# ASTRO 4: THE STARS

### NOTE!   THIS CLASS IS NOT ABOUT:

 Planets The Big Bang The Expansion of the Universe Galaxies Dinosaur-Murdering Killer Asteroids

### Some "Q" examples

• Q. If someone moved the Sun to TWICE its current distance, how would its brightness change?

Qualitative answer: It would get fainter.

Quantitative answer: Based on the inverse square law with

 Brightness 1 , Distance2

 the Sun would be only 1 = 1 as bright. 22 4

• Q. How fast is a gaucho, who is napping at the equator, traveling due to the Earth's rotation?

Distance traveled = Earth Circumference   =   [ * diameter ]   =   24,000 miles

Time for gaucho to make a "trip around the world"   =   24 hours.

 Speed   = distance traveled = 24,000 miles = 1000 miles/hour time taken 24 hours

• Q. How fast are we all moving through space due to the Earth's orbit around the Sun?

 Distance traveled = circumference of Earth's orbit = x 186,000,000 miles (diameter of Earth's orbit) = 584,600,600 miles   =   5.846 x 108 miles

 Time taken:   1 year   =   365 days x 24 hours =   8,760 hours 1 day

 Speed   = distance traveled = 5.846x108 miles = 66,671 miles/hour (!) time taken 8,760 hours

### "Dimensional Analysis"

• Note that the "units" are important in these equations. They have to work out, and they can be used to divine the correct equation if your memory or physical reasoning abilities abandon you for some reason. For example:

• Q. How fast are we moving through...

Suppose you knew this was somehow related to how far we travel and how long it takes, but you can't remember the exact equation. You CAN remember that "how fast" must come out in units of velocity like miles/hour. So, lets try:

Speed = Distance traveled x Time taken

The units for the multiplication on the right-hand side are [miles x hours]

This can't be right. So, work backwards from the units; the way to end up with the right velocity units is clearly to take the distance traveled divided by the time taken. Then the units are: miles per hour [miles/hour]

Cosmetology is the cosmetic treatment of the skin, hair, and nails; Cosmology is the study of the origin and structure of the universe.
The goal of the Human Genome Project is to identify all of the genes and chemical bases in human DNA. Click on the link for more info.
Astrology is the study of how events on earth correspond to the positions and movements of astronomical bodies. Astrology professes to foretell the future and interpret the influence of the heavenly bodies upon the destinies of men.
Astronomy is a scientific study of celestial bodies to determine their positions, motions, compositions, etc...
Physics is the study of matter, motion, light and energy.

### Questions that you will learn the answers to in this class...

Q. Astronomy is most closely related to:

Q. While "at" the telescope, most astronomers wear:

(a)   Down jackets
(b)   Trendy Patagonia Synchilla jackets
(c)   Politically incorrect animal furs
(d)   Bermuda shorts and loud shirts