PURDUE UNIVERSITY

EAS 105-THE PLANETS

Prof. Robert L. Nowack

 

Lecture 1

 

Science is an organized method for exploring nature.  Science involves 5 basic steps:

 

 

 

(1) An observation is noted.

 ------------------ >

 

 

(2) A hypothesis is put forward to explain observation in terms of a physical model.

 ------------------ >

 

 

(3) Use model to compare with new observations.

 ------------------ >

Physical model must be revised.  < ---No

Go to (2)

 

(4) Does model predict new observations?

 

                        Yes!

 

Without the possibility of checks or tests, a hypothesis is just speculation and not a part of science!

 

            Ex.)   Apple falls from tree > theory of gravity formulated > Moon's orbit around Earth predicted by theory of gravity.

 

            Ex.)   Hypothesis: Humans live in the Galaxy Andromeda.   Test?

 

Science is not all-inclusive.  It is simply a set of methods for investigating nature.

 

Planetary Science - the study of other worlds.  Although astronomers are now finding evidence of planetary bodies around different star systems, we will here emphasize planets we can visit with existing technology.  This means the Solar System.

 

There are two approaches to study planets:

 

(1)  Catalog facts - What is out there?

(2)  What physical and geologic processes shaped the planets?  What might be out there?

 

We will try to emphasize both of these at an elementary level.

 

 

 

Space, Time and Matter

 

The universe is measured in terms of three basic concepts:

 

(1) Length - How much space does something take up?  Where is it located?

(2) Time - When did that object arrive?  How long will it stay?

(3) Mass - How much material occupies a given space?

 

In Medieval England:

Length > feet

Mass > pounds

Time > hours

 

These are in common usage in the U.S., but almost nowhere else.  In science, as with the rest of the world, the metric system has been adopted.

 

 

Length - 1 meter

 

Originally defined as 1/40,000,000 - the circumference of the Earth.  1 meter = 39.37 inches (3.37 inches longer than a yard)

 

Ex.)   My height is 5'8" (68 inches); height in meters = 68 in. ´ 1.0 m / 39.37 in. = 1.73 meters (inches "cancel")

 

For shorter lengths:

1 cm = centimeter = 1/100 meter ~ width of little fingernail

1 mm = millimeter = 1/1000 meter ~ width of a tooth on edge of postage stamp

1 micron = micrometer = 1/1,000,000 meter ~ length of small bacterium.  Need a microscope.

("~" means approximately.)

 

For greater lengths:

 

1 km = kilometer = 1000 meters ~ 0.621 mile

(1 mile = 1.61 kilometers)

 

 

Time – The unit of time is the second

 

This was originally defined in terms of an average solar day.  There are 86,400 seconds in an average day.  24 hrs/1 day x 60 min/1 hr x 60 sec/1 minute = 86,400 sec/day.  However, due to slight changes in the solar day, one second is now defined in terms of an "atomic clock".  It is the time it takes a cesium-133 atom to vibrate 9,192,631,770 times.  (Chosen to be close to the old standard second.)

 

For short time events:

 

1 ms = millisecond = 1/1000 second
1 micron = microsecond = 1/1,000,000 second

 

For longer time events:

 

1 minute = 60 seconds
1 hour = 3,600 seconds (60 x 60)
1 day = 86,400 seconds

1 average year = 365.242 days = 31,556,925.511 seconds

 

 

Note:  Don't memorize!! Approximate: 1 Average year ~ 31.5 million seconds

 

 

Mass - unit of mass or amount of material is the kilogram.

 

The standard is a piece of platinum-iridium stored in France.  1 kilogram = 2.204 lbs.

 

Warning: Mass and weight are different!

 

An astronaut can experience weightlessness in space away from Earth, but still would have the same mass.

 

1 kilogram is approximately the same mass as 1 liter of water

(1 liter is a measure of volume or capacity 10 cm on a side (3.93 in.).

 

 

 

 

 

 

 

 

 

 

 

For small masses:

 

1 gram = 1/1000 kilogram ~ mass of a pill.

1 milligram = 1/1000 gram ~ mass of a mosquito.

 

For larger masses:

 

1 metric ton = 1000 kilograms ---- >Mass of 1 meter "cubed" of water.

