Lesson 2

• In the early 1600s, Johannes Kepler proposed three

  laws of planetary motion.
• Kepler was able to summarize the carefully collected

  data of his mentor, Tycho Brahe, with three

  statements that described the motion of planets in a

  sun-centered solar system.
• The Law of Ellipses - The path of the planets

  about the sun is elliptical in shape, with the center

  of the sun being located at one focus.
• The Law of Equal Areas - An imaginary line

  drawn from the center of the sun to the center of

  the planet will sweep out equal areas in equal

  intervals of time.
• The Law of Harmonies - The ratio of the squares

  of the periods of any two planets is equal to the

  ratio of the cubes of their average distances from

  the sun.
• An ellipse is a special curve in which the sum of the

  distances from every point on the curve to two other

  points is a constant.
• The two other points (represented here by the tack

  locations) are known as the foci of the ellipse. The

  closer together that these points are, the more

  closely that the ellipse resembles the shape of a

  circle. In fact, a circle is the special case of an ellipse

  in which the two foci are at the same location.
• An ellipse has two foci (focus 1 & focus 2).

  An ellipse has two axes.

  The long one is called the major axis. Half of it is

  called semi major axis

  The short one is called the minor axis.
• The orbital period of the planet is the length of time it

  takes for it to travel a complete orbit around the sun.

  The Earth’s orbital period is 365 days or 1 year.
• THE FIRST LAW: THE LAW OF ELLIPSES


  Explains that planets are orbiting the sun in a

  path described as an ellipse.
• Kepler's First Law states that all planets move along an elliptical orbit with the Sun at one focus.
• The eccentricity of an ellipse can be defined as the

  ratio of the distance between the foci to the major

  axis of the ellipse.
• The eccentricity is zero for a circle.
• THE SECOND LAW: THE LAW

  OF EQUAL AREAS


  An imaginary line joining a planet and the sun

  sweeps out an equal area of space in equal

  amounts of time.
• In law of equal areas, Planets move fastest when they are at their closest point to the Sun (called perihelion) and slowest

  when they are at their farthest point from the Sun

  (called aphelion).
• THE THIRD LAW: THE LAW OF HARMONIES

  planet, the square of its time period will always be the same as the cube of the length of its semi-major axis or from the sun.
• The third law is the only law that compares one planet’s orbital characteristics to another planet’s orbital characteristics.
• It is FALSE that the time for the Earth’s one complete

  revolution is equal to 365.25 days since it should be

  365 days.
• During JULY, the Earth is moving the slowest.
• MERCURY AND VENUS are the planets between

  Earth and the sun since the order of the planets

  from the sun are Mercury, Venus, Earth, Mars,

  Jupiter, Saturn, Uranus, and Neptune.
• The Earth’s radius is 4,000 miles or 3958.9 miles

  long to be exact, and its circumference is 24,873.6

  miles.
• The Earth sized the FIFTH LARGEST compare to

  other plants since the order of the planets from

  largest to smallest are Jupiter, Saturn, Uranus,

  Neptune, Earth, Venus, Mars, and Mercury.
• 7.5 BILLION PEOPLE currently live on Earth

  although technically this number changes everyday.
• The scientists think life began on Earth 3.8 BILLION

  YEARS AGO and the Earth is at least 4.5 BILLION

  YEARS OLD
• We have been calling this planet “Earth” for AT

  LEAST 1,000 YEARS and Earth is the only planet

  that is not named after a Greek or Roman god or

  goddess.
• Earth is a terrestrial planet which means that IT IS

  MADE MOSTLY OF ROCK. The other terrestrial

  planets are Mercury, Venus, and Mars.
• The have FOUR LAYERS. They are the inner core,

  the outer core, the mantle, and the crust.
• The Earth core has 9,200 DEGREES FAHRENHEIT

  or 5426.667 DEGREES CELSIUS. A more recent

  study suggests that it could be even hotter perhaps

  even as hot as the sun.