Star
A star is a luminous spheroid of plasma held together by self-gravity. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most well-known stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names.
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- Space is so big that light from distant stars takes millions of years to reach us!
- There are more stars in the universe than grains of sand on all Earth's beaches.
- A day on Venus is longer than a year on Venus!
Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy.
A star's life begins with the gravitational collapse of a gaseous nebula of material largely comprising hydrogen. Helium, and traces of heavier elements. Its total mass mainly determines its change over time and eventual fate.
A star shines for most of its active life due to the thermonuclear fusion of hydrogen into helium in its core. This steps that happen releases energy that traverses the star's interior and radiates into outer space. At the end of a star's lifetime.
Fusion ceases and its core becomes a stellar remnant: a white dwarf, a neutron star, or.
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