Star
A star is a massive, self-luminous sphere of plasma held together by its own gravity. It shines by converting hydrogen into helium through nuclear fusion in its core, releasing energy across the electromagnetic spectrum.
Stars form in large clouds of gas and dust—called nebulae—where regions collapse under gravity, creating protostars. When core temperatures reach millions of degrees, fusion ignites, marking the birth of a star. Observatories like Hubble and missions such as NASA’s Infrared telescopes have imaged this process in action.
The majority (~90%) of stars are main-sequence stars, fusing hydrogen into helium. These include a broad range of masses—from red dwarfs (small, long-lived, faint) to blue giants and supergiants (massive, hot, and short-lived). Our Sun is a middle-aged G-type main sequence star.
As stars exhaust their hydrogen fuel, their evolution depends on mass. Lower-mass stars become red giants then white dwarfs. More massive stars undergo successive fusion stages, end in supernova explosions, and leave behind neutron stars or black holes.
Stars vary in brightness, size, and color. They are classified using spectral types (O, B, A, F, G, K, M) based on surface temperature and absorption lines. For example, O- and B-type stars are hot and blue; M-type are cool and red.
Stellar remnants include white dwarfs (Earth-sized cores of former stars), neutron stars (city-sized remnants of supernovae), and black holes (extreme-density objects from the most massive stars).
Stars are not static—many rotate, exhibit magnetic activity (like sunspots and flares), and broadcast stellar winds. Their lifecycle enriches the interstellar medium with heavier elements, seeding future generations of stars and planets.
Stars often exist in groups—binary or systems within star clusters and galaxies. Their properties are studied via brightness, spectra, parallax, variability, and statistical surveys by missions like Gaia and Kepler.
Sources
APODs including "Star"
LDN 1295: The Giraffe Nebula
10 September 2026
What does this image look like to you? Many see a giraffe facing right, with neck stretched high and long legs mid-stride (but some may see a squirrel instead). The featured image shows LDN 1295, also called the Giraffe Nebula, in the constellation of the mythical queen of Aethiopia (Cassiopeia). It is an object in the Lynds Catalogue of Dark Nebulas, compiled in 1962 by American astronomer Beverly Lynds, a pioneer for women in astronomy and astrophysics. Dark nebulas are interstellar clouds of dust and gas that block the visible light of the stars behind them. These nebulas are often faint and challenging targets for astrophotographers. Why do we see animal shapes and faces in nebulas, clouds, and pretty much everywhere? It is due to pareidolia, our tendency to look for familiar patterns. Pareidolia may provide animals with an evolutionary advantage, for example in identifying (and avoiding) predators. APOD's main NASA site is moving : From apod.nasa.gov to science.nasa.gov/apod