John K. Grammatico
The Sun is one of the billions of stars in our galaxy. Since it is so close to the Earth, we are able to use it as a learning link to the other stars in the galaxy. It is the only star whose surface and atmosphere can be observed directly from earth. We are able to study its basic properties such as size, temperature, mass, age, and chemical composition. By observing our Sun and Solar System, scientists have developed theories of their formation. To back up these theories, scientists are able to study the formation of new stars in our galaxy, which they believe is a process that is identical to the way our Sun and planets formed.
The Sun is about 93,000,000 miles away from Earth. Its light reaches us in a little more than eight minutes. It is thought by some that we experience seasons due to the changing distance from the Sun. In other words, the Earth is closer to the Sun during the summer and farther from the Sun during the winter. This is not true. As a matter of fact, the Earth is actually slightly closer to the sun in the middle of winter. If this is the case, then how do we experience seasons and temperature extremes? The Earth's equator is tilted 23 and a half degrees from the plane of its orbit around the Sun. This tilt affects the amount of sunlight different places on the Earth receive throughout the year. When the Northern Hemisphere is tipped towards the Sun, we receive sunlight for more than 12 hours a day, which is the reason for our long summer days. Moreover, since the Northern Hemisphere is tipped towards the Sun, we receive more direct sunlight than during the winter months. That is to say, the sun seems to be directly over us during the summer and the sunlight hits us more directly causing hotter days. During the winter months, the Sun's light hits us at an angle. Because of this angle, the light is more spread out and diluted causing cooler temperatures. To view this in another way, point a flashlight directly onto a wall a couple of feet in front of you. Notice how the light is dense and concentrated. This is the effect the Sun has on the Northern Hemisphere during the summer. Now take the flashlight and point it about 6 feet above your head onto the wall. Notice how the light is less concentrated in one area. Its luminosity is not as strong. The Sun has a similar effect during the winter when the Northern Hemisphere is tipped away from it.
The Sun's diameter is 865,280 miles, which is equivalent to 109 Earth diameters. Also, its mass is 332,946 times that of the Earth. Its gravitational pull is stronger than the Earth's. To escape the gravitational pull of the Sun, an object would have to travel 617.5 km per second. An object would have to travel 11.2 km per second to escape Earth's gravitational pull.
The surface temperature of the Sun is about 5,800 degrees Kelvin. The core is about 15,000,000 degrees Kelvin. The composition of the Sun is 92.1% hydrogen, 7.8% helium, and 0.1% other elements. All of these elements are in a gaseous state.
For most of its lifetime, a star gets its energy from a process called nuclear fusion. Stars, like our Sun, during this period are called main sequence stars. Our Sun has been in this phase for about 4.5 billion years. It has about another 5 billion to go before it depletes its hydrogen supply and will have to burn other elements. Each second, the Sun converts 5 million tons of hydrogen atoms into energy. All of this energy production is at the Sun's core.
THE SUN'S ATMOSPHERE
The atmosphere of the Sun begins with the photosphere. It is from this layer that almost all of the Sun's light is emitted. This layer has the lowest temperature of about 5,800 degrees Kelvin. It is also in this layer that sunspots are seen, which will be discussed later.
Just above the photosphere is the chromosphere. It is about 6,000 miles thick. In this layer, spikes of gases occur called spicules. Spicules have the appearance of a thick line of trees coming off of the Sun's surface. They rise to heights of 3,000 to 6,000 miles above the Sun's photosphere and last for about 10 minutes.
Finally, the corona extends above the chromosphere. This outer atmosphere is much hotter than the Sun's photosphere. It has an average temperature of about 2,000,000 degrees Kelvin. From this layer, gaseous streams extend millions of miles into space.
SUNSPOTS
High magnetic fields on the photosphere layer cause dark patches on the Sun called sunspots. They appear black or darker than their surrounding area because they are about 1,500 degrees Kelvin cooler. The sunspot's dark central region is called the umbra and the lighter outside region is called the penumbra. The penumbra acts like little metal shavings near a magnet, which gives scientists the idea that sunspots act as magnetic fields. Sunspots tend to be features that change shape and location and can last for days or months.
