The Discovery of Pluto

Pluto was discovered in 1930 by Clyde Tombaugh in America. He photographed various parts of the sky and used a 'blink comparator' to find objects in a Solar System orbit. This device allowed him to display two images of the same region taken on different dates and quickly switch between the two. Objects that had moved revealed themselves.

Pluto is the outermost planet in the Solar System. Pluto has an orbit approximately 15 degrees from the ecliptic. Its orbit brings it nearer to the Sun than Neptune for 20 years in its 249 year orbit.

Pluto is the smallest planet in the Solar System and is smaller than our own Moon. Pluto has a Moon of its own called Charon, discovered in 1978. Charon is quite large compared to Pluto; other planets' moons are quite small compared with their parent planet. The Pluto system can be considered to be a double planet. Charon has both a synchronous orbit and rotation meaning the same side of Charon faces Pluto at all times. Charon would also appear to stay in the same part of the sky if you were standing on Pluto. Pluto has a very weak atmosphere.

Because of Pluto's size and orbit, some astronomers questioned whether Pluto should be called a planet. It could instead be thought of as the largest body in the Kuiper belt, an area beyond Neptune containing many asteroids and minor planets such as Pluto. Large bodies with extended and eccentric orbits such as Pluto have been discovered in recent years.

One object was found to be larger than Pluto and was later called 'Eris'. Rather than add Eris to the list of planets, astronomers reclassified Pluto as a "Dwarf Planet" (along with Eris).



- Clive Tombaugh
- 1930
- Photography


Photographic discovery of Pluto by Clyde Tombaugh. Hover over the image below to see how Pluto was found using a blink comparitor.

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Did you know?

Pluto was visited by a probe called 'New Horizons" in 2015.

Until 2006, Pluto was recognised as a planet. An International Astronomy Union (IAU) vote downgraded it to a 'dwarf planet'.

See Also

Pluto Nine Planets