The Sun

The diameter ofour closest star,the Sun, is 1,392,000 kilometers. The Sun is thought to be4.6 billion years old.The Sun is a medium–size star known asa yellow dwarf.It is a star in theMilky Way galaxyand the temperature in its core is estimated to be over15,000,000 degrees Celsius.

In the Sun's core,hydrogen is being fusedto form helium. Theenergy created by this process radiatesup to the visible boundary of the Sun and thenoff into space.It radiates into space in the form ofheat and light.

Because the Sun isso massive,it exerts apowerful gravitational pullon everything in our solar system. It is because of the Sun's gravitational pull thatEarth orbits the Sunin the manner that it does.

The Sun has several layers:the core, the radiation zone, the convection zone,andthe photosphere(which is the surface of the Sun). In addition, there are two layers of gas above the photosphere calledthe chromosphereandthe corona.

Events that occur on the Sun include sunspots, solar flares, solar wind, and solar prominences.Sunspotsaremagnetic stormson the photosphere that appear as dark areas. Sunspots regularly appear and disappear in eleven-year cycles.Solar flaresare spectacular discharges ofmagnetic energyfrom the corona. These discharges send streams of protons and electrons outward into space. Solar flares can interrupt the communications network here on Earth.Solar windsare the result ofgas expansionin the corona. This expansion leads to ion formation. These ions are hurled outward from the corona at over 500 kilometers per second.Solar prominencesarestorms of gaswhich erupt from the surface in the form of columns which either shoot outward into space or twist and loop back to the Sun's surface.

The Sun gives off many kinds of radiation other than light and heat. It also emitsradio waves, ultraviolet rays,andX-rays.The Earth's atmosphere protects us from the harmful effects of the ultraviolet rays and the X-rays.

The Sun does rotate, but because it is a large gaseous sphere, not all parts rotate at the same speed. This is known as adifferential rotation.

TERMS TO KNOW

ATMOSPHEREThe layers of gases which surround a star, like our Sun, or a planet, like our Earth.

CORONAThe very hot outermost layer of a star's atmosphere. Our Sun's corona can only be seen during a total solar eclipse.

ENERGYUsable heat or power; in physics, it is the capacity of a physical system to perform work.

GALAXYA cluster of stars, dust, and gas held together by gravity.

GRAVITY我的两个物体之间的引力s influenced by the mass of the two objects and the distance between the two objects.

ORBITA specific path followed by a planet, satellite, etc.

RADIO WAVESA type of electromagnetic radiation which has the lowest frequency, the longest wavelength, and is produced by charged particles moving back and forth. Radio waves are not blocked by clouds in the Earth's atmosphere.

ROTATIONThe spinning of an object on its axis.

SOLAR FLARESA magnetic storm on the Sun's surface which shows up as a sudden increase in brightness.

SOLAR PROMINENCESGases trapped at the edge of the Sun which appear to shoot outward from the Sun's surface.

SOLAR SYSTEMThe Sun and all of the planets, comets, etc. which revolve around it.

SOLAR WINDA continuous stream of charged particles which are released from the Sun and hurled outward into space at speeds up to 800 kilometers per second. Solar winds are very prominent after solar flare activity.

SUNSPOTA magnetic storm on the Sun's surface which appears as a dark area. A sunspot is approximately 1500 degrees Celsius cooler than it's surrounding material. The number of sunspots we see on the Sun at any given time appears to cycle every 11 years.

ULTRAVIOLET RAYSInvisible electromagnetic radiation which is comprised of very short wavelengths. Human beings get a sunburn from the ultraviolet rays emitted by the Sun.

X-RAYSPenetrating electromagnetic radiation which has an extremely short wavelength.