Vocabulary - Understanding Revolution in. our Solar System

Transcription

1 Vocabulary - Understanding Revolution in Universe Galaxy Solar system Planet Moon Comet Asteroid Meteor(ite) Heliocentric Geocentric Satellite Terrestrial planets Jovian (gas) planets Gravity our Solar System Revolution Kepler s Laws of orbits Orbit Ellipse Eccentricity Foci (focal points) Major axis Apogee Aphelion Perigee Perhelion Orbital speed Astronomy Cosmology

2 ORBITS work according to very set mathematical rules. Kepler figured this all out and gave us the laws of orbital motion!

3 Remember, gravity is the force of revolution. Gravity makes the world go around the sun and keeps us, the atmosphere, and everything else firmly in place. Closer together or bigger mass means stronger gravity field Further apart or smaller mass means weaker gravity field It s a mass and distance thing!

4 The elliptical shape of the orbits and gravity are the key to understanding a satellite s speed in orbit, so let s first investigate the orbit shape an ellipse! Which of these shapes is an ellipse?

5 Draw some ellipses. Be sure to number the foci and the ellipses so you know how they relate. What happens to the shape of the ellipse when the foci are close together or far apart?

6 Using this simple change from circular orbits to elliptical orbits, the theory of revolution was updated to match the observations of astronomers! Finally, the math could be done and Kepler s Laws of Orbits unified the heliocentric theory and revolution! Of course, it took Newton, and eventually Einstein, to figure out gravity made it work but that s another story!

7 KEPLER s LAWS of ORBITS e = distance between foci length of major axis LAW 1 - ORBIT SHAPE: Orbit s shape is slightly elliptical and is mathematically described its eccentricity (e)

8 KEPLER s LAWS of ORBITS LAW 2 - SATELLITE s SPEED in ORBIT: closer = faster and further = slower because gravity field is stronger when a planet is closer to sun Fastest at perigee (closest place on orbit path) slowest at apogee (farthest away).

9 KEPLER s LAWS of ORBITS LAW 3 - ORBIT SIZE: uses math to say that further away from sun results in a bigger orbit and a longer year!

10 The elliptical shape of the orbits and gravity are the key to understanding a satellite s speed in orbit, so let s start with Kepler s first law of orbits Which of these shapes is an ellipse?

11 But this is an ellipse, too! WHY? CIRCLE with one center point and an EQUAL RADIUS and DIAMETER in all directions We usually think of extreme ELLIPSES like this

12 REVIEW Ellipses DO NOT HAVE one radius CIRCLE with one center point and an EQUAL RADIUS in all directions Ellipses HAVE UNEVEN DIAMETERS in different directions Ellipses HAVE TWO FOCAL POINTS (FOCI) along their major axis at their center

13 But ellipses are not circles! SOME TERMS FOR ELLIPSES MAJOR AXIS is the LONGEST DISTANCE and goes through the two focal points (foci) Why is the sun in this picture? It s one of the foci in the solar system. The other focal point is just math! FOCAL POINTS (FOCI) are the 2 mathematical center points along the major axis

14 Draw some ellipses. Be sure to number the foci and the ellipses so you know how they relate. What happens to the shape of the ellipse when the foci are close together or far apart?

15 Eccentricity = a measure of how circular or elliptical an orbit is Eccentricity (e) = _distance between foci (d) length of the major axis (L) MAJOR AXIS is the LONG DIAMETER FOCAL POINTS (FOCI) are the 2 center points.

16 Now calculate the eccentricity of two of the ellipses you drew Mathematically, what happens to the shape of the ellipse when the foci are close together or far apart? When measuring with the ruler, round to tenths of a centimeter After calculating, round eccentricity to thousandths

17 Let s make sure we get it! Lab Elliptical Path Note: this concept is 1/3 of your lab test in June!

18 Eccentricity (e) = _distance between foci (d) length of the major axis (L) FOCI CLOSE TOGETHER LOOKS MORE CIRCULAR Call it SLIGHTLY ELLIPTICAL LESS ECCENTRIC e closer to 0 FOCI FURTHER APART LESS CIRCULAR Call it MORE ELLIPTICAL MORE ECCENTRIC e closer to 1

19 Are the orbits of the planets around the sun very elliptical or only slightly elliptical? Is there a difference between terrestrial and jovian planets?

20 Are the orbits of the planets very elliptical? Is there a difference in eccentricity between terrestrial and Jovian planets orbits? 1. Get your evidence first! Rank the planets orbits in order of increasing eccentricity. Do they group together? Calculate the average eccentricity for all the planets in our solar system, the Jovian planets, and the terrestrial planets. MAKE A DATA TABLE to summarize your results! GROUP MOST ECCENTRIC LEAST ECCENTRIC AVG ECCENTRICITY ALL PLANETS TERRESTRIALS JOVIANS

21 Which planets orbits are least elliptical and most elliptical? Larger eccentricity values mean orbit is more elliptical.