What is the TRUE shape of Earths orbit

What is the TRUE shape of Earth’s orbit? By the end of this lesson (and the lab) you should be able to: • Explain the shape of the planet’s orbits • Identify the focus and major axis • Describe and calculate eccentricity • Draw ellipses

Describe a circle without using the word round. • A closed loop where all points on it are the same distance from the center.

Johannes Kepler • Carefully studied the position of planets in the sky (and the moon) and proposed 3 Laws of Planetary Motion

Kepler’s First Law • The orbits of the planets are ellipses with the sun at one focus. • Huh? What’s an ellipse? What’s a focus?

An ellipse is a shape which is a closed curve drawn around TWO fixed points. The points of an ellipse are the foci (singularfocus)

So if this were Earth’s orbit, the sun is located at one focus of the ellipse! • But this is actually WAY exaggerated! • So how can we compare ellipses?

Eccentricity • Eccentricity describes how “un-round” an ellipse is. Increasing Roundness

ES R T Calculating Eccentricity • Eccentricity = distance between the foci length of the major axis ALWAYS SHOW WORK IN THREE STEPS AL ER T!

• Eccentricity (“e”) will always be a number between 0 (a circle) and 1 (a straight line)

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Johannes Kepler’s 3 laws 11