Science of Stars

Stars are well recognized astronomical objects in our solar system and represent building blocks of galaxies. The history and dynamics of a star in a galaxy depends on its age, distribution, and composition. The stars are responsible for elements such as carbon, nitrogen, and oxygen. A star’s life begins very small, like many more things in the universe. They begin as, apart from anything else, particles in clouds of dust and gas. They remain cold for ages. The disturbance of a comet or other object that moves through the cloud will then make particles collide and clumps will begin to form. Over the course of a million years, clumps will grow into what we call â€Å"protostar† and draw in more gases and grow even hotter. This is how stars are formed and is a point in a star’s life. Astronomers determine composition, color, and temperature of stars and other distant objects with an essential tool called a spectroscopy. Astronomers have used this tool since the 1800’s to analyze emitted light spectra. When a star gives off light and the light splits by prism, the spectral pattern reflects a star’s composition. All stars are 95% hydrogen, so the variations in composition reveal its age, luminosity, and origin. Composition of gases can be determined by observing the light of a star. Astronomers can determine the temperature of a star from its color and its spectrum. All stars have different colors. They have different colors due to its light radiation. There are a few different ways astronomers can determine a star’s temperature. One way is to measure a star’s color. They use three filters that transmit light in three different wavelength ranges. Astronomers then take the intensity ratio of the light. Another way to determine the temperature of a star is to examine the spectral lines in the starlight. Science of Stars3 Astronomers also use a tool called the electromagnetic spectrum to determine the composition, temperature, speed, and rotation rate of stars and other distant objects. Rotation rates are measured by using telescopes or space probes. Astronomers pick a particular feature on an object and then determine how long the feature takes to move from one side to the other side. For an example, the Sun has a rotation rate of about 25 days. One planet in our solar system that is difficult for astronomers to observe rotation rate is Earth. That is because we live on Earth and rotate with it. As stars progress through their lives they move around in the H-R diagram since their properties change over a period of time. In the H-R diagram it plots luminosity, spectral type, and also temperature. If a star is plotted higher up on the diagram on the vertical plane, this means that the stars are brighter. If a star is plotted in the horizontal plane to the left, this means that these stars are the hottest. Stars spend most of their lifetime in what is known as the main sequence in the H-R diagram. In this phase of a star’s life, they burn hydrogen into helium. Also at this point, the star’s size and luminosity remain constant because their forces have reached a near-equilibrium. Stars will remain in the main sequence until they reach a certain mass. Stars that are called supergiants in the H-R diagram and lie along the top right are luminous and cool. The stars that are called white dwarfs and are plotted at the bottom left of the diagram are fainter, hotter stars. The red giant stars are the stars of great luminosity and size. They form a thick horizontal band that joins the main sequence. All the stars on the H-R diagram are plotted by their color horizontally and their luminosity vertically. All the colors are coded from O (blue), B (blue), A (blue-white), F (white), G (yellow), K (orange), and M (red). Science of Stars4 In the center of our solar system lies a star called â€Å"the Sun†. Its color is white, but appears to us on Earth as yellow and is considered a main sequence star. The life cycle of the Sun, just like any other star starts with a cloud of gas and dust composed mainly of hydrogen collapses under gravitational forces. It was formed about 4. 5 billion years ago determined by scientists using the Sun’s current main sequence age. Right now, the Sun is believed to be about halfway through its main sequence evolution. The Sun should spend about 10 billion years as a main sequence star. It will enter the red giant stage in about 5 billion years. By the time it reaches to be a giant star stage, the Sun will have lost about 30% of its mass due to a stellar wind. The orbits of the planets will move outward then. Eventually our Earth will be swallowed by the Sun. The Sun living in the main sequence is gradually becoming more luminous and its temperature is slowly rising. After the red giant stage, the Sun’s outer layers will be thrown off. It will cool and fade into the white dwarf stage. As of right now, the Sun’s life cycle is the main sequence stage. It is considered middle aged at 4. 5 billion years old. The Sun is currently fusing hydrogen in its core and has been for the last 5,000 million years, and it is expected to continue fusing hydrogen for at least another 4,000 million years. The main sequence stage is the longest and most stable phase of its existence and this stage lasts about 10 billion years for a star. The main sequence is also the first stage of a star after becoming a star, right after the protostar stage. The following stage after the main sequence stage would be the red giant stage. I have now discussed in this paper how astronomers determine composition, temperature, speed, and rotation rate of distant objects. I explained the properties of the stars in the H-R Science of Stars5 diagram, summarized the life cycle of the Sun, and also stated where the Sun is currently in its life cycle.