[chris (OP)]

Someone mentioned a comment she'd heard recently - that there are more stars in the Universe than grains of sand on Earth.

Is this true?

I had intended to stop there, but I was so intrigued by the question, and my gut instinct was that this statement is probably true, that I went ahead and did some digging around.

According to Daily Mail Science Editor Mike Hanlon, he writes in his book Science of the Hitchhiker's Guide to the Galaxy, "In July 2003, scientists at a meeting of the International Astronomical Union in Australia announced their latest estimate for the number of stars in the Universe - 70 sextillion. That is 7 followed by a mind-boggling 22 zeros... The new estimate means that the number of stars in the visible Universe is larger - quite a bit larger, actually - than the total number of all the grains of sand on all the beaches on Earth..."

Discuss...

[LeeE]

The famous Hubble 'Deep Field' image suggests that it is true.

[ATremor]

These large numbers are too mind boggling for me. How many grains of sand would there happen to be in say a gallon of milk? Also, when talking about so many grains of sand, I suppose the size of the grain would have a significant change to the number.  How big is a grain? Or how much variation is there from the smallest grain to the largest?
AT

[ATremor]

Actually this question isn't fair for the sand.  The meeting took place in 2003. We've lost considerable sand grains on the earth's beaches due to the sea level rising!
AT

[chris (OP)]

These large numbers are too mind boggling for me. How many grains of sand would there happen to be in say a gallon of milk? Also, when talking about so many grains of sand, I suppose the size of the grain would have a significant change to the number.  How big is a grain? Or how much variation is there from the smallest grain to the largest?
AT

I'd hope there aren't any grains of sand in a bottle of milk - might be painful for the cow otherwise!

[ATremor]

Haha very good point! I think the fact that I was drinking milk at the time had an influence on my wording.

[stereologist]

It's not even close.

So let's do some simple math. A sand grain is defined as having a range of sizes, but 1mm diameter is typical. So for simplicity let's use that size.

The earth has an average radius of 6371km. This gives the earth a surface area of 1.28 times 10^14 square millimeters of surface area.

There are 7 times 10^22 stars. Divide this by the surface area of the earth and we learn how deep the sand across the entire earth would have to be to equal the number of stars.

The depth is 550km.

So it seems reasonable to conclude that there are more stars than there are grains of sands on all the beaches.

[neilep]

...and say that even just a soupçon of a percentage of those stars have orbiting planets and even a teensy percentage of those are habitable by life.....I am sure we are not alone !..in MY opinion !

[Geezer]

Me too. For more insight into this you might see Dr Seuss' "Horton Hears a Who", or maybe it was "Horton Hires a Ho"? Something like that anyway.

[fontwell]

Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. - Douglas Adams

[Karen W.]

I have always heard that statement also and am glad to hear it confirmed.. it boggles my mind because just to think about each little grain of sand in the expanse of my own eye view would be totally incomprehensible and I absolutely cannot imagine all the sands on beaches in the world... Such a crazy thought and wow what a site it makes all those stars in the sky.

[Hadrian]

dont forget to include me.  i am a star too.................. lol 

well star dust anyway, so is not the sand also star dust?

[doppler1]

Just thinking about the numbers of stars and planets out there makes me think that it is impossible for there not to be other "intelligent" life forms out there......sheesh the possbilities which lie outside of our technological grasp are very exciting

[Hadrian]

Just thinking about the numbers of stars and planets out there makes me think that it is impossible for there not to be other "intelligent" life forms out there......sheesh the possbilities which lie outside of our technological grasp are very exciting

well of course i am out here.... tut tut!

[voiceofreason]

lol ur all ******* idiots, for startets its an estimate nothing more and you seem to forget the question "are there more stars in the universe than grains of sand on earth" not "are there more stars in the universe than grains of sand on the beaches on earth". Hmmmmmmm i wonder if theres any sand on land and under the water hmmmmmmmm i wonder maybe a little a bit hmmmmmmmmmmmmmmmmmm?

[LeeE]

Thank you for reminding us of the true nature of idiots.  You are an example to us all.

[Geezer]

Thank you for reminding us of the true nature of idiots.  You are an example to us all.

not to mention a reminder that it's OK to use the spell checker before postiong.

[piktor67]

Well, my math went for a different path. Not 1.28 times 10^14, but 5.1 times 10^20. Why is that? isn't it 6371000000 (mm) squared times Pi times 4???

[CliffordK]

It's not even close.

So let's do some simple math. A sand grain is defined as having a range of sizes, but 1mm diameter is typical. So for simplicity let's use that size.

The earth has an average radius of 6371km. This gives the earth a surface area of 1.28 times 10^14 square millimeters of surface area.

There are 7 times 10^22 stars. Divide this by the surface area of the earth and we learn how deep the sand across the entire earth would have to be to equal the number of stars.

The depth is 550km.

So it seems reasonable to conclude that there are more stars than there are grains of sands on all the beaches.

[]

I'm having troubles following your math.

Earth: 6371km radius.

Surface area of a sphere: 4πr²

That gives us a surface area of:

4*π*(6371)² = 5.1 x 10⁸ km²

1000x1000 mm² in a m²
1000x1000 m² in a km²

So that gives us 10¹² mm² in a km²

So we get the surface area of the earth being about 5.1 x 10²⁰ mm²

So, the difference between the number of stars and the number of square mm on the planet surface is only a factor of 10²  (assuming the accuracy of all the estimates).

or, about 100mm, or about a shell 10cm thick.

So, the question is how much of the earth is covered by sand.

Beaches
Sand Dunes
Great Deserts
Ocean Floor
Mountains
Sandstone
Component of dirt
Loam
Etc.

I think you would find out that you would have more than adequate sand to cover the earth several times over with 10cm of sand.


(Oh, it looks like piktor67 was on the same track).