Discovering Families of Planets
Our Sun's family of planets (sizes and distances not to scale). Credit: NASA


When early astronomers looked into the night sky, they saw mostly stars, but five of those points of light “wandered” among the constellations of stars. The word “planet” comes from a Greek term meaning “wanderer.”

planets line up in April 2002From our vantage point on Earth, the five other planets, Mercury, Venus, Mars, Jupiter, and Saturn all can be seen changing positions against the background of stars as they orbit our Sun.
Without telescopes, early astronomers were not aware of Uranus, Neptune, Pluto, or any of the other dimmer bodies wandering through our own Solar System.

The invention of the telescope ushered in the discovery of even more wanderers within our Solar System.  The planet Uranus was discovered in 1781, over 170 years after the telescope was invented. Then came the discovery of the asteroid Ceres, then Neptune, and finally little Pluto in 1930. And that was the end of planet-finding for more than 60 years.

(Diagram of the visible planets gathered in the western evening sky in April of 2002. Next time is June 2040.)

Astronomers wanted to search among the stars, but planets around other stars are usually too faint to be observed directly, even with our best telescopes.
artist conception of planets around a distant star
In 1995 astronomers used instruments to detect the tiny wobble of distant stars that revealed the presence of orbiting planets. This “wobble” technique led to a surge of planet discoveries.  Watch the short Activity Video to learn more about the "wobble" technique:
http://nightsky.jpl.nasa.gov/download-view.cfm?Doc_ID=59

These weren’t more wanderers circling our own Sun — these planets orbited other stars — stars that are thousands of times more distant than the planets in our own Solar System.

Over the following years, astronomers gathered evidence for hundreds of stars with families of planets, each family of planets different from our own. The search continues today, using multiple techniques for discovery.
Gemini

Which is the brightest other star with a planet orbiting it?


One of the very brightest stars with an orbiting planet is Pollux, a star in the same constellation where Pluto was first spotted — in Gemini. Pollux’s planet was confirmed in 2006. This is the same year that Pluto was re-classified as a dwarf planet.

Pollux gained a planet and our Solar System lost one!


To see our own Solar System's planets through a telescope, click here to locate your nearest astronomy club.




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Discovering the Sky (Photo Credit: Lake County Astronomical Society)

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Go StarGaze, the NASA Night Sky Network astronomy app, developed by the Astronomical Society of the Pacific, helps you find astronomy clubs and their stargazing events on the go!





 
Distant Suns, your personal guide to the cosmos, lists Night Sky Network astronomy club star parties, safe solar gazing events, and lectures in the main navigation bar. Distant Suns is available on iPhone, iPad, Kindle, and NOOK.




SkySafari, a powerful planetarium that fits in your pocket, lists Night Sky Network astronomy club star parties, safe solar gazing events, and lectures in the help menu. SkySafari is available for Android and the iPhone, iPad, and iPod Touch.


Clear skies and happy stargazing!


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