Whenever we speak about the stars and their nature, it is also necessary to talk about electromagnetic waves, because stars produce one of the most widespread electromagnetic waves known as light. Being a form of electromagnetic energy light is let out from a point source, in our case it is a star. The light is a small part of the visible electromagnetic energy. Different frequencies or wavelengths characterize electromagnetic waves.
Wavelengths of different types form the electromagnetic spectrum, including radio waves, heat waves, infrared, visible waves, ultraviolet waves and roentgen and gamma rays.
So, light is spread in the form of the wavefront (spherical shape) in all directions; however, the human eye can catch the light only when it falls onto the retina, despite the fact that light is spread in all directions. One of the main characteristics of light is the speed of light, which is 186,000 miles per second (300,000 Km per second) in the vacuum. The rate of light has become a universal constant of the theory of relativity which is denoted as “c.” The speed of light is lower in such substances as water or glass. The importance of light is excellent for all species living on the Earth. Light makes different objects visible; it helps to differentiate colors and shapes; sunlight serves as the central resource for photosynthesis in plants while being necessary for other chemical reactions.
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Speaking about the Universe and its structure it is necessary to take into consideration the fact that it’s is possible to see what Universe is formed by only with the help of a unique device – telescope. Universe constitutes a hierarchy of stars and planets.
The grouped stars build a unique structure called a galaxy. The universe consists of more than 100 billion galaxies, while each galaxy comprises about 100 billion of stars. Without a telescope, a human eye may only see about 3,000 stars. The Sun is also a star, which illuminates and warms the Earth. “The sun is in a galaxy called the Milky Way that contains more than 100 billion stars” [4].
A star is a hot incandescent sphere of gas, held together by its gravitation, and emitting light and other forms of electromagnetic radiation whose ultimate source is nuclear energy. [2].
Every star is characterized using five main features, including brightness, which is described star’s luminosity or magnitude; color; size; mass, which describes the amount of matter a star posses; and temperature on the surface. According to the magnitude, it is possible to distinguish six types of stars, starting with the stars of the first magnitude, representing the brightest stars in the galaxy, and ending with six magnitude stars, which are the faintest ones. Regarding color, it is possible to distinguish dark and bright red stars, yellow stars and blue stars. The color of a star depends on its surface temperature, and very few stars possess only one color. For example, the temperature of “dark red stars have surface temperatures of about 2500 K; surface temperature of a bright red star is approximately 3500 K; that of the sun and other yellow stars, roughly 5500 K; blue stars range from about 10,000 to 50,000 K in surface temperature” [4]. Sizes of different stars are measured with the help of radius of the sun. Size and temperature of the star determine how bright it will be (star’s luminosity).
Looking at the night sky gives the idea that stars remain there forever, however, it is not so. Every star has its life cycle, the length of which is determined by individual characteristics of a star.
Stars are born in nebulae, which is a huge cloud of dust and gas. Under the forces of gravitation, these clouds began to collapse, forming protostars (young stars). Young stars consist of 97% of hydrogen and 3% helium. Later these young stars collapse again and they enter another phase known as the main sequence. This is the longest phase of a star. For example, “a medium-size star will live in the hydrogen phase, called the main sequence phase, for about 50 million years” [3]. Mass and temperature are principle characteristic features determining how long a star will live. To live longer, a star needs to be stable, which means that force of gravitation must be balanced with the amount of gas expanding. As it has been mentioned above, the longest phase of all-stars is the main sequence, during which a star burns it hydrogen fuel. Stars begin to fade when their helium reserves start to burn, however, the fading period may last for billions of years for stars with low mass (the sun, for example).
In conclusion, life cycles of stars last billions of years, but it is still possible to notice that stars are changing and don’t live forever, like everything on the Earth.
Bibliography
Hale, George Ellery. (1926). Beyond the Milky Way. C. Scribner’s Sons.
Star. (2004). The Columbia Encyclopedia, Sixth Edition,
Star Life Cycle
http://aspire.cosmic-ray.org/labs/star_life/starlife_main.html
Stars. http://www.nasa.gov/worldbook/star_worldbook.html
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