## Astronomy

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# Energy flux

Energy Flux
the rate of flow of energy through a reference surface. In cgs units, measured in erg s-1. Also measured in watts, where 1 watt = 1 x 107 erg s-1. Flux density, the flux measured per unit area, is also often referred to as "flux".

Energy Flux - The rate at which a wave carries energy through a given area
Energy Level - Any of the many energy states that an atom may have. Different energy levels correspond to different distances of the electron from the nucleus ...

Sum of the energy flux from all the gamma ray bursts =
1.942E8 joules/m^2 ...

sound energy flux The average rate of flow of sound energy for one period through any specified area.

where S is the energy flux and T is the absolute temperature. For a , , and for a transparent gas cloud, .

sound ~ density (NASA SP-7, 1965) = sound intensity. sound field (NASA Thesaurus / NASA SP-7, 1965) A region containing sound waves. See near field, far field.

If absorbed, the pressure is the ~ density divided by the speed of light. If the radiation is totally reflected, the radiation pressure is doubled. For example, the radiation of the Sun at the Earth has an ~ density of 1370 W/m2, so the radiation pressure is 4.

Calculate the ~"that is, the energy received per unit area per unit time"that would be observed at Earth from a 1037-W Seyfert nucleus located at the Galactic center, neglecting the effects of interstellar extinction.

If you add up all the light emitted by a blackbody then you would get the total ~ carried by that light.

Recall that the ~ in a blackbody goes like temperature to the fourth power, so a small change in temperature amounts to a substantial reduction in the emitted flux or brightness. Hence sunspots are dark.

The decreased transparency of the stellar material blocks the ~ and heats the gas, and the increased pressure pushes the envelope out, thus increasing the star's size and luminosity. As the star expands, it cools and He2+ gains an electron, converting back to He+.

Their importance to the solar corona mystery may be critical. "These waves must eventually dissipate and dump their energy into the corona," Liu tells Astronomy Now. "The waves have a very large ~, 10,000 watts per square metre, comparable to the flux needed to heat the corona." ...

(b) In radio astronomy energy is usually measured in units of 10-26 W m-2 Hz-1. The factor seems to have been first used in 1951; it is interesting to note that radio astronomers have always measured ~ in terms of square metres. (see Jansky) [JM92]
FOC ...