Our Sun is a star, a powerhouse of energy, a gigantic ball of incandescent gas. Our home galaxy, the Milky Way, contains between four hundred billion to possibly one trillion stars. Out of this enormous selection, planet Earth happens to have the best one in the galaxy's inventory of stars. It is just at the correct distance ( 93,000,000 miles) and correct temperature for life to exist. The sun drives our weather systems and gives the Earth light to grow crops. A nudge either way in distance or an increase in the tilt of the Earth would make life on this planet very difficult. Things would change and not for the better.
In the core of the sun, thermonuclear fusion is taking place, that is to say that hydrogen is fusing (converting) into helium. This process converts 665 million tons of hydrogen into 660 million tons of helium every second. The missing 5 million tons of matter is not missing at all. It is the light and heat that we see and feel from the sun.In order for fusion to take place exactly in a star like the sun, there must be searing heat ( 16,000,000 degrees Celsius / 28,000032 degrees Fahrenheit) and tremendous pressure ( nearly 3 billion times that of Earth's atmospheric pressure at sea level ) and an abundance of hydrogen (approximately 74% of the sun's mass). The result of thermonuclear fusion in the core of the sun is a material called Plasma, which is the fourth state of matter. Plasma is gas that is ionized and separated into its positive particles (nuclei) and negative particles (electrons). Television manufacturers boast plasma screen TV sets, the material in the sun , I can assure you it is not the same as in the TV set. This gaseous material is between 13-14 times denser than lead. The core of the sun is a very crowded place.
Often student visitors will ask me this question. If all of the planets revolve around the sun, does the sun just sit there in space? It appears so from our perspective. Actually it does move, and how! Remember that gravity is the mutual attraction of all things with mass and gravity therefore is a function of mass. As the sun has most of the mass in the solar system, it controls all in the system. Planets, their moons and asteroids have mass but not to the degree that the sun has, simply stated, they take orders from the sun. Only other stars influence the sun. Our sun and its system revolves around the center of our galaxy, a trip that takes 240 million years (a galactic year) and our galaxy moves through space, because other galaxies influence our galaxy. Ready for the ride of your life? Spaceship Earth travels at the speed of 66,636 miles per hour as it orbits the sun. The sun and its system travels at the speed 540,000 miles per hour as it revolves around the center of the galaxy and the Milky Way travels through space at 1,100,000 miles per hour. Thanks to gravity on Earth and the exquisite balance of gravity in the universe, we need not be tied, nailed or glued to the planet, we simply go about our daily lives while all of these amazing speeds are taking place.
Earth is a terrestrial planet (terra firma). Solid surface. The sun does not have a solid surface as it is a ball of hot gas. The surface of the sun is called the photosphere and that is where the light and heat escapes the sun and is radiated out into space. The temperature of the photosphere is 6,000 degrees Celsius. The sun's gas layers rotate at different speeds. All of these actions create magnetic storms in the photosphere and sunspots form. These sunspots are the dark areas that we observe on the sun's surface. The sun has a solar maximum (when sunspot activity is increased and huge prominence and flares erupt in the photosphere) and a solar minimum( when sunspot activity decreases). This is known as the sunspot cycle, which takes place every 11 years from maximum to maximum. Recently a visitor asked me if studying sunspots were important to science. Absolutely. Sunspots give us volumes of information on the health of the sun. The cycle of sunspots from maximum to maximum is not always the same. It becomes serious when sunspot maximums do not increase to their normal levels as they should. Look back in history at the Maunder Minimum. The sun went for many cycles during the 1700's without achieving it's normal increase in activity as the maximum came around. It has been called the little ice age. Vast forest areas were timbered to keep people warm in their houses, all over the planet. Earth's climate changed during this period of inactivity of the sunspot cycle. If it happens in the future, the consequences could be more serious. Populations will then number into the tens of billions. Increasing demands for food and energy are just a few of the concerns we will have to deal with if the sunspot cycle takes a vacation or as one student put it, the sun catches a cold.