comet tails

comet tailsclick for a larger image
comet tails

comet tails

Tails of gas and dust that point in the antisolar direction away from the cometary nucleus and appear only when a comet is near the Sun, i.e. closer than about 2 AU (see illustration). Not all comets have tails. The luminosity is due to both molecular and atomic emission and to reflection of sunlight. The gas and dust is forced away by radiation pressure and by solar-wind interactions. There are two markedly different types of comet tails. The ion tail (or plasma tail) is usually straight and bluish, showing many diverse visible and rapidly changing structures. It consists exclusively of ionized molecules, moving at velocities between 10 and 100 km s–1, the repulsive force being 20 to 100 times greater than gravity. The tail can be a million km wide and lengths of 10 million km are not uncommon. Sometimes large sections of the ion tail can break away (see disconnection event). Dust tails are more strongly curved than ion tails. They contain solid particles, which simply reflect sunlight. Particles are ejected from the nucleus along curved paths known as syndynames. The tail is an envelope over the reflection regions of particles of similar mass. The closer the dust tail is to the ion tail in curvature the smaller are the dust particles responsible for reflecting sunlight; they are usually 10–100 micrometers in diameter.

References in periodicals archive ?
The 6-wk group was further investigated by linear regression analysis between olive tail moment (reflecting both the length and intensity of Comet tails) and percentage tail DNA (reflecting only Comet tail intensity) (Fig.
space where comet tails flash the sky before we can blink reflections in
I'll start with comet tails, but our main topic this month is the many constellation tails that appear on the May meridian.
comet tails, planetary rings, and star-forming regions) for over four decades.
Since comet tails have ionized gases, they are also affected by the sun's magnetic field, and can act as tracers of the complex magnetic system higher up in the solar atmosphere.
She said: "It's a firework with strobe effects, bursts, swirls, comet tails and a finale of golden glitter.
Plasmas are dusty when they contain solid or liquid particles with negative or positive charges; they show up in such places as planetary rings, comet tails, interplanetary and interstellar clouds, and around artificial satellites and space stations.
Overlapping comet tails decrease the credibility and accuracy of the assay.
These hard spots, according to Sadayappan, are reactions between the boron grain refiner and impurities in the alloys, and can produce comet tails during polishing causing rejection of finished components.
A spacecraft could travel through regions of the solar system picking up ions from the many invisible comet tails that probably crisscross our solar system," says George Gloeckler of the University of Maryland, College Park.
Mr Jones said: "Now we can learn a great deal more about what conditions are like in comet tails by studying data from instruments which have actually been there.
Now we can learn a great deal more about what conditions are like in comet tails by studying data from instruments that have actually been there, rather than trying to work it out from observations made from the Earth.