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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

Perihelion

The point in an orbit where a body is closest to the Sun. Earth reaches perihelion in early January. The changing distance affects incoming solar energy, while Earth’s axial tilt explains the opposite seasons of the two hemispheres.

What to look for

Hubble observed Comet ISON on 2 November 2013, before its closest approach to the Sun. Perihelion names that closest orbital point; the coloured filters show coma and tail structure, not a map of the orbit.

Related labs

Why seasons happen →
Hubble observations of Comet ISON's bright coma and tail on 2 November 2013, before perihelion.
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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.