 

 

Note: An English ton = 2000 pounds = 907.18 kilograms.  A "long" English ton = 2240 pounds = 1016.047 kilograms

 

 

Ex.)   I "weigh" 165 lbs.  Mass in kilograms = 165 pounds x 1 kg /2.204 pounds = 74.86 kilograms.

 

 

Note: 110 pounds ~ 50 kilograms and 220 pounds ~ 100 kilograms

 

 

It is helpful to use Powers of Ten for measuring quantities:

 

Larger Units:

 

    Size

     Prefix

Name

Scientific Notation

 1 unit
(i.e. meter)

  unit (meter)

one unit

1 ( = 100 )

10 units

-------

ten units

10 ( = 101)

1000 units

kilo(meter)
km

one thousand units

10*10*10
 ( = 103 )

1,000,000
units

mega(meter)

one million

( = 106 )

1,000,000,000
units

giga(meter)

one billion
(American)

( = 109 )

 

Smaller Units:

 

    Size

     Prefix

Name

Scientific Notation

1 unit
(i.e. meter)

unit (meter)

one unit

1 ( = 100 )

1/10 unit

-----------

one tenth

1/10 
( = 10-1)

1/100 unit

centi(meter)
cm

one hundredth

1/100 ( = 10-2 )

1/1000 unit

milli(meter)
mm

one thousandth

1/1000
( = 10- 3 )

1/1,000,000
unit

micro(meter)

one millionth

( = 10- 6 )

1/1,000,000,000
unit

nano(meter)

one
billionth
(American)

( = 10- 9 )

 

Scientific notation can be very useful for large or small quantities.

 

Ex.)   Mass of Sun = 2,000,000,000,000,000,000,000,000,000 metric tons = 2.0 x (1,000,000...) = 2.0 x 10+27 metric tons

 

Ex.)   Mass of hydrogen Atom = 0.000 000 000 000 000 000 000 000 00167 grams = 1.67/(1,000...) = 1.67 x 10 -27 grams

 

Ex.)   3700 = 3.7 x 10+3

 

Ex.)   0.0037 = 3.7 x 10-3

 

 

 

Scientific notation can also make calculations easier!

 

Ex.)   200 x 4000 = (2 x 10+2) x (4 x 10+3) "pull out the tens" >8 x 10+5 = 800,000

 

 

(a x 10n) x (b x 10m) = (a x b) x 10n+m

 

Ex.)   4000/200 = (4 x 103)/(2 x 102) = 2 x 101 = 20.

 

(a  x 10n)/(b x 10m) = (a /b) x 10n-m

 

 

The Measure of Things

Object                                                       Value

Mass of mosquito                                       ~ 1 milligram (10-3 grams)

Mass of an aspirin                                       ~ 1/3 gram

 

Mass of 1 liter of water                               = 1 kilogram

Mass of average adult male                         ~ 80 kilogram

 

Width of lead in pencil                                = 2 millimeters (2 x 10-3 meters) = 0.002m

Average height of adult male                       ~ 1.8 meters

Average room height                                   ~ 2.5 meters

 

Height of Empire State Bldg.                       = 381 meters

Average depth of ocean                              ~ 4 kilometers (4000 meters) ~ (2.48 miles)

Distance from NYC-S.F.                            ~ 4,800 kilometers ~ (2982 miles)

 

Average radius of the Earth                         ~ 6,371 kilometers (3958 miles)

Ave. distance from Earth to Moon              ~ 384,401 km (60.33 x 1 Earth radius)

 

Average distance from Earth to Sun            ~ 149,597,870.7 kilometers

                                                                   (389 x Earth-Moon distance)

                                                                  = 1 Au, astronomical unit  = 93 million miles

Distance from Sun to Jupiter                             ~ 5.2 Au

Distance from Sun to Pluto                                ~ 39.44 Au

 

Time                                                              Value

Age of person                                             70 years ~ 25,566 days ~ 613,603 hours

                                                                  = 36,816,192 minutes = 2.2 x 109 seconds

Age of Earth                                               4.6 x 109 years
Age of Universe                                          ~ 13.7 x 109 years