Radiative Properties of Cosmic Dust
A dust particle interacts with electromagnetic radiation in a way that depends on its cross section, the wavelength of the electromagnetic radiation, and on the nature of the grain: its refractive index, size, etc. The radiation process for an individual grain is called its emissivity, dependent on the grain's efficiency factor. Furthermore, we have to specify whether the emissivity process is extinction, scattering, absorption, or polarisation. In the radiation emission curves, several important signatures identify the composition of the emitting or absorbing dust particles.
Dust particles can scatter light nonuniformly. Forward-scattered light means that light is redirected slightly by diffraction off its path from the star/sunlight, and back-scattered light is reflected light.
The scattering and extinction ("dimming") of the radiation gives useful information about the dust grain sizes. For example, if the object(s) in one's data is many times brighter in forward-scattered visible light than in back-scattered visible light, then we know that a significant fraction of the particles are about a micrometer in diameter.
The scattering of light from dust grains in long exposure visible photographs is quite noticeable in reflection nebulae, and gives clues about the individual particle's light-scattering properties. In X-ray wavelengths, many scientists are investigating the scattering of X-rays by interstellar dust, and some have suggested that astronomical X-ray sources would possess diffuse haloes, due to the dust.
Read more about this topic: Cosmic Dust
Famous quotes containing the words properties, cosmic and/or dust:
“The reason why men enter into society, is the preservation of their property; and the end why they choose and authorize a legislative, is, that there may be laws made, and rules set, as guards and fences to the properties of all the members of the society: to limit the power, and moderate the dominion, of every part and member of the society.”
—John Locke (1632–1704)
“A cosmic philosophy is not constructed to fit a man; a cosmic philosophy is constructed to fit a cosmos. A man can no more possess a private religion than he can possess a private sun and moon.”
—Gilbert Keith Chesterton (1874–1936)
“Their errors have been weighed and found to have been dust in the balance; if their sins were as scarlet, they are now white as snow: they have been washed in the blood of the mediator and the redeemer, Time.”
—Percy Bysshe Shelley (1792–1822)