# What is an ellipse circle kepler s first law the

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What is an Ellipse?
Keplers First Law:The orbit of each planet aroundthe Sun is anellipsewith the Sun at one focus.What are Keplers 3 laws of planetarymotion?planetClosest pointto SunFarthest pointfrom SunNote: This is an extreme ellipse. Noplanetary orbits are this elliptical. That is, the foci are closertogether.
Keplers Second Law:As a planet moves aroundits orbit, it sweeps out equal areas in equal times.it means that a planet travelsfasterwhen it isnearer to the Sunandslower when it is farther from the Sun.The speed of a planetsmotion is NOT constant.
p2=a3p=orbital period inyearsa=average distance from Sun inAU(In words: the period squared equals the orbitsemi-major axis cubed. If you know the period,you know the distance from the Sun, and viceversa.)Keplers Third Law:More distant planets orbitthe Sun at sloweraveragespeeds, obeying therelationship:1 AU = 1 Astronomical Unit = 150 million km = 93 million miles = 8 lightminutes = the average distance from Earth to Sun
Class PollAn asteroid orbits the Sun at an averagedistancea= 4 AU. How long does it take toorbit the Sun?
Hint: Remember thatp2=a3.
Class PollAn asteroid orbits the Sun at an averagedistancea= 4 AU. How long does it take toorbit the Sun?a3
How did Galileo solidify the Copernican revolution?Galileo Galilei (1564-1642) overcame majorobjections to the Copernican view.Three key objections rooted in Aristotelianview were:1.Earth could not be moving becauseobjects in air would be left behind.2.Non-circular orbits are notperfectas heavens should be.3.If Earth were really orbiting Sun,wed detect stellar parallax.Again, the Scientific Method at work. The doubters were notbeing unreasonable, and it took EVIDENCE to reveal the truth.
Galileos detailed mechanical experiments showed thatobjects in air wouldstaywith a moving Earth.Overcoming the 1st objection (nature of motion):Aristotle thought that all objects naturally come torest.This is not true.Galileo showed that objects willstay in motionunless a force acts to slow them down• This is explained more fully by Isaac Newtons FirstLaw of Motion; Newton was born the year Galileodied. [We will study Newtons work soon.]
Overcoming the 2nd objection (heavenly perfection):Tychos observations oftransitory objects like comets andsupernovas (the suddenappearance of a new star) alreadychallenged this idea.• Using his newly inventedtelescope, Galileo saw:üsunspots orimperfectionson the Sun.

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