Astronomers Analyze Electromagneti Emissions of Stars and...

In order to glean information about stars, astronomers analyze electromagnetic emissions, or the light, that reaches Earth. A spectroscope is basically a device that focuses a beam of light through a prism, which divides the light into characteristic colors that can then be seen using an eyepiece or screen. The resulting spectrum is used to determine the chemical composition of stars. The lines on the spectrum, or spectral lines, are associated with known elements. In 1868, an unknown element was discovered and given the name helium. It was almost thirty years before the element would be detected on Earth (McMillan, 2011). The accepted classification scheme is a combination of two, the Harvard system types stars based on†¦show more content†¦For about another thirty million years, the star continues to contract and its central density, central temperature, and surface temperature increase; then it is a main sequence star where pressure and gravity are balanced and nucle ar energy is being generated in the core. It takes forty to fifty million years for a star to reach this stage. The Sun is a main sequence star (McMillan, 2011). Stars spend approximately eighty percent of their lives on the main sequence before evolving into something else. A star leaves the Main Sequence when it has exhausted most of the hydrogen in its core, which causes it to lose equilibrium. It begins to contract again as radiation and thermal pressure decrease, and gravity dominates. Even though core hydrogen fusion ceases, energy is still generated in the core because of gravitational contraction. While the Main Sequence is the hydrogen core fusion stage, the first stage after the Main Sequence is the hydrogen shell fusion stage of a star’s life. During the hydrogen shell fusion stage, the nuclear fusion rate is considerably greater than during the Main Sequence. Changes in the outer layers of a star occur as the internal changes are happening. Increased pres sure causes enormous expansion in the outer layers of the star, which leads to them cooling because they are farther away from the core. Visible