Glossary term: Optical Astronomy

Description: Optical astronomy is the practice of studying and observing the Universe (stars, planets, dwarf planets, asteroids, etc.) in the near-infrared, in visible light, and in ultraviolet light. The reason for lumping those three kinds of electromagnetic radiation together is that the optical telescopes, with glass lenses and/or metallic mirrors, that astronomers had originally constructed for observing visible light from celestial objects, are equally well-suited for observing near-infrared or ultraviolet light. In addition, the Earth's atmosphere is transparent not only for visible light, but for the directly adjacent infrared and ultraviolet regions, allowing all three kinds of observations from the ground. Last but not least, the camera chips astronomers use for visible-light observations can also detect near-infrared and ultraviolet light. Put all of this together, and the telescopes and instruments astronomers use to observe visible light work just as well for near-infrared and ultraviolet observations. In consequence, it makes sense for astronomers to collectively describe observations in that range of the electromagnetic spectrum with a single term, namely optical astronomy. The adjective "optical" is also used to describe the spectral range, as in "the optical part of the spectrum." Observations in that range are "optical observations".

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

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The silver-coloured Hubble Space Telescope with the blue ocean and white clouds of the Earth visible underneath.

Hubble Space Telescope over Earth

Caption: The NASA/ESA Hubble Space Telescope orbiting Earth. This picture was taken by astronauts on board the space shuttle Columbia, right after the Servicing Mission 3B to the space telescope itself. The telescope has an opening that allows light in (seen here on the left). The light travels through the telescope optics to the cameras and spectrographs located in the bulge at the other end of the observatory (seen here on the right). Data from these instruments is then sent back to Earth using an antenna. The black rectangles on either side of the observatory are the solar panels that provide it with power.
Credit: NASA/ESA credit link

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

The two Keck telescopes seen from above. The domes are open and the telescopes' mirrors can be seen inside.

Keck Telescopes

Caption: The two Keck telescopes on Mauna Kea on the island of Hawai`i. These two telescopes are reflecting telescopes with primary mirrors 10m across.
Credit: NASA/JPL credit link

License: PD Public Domain icons