Rowan Introduction to Astronomy
/ An Introduction to Kepler’s
Reproducing ellipses via the “string
pencil method,” stu
dents will draw ellipses and determine their eccentricities.
g the orbits of five of Jupiter’
moons, students will test Keple’
s third law.
By using characteristics of Pluto
students will confirm Kepler’
s second law.
Kepler's three laws are simply a mathematical way of describing motions of objects that orbit a large central mass, such as the planets
which orbit around the Sun or the moons which orbit around Jupiter. This lab explores each of Kepler's three laws.
Kepler's First Law
[45 pts; you must draw and submit
ellipses to receive credit for this part]
Kepler’s first law states that
rbiting objects travel in
paths with the central mass at one focus. In this section, you will get
acquainted with ellipses by sketching one yourself.
Steps to draw an ellipse
Get two tacks or push pins and a piece of string. On your paper, place the two tacks or pins a small distance apart. Place your
string loop around the pins. Be sure to leave some slack in the string. Use a piece of cardboard to help secure the pins or tacks.
Using the string as a guide (i.e., place the pencil inside the string loop and pull the loop taut), draw an ellipse.
Attach your sketch to this lab report. [Answers for (c) and (d)
come from your drawing; guesses are
Now measure and write down the distance between the foci and the length of the major axis of the ellipse.
(d) Divide the distan
ce between the foci by the length of the major axis. This quantity is known as the eccentricity, “e.”