29:52 Characteristics and Origins of the Solar System

January 28, 2004

. Addendum to Lecture 3

1. Diagram of why leap years are necessary, see text of Lecture. Diagram below shows progressive lagging behind of the Earth in its orbit if every years consisted of 365 mean solar days.

2. For internet students: we are mailing you your very own SC1 chart. Use it to follow along. It should arrive by the beginning of next week.
3. Addendum to item 7 of the lecture notes. Let’s demonstrate that something I said was true a couple of lectures ago. Below are the celestial coordinates of the four planets visible in the evening sky. These coordinates are valid for late January, 2004.

Planet	Right Ascension	Declination
Venus	23h 24m	-5d
Mars	1h 43m	+11d 17m
Saturn	6h 42m	+22d 25m
Jupiter	11h 21m	+5d 31m

Note: 5d 31m (for declination) means 5 degrees and 31 minutes of arc. One minute of arc is 1/60 of a degree, so this is about 5.5 degrees.

4. Where do we see planets in the sky?

Let’s talk about with relation to the Sun.

This shows the orbit of a planet inside the orbit of the Earth. When the planet is closest to the Earth, it is at inferior conjunction. When it is at its most distant from the Earth, it is at superior conjunction.

See figure 3.2 of the textbook for further illustrations, and the definition of opposition and conjunction for a planet outside the orbit of the Earth.