Several years later, the classifications were reordered to be in what scientists now know to be the order of decreasing temperature: O, B, A, F, G, K, M, in order to have a smooth transition between the class boundaries. At the time, she did not know that these lines were due to hydrogen, but since they were visible in almost all stellar spectra, they provided a convenient means by which to organize her data. Scottish-American astronomer Williamina Paton Stevens Fleming (1857 –1911) initially classified 10,000 stars using the letters of the alphabet to denote the strength of their hydrogen absorption lines, with A being the strongest, followed by B, C, etc. The basis of the current system of classification of spectral types began in the late 1800s at the Harvard College Observatory, under the direction of Professor Edward C. He eventually extended this categorization, dividing more than 4,000 stars into four classes. In 1863, Italian astronomer Father Angelo Secchi (1818 –1878) made one of the first attempts at trying to classify stars, when he divided stars into two groups based on their spectral lines. In an attempt to understand the processes that formed the spectra, similar stars with similar spectra were grouped together in the hopes that stars that were alike would produce similar spectra. The first stellar spectra were observed in 1814, long before the atomic physics that creates them was understood. Thus, the number, strengths, and positions of these lines vary from star to star. Atomic physics predicts the positions and intensities of these lines, called absorption lines, based on the temperature and composition of the star. These layers absorb light at specific wavelengths, which are unique for each type of atom or ion. These lines are created by atoms and ions (atoms missing or acquiring one or more electrons) in the outer layers of a star ’s atmosphere. When the light from a star is divided into its component colors using a spectrograph, it appears as a continuous band of colors, broken up by dark, narrow lines. Although roughly 10% of stars do not fit into the classification scheme, it provides a convenient way to understand the systematics of stellar formation and evolution. Stars are classified according to the patterns and relative strengths of their dark spectral lines, which are indicators of both their temperature and their intrinsic luminosity, or brightness. This is the basis for the classification scheme used by astronomers. In order to be able to study stars systematically, it is useful to classify stars with others that have similar properties. The positions, strengths, and shapes of these lines are determined by the temperature, density, gravitational fields, velocity, and other properties of the star. A typical star has a spectrum consisting of a continuous range of colors overlaid with dark lines. Although the composition of most stars is very similar, there are systematic variations in stellar spectra based on their temperatures.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |