Re: Atomic density of interplanetary space

Subject: Re: Atomic density of interplanetary space
Date: Tue, 28 Oct 1997 19:50:20 -0500 (EST)

Hi David,

Intestellar space ain't dense, ain't dense, ain't dense, ... tra la tra la.

*Astronomy: A Self-Teaching Guide* 2nd Ed. by Dinah Moche, publisher John
Wiley & Sons) is a good book that, weel, you can use to ...

Dinah Moche says: 

Astronomy, page 98
"The space between the stars is virtually empty. The interstellar medium, the
matter and radiation between the stars, is much denser than the air in the
best vacuum produced on Earth. Interstellar matter is about 99 percent gas
(mainly hydrogen) and 1 percent tiny solid particles called interstellar
dust. Interstellar matter is particularly important, because it is the raw
material for new stars and planets."

[Note. Using not the best, but a good vacuum pump, you can pump most of the
air out of a transparent cylinder and run an experiment in which a feather
and a steel ball drop at about the same speed/acceleration and hit the bottom
of the cylinder at about the same time. You can also drop another feather and
steel ball outside the cylinder at the same time and see the steel ball hit
at about the same time as the ball & feather inside the cylinder, while the
outside feather flutters leisurely down (unless a miracle happens). To make
everything drop at the same time, use electromagnets. Attach an insignificant
bit of iron or steel to the feather to hold it to the electromagnet. Attach
the same insignificant amount of iron or steel to the outside feather. Open
the circuit and--presto--everything begins dropping at the same time. May
dragons of good fortune smile on your experiment.]
Astronomy, page 132:
"The density of matter in the universe required for the force of gravity to
stop the expansion of the universe according to the oscillating model is 5 x
10^-30 grams per cubic centimeter. Today (2nd edition is copyright 1981) the
observed density of galactic material throughout the universe is not half of
that ... ." 

[Notes:  1. I use calculator notation such as 5E-30 for 5 x 10^-30 because
that's what students and teachers actually plug into calculators and
computers to crunch numbers.  2. The standard SI unit of density is kilograms
per cubic meter. 5E-30 grams per cubic centimeter = 5000E-30 kilograms per
cubic meter.  3. The density of Earth's air at standard pressure (1013
millibar) and 20 degrees Celsius is 1.20 kilogram per cubic meter. What is
the mass of air in your classroom? How many cubic meters in your Mars
habitat? How many kilograms of air do you need to maintain? How do you do it?
Et cetera, et cetera, et cetera.]

Beginning November 1, I'll be a volunteer mentor in a 5th grade classroom
every Monday 2-3 pm doing Mars stuff on the Internet and hands-on physics
related to Mars. On Tuesdays, I'll spend the morning (9:20 - noon) in Richard
Zimmer's Mars Colony course at Sonoma State University. Most students plan to
be elementary school teachers. I encourage them and Richard cajols them to
join my favorite forum, ***discuss-lfm***. More later.


Bob Albrecht
George Firedrake