Proper noun

Sun

1. The star at the center of our solar system, represented in astronomy and astrology by ☉.
2. (newspapers) An English tabloid newspaper.

Related terms

• sun

Abbreviation

Sun

1. Sunday.

The Sun is the star at the center of the Solar System. It has a diameter of about 1,392,000 kilometers (865,000 mi), about 109 times that of Earth, and its mass (about 2 × 10 kilograms, 330,000 times that of Earth) accounts for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. Less than 2% consists of heavier elements, including oxygen, carbon, neon, iron, and others.

The Sun's color is white, although from the surface of the Earth it may appear yellow because of atmospheric scattering of blue light. Its stellar classification, based on spectral class, is G2V, and is informally designated a yellow star, because its visible radiation is most intense in the yellow-green portion of the spectrum. In this spectral class label, G2 indicates its surface temperature of approximately 5,778 K (5,505 °C; 9,941 °F), and V (Roman five) indicates that the Sun, like most stars, is a main sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 430–600 million tons of hydrogen each second. Once regarded by astronomers as a small and relatively insignificant star, the Sun is now presumed to be brighter than about 85% of the stars in the Milky Way galaxy, most of which are red dwarfs. The absolute magnitude of the Sun is +4.83; however, as the star closest to Earth, the Sun is the brightest object in the sky with an apparent magnitude of −26.74. The Sun's hot corona continuously expands in space creating the solar wind, a stream of charged particles that extends to the heliopause at roughly 100 astronomical units. The bubble in the interstellar medium formed by the solar wind, the heliosphere, is the largest continuous structure in the Solar System.

The Sun is currently traveling through the Local Interstellar Cloud in the Local Bubble zone, within the inner rim of the Orion Arm of the Milky Way galaxy. Of the 50 nearest stellar systems within 17 light-years from Earth (the closest being a red dwarf named Proxima Centauri at approximately 4.2 light years away), the Sun ranks 4th in mass. The Sun orbits the center of the Milky Way at a distance of approximately 24,000–26,000 light years from the galactic center, completing one clockwise orbit, as viewed from the galactic north pole, in about 225–250 million years. Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of constellation Hydra with a speed of 550 km/s, the sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo.

The mean distance of the Sun from the Earth is approximately 149.6 million kilometers (1 AU), though this varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds. The energy of this sunlight supports almost all life on Earth by photosynthesis, and drives Earth's climate and weather. The enormous effect of the Sun on the Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity. An accurate scientific understanding of the Sun developed slowly, and as recently as the 19th century prominent scientists had little knowledge of the Sun's physical composition and source of energy. This understanding is still developing; there are a number of present-day anomalies in the Sun's behavior that remain unexplained.

Quotations about the Sun.

Sourced

• Legends can be now and forever Teaching us to love for goodness sake. Legends can be now and forever Loved by the sun, loved by the sun.
  • Jon Anderson, in lyrics of "Loved by the Sun", written for the "Unicorn Theme" of Legend (1986)

• 9:13, Personal note: When I was a little kid my mother told me not to stare into the sun. So once when I was six, I did. At first the brightness was overwhelming, but I had seen that before. I kept looking, forcing myself not to blink, and then the brightness began to dissolve. My pupils shrunk to pinholes and everything came into focus and for a moment I understood. The doctors didn't know if my eyes would ever heal. I was terrified, alone in that darkness. Slowly daylight crept in through the bandages, and I could see, but something else had changed inside of me. That day I had my first headache.
  • Max Cohen in π (1998), by Darren Aronofsky

• Law, say the gardeners, is the sun, Law is the one All gardeners obey To-morrow, yesterday, to-day.
  • W. H. Auden in "Law, Say The Gardeners, Is The Sun"

From Wikiquote under the GNU Free Documentation License.
Mon Aug 2 13:42:04 2010