass_solar_min=
mass_solar_typical=
temperature_max_kelvin=2500
temperature_min_kelvin=1300
temperature_note=
temperature_typical_kelvin=1900
mass_jupiter_max=65
mass_jupiter_min=13
mass_jupiter_typical=30
object_type=Brown dwarf or cool star

[item.t-type]
code=T
slug=t-type
name=T-type Dwarf
description=Cool brown dwarfs with methane absorption bands.
abundance_percent=
color=Magenta/Black
example_stars=["Gliese 570 D","WISE J0350-5658","2MASS J0559-1404"]
lifespan=
mass_solar_max=
mass_solar_min=
mass_solar_typical=
temperature_max_kelvin=1500
temperature_min_kelvin=600
temperature_note=
temperature_typical_kelvin=1000
mass_jupiter_max=80
mass_jupiter_min=13
mass_jupiter_typical=50
object_type=Brown dwarf

[item.y-type]
code=Y
slug=y-type
name=Y-type Dwarf
description=The coldest brown dwarfs with ammonia absorption features.
abundance_percent=
color=Black (detectable only in infrared)
example_stars=["WISE J0855-0714","WISE J1828+2650","WISE J1738+2732"]
lifespan=
mass_solar_max=
mass_solar_min=
mass_solar_typical=
temperature_max_kelvin=600
temperature_min_kelvin=200
temperature_note=
temperature_typical_kelvin=400
mass_jupiter_max=80
mass_jupiter_min=13
mass_jupiter_typical=50
object_type=Brown dwarf