The Physics Factbook
Edited by Glenn Elert -- Written by his students
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|Starlight. Astronomy. Microsoft Encarta. 2001.||"Astronomers use a star's light to determine the star's temperature,composition and motion.Astronomers analyze a star's light by looking at it's intensity at different wavelengths.Also known as Wien's displacement law (developed by German physicist Wilhelm Wien) links the wavelength at which the most energy is given out by an object and its temperature. Astronomers put filters of different standard colors on telescope to allow only light of a particular color from a star to pass. In this way, astronomers determine the brightness of a star at particular wavelengths. From this information, astronomers can use Wien's law to determine the star's surface temperature."||N/A|
|What is the Hottest Star? Ask IO. [Excerpted from Compton's Interactive Encyclopedia, 1993, 1994.]||[see table below]||100,000 K|
|Harvard classification system. Encyclopedia Britannica. 2000.||"Class O includes bluish white stars with surface temperatures typically of 25,000-50,000 K (although a few O-type stars with vastly greater temperatures have been described); lines of ionized helium appear in the spectra."||50,000 K|
A star is a hot celestial body of glowing gas that varies in size, mass, and temperature with other stars. The smallest of stars are called dwarfs, and the largest of stars are called super giants. The density, temperature and pressure of the gas increase from the outside towards the center of the star. At each point within the star, the pressure of the gas is proportional to the weight of the upper layers.
Stars have a noticeable color and it's by a star's color that we are able to calculate its temperature. Stars differ in color ranging from blue-white to red. These stellar colors can be measured by several methods. The most commonly used method is the use of a photoelectric photometer, which can measure stellar colors with the aid of filters. The temperature of a star can be estimated by studying its spectrum because temperature determines the types of absorption lines present. Astronomers can obtain the surface temperature of star from measurements of its brightness at different frequencies.Then the astronomer will use the plank curve to obtain the surface temperature.
Stars are divided into seven broad groups by the system of spectral classification known as the Henry Draper Catalog. These groups have a sequence in order of decreasing temperature which goes as follows: O, B, A, F, G, K, and M. The O type stars are the hottest and the M type stars are the coolest. R, N, and S type stars supplement this sequence. These stars are not included in the Henry Draper Catalog because of their different chemical composition.
There is a more modern system of spectral classification called the MA system. The luminosity class is assigned to the star along with the Draper spectral class. One example is the Alpha Percy; it would be classified as H5 Id, which means that it falls about halfway between the beginnings of type F and type G. The Id suffix means that it is a particularly luminous star. The temperature of a star is usually measured on the Kelvin scale. The chart below shows the star types and their ranges of temperature.
|Star Type||Temperature Range (K)|
Asser Estriplet -- 2001
|NGC 2440 Nucleus: The Hottest Star? Astronomy Picture of the Day. 30 November 1995. Goddard Space Flight Center||"In the center of the above photograph lies a star with one of the hottest surface temperatures yet confirmed. This bright white dwarf star's surface has been measured at greater than 200,000 degrees Celsius - more than 30 times hotter than that of our own Sun. The white dwarf's extreme heat makes it glow extraordinarily bright: intrinsically more than 250 times brighter than the Sun."||200,000 K|
|Francis, Mike. What is the hottest star or asteroid in the universe? Mad Scientist Network.||"Bellatrix, the other shoulder in Orion, is one of the hottest stars we can see with the naked eye with an effective temperature of about 30,000 deg K."||30,000 K|
|Space Trivia. Stars R Us Amateur Astronomy.||"The central stars of planetary nebulae are the hottest known stars. They have been detected with surface temperatures up to 250,000 K. One example of a planetary nebula with such a hot central star is NGC 2240. At such high temperatures, most of the radiation is emitted in the ultraviolet part of the spectrum so the star is often not obvious in visual images of the nebula."||250,000 K|
|What are stars made of? Dr. Universe.||"The hottest star found is 40 times as hot as the sun."||220,000 K|
Editor's Supplement -- 2001
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