Astronomical Unit temperature

The extinction for dust particles is found to follow the empirical relation sx = 0.008 k 4/3 mag pc-1 (Equation 5.3 - a truly terrible astronomical unit for a scientist ). Calculate the extinction per metre at a wavelength of 501 nm. The light from a star at 501 nm is 0.25 of that expected for a star with that surface temperature and the extinction is attributed to dust in an interstellar cloud. Calculate the diameter of the cloud along the line of sight. 

Astronomical units 1AU = 1.496 x 10s km. 1 Maximum day-time high temperature at the equator,... 

The age of the sun is 4.6 x 109 years. Its composition is 75% H, 24% He, and at least 70 other elements, up to 1% of the total. Its distance from the earth is minimum (= perihelion) 147.1 x 109m on about 3 January, maximum (= aphelion) 152.1 x 109 m on about 4 July, mean 149.6 x 109 m (this mean value is defined as the astronomical unit of length, AU). Summers are warmer in July in the Northern Hemisphere because the solid angle subtended by the earth is bigger in July than in January (even though the sun is farther). The surface temperature of the sun is 5500° C the temperature at the center of the sun is estimated at 1.5 x 107oC. 

Figure 5.5 Winds in the solar nebula might be one of the possible processes responsible for the mixing of hot and cold components found in both meteorites and comets. Meteorites contain calcium-aluminum-rich inclusions (CAIs, formed at about 2000 K) and chondrules (formed at about 1650K), which may have been created near the proto-Sun and then blown (gray arrows) several astronomical units away, into the region of the asteroids between Mars and Jupiter, where they were embedded in a matrix of temperature-sensitive, carbon-based cold components. The hot component in comets, tiny grains of annealed silicate dust (olivine) is vaporized at about 1600 K, suggesting that it never reached the innermost region of the disk before it was transported (white arrows) out beyond the orbit of Pluto, where it was mixed with ices and some unheated silicate dust ( cold components). Vigorous convection in the accretion disk may have contributed to the transport of many materials and has been dramatically confirmed by the Stardust mission (Nuth 2001).

Photo/thermal Degradation. Samples of etched ( <2.5 pm) and unetched ( X/7.5 pm) POP film were placed in quartz tubes which were continuously evacuated while being heated at temperatures >450 C in a constant temperature block, controlled to 2 C. Other film samples contained in quartz tubes evacuated to <10 Torr were exposed to a Hanovia 450-watt mercury lamp with the etched side facing the lamp. At 14 cm from the lamp, the intensity of the uv radiation incident on the films was equivalent to <5.9 times that of the Sun in the 2000-3500-A range at 1 astronomical unit, i.e., just outside the atmosphere. At that distance from the lamp, the temperature of... 

FIGURE 2.6 Midplane solar nebular temperatures (K) calculated for 0.04 and 0.02 solar masses in the accreting disk, and estimated temperatures from meteorites and comets, plotted against distance from the sun, expressed both as astronomical units (1 AU = Earth-Sun distance) (bottom) and planetary distance (top). The temperatures presented here are indicative only, as they are dependent upon the size of the disc and the thermal model used (after Boss, 1998). 

The solar constant is defined as the total radiative energy flux outside the Earth s atmosphere. This parameter is used to characterize the total solar radiation input. The magnitude of this constant is estimated by Brusa and Frohlich (1982) to be 1367 W m-2, at 1 AU (astronomical unit), which corresponds to an effective solar temperature of 5780 K. 

Where radiative control dominates, the luminosity (L) of the proto-Sun soon provides a radiant flux that drops off according to an inverse square law (L/47tr ), in which solid particles absorb that flux rather efficiently and re-radiate it in a steady state as thermal radiation (oT ). In this radiatively controlled regime, T varies as l/r, and T is therefore proportional to 1/r, a much weaker dependence. Nonetheless, from the perihelion of Mercury (0.31 Astronomical Units from the Sun) to the aphelion of Mars (1.68 AU), the temperature must still have varied by a factor of 2.3. Since the vapor pressures of solids vary exponentially with 1/T, this is a very significant difference. 

Temperature scales Hot and cold are qualitative terms. For quantitative descriptions of temperature, you need measuring devices such as thermometers. In a thermometer, a liquid expands when heated and contracts when cooled. The tube that contains the liquid is narrow so that small changes in temperature can be detected. Scientists use two temperature scales. The Celsius scale was devised by Anders Celsius, a Swedish astronomer. He used the temperatures at which water freezes and boils to establish his scale because these temperatures are easy to reproduce. He defined the freezing point as 0 and the boiling point as 100. Then he divided the distance between these points into 100 equal units, or degrees Celsius. 

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