ASTR 217 - Wenatchee Valley College



ASTR 101 Name:

Lab 2 Planetary Orbits In Terms of Kepler’s 3 Laws of Planetary Motion

Kepler found that the planets all have elliptical orbits. He was the first to discover this.

What do Kepler’s three laws of planetary motion say?

Write all three of Kepler’s laws of planetary motion down on a separate piece of paper, or in a digital document on a computer, that you submit prior to performing this lab. Keep in mind that:

(1) You must clearly cite your source(s) of information.

(2) If you quote, you must use quotation marks.

(3) Many web sites and some books state some of the laws incorrectly or imprecisely.

(4) Original writing by you is required. Therefore, if you quote the three laws from a source (using quotation marks, of course), you will at least need to follow each quoted law with your comment on what it means, using your own completely original composing.

An ellipse is shown below.

[pic]

Semi- means half, so the semi-major axis is half of the major axis. By the same token, half of the minor axis is the semiminor axis. The semi-major axis of a planet’s elliptical orbit is its average distance from the Sun.

Draw an ellipse on the next page by putting the page on a piece of cardboard, putting pins or thumbtacks in each focus (big black dot), and tying a loop of thread or string so that the ellipse you draw stays within the left and right boundaries of the grid. Then answer the questions on that page.

Reminders: If units of measurement are involved, always write down the units. If numbers are involved, never put down more digits in your answer that can be justified by the input data.

| | | | | | |

|Mercury |0.3871 |0.2408 | | | |

|Venus |0.7233 |0.61515 | | | |

|Earth |1.0000 |1.0000 | | | |

|Mars |1.5237 |1.8808 | | | |

|Ceres |2.767 |4.5998 | | | |

|Jupiter |5.2028 |11.86461 | | | |

|Saturn |9.5388 |29.4589 | | | |

|Uranus |19.18 |84.0013 | | | |

|Neptune |30.0611 |164.8095 | | | |

|Pluto |39.44 |247.68 | | | |

1. Which planet or minor planet has the greatest absolute discrepancy

between the actual value and the calculated value of its period? _____________________

a. What percentage of the actual period is this discrepancy? Divide the discrepancy into the actual period and multiply the result by 100 to get your answer. Show your complete calculation here:

2. Which planet or dwarf planet has the greatest percentage discrepancy? _________________

a. What percentage is this discrepancy? Show your calculation and result in the following space:

3. What may be the cause of some of the actual periods varying a tiny bit from the theoretical periods?

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A

B

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