29:52 Characteristics and Origins of the Solar System

Lecture 1....August 27, 2001

Overview of the Solar System

Incipitur: Introduction and Niceties

· Class List

· Purpose and goal of class; concentration on solar system astronomy. A case where one can develop and introductory science class almost totally with "hot off the press material".

· Course will also cover some very fundamental material that was known to the ancients. Will give you the pleasure of identifying the objects we discuss in the night sky, and seeing for yourself some of the fundamental things like the orbital motion of the planets (we can do this in the course of the semester).

· Introduction to the Web page (a clearinghouse for material in the course).

Topic 1: The Size and Geography of the Solar System, its Relation to the Stellar Universe

Let's pick some numbers out of the Appendices and talk about them.

(1) Radius of Earth = 6378 kilometers. (Basic unit of distance in the course will be kilometer; more fundamentally the meter.1 kilometer = 0.6214 miles. > Earth on blackboard

Let's go out in Outer Space

(2) Typical orbit of space shuttle is 250 - 400 kilometers above sea level. A long way to fall but not very far from Earth.

(3) Distance to Moon (nearest major astronomical object) = 384,000 kilometers. I should be picky and say that this is the average distance between the Earth and Moon. For those of you who have had some astronomy, I can be even more exact and say this is the semimajor axis. There is an excellent drawing of the Earth-Moon relationship in Figure P.6 on p7 of your textbook. The Moon is the furthest human beings have gone out into space, and that is likely to remain so for the foreseeable future.

(4) The next jump is a big one, to the Sun, which is the dominant object in the sky.

> Drawing of Sun-Earth relationship on BB. Also Mars Odyssey 2001 webpage with inner solar system right now.

The average distance of the Sun is 149.6 million kilometers (93 million miles). In terms of scientific notation this is 1.496 X 10**11 meters. This distance is so important in solar system astronomy that is has a special name, the astronomical units or au. The average distances of the planets in the inner solar system from the Sun are as follows:

· Mercury 0.387 au

· Venus 0.723 au

· Earth 1.0000000 au

· Mars 1.524 au

The picture on the MGS webpage shows how they are all oriented, even as I speak.

(5) The outer solar system contains big, massive, gaseous, weird planets.

> Galileo home page showing orbits of Jupiter and Earth.

You can see how much further Jupiter is from the Sun than the Earth; it is the closest of the outer or Jovian planets. The distances of the Jovian planets are as follows ( Nota Bene: I am taking these numbers from Appendix 7 of your book)

· Jupiter 5.20 au

· Saturn 9.54 au

· Uranus 19.19 au

· Neptune 30.06 au

A reality check: Uranus is 2.87 billion kilometers from Earth (1.78 billion miles) and Neptune is 4.50 billion kilometers (2.79 billion miles). We will see both of these objects in the evening sky, giving you a feel of the vastness of the solar system.

> Comments on where the planets are right now

(6) Neptune is the furthest out of the major planets, but objects are further out, including ones you could stand on. An important class is the Kuiper Belt objects, which are frozen worlds (including the planet Pluto) that extend outwards tens of astronomical units. It is believed they are the most primitive objects in the solar system.

Even further out is the Oort Cloud a frozen locker for comets, which extends out to tens of thousands of astronomical units.

(7) Finally we have the starry sky. When we get to the stars, we need a whole new unit of distance.

>blackboard drawing with dots representing stars

We use the parsec, which is 206,265 au (3.26 light years). The typical spacing between stars is a couple of parsecs.

But now let's go back to the solar system