Appearance
Zodiacal light is produced by sunlight reflecting off dust particles in the solar system known as cosmic dust. Consequently, its spectrum is the same as the solar spectrum. The material producing the zodiacal light is located in a lens-shaped volume of space centered on the sun and extending well out beyond the orbit of Earth. This material is known as the interplanetary dust cloud. Since most of the material is located near the plane of the solar system, the zodiacal light is seen along the ecliptic. The amount of material needed to produce the observed zodiacal light is quite small. If it were in the form of 1 mm particles, each with the same albedo (reflecting power) as Earth's moon, each particle would be 8 km from its neighbors. The gegenschein may be because particles directly opposite the sun as seen from Earth would be in full phase.
According to Nesvorny and Jenniskens, when the dust grains are as small as about 150 micrometres in size, they will hit the Earth at an average speed of 14.5 km/s, many as slowly as 12 km/s. If so, they pointed out, this comet dust can survive entry in partially molten form, accounting for the unusual attributes of the micrometeorites collected in Antarctica, which do not resemble the larger meteorites known to originate from asteroids. In recent years, observations by a variety of spacecraft have shown significant structure in the zodiacal light including dust bands associated with debris from particular asteroid families and several cometary trails.
Read more about this topic: Zodiacal Light
Famous quotes containing the word appearance:
“You speak of poverty and dependence. Who are poor and dependent? Who are rich and independent? When was it that men agreed to respect the appearance and not the reality?”
—Henry David Thoreau (1817–1862)
“What! Would you make no distinction between hypocrisy and devotion? Would you give them the same names, and respect the mask as you do the face? Would you equate artifice and sincerity? Confound appearance with truth? Regard the phantom as the very person? Value counterfeit as cash?”
—Molière [Jean Baptiste Poquelin] (1622–1673)
“February is a suitable month for dying. Everything around is dead, the trees black and frozen so that the appearance of green shoots two months hence seems preposterous, the ground hard and cold, the snow dirty, the winter hateful, hanging on too long.”
—Anna Quindlen (b. 1952)