Kepler's Laws

Planetary Motion-Kepler's Laws

Mrs. Bertram

How do Kepler’s laws describe Earth’s orbit?

Beginnings

Johannes Kepler, working with data painstakingly collected by Tycho Brahe (from 1576-1601) without the aid of a telescope, developed three laws which described the motion of the planets across the sky. 

Kepler’s First Law

Law of Orbits: All planets move in elliptical orbits, with the sun at 1 focus.

An ellipse is an oval shape centered on 2 points instead of 1 point.

The orbital period of a planet is how long it takes for it to travel a complete orbit around the Sun… a year!

Perihelion

Aphelion

Kepler’s Second Law

Law of Areas: A line that connects a planet to the Sun sweeps out equal (=) areas in equal (=) times.

Earth sweeps out a longer path when it is closer to the Sun.

Earth moves fastest when it is closest to the Sun

Kepler’s Third Law

Law of Periods: The square of the orbital period of any planet is proportional to the cube of the semi major axis of its orbit. 

P² = a³ If you know the distance of a planet to the Sun, you would be able to figure out its… orbital period. Basically… The closer a planet is to the Sun, the shorter its orbital period is. 

​Watch ME!

Multiple Choice

Which term describes the time it takes for Earth to complete one circle around the sun.

• Rotation
• Revolution
• Kepler's 1st Law
• Barycenter

Multiple Choice

Which term describes when the Earth spins on its axis.

• Rotation
• Revolution
• Kepler's Laws
• Precession

Multiple Choice

Kepler's first law states that the orbits of the planets are oval in shape or 

• ellipses
• perfect circles

Multiple Choice

A planet moves __________ when it is farthest from the sun. (faster or slower)

• faster
• slower

Multiple Choice

Kepler's 2nd Law deals with 

• the shape of the planets' orbits
• the speed/area the planet travels 
• the length of time it takes the planet to orbit the sun

Multiple Choice

The place where a planet is farthest away from the Sun in its orbit around the Sun is called the

• aphelion
• perihelion

Multiple Choice

The place where a planet is closest to the Sun as it orbits the Sun is called the

• perihelion
• aphelion

Multiple Choice

Planets orbit the Sun in a shape called a(n)

• circle
• ellipse
• focus
• perihelion

Multiple Choice

Which planet has an orbit with an eccentricity most similar to the eccentricity of the Moon's orbit around Earth?

• Saturn

• Mercury

• Earth

• Jupiter

Multiple Choice

Which bar graph correctly shows the orbital eccentricity of the planets in our solar system?

Multiple Choice

Which of the following planets has the least distance between the two foci of its elliptical orbit?

• Mercury
• Mars
• Venus
• Jupiter

Fill in the Blanks

Calculate the eccentricity of the ellipse to the nearest thousandth.

Multiple Choice

If the distance from F1 to F2 is 42,000 kilometers and the distance from A to C is 768,000 kilometers, what is the eccentricity of the orbit?

• .0356

• .0547

• 18.286

• .0005

Multiple Choice

Which sequence correctly lists the relative sizes from smallest to largest?

• our solar system, universe, Milky Way

  Galaxy

• our solar system, Milky Way Galaxy,

  universe

• Milky Way Galaxy, our solar system,

  universe

• Milky Way Galaxy, universe, our solar

  system

Multiple Choice

To an observer on Earth, the Sun appears

brighter than the star Rigel because the Sun is

• hotter than Rigel

• more luminous than Rigel

• closer than Rigel

• larger than Rigel

Draw

construct a bar graph to represent the average surface temperature for each planet

• Mercury: 440K

• Venus: 737K

• Earth: 288K

• Mars: 208K

• Jupiter: 163K

• Saturn: 133K

• Uranus: 78K

• Neptune: Minus 73K

Multiple Choice

Light and other forms of electromagnetic radiation are given off by stars using energy released during

• nuclear fusion

• conduction

• convection

• radioactive decay

Multiple Choice

Which two stars are most similar in luminosity?

• Betelgeuse and Barnard's Star

• Procyon B and Proxima Centauri

• Polaris and the Sun

• Alpha Centuri

Multiple Choice

The life-cycle path followed by a star is determined by the star’s initial

• mass and size

• temperature and origin

• luminosity and color

• luminosity and structure

Draw

Draw a line to describe the relationship on the graph