So how many grains of sand are there in the world? You could start
off by trying to guess how many grains of sand there are in a spoon of
sand. Use a magnifying glass to count how many grains fit in a small
section. Then, count how many of those sections fit in your spoon.
Multiply the two numbers together to get an estimate.
"Using this same principle, plus some additional information,
mathematicians at the University of Hawaii tried to guess how many
grains of sand are on the world's beaches. They came up with
7,500,000,000,000,000,000, or seven quintillion five quadrillion
grains of sand."
How many grains of sand are in the world?
http://www.miamisci.org/tripod/whysand.html
The calculation is detailed here:
http://www.hawaii.edu/suremath/jsand.html
That number is 7.5 x 10^18 or 7.5 billion billion.
How many stars, galaxies, clusters, QSO's etc. in the Universe?
http://www.faqs.org/faqs/astronomy/faq/part8/section-3.html
"To get the total stellar population in the Milky Way [that is, in our
galaxy alone], we must take the number of luminous stars that we can
see at large distances and assume that we know how many fainter stars
go along with them. Recent numbers give about 400,000,000,000 (400
billion) stars, but a 50% error either way is quite plausible."
So in our galaxy alone, there might be between 2 x 10^11 and 6 x 10^11 stars
How many galaxies in the Universe?
http://www.faqs.org/faqs/astronomy/faq/part8/section-4.html
"the Hubble telescope is capable of detecting about 80 billion
galaxies (although not all of these within the foreseeable future!).
In fact, there must be many more than this, even within the observable
Universe, since the most
common kind of galaxy in our own neighborhood is the faint dwarfs
which are difficult enough to see nearby, much less at large
cosmological distances. For example, in our own local group, there are
3 or 4 giant galaxies which would be detectable at a billion
light-years or more (Andromeda, the Milky Way, the Pinwheel in
Triangulum, and maybe the Large Magellanic Cloud). However, there are
at least another 20 faint members, which would be difficult to find at
100 million light-years, much less the billions of light years to
which the brightest galaxies can be seen."
So the lower end estimate for the number of galaxies is 8 x 10^10
If we accept even the lower end of these Hubble figures, and if our
Milky Way has a typical number of stars in it, that puts the number of
stars in the universe to be at least
(2 x 10^11) x (8 x 10^10) = 16 x 10^ 21
So if we round the number of sand grains to, say, 10^20
and round the number of stars to, say 10^22
then there are at least 100 stars in the universe for every grain of sand on earth.
