Sun

Introduction

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields.

It has a diameter of about 1,392,684 km (865,374 mi), around 109 times that of Earth, and its mass (1.989×1030 kilograms, approximately 330,000 times the mass of Earth) accounts for about 99.86% of the total mass of the Solar System.

The_Sun_by_the_Atmospheric_Imaging_Assembly_of_NASA's_Solar_Dynamics_Observatory_-_20100819

The Sun photographed by the Atmospheric Imaging Assembly (AIA 304) of NASA's Solar Dynamics Observatory (SDO). This is a false-color image of the Sun observed in the extreme ultraviolet region of the spectrum. image: wikipedia/NASA


Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The remainder (1.69%, which nonetheless equals 5,600 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon and iron, among others.

The Sun formed about 4.567 billion years ago from the gravitational collapse of a region within a large molecular cloud. Most of the matter gathered in the center, while the rest flattened into an orbiting disk that would become the Solar System

The overall structure of the Sun. image: Kelvinsong /wikipedia

The central mass became increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is thought that almost all stars form by this process. 

The Sun is a G-type main-sequence star (G2V) based on spectral class and it is informally designated as a yellow dwarf because its visible radiation is most intense in the yellow-green portion of the spectrum, and although it is actually white in color, from the surface of the Earth it may appear yellow because of atmospheric scattering of blue light.

In the spectral class label, G2 indicates its surface temperature, of approximately 5,778 K (5505 °C), and V 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 about 620 million metric tons of hydrogen each second.

Sourcehttp://en.wikipedia.org/wiki/Sun


An impressive animation of the Sun over 5 years from the NASA Solar Dynamics Observatory


Commentary

The sun, also known as sol, is the closest star. It is perhaps the most obvious feature in the sky during the day. It is the primary source of energy for most life on Earth.

It is perhaps one the first astronomical objects to be measured and is the basis of the study of astronomy for example through the use of sundials.  The Greek word for the Sun is hélios and many sun related features use this word as a prefix.

For a photon in the middle of the sun it takes between about 10,000 and 170,000 years to reach the surface. Ref This is mostly due to the photon being constantly scattering and bouncing about between other atoms that are much closer together.