The Sun
The Sun is a yellow dwarf star (G2V), about 4.6 billion years old, and the dominant gravitational force in the Solar System. It has a diameter of roughly 1.4 million kilometers and contains around 99.8% of the Solar System’s mass. Nuclear fusion in its core converts hydrogen into helium, producing energy that warms the planets. Above the core lie the radiative and convective zones, followed by the visible photosphere (~5,500 °C), the chromosphere, and the much hotter corona (~2 million °C).
Source: science.nasa.gov
APODs including "The Sun"
Genesis Mission's Hard Impact
14/09/2004
A flying saucer from outer space crash-landed in the Utah desert last week after being tracked by radar and chased by helicopters. No space aliens were involved, however. The saucer, pictured above, was the Genesis sample return capsule, part of a human-made robot Genesis spaceship launched three years ago by NASA itself to study the Sun. The unexpectedly hard landing at over 300 kilometers per hour occurred because the parachutes did not open as planned. The Genesis mission had been orbiting the Sun collecting solar wind particles that are usually deflected away by Earth's magnetic field. A big question remains -- are the returned samples in good enough condition to recover information about the real composition of the Sun? Genesis team scientists and engineers are working hard to find out.