Wednesday January 13th 1999
Announcements:

Lecture notes:
How big is the Universe?
How small are we?

Demonstration of how to find the Big Dipper

Title of class
    We will cover atoms (5x10^-9cm) to galaxies (1x10²³ cm)
    100 000 000 000 000 000 000 000 cm in a big galaxy
want a way to write down very large numbers without all the zeroes
--called scientific notation

To use scientific notation count the zeroes
Examples:
10cm = 1 x 10¹ cm
100 cm = 1 x 10 ² cm
1000cm = 1 x 10³cm
Million stars in glob cluster = 1000000 stars = 1x10⁶ stars
for 2 billion stars = 2x10⁹
for 2.5 billion stars = 2.5x10⁹

Now we also want to be able to do simple math with scientific notation to get relative sizes
radius of earth is 6x10⁸cm
radius of solar system is 6x10¹⁴
How many times bigger is radius of solar system than the radius
of the earth?
=1x10⁶

Simple rule is 10^a/10^b = 10^(a-b)
in the above example 14-8 = 6 so 1x10⁶
solar system radius is about a million times larger than the
earth's radius

A few more useful numbers

• distance to nearest star = 4x10¹⁸ cm
• size of a galaxy = 3x10²² cm
• distance to nearest galaxy = 2x10²³ cm

So how much bigger is the distance to the nearest galaxy as the
size of our galaxy
2x10²³ / 3x10²² = 2/3 x10¹ = 6.6

Scale model of solar system
Earth is 1/10 of a cm in size
The solar system is the size of campus
Where is the nearest star?  about the distance to Los Angeles

Discuss Video
    Lots of distances in that video
    In this course you will learn how people actually measure
those giant distances

Today we'll start with a well known method to astronomers called parallax
Parallax = a method for finding the distances to fairly nearby objects like planets and some stars.

Far away objects move less.
Astronomers use the same effect with 2 telescopes to determine
distances