Science Starter Answer the following in your notebook: 1. When is the Earth closest to the Sun? 2. Does the speed of the Earth’s revolution change? 3. How can we tell if we are moving faster?

Today’s Agenda Science Starter History of Astronomy Lab Simulation Vocabulary Review Activity Haley’s Comet Summarizer

Lesson Essential Question How do planets move through space?

Historical Models of our Solar System and Kepler’s Laws of Planetary Motion

Geocentric Model Earth is center of our Solar System Aristotle- Over 2000 years ago Unexplained on how planets appear to move backwards Ptolemy- Planets move in small circles or epicycles

Heliocentric Model Sun is center of our Solar System Copernicus- Over 450 years ago (1543 ad) First to suggest heliocentric theory and vaguely mapped out the planets orbiting the sun in a circular orbit. Theory published on his deathbed. Initially not supported and took over 50 years for it to be accepted. Now backwards motion of planets (retrograde) was explained.

Galileo Supporter of Copernicus’s Heliocentric theory House arrest Observed moons orbiting Jupiter and theorized objects can revolve around other planets not just Earth placed under house arrest and was forced to denounce theory or be executed

Solar System precisely measured Tycho Brahe- studied Solar System and made very accurate recordings of his observations Tycho’s assistant, Kepler, used information for the details of orbits Tycho’s published recording of the solar system not used by Kepler until after Tycho’s death

Kepler’s Laws of Planetary Motion 1st Law - Law of Ellipses Each planet orbits the Sun in a path called an ellipse or elongated circle Ellipse is a closed curve whose path is determined by 2 points or foci within the ellipse Focus 1 is the Sun and Focus 2 is an imaginary point 1st Law) Law of Ellipses Each planet orbits the sun in a path called an ellipse or elongated circle Ellipse is a closed curve whose path is determined by 2 points or foci within the ellipse (circle use 1 point or focus ) One focus or point is located within the sun The other focus or point is not within an object The major axis runs through both foci points and the semimajor axis is the planet’s average distance from the sun

Eccentricity Degree of elongation or shape of planet’s orbit Ratio between the foci and length of major axis Circular =0 Very elongated =1 Elliptical orbits can vary in shape and can be described in terms of Eccentricity (e) Eccentricity is the degree of elongation or shape of a planet’s elliptical orbit. It is the ratio of the distance between the foci and the length of the major axis. circular =0 and extremely elongated e=1

2nd Law – Law of Equal Areas An imaginary line between the Sun and a planet sweeps out equal areas in equal times as the planet travels around the ellipse. Perihelion planet is closest to the sun, Aphelion planet is furthest away from sun

Keplers’ 2nd Law- Law of Equal Areas This also means that as the planet comes closer to the Sun in its orbit, it travels faster. So, the planets speed is slowest when it is the farthest from the Sun

What time of the year is Earth moving faster in its orbit? Challenge Question What time of the year is Earth moving faster in its orbit?

Challenge Question What time of the year is Earth moving faster in its orbit? Winter (closer to the sun)

3rd Law – Law of Periods Mathematical relationship P2 = a3 a= semi-major axis (planets average distance from Sun measured in AU’s) p= planet’s orbital period (time) Simply means that the farther a planet is from the Sun, the longer it takes to orbit around the Sun We can predict the period of rotation if we know the length of the semimajor axis Or we can predict the length of the semimajor axis if we know the period of rotation

Einstein (1879-1955) Changed Newton’s gravitational theory based on findings of Mercury’s orbit. Developed Theory of Relativity. It completely changed the way we study gravity and even changed our understanding of the universe. Theory of relativity- gravitational mass is identical to inertial mass. Einstein’s theory of general relativity is based on the idea that we live in a four dimensional universe called space-time. It tells us that all matter shapes space-time by curving it, so to speak, and that these curves determine how matter moves through space-time. In other words, the orbits of the planets are not caused by a direct attraction to the Sun, they simply follow straight lines in curved space.

Kepler’s Lab Simulation Each group will sign out a laptop (1 per group) Each person at the group will have a lab sheet to fill out Work together in your group to answer the questions and make sure everyone understands! DO NOT VISIT OTHER SITES BEYOND THE SIMULATION!! (LOSS OF LAPTOP) If you finish early: show Mr. Houtz your work, return your laptop, and grab a vocabulary activity from the front

Kepler’s Lab Simulation Suggested that you break up the work like so: Computer Manager (signs out laptop) Question Answerer (makes sure all group understands) Task Manager (makes sure group is working at ALL times & follows the procedures) Researcher (Keeps notes out to answer analysis questions, ask Mr. Houtz for help)

Vocabulary Activity Grab a vocabulary activity from the front of the classroom The sheet has 4 activities for you to complete You can use your notes or the book to answer (Ch.22-24) Should be completed by the end of class

Haley’s Comet Haley’s Comet follows the orbit path above, cycling once every 80 years. When is Haley’s comet moving fastest & how do you know? (close or far from the sun) Why does Haley’s comet not orbit the Sun in a circle? How is Haley’s orbit similar to the Earth’s revolution?