Here's an old, old, question, but this time with a surprise twist. The question is — and I bet you asked it when you were 8 years old and sitting on a beach: Which are there more of — grains of sand on the Earth or stars in the sky?
Obviously, grains and stars can't be counted, not literally. But you can guestimate.
Science writer David Blatner, in his new book Spectrums, says a group of researchers at the University of Hawaii, being well-versed in all things beachy, tried to calculate the number of grains of sand.
Emilian Robert Vicol via Flickr
They said, if you assume a grain of sand has an average size and you calculate how many grains are in a teaspoon and then multiply by all the beaches and deserts in the world, the Earth has roughly (and we're speaking very roughly here) 7.5 x 1018 grains of sand, or seven quintillion, five hundred quadrillion grains.
That's a lot of grains.
Gilles Chapdelaine/NASA & ESA
OK, so how about stars? Well, to my amazement, it turns out that when you look up, even on a clear and starry night, you won't see very many stars. Blatner says the number is a low, low "several thousand," which gives the sand grain folks a landslide victory. But we're not limiting ourselves to what an ordinary stargazer can see.
Our stargazer gets a Hubble telescope and a calculator, so now we can count distant galaxies, faint stars, red dwarfs, everything we've ever recorded in the sky, and boom! Now the population of stars jumps enormously, to 70 thousand million, million, million stars in the observable universe (a 2003 estimate), so that we've got multiple stars for every grain of sand — which means, sorry, grains, you are nowhere near as numerous as the stars.
So that makes stars the champions of numerosity, no?
Ummm, no. This is when Blatner hits us with his sucker punch. Yes, he says, the number of stars in the heavens is "an unbelievably large number," but then, very matter-of-factly, he adds that you will find the same number of molecules "in just ten drops of water."
Plinkk via Flickr
Let me repeat: If you took 10 drops of water (not extra-big drops, just regular drops, I'm presuming) and counted the number of H2O molecules in those drops, you'd get a number equal to all the stars in the universe.
This is amazing to me. For some reason, when someone says million, billion or trillion, I see an enormous pile of something, a grand scene, great sweeps of desert sand, twirling masses of stars. Big things come from lots of stuff; little things from less stuff. That seems intuitive.
But that's wrong. Little things, if they're really little, can pile up just like big things, and yes, says Blatner, water molecules "really are that small."
So next time I look up at the sky at all those stars, I will be impressed, of course, by the great numbers that are out there. But I will remind myself that at the other end of the scale, in the nooks and crannies of the physical world, in the teeniest of places, there are equally vast numbers of teenier things.
We are surrounded by vastness, high and low, and either way, as Blatner's book says, we "can't handle the biggitude."
David Blatner's forthcoming book is called Spectrums: Our Mind-Boggling Universe, from Infinitesmal to Infinity.We can measure how fast they move, and use that to figure out how much gravitational force there is to cause those speeds, and from that, get a mass. We can also measure how bright our Milky Way is. By figuring out how bright our Milky Way is, we can then figure out how much power (like a light bulb) it has, and then how many stars we need to generate that power.
I set out to tackle this more than 20 years ago, during my 16th year with Discover magazine. I initially tried to research the answer, with no luck. You’d think someone would have already attempted to confirm this well-worn cliché, but I had to do it myself.
First, I grabbed some beach sand and, using a reversed telescope eyepiece, which makes a fabulous magnifying glass, laboriously counted the number of grains in a cubic centimeter — a sugar cube’s volume of beach. This tells you how important my time was back then. It took over an hour. But, it turned out, that was the easy part.
Next, I multiplied this number by the total number of cubic centimeters of earthly beaches. There’s no way to do this with any precision. Merely learning how many square miles of beaches are on this planet is not simple to find. I had to extrapolate and make educated guesses.
The other part of the equation was easier. To find the number of stars, we simply multiply the total per galaxy (we’ll say 100 billion because most galaxies are smaller than ours) by the number of galaxies, which is somewhere between 200 billion and 2 trillion.
Astronomy clichés are common, but are they accurate? Comparing the number of sand grains on Earth and the number of stars in the visible universe yields a surprising result.
From left: Fotoschab/Dreamstime; NASA, ESA
That takes care of the observable universe. We can’t tackle the actual universe, the part farther than the distance light has had time to travel across since the Big Bang, because we cannot see it and hence have no idea what’s there. So perforce, we’re limited to the cosmos within view.
I got a surprise. The numbers pretty much matched. There are about the same number of stars in the observable universe as there are sand grains in all of Earth’s beaches.
Ah, but that’s not how the cliché is commonly phrased. Usually, people say “sand grains on Earth.” Which means you’d have to go beyond beaches to include all the vast deserts and undersea sand. Obviously if you include all that, there are incomparably more earthly sand grains than stars.
More sand than stars — that takes care of that chestnut. Maybe now we can tackle other famous astronomy quotes. Roget’s Thesaurus and a Google search uncovered a bunch of well-known celestial expressions and astro-nuggets, but some are too lovely to find fault with.
Let’s list merely a few of the most famous:“Many a night from yonder ivied casement, ere I went to rest, / Did I look on great Orion sloping slowly to the West. / Many a night I saw the Pleiades, rising thro’ the mellow shade, / Glitter like a swarm of fire-flies tangled in a silver braid.” — Alfred, Lord Tennyson, Locksley Hall
“Of all tools, an observatory is the most sublime. . . . What is so good in a college as an observatory? The sublime attaches to the door and to the first stair you ascend, that this is the road to the stars.” — Ralph Waldo Emerson, as quoted in A Year with Emerson, a Daybook
“You’re in charge but don’t touch the controls.” — astronaut Shannon Lucid, recounting what the two Russian cosmonauts told her every time they left the Mir space station for a spacewalk
Whoa, this last one brings us back to myth-busting. Twain, who loved astronomy and probably knew better, was disseminating the common myth that the Moon has a permanent dark side. He meant far side; although, granted, that would have made his metaphor meaningless.
Who said there are more stars than grains of sand?
Carl Sagan wrote in his book Cosmos that there are more stars in the universe than all the sand grains on Earth. You still hear this from time to time; it's one of those astronomy clichés that never goes away.
Are there more stars in the Milky Way than grains of sand on Earth?
Our universe contains at least 70 septillion stars, 7 followed by 23 zeros. Astronomers estimate there exist roughly 10,000 stars for each grain of sand on Earth. That's a lot of stars. Astronomers recently discovered the origin of sand grains.
Are there more galaxies than sand on Earth?
Considering that, 300 billion galaxies with 100 billion stars each gives us 30,000,000,000,000,000,000,000, or 30 followed by 21 zeroes worth of stars in the universe. Now that is more than grains of sand on the Earth.
Are there more planets than grains of sand?
The result is about 10^24 planets in the universe. That's about 100,000 times as many as grains of sand. It's one septillion planets! The numbers are subject to huge estimation errors and are both “astronomical.” One estimate has us with 7.5*10^18 grains of sand on Earth.