THE SUN, OUR NEAREST STAR

STARS ARE FORMED IN GIANT CLOUDS OF DUST CALLED NEBULA.

EAGLE NEBULA, OFTEN CALLED THE PILLARS OF CREATION

OUR SUN LIKELY FORMED IN SUCH A CLOUD 4.5 BILLION YEARS AGO - PART OF WHICH CONTAINED GAS LEFT OVER FROM AN EXPLODED STAR. OUR SOLAR SYSTEM CONTAINS ELEMENTS OTHER THAN HYDROGEN OR HELIUM, AND THESE ELEMENTS WOULD HAVE HAD TO HAVE FORMED IN THE CORES OF EARLIER STARS. STARS HAVE FINITE LIFETIMES, AND ONE WAY THEY END IS IN AN EXPLOSION KNOWN AS A SUPER NOVA.

EVOLUTION OF OUR SOLAR SYSTEM

IN THE CLOUD OF DUST AND GAS, PART ENDED UP WITH MORE MATERIAL (AND MORE GRAVITY), SO IT ATTRACTED ADDITIONAL MATERIAL. A BALL OF DUST AND GAS FORMED. AS THIS GREW LARGER, IT STARTED SPINNING. A RING OF DUST AND DEBRIS FORMED AROUND THE MAIN BODY.

A TELESCOPE IMAGE OF A PROTOPLANETARY DISK AND AN ARTIST’S IMAGE.

MOST OF THE MATERIAL WENT TO FORM THE SUN (OVER 99%). THE REMAINING MATERIAL WENT TO FORM THE PLANETS. SMALL OBJECTS COLLIDED TO FORM LARGER OBJECTS UNTIL MOST OF THE MATERIAL WAS COLLECTED INTO THE PLANETS. THIS PROCESS IS CALLED ACCRETION.

IN THE GASEOUS DISK THAT WOULD BECOME THE PLANETS, GRAVITY SEPARATED OUT SOME OF THE ELEMENTS, SO THAT THE INNER PLANETS ARE ROCKY, AND THE OUTER PLANETS ARE GASEOUS. ALSO, WHEN THE SUN REACHED IGNITION TEMPERATURE, THE SHOCK WAVE WOULD BLOW AWAY ANY GAS IN THE INNER SOLAR SYSTEM.

ALL OF THE PLANETS WITH THE EXCEPTIONS OF MERCURY AND PLUTO ARE ON THE ECLIPTIC. THE ECLIPTIC IS ALMOST AT RIGHT ANGLES TO THE PLANE OF THE MILKY WAY GALAXY.

Energy is produced in the sun’s core through nuclear fusion of hydrogen to helium. The core is approximately 15,000,000 o C. The sun is mostly hydrogen (92% in terms of number of atoms, 75% of mass). Helium is the second most abundant element at 7.8% in terms of number of atoms and 25% in terms of mass. The sun is 0.1% other elements. The sun makes up 99.9% of the mass of our solar system. The sun is not a liquid or a solid. It is a plasma - a mixture of atomic nuclei and free electrons.

The diameter of the sun is 1.4 million km or about 109 earth diameters. The sun is almost 6,000 times the mass of Earth. The sun is 93, miles from Earth (1 au). The core occupies about about 1/4 of the sun’s diameter. In the core, hydrogen is being fused into helium in nuclear fusion reactions. In this reaction, a small amount of mass is lost and converted into energy. Outside of the core, you have the radiative zone and the convective zone.

Light is emitted in the radiation zone. It can take photons millions of years to make it out to the surface, because they keep getting absorbed and re-emitted.

In the convection zone, cells act like pots of boiling water with cooler gases sinking and hotter gases rising. ce-sci/solar-system/sun-101-sci/

THE PHOTOSPHERE IS THE VISIBLE SURFACE OF THE SUN. THE SUN IS COMPOSED OF A GAS OR PLASMA, SO THINK OF THE PHOTOSPHERE AS THE DEPTH AT WHICH YOU CAN NO LONGER SEE TOWARDS THE CORE.

YOU WILL ALSO SEE SUN SPOTS ON THE PHOTOSPHERE. THESE APPEAR DARK, BECAUSE THEY ARE ABOUT 2000 o COOLER THAN THE REST OF THE PHOTOSPHERE. THEY ARE PLACES WHERE INTENSE MAGNETIC LINES OF FORCE EMERGE FROM THE SURFACE.

No matter how dark the night, somehow the sun rises once again and all shadows are chased away.

ABOVE THE PHOTOSPHERE IS THE CHROMOSPHERE. THE CHROMOSPHERE IS A LAYER OF GAS ABOUT 2500 KM THICK. IT CAN ONLY BE SEEN DURING AN ECLIPSE. IT HAS A REDISH APPEARANCE BECAUSE OF HYDROGEN EMISSIONS. THE CHROMOSPHERE HAS A TEMPERATURE OF 30,000 o.

Beyond the chromosphere is the corona. The corona can have temperatures ranging from 1 to 2 million o K. The chromosphere and the corona are not normallly visible. Gas flows outward from the corona as the solar wind. Plasma particles flow out at rates of approximately 400 km/s.

A PROMINENCE IS A LOOP OF HOT GAS THAT CAN ERUPT FROM THE SURFACE OF THE SUN HUNDREDS OF THOUSANDS OF MILES INTO SPACE. IT IS HELD IN PLACE BY MAGNETIC LINES OF FORCE.

The sun is not a solid. The area around the equator rotates in approximately 25 hours. The area around the poles rotates at approx. 35 hours. This stretches the magnetic lines of force and results in magnetic disturbances or sun spots. The sun spots appear dark, but taken in reference to a normal background, they glow red. Sun spots are disturbances in the magnetic field. They can result in coronal mass ejections where huge amounts of plasma are shot into the solar system.

THIS VIDEO SHOWS THE SUN’S ACTIVITY AS SEEN BY NASA’S SOLAR DYNAMICS OBSERVATORY DURING AT THE PEAK OF SOLAR ACTIVITY, 2 OR 3 CME’S CAN OCCUR EACH DAY. IF THEY COME TOWARD EARTH, THEY CAN DISRUPT SATELLITE COMMUNICATIONS AND KNOCK OUT POWER GRIDS. - NASA’s STEREO Sattelites

A GOOD SITE TO USE TO CHECK ON SPACE WEATHER IS THIS SITE GIVES SUN SPOT ACTIVITY AS WELL AS INFORMATION ON NEAR EARTH ASTEROIDS. -rain.htmlhttp:// -rain.html A LARGE SOLAR FLARE PHOTOGRAPHED BY SDO IN 2012