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Name: Darrell
Status: other
Grade: other
Location: NV
Country: N/A
Date: N/A

Pluto was discovered in 1930. It is said to orbit the sun in 248 years. We have had 78 years to observe Pluto. How do we know it takes 248 years to orbit the sun? Also how do we know the orbit varies 3 billion Km in those 248 years?

Once astronomers figure out exactly where the planet is and what speed and direction it is moving at that time, they can calculate its past and future orbit from Newton's equations of gravity and Kepler's Laws of Planetary Motion.

Richard Barrans, Ph.D., M.Ed.
Assistant lecturer, Department of Physics and Astronomy
University of Wyoming

Dear Darrell,

We know that Pluto takes 248 years to orbit the Sun because we now understand its orbit. You answered your question in the question! With so many observations, we know it well enough to plot its obit-- 248 year period-- and know its location well enough in the future to send a spacecraft to it! For the same reason, we know that Pluto's orbit sits so far from the Sun.

Good questions.

David H. Levy

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