SOLAR FLARES
A solar flare is a quick and powerful eruption which occur near large sunspot groups and extend from the Sun. Flares release a huge amount of energy in a very short time. Erupted materials can reach speeds of up to 600 miles per second. A flare can have a lifetime of from 10 minutes to several hours.
PROMINENCES
A prominence can look like a solar flare. However, they can last from hours to days. Moreover, they can reach thousands of miles in altitude. Although a prominence appears to be erupted material from the Sun, as do solar flares, they are cool regions of the Sun's outer atmosphere that are moving along a magnetic field.
SOLAR ECLIPSE
A solar eclipse occurs when the Moon covers the Sun. When the Sun is completely covered by the Moon, it is called a total eclipse. When it is not fully covered it is called an annular eclipse. Some of the phases of a solar eclipse are known as a Bailey's bead. This occurs when parts of the Sun's photosphere are visible through lunar valleys. Another phase of a solar eclipse is called a diamond ring. This happens when an oval patch of light shines from behind the Moon giving it the effect of a diamond ring set on a circular disk. A schedule of solar eclipses will be included in this unit.
RAINBOWS
Rainbows are a beautiful sight and we usually see a correlation between a rain shower and the presence of a rainbow. When we see a rainbow we are seeing the Sun's light passing through water droplets. The light refracts or bends on waterdrops that behave like prisms and spread sunlight into their separate colors. When this refracted light reflects off the inside of the water droplet, a rainbow occurs. Its colors include violet, blue, green, yellow, orange, and red. The most effective rainbows occur when the Sun is near the horizon. Rainbows do not occur when the Sun is high in the sky.
SUN HALO
One may witness a phenomenon that looks like a circular rainbow surrounding the Sun. This is called a Sun Halo. It occurs when the Sun's light refracts in the ice crystals that form in the very high cirrus clouds. The colors of a Halo are not as vivid as a rainbow's because the ice crystals have a variety of shapes and sizes.
EARLY ASTRONOMERS AND THEIR DISCOVERIES
The so-called "Golden Age" of astronomy was from about 600 B.C. -150 A.D. and celebrated in Greece, although some scientists argue that the Golden Age is right now. Although the Greeks used philosophical thought to render decisions of astronomical anomalies, they also relied on empirical data. As they developed geometry and trigonometry, they were able to assess sizes and distances of the Sun and Moon.
The Greeks, however, believed that the Earth was a motionless body at the center of the Universe. Some early Greeks believed in a rotating Earth, but most thought that the Earth was too large to move and in fact they had no feeling of motion.
The early Greeks also noticed that all of the stars, except for seven, remained in the relatively same position to one another. The seven bodies, called planets by the Greeks, included the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn. Each was thought to have a circular orbit around the Earth.
One of the first important astronomers to emerge after the Middle Ages was Nicolaus Copernicus. He purported that the Earth was a planet and that a rotating Earth could explain the motions of the heavenly bodies. Upon this conclusion, Copernicus reconstructed the Solar System with the Sun at the center and the Planets rotating around it.
Another scientist, Galileo Galilei, became interested in constructing telescopes after hearing about a Dutch lens maker that devised a system for magnifying objects. With his telescope, he made some important observations. One relative to this unit is the discovery of sunspots. Be tracking these blemishes, he concluded that the Sun has a rotational period of about a month.
In the 1600's, the Roman Church refused the Copernican theory because of beliefs that it was contrary to scripture. They also told Galileo to abandon his beliefs of the Copernican theory. He, however, refused and began working on a written work called Dialogue of the Great World Systems. Although this book was published, readers became aware that it held the views that were contrary to the Roman Church. Galileo was placed under house arrest and remained there for the last ten years of his life. Despite his restrictions, including total blindness, he continued working.