Sand Grains,Cells and Stars

"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?


That number is 7.5 x 10^18 or 7.5 billion billion.

How many stars, galaxies, clusters, QSO's etc. in the Universe?
"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?
"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.

Galaxies, on the other hand, are made up primarily of stars. (At least, the portion of them that we can see is!)
So my quiz question for you is this:

Are there more cells in the typical human body or more stars in a typical galaxy?

The numbers are tremendous for both of these. Let’s start with humans. We start out as a zygote: a single fertilized egg cell.
From that, we grow up into full-grown adult humans, containing (are you ready?) 75 to 100 trillion cells! Now, things are even more interesting than that, because the cells that make up your skeleton and internal organs, your nervous system and your skin, your blood vessels and brain, only number about 4 trillion.
So where are the rest of them? Moving through your body, keeping you alive and functioning. Your body contains about one trillion white blood cells of various types, about two trillion platelets, and a whopping 30 trillion red blood cells! This means every time you donate a pint of blood, you’re losing 4,000,000,000,000 cells!
There are also about 40 trillion bacterial cells that live in your body (mostly your intestine), aiding in digestion. All told, that’s over 75 trillion cells in your body; fully half of them were made by you. That’s going to be tough to beat.
Let’s look at a typical galaxy now, like our own, or perhaps our nearest neighbor (above), Andromeda. Our Sun is not typical of stars in galaxies, it’s actually pretty bright. Only about 10% of stars are as massive as our Sun (a G-type star), which means 90% of them are dimmer, cooler, and smaller.
In fact, when you look up at the night sky, of the hundreds or even thousands of stars that are close to us (within about 30 light years), you know how many are type O? Zero. Know how many are type B? Also zero. Know how many are type A? Four.
Most of the stars that are there are not the stars you think of, much like the red blood cells and digestive bacteria in our bodies are not the cells that you think of when you think of our bodies. But when we count up all the stars in a typical galaxy, we get a pretty large number, too: 400 billion. That’s still nowhere close to the 75 trillion cells in a human body, but that’s the answer for typical galaxies. What about the largest galaxy in the Universe, though, can that compete?
In the center of one of the hugest galaxy clusters we’ve ever found, Abell 2029, lies a galaxy 6 million light-years across, or more than 60 times the diameter of the Milky Way (at only 100,000 light years). The number of stars in this galaxy? Estimated to be just over 100 trillion. The galaxy itself, the largest known galaxy in the Universe, is IC 1101: