The diameter of our closest star, the Sun, is 1,392,000 kilometers. The Sun is thought to be 4.6 billion years old. The Sun is a medium–size star known as a yellow dwarf. It is a star in the Milky Way galaxy and the temperature in its core is estimated to be over 15,000,000 degrees Celsius. In the Sun’s core, hydrogen is being fused to form helium. The energy created by this process radiates up to the visible boundary of the Sun and then off into space. It radiates into space in the form of heat and light. Because the Sun is so massive, it exerts a powerful gravitational pull on everything in our solar system. It is because of the Sun’s gravitational pull that Earth orbits the Sun in the manner that it does. The Sun has several layers: the core, the radiation zone, the convection zone, and the photosphere (which is the surface of the Sun). In addition, there are two layers of gas above the photosphere called the chromosphere and the corona. Events that occur on the Sun include sunspots, solar flares, solar wind, and solar prominences. Sunspots are magnetic storms on the photosphere that appear as dark areas. Sunspots regularly appear and disappear in eleven-year cycles. Solar flares are spectacular discharges of magnetic energy from the corona. These discharges send streams of protons and electrons outward into space. Solar flares can interrupt the communications network here on Earth. Solar winds are the result of gas expansion in the corona. This expansion leads to ion formation. These ions are hurled outward from the corona at over 500 kilometers per second. Solar prominences are storms of gas which 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 emits radio waves, ultraviolet rays, and X-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 a differential rotation.
TERMS TO KNOW
ATMOSPHERE The layers of gases which surround a star, like our Sun, or a planet, like our Earth. CORONA The very hot outermost layer of a star’s atmosphere. Our Sun’s corona can only be seen during a total solar eclipse. ENERGY Usable heat or power; in physics, it is the capacity of a physical system to perform work. GALAXY A cluster of stars, dust, and gas held together by gravity. GRAVITY The force of attraction between two objects that is influenced by the mass of the two objects and the distance between the two objects. ORBIT A specific path followed by a planet, satellite, etc. RADIO WAVES A 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. ROTATION The spinning of an object on its axis. SOLAR FLARES A magnetic storm on the Sun’s surface which shows up as a sudden increase in brightness. SOLAR PROMINENCES Gases trapped at the edge of the Sun which appear to shoot outward from the Sun’s surface. SOLAR SYSTEM The Sun and all of the planets, comets, etc. which revolve around it. SOLAR WIND A 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. SUNSPOT A 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 RAYS Invisible electromagnetic radiation which is comprised of very short wavelengths. Human beings get a sunburn from the ultraviolet rays emitted by the Sun. X-RAYS Penetrating electromagnetic radiation which has an extremely short wavelength.
