29:52 Characteristics and Origins of the Solar System

            Lecture 1….January 21, 2004            Overview of the Solar System

 

Incipitur: Introduction and Niceties

             http://skyandtelescope.com/   (Picture of  “Spirit” Landing Site)

·                     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".   A perfect example is the Mars Exploration Rover that “rolled out” about a week ago. 

·                     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). 

·                     This is the best semester possible to view the important objects in the solar system.  This semester, you will see in the evening sky :  (1)  Four of the five major planes which are visible to the naked eye (Venus, Mars, Jupiter, and Saturn),  (2) Saturn at its best apparition in over a decade, (3) the asteroid Ceres will be an easy binocular object in the constellation of Gemini, (4) A transit of Venus (Venus moves across the Sun) in June, (5) the arrival of the Cassini spacecraft at Saturn in October.

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

·                     An apology to my students from Modern Astronomy from last semester.  The course you took last semester and this one do have a bit of overlap,  and at times (like today)  you might think you are hearing a rehash of material.  However,  there  will be more than enough new material presented to justify this as a completely independent 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.  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 Exploration Rover webpage with inner solar system right now.   http://mars.jpl.nasa.gov/mer

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 MER  (Mars Exploration Rover)  webpage shows how they are all oriented, even as I speak.

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

Ø       Cassini  home page showing orbits of Jupiter and Earth.  http://saturn.jpl.nasa.gov/index.cfm

Ø        

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

·                     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).

 

> Comments on where the planets are right now:   Venus is the very bright object in the western sky right after sunset.  Mars is further up and to the east.  Saturn is a bright object in the eastern sky   as soon as it gets dark,  and Jupiter rises around 10PM. 

 

(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