DICTIONARY LOOKUP
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The Hottest Planet
Venus is a dim world of intense heat and volcanic activity. Similar in structure and size to Earth, Venus' thick, toxic atmosphere traps heat in a runaway 'greenhouse effect.' The scorched world has temperatures hot enough to melt lead. Glimpses below the clouds reveal volcanoes and deformed mountains. Venus spins slowly in the opposite direction of most planets.

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  News Features People Extreme Facts Dictionary

 
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habitable zone

A region around a star within which a planet can have temperatures that permit liquid water.

heliocentric

Sun-centered. The planets in our solar system are in heliocentric orbit around the sun.

heliopause

the point at which the solar wind meets the interstellar medium or solar wind from other stars. Click on the diagram to the right to see a detailed diagram of our solar system's boundaries.

Diagram of heliopause and heliosphere
heliosphere

The space within the boundary of the heliopause containing the Sun and solar system.

helium

The second lightest and second most abundant element. Helium was first discovered in our Sun. Roughly 25 percent of our Sun is helium. This gas is very light and is used to inflate balloons.

high sun

The condition of the sun being directly overhead (analogous to noon) which eliminates shadows on the surface. When planetary images are obtained in high sun conditions they are examined for albedo information rather than morphologic information (see Terminator). Areas imaged under both high and low sun conditions can be compared to link albedo and morphologic features.

hydrogen

The lightest and most abundant element. A hydrogen atom consists of one proton and one electron. Hydrogen composes about 75 percent of the Sun but only a tiny fraction of the Earth.

 
Can't find it? Don't understand it? Ask us.
Q
habitable zone

A region around a star within which a planet can have temperatures that permit liquid water.

heliocentric

Sun-centered. The planets in our solar system are in heliocentric orbit around the sun.

heliopause

the point at which the solar wind meets the interstellar medium or solar wind from other stars. Click on the diagram to the right to see a detailed diagram of our solar system's boundaries.

Diagram of heliopause and heliosphere
heliosphere

The space within the boundary of the heliopause containing the Sun and solar system.

helium

The second lightest and second most abundant element. Helium was first discovered in our Sun. Roughly 25 percent of our Sun is helium. This gas is very light and is used to inflate balloons.

high sun

The condition of the sun being directly overhead (analogous to noon) which eliminates shadows on the surface. When planetary images are obtained in high sun conditions they are examined for albedo information rather than morphologic information (see Terminator). Areas imaged under both high and low sun conditions can be compared to link albedo and morphologic features.

hydrogen

The lightest and most abundant element. A hydrogen atom consists of one proton and one electron. Hydrogen composes about 75 percent of the Sun but only a tiny fraction of the Earth.