Our Solar System The solar system is the

Our Solar System

• The solar system is the sun and all objects that orbit the sun under its gravitational influence. • Our solar system has 1 sun and 8 planets, several dwarf planets, an asteroid belt, a bunch of moons, some Kuiper Belts things. . .

Regents Question Which event takes the most time? (1) one revolution of Earth around the Sun (2) one revolution of Venus around the Sun (3) one rotation of the Moon on its axis (4) one rotation of Venus on its axis Answer is… 1

Regents Question Compared to Pluto, Mercury moves more rapidly in its orbit because Mercury (1) is larger (2) is more dense (3) is closer to the Sun (4) has a more elliptical orbit Answer is… 3

Elliptical Orbits • An ellipse is an oval shape. • All planets’ orbit are somewhat elliptical. • Within an ellipse, there are two fixed points called foci. • In our solar system, the sun is ALWAYS ONE of those foci.

Eccentricity • The more oval the orbit is, the more eccentric it is, or the higher the eccentricity. Increasing Eccentricity

Eccentricity • The degree of flatness or “ovalness” of an ellipse is measured by eccentricity. • This formula is on page 1 of your ESRT!

• Calculating Eccentricity: • (always a question on the exam or the practical. ) Major Axis X Focus 1 X Focus 2

An ellipse is an example of a “conic section”. Circles and hyperbolas are others. All are possible forms for orbits. You can make an ellipse with 2 tacks and a string. The tacks are the “foci”, and if you put them further apart, the ellipse is more “eccentric” (one tack would make a circle).

• Calculating Eccentricity: • When calculating eccentricity, it will never be greater than 1! If you get an eccentricity greater than 1, you’ve done something wrong. • The closer to 1 you are the more oval or eccentric the orbit. • The closer to 0 you are the less oval or eccentric the orbit.

Definitions Perihelion – when Earth is closest to the Sun Aphelion – when Earth is farthest from the sun

Regents Question Which planet’s orbit around the Sun is most nearly circular? (ESRT 15) (1) Mercury (2) Pluto (3) Neptune (4) Venus Answer is… 4

Gravity • The closer 2 objects are to each other, the greater the gravitational pull between them. • So, during the perihelion – when Earth is closer to the sun, there is a greater gravitational pull between it and the sun. • This makes the Earth speed up a bit in its orbit around the sun during that time.

When is Earth at Aphelion and Perihelion? Perihelion – Aphelion – January 2 -5 July 3 - 6 (depending on the year)

Planets move What do you noticequicker about the planets orbital velocity? the closer they are to the Sun Aphelion Perihelion

Kepler’s Second Law

Kepler’s Second Law of Planetary Motion 2. An imaginary line connecting the Sun to any planet sweeps out equal areas in equal time. . Area 1 Area 2

Distance between foci length of Major Axis X X Write the formula for eccentricity below: Page 1 of ESRT’s Calculate the eccentricity of the ellipse. 8. 8 Length of major axis: _______ 6. 4 Distance between foci: _______. 72 Eccentricity= _______

Distance between foci Length of Major Axis X X Calculate the eccentricity of the ellipse. 5. 4 Length of major axis: _______ Distance between foci: _______ 1. 3. 24 Eccentricity= _______

What is the minimum value that eccentricity 0 can be? ____ Doesn’t a circle look like a zero? ? 1

What is the maximum value that 1 eccentricity can be? ____ The more eccentric the more stretched out until you get a straight line Looks like the # one.