Tuesday, January 31, 2012

Plenty of Empty

Barnard 68 molecular cloud is the exact opposite of the fiercely hot radiation Sun.

It is very cold and very empty.

The idea that such clouds are the wombs giving birth to stars is, as far as I know, quite novel in astronomy and truly surprising. The theory is also difficult to study because these clouds are hard to see.

Astronomers suggest that the "temperature" - or rather lack of it - is about 16 Kelvin.
That is way below freezing cold at -257o Celsius and uncomfortably near absolute zero.

lollipop asked three years ago from Yahoo answers:
Find the density in atoms per cubic entimeter of a Bok globule having a radius of 1 light year and a mass of 100 M. how does your result compare with the desnity of a typical H II region, between 80 and 600 atoms per cm3? (Assume that the globule is made purely of hydrogen atoms). please help with astronomy hw!?! 

And got this answer from ronwizfr:
100 Sun masses = 100 x 2 × 1033 gram = 2x1035 gram x 6 x1023 atoms/gram = 1.2x1058 atoms.
The volume of the sphere is 4/3*pi*1 lyr3 = 4.19 x (9.46 × 1017)3 cm3 = 3.55 x 10^54 cm3
So the density is 1.2x1058 atoms/3.55 x 1054cm3 = 3400 atoms/cm3


Really empty
Let us think the average density of Barnard 68 and other Bok globules given there: between 80 and 600 atoms per cubic centimetre.

Well, what does that mean in human language?

6.023 x 1023
Amadeo Avogadro (1776-1856) was the author of Avogadro's Hypothesis in 1811, which, together with Gay-Lussac's Law of Combining Volumes, was used by Stanislao Cannizzaro to elegantly remove all doubt about the establishment of the atomic weight scale at the Karlsruhe Conference of 1860.

The name "Avogadro's Number" is surely just an honorary name attached to the calculated value of the number of atoms, molecules, etc. in a gram molecular weight of any chemical substance. Of course if we used some other mass unit for the mole such as "pound mole", the "number" would be different.

The first person to have calculated the number of molecules in any mass of substance seems to have been Josef Loschmidt, (1821-1895), an Austrian high school teacher, who in 1865, using the new Kinetic Molecular Theory (KMT) calculated the number of molecules in one cubic centimeter of gaseous substance under oridnary conditions of temperature of pressure, to be somewhere around 2.6 x 1019 molecules. This has always been known as the "Loschmidt Number."
Avogadro's number

So upon earth there are about 1.0 x 1017.

Not so in the Barnard 68 cloud.

What does that mean in our normal world down hear upon the earth?
How can we grasp the meaning of such a numerical fact given to us by scientist and students of astronomy?

I have no words to compare the situation to grains of mustard in football stadium or stuff like that.

Instead, I give up and just say "plenty of empty".

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