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Stars

The Cosmic Furnaces

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Did You Know?

The nearest star to Earth (besides the Sun) is Proxima Centauri, 4.24 light-years away.

What Are Stars?

The cosmic furnaces that light up the universe

Stars are massive, luminous spheres of plasma held together by gravity. They are the fundamental building blocks of galaxies and the source of light and energy in the universe. Our Sun is a star, and there are billions of other stars in our galaxy alone, each with its own unique characteristics and life cycle. Stars form from collapsing clouds of gas and dust, and their life cycles depend on their mass.

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Nearest star (after Sun)

Proxima Centauri (4.24 ly)

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Stars in Milky Way

100-400 billion

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Sun's surface temp

5,500°C

Explore the Sun →

Star Formation

Where cosmic dust becomes stellar fire

Stars form from collapsing clouds of gas and dust called nebulae. When a region of a nebula becomes dense enough, gravity causes it to collapse. As the cloud collapses, it heats up and forms a protostar. When the core temperature reaches about 10 million degrees Celsius, nuclear fusion begins, and a star is born. This process can take millions of years. The mass of the collapsing cloud determines the star's size and type.

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Fusion ignition temp

10 million°C

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Formation time

Millions of years

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Nebula size

Light-years across

Discover Nebulae →

Star Classification

The cosmic spectrum from blue giants to red dwarfs

Stars are classified by their temperature and brightness using the Morgan-Keenan system. The main sequence stars are categorized as:

O-type: Hottest, bluest stars (30,000-50,000 K) - rare and short-lived
B-type: Hot, blue-white stars (10,000-30,000 K)
A-type: White stars (7,500-10,000 K)
F-type: Yellow-white stars (6,000-7,500 K)
G-type: Yellow stars like our Sun (5,200-6,000 K)
K-type: Orange stars (3,700-5,200 K)
M-type: Coolest, reddest stars (2,400-3,700 K) - most common type

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Hottest stars (O-type)

50,000°C

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Coolest stars (M-type)

2,400°C

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Our Sun (G-type)

5,500°C

Star Life Cycle

From birth to death, the cosmic journey of stellar evolution

A star's life cycle depends on its mass. Low-mass stars like red dwarfs can burn for trillions of years. Medium-mass stars like our Sun live for billions of years, eventually becoming red giants and then white dwarfs. High-mass stars live fast and die young, ending their lives in spectacular supernova explosions that can form neutron stars or black holes. The death of massive stars enriches the universe with heavy elements.

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Red dwarf lifespan

Trillions of years

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Sun's lifespan

10 billion years

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Supernova explosion

Brighter than galaxies

Learn About Supernovae →