![]() ![]() ![]() Much of the work on the project was done by Annie Jump Cannon, Williamina Fleming and Antonia Maury and Edward Pickering. It was called the Henry Draper Catalogue because the funding for the project had been provided by Henry Draper. An A-type main-sequence star (A V) or A dwarf star is a main-sequence ( hydrogen burning) star of spectral type A and luminosity class V (five). They are fairly rare, making up only 0.13 of main-sequence stars. They are typically colored blue-white, slightly less blue than O-type stars. The new system of classification was published in the 1920s and included 225,300 stars. Community in: Astronomy, Stars, True Stars Class B star View source A Class B star is the second-brightest type of main sequence star. Next to the O-type star is the B-star for having a higher mass than the A-type, F-type, G-type. Stars near the beginning or end of their lives are not part of this classification. In terms of the highest mass, an O-type star is an answer. O stars are the least common and M are the most common found in the main sequence of stars. Each letter was also divided into tenths of the range by adding a number 0-9 to the end. The new system reordered the classes into the order OBAFGKM where O stars are the hottest and each successive class is cooler with M being the coolest stars. They adapted an existing spectral class system which had assigned stars a letter from A to O based on the strength of Balmer series absorption lines. They wanted to develop a detailed spectral classification system based on the absorption lines they were seeing. Examples of O-type stars are Mu Columbae (spectral type O9.5 V) and Mu Normae (a supergiant, spectral type O9.7Iab). Nevertheless in the early 1900s, a team of astronomers at Harvard College Observatory started a project to examine the spectra of hundreds of thousands of stars. At first astronomers did not understand why different stars would have different absoprtion lines. He found that different stars have different absorption lines in their spectra. In 1817 a German instrument maker named Joseph von Fraunhofer attached a spectroscope to a telescope and pointed it at the stars. Red dwarfs are the most common type of star. A normal star forms from a clump of dust and gas in a stellar nursery. Astronomers have always been fascinated by the different sizes and colors of stars that they observed. A red dwarf is a small, cool, very faint, main sequence star whose surface temperature is under about 4,000 K. Main sequence stars with a spectral type of O are the coolest stars in the universe they have a surface temperature of only 3,500 Kelvin. NASA’s Solar Dynamics Observatory captured this image of our 4.6-billion-year-old Sun, a main sequence. ![]()
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