Nebulosas
jueves, 27 de febrero de 2014
miércoles, 26 de febrero de 2014
WHAT ARE THE INGREDIENTS OF THE COSMIC RECIPE?
People have always known that stars and any other of our cosmic neighbors are very far away. So far, that in the XIXth century August Comte, a prominent philosopher, argued:
Of all objects, the planets
are those which appear to us under the least varied aspect. We see how we may
determine their forms, their distances, their bulk, and their motions, but we
can never known anything of their chemical or mineralogical structure; and,
much less, that of organized beings living on their surface ... (The Positive Philosophy, Book II, Chapter 1, 1842)
However, just a few decades
later, astronomers started to identify elements in the solar atmosphere. And
nowadays we have a good idea about the chemical makeup not only of the stars, but of
the entire visible universe.
According to spiff.rit.edu, the Earth, the easiest
celestial body to measure, is made up of the following elements:
- the
atmosphere
- 78%
nitrogen
- 21%
oxygen
- 1% other stuff (carbon dioxide, water vapor,
argon, etc.)
- the
oceans
- water:
2 hydrogen, 1 oxygen
- the
solid crust
- 62% oxygen (by number of atoms)
- 22%
silicon
- 6.5%
aluminum
- bits of iron, calcium, potassium, sodium
- a
central core
- mainly
iron
- smaller amounts of nickel and cobalt
- an
intermediate mantle
- mostly
oxygen and silicon
- some
iron, magnesium, etc.
The composition of stars is largely
different, comprising:
- 90% hydrogen (by number of atoms)
- 10%
helium
- tiny traces of heavy
elements (everything else)
Our galaxy contains not only
stars, but also clouds of gas and dust. Some glow brightly, lit up by nearby
stars. Other clouds appear dark, because they absorb and scatter the light
which tries to pass through them. It is often easier to determine the
composition of nebulae than of stars, since we can see into the center of the
nebula. The spectra of these objects show that they, too, are almost completely
made of hydrogen and helium, with tiny amount of other elements.
The blog spiff.rit.edu
posts three important questions:
- Is there any particular reason that
galaxies should have started out with a mixture of 12.5 hydrogen atoms for
every 1 helium atom?
- Is there any reason why the initial
mixture should contain only hydrogen and helium, with (almost) no heavier
elements?
- Whence came the mixture of oxygen,
silicon, iron, etc., which make up the Earth and everything on it?
Reference:
http://spiff.rit.edu/classes/phys240/lectures/elements/elements.html
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