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"
Noctilucent Clouds over Moscow
27/06/2013
This panoramic night scene from June 8 looks out across a Moscow skyline from atop the main building of Lomonosov Moscow State University. Shining in the darkened sky above are widespread noctilucent clouds. From the edge of space, about 80 kilometers above Earth's surface, the icy clouds can still reflect sunlight even though the Sun itself is below the horizon as seen from the ground. Usually spotted at high latitudes in summer months the diaphanous apparitions, also known as polar mesospheric clouds, have come early this season. The seasonal clouds are understood to form as water vapor driven into the cold upper atmosphere condenses on the fine dust particles supplied by meteor smoke (debris left by disintegrating meteors) or volcanic ash. Their early start this year may be connected to changing global circulation patterns in the lower atmosphere. During this northern summer, NASA's AIM mission provides daily projections of the noctilucent clouds as seen from space.