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"
Shuttle and Meteor
14 August 2009
This early morning skyscape was captured last week on August 4th, looking northeast across calm waters in the Turn Basin at NASA's Kennedy Space Center. In a striking contrast in motion, the space shuttle Discovery, mounted on a massive transporter, creeps toward launch pad 39A at less than two miles per hour, while a brilliant meteor streaks through the sky traveling many miles per second. Of course, this week skywatchers have seen many similar meteor streaks during the annual Perseid meteor shower. But the meteor flashing above Discovery is not likely to be one of the Perseids because its path doesn't point back to that shower's radiant. Seen here near picture center, brilliant planet Venus still dominates the sky as the Morning Star, though. Yellowish tinted Mars lies near the top of the frame and Orion's red giant star Betelgeuse is toward the right.