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The Swiftest Planet
Sun-scorched Mercury is only slightly larger than Earth's moon. Like the moon, Mercury has very little atmosphere to stop impacts, and it is covered with craters. Mercury's dayside is super-heated by the sun, but at night temperatures drop hundreds of degrees below freezing. Ice may even exist in craters. Mercury's egg-shaped orbit takes it around the sun every 88 days.

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Just the Facts
Just the Facts
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  News Features People Extreme Facts Dictionary

 
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nephelometer

An instrument that uses measurements of scatterred light from a laser beam to detect and study cloud particles.

Neptune
Neptune is the eighth planet from the sun. Named for the ancient Roman god of the sea, it is the fourth largest planet in our solar system.
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Neptune
neutrino

A fundamental particle supposedly produced in massive numbers by the nuclear reactions in stars. They are very hard to detect since the vast majority of them pass completely through the Earth without interacting.

nitrogen

A colorless and odorless gas that is makes up the largest part of the Earth's atmosphere.

nuclear fusion

Anuclear process whereby several small nuclei are combined to make a larger one whose mass is slightly smaller than the sum of the small ones. The difference in mass is converted to energy by Einstein's famous equivalence E=mc2. This is the source of the Sun's energy therefore ultimately of (almost) all energy on Earth.

nucleus

A core. In the case of a comet, it is the central, solid part made of ice and dust.

Diagram of parts of a comet - nucleus, coma and tail.
 
Can't find it? Don't understand it? Ask us.
Q
NASA Logo
nephelometer

An instrument that uses measurements of scatterred light from a laser beam to detect and study cloud particles.

Neptune
Neptune is the eighth planet from the sun. Named for the ancient Roman god of the sea, it is the fourth largest planet in our solar system.
HREF="../planets/profile.cfm?Object=Neptune">More on Neptune >>

Neptune
neutrino

A fundamental particle supposedly produced in massive numbers by the nuclear reactions in stars. They are very hard to detect since the vast majority of them pass completely through the Earth without interacting.

nitrogen

A colorless and odorless gas that is makes up the largest part of the Earth's atmosphere.

nuclear fusion

Anuclear process whereby several small nuclei are combined to make a larger one whose mass is slightly smaller than the sum of the small ones. The difference in mass is converted to energy by Einstein's famous equivalence E=mc2. This is the source of the Sun's energy therefore ultimately of (almost) all energy on Earth.

nucleus

A core. In the case of a comet, it is the central, solid part made of ice and dust.

Diagram of parts of a comet - nucleus, coma and tail.