This is planetary radio. Matt Kaplan back from Vac from Vacation with a new edition of our show, well mostly new. If you're one of our KUCI... new

if you're one of our KUCI listeners you may be wondering what happened last week to that

promised repeat of our Arthur C Clark interview program.

Never fear we've included the conversation our Arthur C. Clark interview program.

Never fear, we've included the conversation with Sir Arthur

in this week's show, along with a new visit with Bruce Betts,

a new trivia contest question, and some exciting news about yet another

extra solar planet from the planetary societies, Amir Alexander. Let's get started

with Emily and a new listener question that will put us in orbit. Hi, I'm Emily Lochuwala with questions and answers. A listener asked, how do scientists

calculate a comet or asteroids orbit?

And how do they figure out what areas on Earth are best for observing the body?

How is it all time so perfectly?

The method that scientists use to track comets and asteroids is a perfect example of how we are still indebted to Copernicus, Kepler, and Newton, and their works dating back to the 16th and 17th centuries.

The breakthrough made by Kepler and Newton was to show that all planetary bodies move

in ellipses around the sun. An ellipse is not just any oval-shaped path. It is a mathematical

expression with very specific properties.

Today, if we detect an asteroid approaching Earth, we need only fit its observed position onto an elliptical path

with the sun at one focus of the ellipse and then we can project where it will go.

In principle, as few as three precisely observed positions, measured at three different times,

are adequate to determine the orbital ellipse.

In practice though, observations have errors so dozens or hundreds of observations may be used

to tie down the orbit.

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