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Geolens

Glossary

417 words used in the labs.

Find a term from the labs, understand the process behind it, and see how it appears in the landscape. Each entry connects an explanation with a real observation and a model you can explore.

Term

Astronomical unit

Also written: AU

A defined length of 149,597,870,700 m, approximately Earth's mean distance from the Sun; abbreviated au or AU.

What to look for

SDO's time sequence of the 2012 Venus transit. Such alignments require the planet to be near an orbital node. Historical transit timing helped determine the Earth–Sun distance, now represented by the precisely defined astronomical unit.

Related labs

Solar system →Universe scale →
A sequence of dark Venus silhouettes crosses the Sun in SDO ultraviolet observations.
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Explore further with USGS water glossary · USGS volcano glossary · NPS glacial geology · NASA Earth facts. Photograph acknowledgements are collected on the Image credits page.