DICTIONARY LOOKUP
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Our Nearest Neighbor
Our moon makes Earth a more livable planet by moderating our home planet's wobble on its axis, leading to a relatively stable climate, and creating a tidal rhythm that has guided humans for thousands of years. The moon was likely formed after a Mars-sized body collided with Earth and the debris formed into the most prominent feature in our night sky.

Earth's Moon Icon
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Just the Facts
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  News Features People Extreme Facts Dictionary

 
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Q
valles or vallis

Sinuous valley.

vastitas

Widespread lowlands.

velocity

The speed and direction of an object.

Venus
Second planet from the sun. Named for the Roman goddess of love and beauty.
HREF="../planets/profile.cfm?Object=Venus">More on Venus >>

Full Face of Venus
viscosity

The measure or property of a material to be resistant to flow; the internal friction of a material. Materials with a high viscosity are more resistant to flow, while those with a low viscosity are more fluid.

viscous relaxation

The process whereby topographic features become subdued over time due to the flow of the surrounding geologic material.

volatile

As a noun, this refers to substances that are gases at ordinary temperatures. In astronomy it includes hydrogen, helium, water, ammonia, carbon dioxide and methane.

volcanic

Produced or discharged from a volcano.

volcanism

The eruption of molten material or gas-driven solid fragments onto the surface of a planetary body. On icy moons the phenomenon is sometimes called cryovolcanism to distinguish it from silicate or sulfur volcanism. (Image: A volcano blasts material off the surface of Jupiter's moon Io.)

Volcanic plume from Jupiter's moon Io
volcano

A mountain formed from the eruption of igneous matter through a source vent.

 
Can't find it? Don't understand it? Ask us.
Q
valles or vallis

Sinuous valley.

vastitas

Widespread lowlands.

velocity

The speed and direction of an object.

Venus
Second planet from the sun. Named for the Roman goddess of love and beauty.
HREF="../planets/profile.cfm?Object=Venus">More on Venus >>

Full Face of Venus
viscosity

The measure or property of a material to be resistant to flow; the internal friction of a material. Materials with a high viscosity are more resistant to flow, while those with a low viscosity are more fluid.

viscous relaxation

The process whereby topographic features become subdued over time due to the flow of the surrounding geologic material.

volatile

As a noun, this refers to substances that are gases at ordinary temperatures. In astronomy it includes hydrogen, helium, water, ammonia, carbon dioxide and methane.

volcanic

Produced or discharged from a volcano.

volcanism

The eruption of molten material or gas-driven solid fragments onto the surface of a planetary body. On icy moons the phenomenon is sometimes called cryovolcanism to distinguish it from silicate or sulfur volcanism. (Image: A volcano blasts material off the surface of Jupiter's moon Io.)

Volcanic plume from Jupiter's moon Io
volcano

A mountain formed from the eruption of igneous matter through a source vent.