Astronomy Common Knowledge Quiz.......
Quizzes & Puzzles0 min ago
It Has Been Written That There Are More Stars Than Grains Of Sand On Earth!!
Cannot believe this. I went to Goa and a fistful of sand must have contained thousands
Imageine the whole beach content? Is there any scientific method used to calculate the theory?
Imageine the whole beach content? Is there any scientific method used to calculate the theory?
Answers
A couple of further points: 1. "What about it?" Was in answer to "what about Barry Island?" Your question was quite important and I wasn't meaning to be so blunt about that. 2. This "fact" tends to get stated in all sorts of ways, e.g. More stars than grains of sand on all the beaches on the world, or more stars in the Milky Way galaxy than grains of sand in just one...
17:29 Sun 24th Feb 2013
It's a very solid estimate based on: the average numbers of stars in a galaxy; the number of such galaxies observed; and the size of typical sand grains.
Apparently there are approximately 70,000,000,000,000,000,000,000 stars in the Observable universe. A grain of sand, meanwhile, is typically about a millimetre across or 1mm^3 in volume, so that you would need one Billion or so grains to fill a cubic metre. This means that for the number of grains of sand on earth to match the number of stars you would need about 70,000,000,000 cubic metres of sand. If this were spread evenly over the earth then it would be about a continuous layer one metre or so thick. The earth of course is not covered all over by sand, and a lot of its surface area is bare rock, or ice, or the the like.
In fact the conclusion is that the two numbers are fairly close to each other, but on any reasonable estimates the number of stars comes out on top by a factor of about ten or so.
Apparently there are approximately 70,000,000,000,000,000,000,000 stars in the Observable universe. A grain of sand, meanwhile, is typically about a millimetre across or 1mm^3 in volume, so that you would need one Billion or so grains to fill a cubic metre. This means that for the number of grains of sand on earth to match the number of stars you would need about 70,000,000,000 cubic metres of sand. If this were spread evenly over the earth then it would be about a continuous layer one metre or so thick. The earth of course is not covered all over by sand, and a lot of its surface area is bare rock, or ice, or the the like.
In fact the conclusion is that the two numbers are fairly close to each other, but on any reasonable estimates the number of stars comes out on top by a factor of about ten or so.
Guesswork is a perjorative term that doesn't really convey what we're talking about here.
If I know the volume of a ball and the volume of a lorry and how they pack together I can come up with a pretty reliable estimation of how many balls are in the lorry.
That's certainly not putting your finger in the air and saying "I reckon...."
Guesswork to my mind is coming up with a number without any real reasoning to back it up.
Estimation is very different.
If someone comes up with a number and you don't personally know how that number has been arrived at doesn't maean that their reasoning isn't sound
It doesn't make it "guesswork"
If I know the volume of a ball and the volume of a lorry and how they pack together I can come up with a pretty reliable estimation of how many balls are in the lorry.
That's certainly not putting your finger in the air and saying "I reckon...."
Guesswork to my mind is coming up with a number without any real reasoning to back it up.
Estimation is very different.
If someone comes up with a number and you don't personally know how that number has been arrived at doesn't maean that their reasoning isn't sound
It doesn't make it "guesswork"
BTW there are a number of methods we can use to find out how many stars are in a galaxy like Andromeda (for example)
We know how bright a average star is from set distance (absolute magnitude) from studies of stars in our own galaxy
And we know how far away Andromeda is from it's redshift - so by comparing how bright Andromeda is in the sky we can calculate how bright it would be from a set distance and how many stars would need to make it this bright.
There are other methods too - you can "weigh" a galaxy by looking at its rotation rate. You measure that by looking at the redshift of the two ends of it - if you know the size of it and how far away it is you can then deduce its mass and hence the number of stars.
It was exactly this experiment that first highlighted the existance of dark matter 30 years or so ago - so these numbers have had a lot of attention and it's pretty sure they're reasonably accurate
We know how bright a average star is from set distance (absolute magnitude) from studies of stars in our own galaxy
And we know how far away Andromeda is from it's redshift - so by comparing how bright Andromeda is in the sky we can calculate how bright it would be from a set distance and how many stars would need to make it this bright.
There are other methods too - you can "weigh" a galaxy by looking at its rotation rate. You measure that by looking at the redshift of the two ends of it - if you know the size of it and how far away it is you can then deduce its mass and hence the number of stars.
It was exactly this experiment that first highlighted the existance of dark matter 30 years or so ago - so these numbers have had a lot of attention and it's pretty sure they're reasonably accurate
I don't know how much sand there is in Germany or the world but I can put an upper bound on how much sand there can be on the planet from the methods I was suggesting earlier, i.e. how big is the earth's surface and how thick the sand would have to be over the entire surface to reach a specific volume. Since the earth is blatantly not covered with a thick layer of sand all over, this limits the room you have to fit all the sand you need. So anyway it's a reasonable statement. The two numbers are close to each other -- more reasonable estimates put the difference as I have said at a factor of only about 10. That's therefore a lot of sand, i.e about 7,000,000,000,000,000,000,000 grains.
True, I'll try in the long run to refine that calculation.
Apparently about 29% of the earth's surface is land, a third of the land is desert, and a fifth of the desert is sand. So all that sand would have to form a layer about 7 metres deep across all of this desert in order to reach the total required. Also this sand is reckoned to be about 85% of all "mobile sand". So the question is anyway reduced to how thick is the desert's sand on average. I don't know if there is an answer to that question. I also don't know how much sand is hidden in the oceans -- and it's quite possible that no-one's ever included that when doing this calculation before.
But anyway the point is that the two numbers (stars and sand) are both colossal, and probably about the same, but people who've tried to do this calculation before have ended up at an answer that they differ by a factor of ten. Without checking their calculations myself I can't tell you how they've reached this number. I've tried to give an idea of how you might go about answering the question, rather than insisting upon one answer or the other.
Apparently about 29% of the earth's surface is land, a third of the land is desert, and a fifth of the desert is sand. So all that sand would have to form a layer about 7 metres deep across all of this desert in order to reach the total required. Also this sand is reckoned to be about 85% of all "mobile sand". So the question is anyway reduced to how thick is the desert's sand on average. I don't know if there is an answer to that question. I also don't know how much sand is hidden in the oceans -- and it's quite possible that no-one's ever included that when doing this calculation before.
But anyway the point is that the two numbers (stars and sand) are both colossal, and probably about the same, but people who've tried to do this calculation before have ended up at an answer that they differ by a factor of ten. Without checking their calculations myself I can't tell you how they've reached this number. I've tried to give an idea of how you might go about answering the question, rather than insisting upon one answer or the other.
A couple of further points:
1. "What about it?" Was in answer to "what about Barry Island?" Your question was quite important and I wasn't meaning to be so blunt about that.
2. This "fact" tends to get stated in all sorts of ways, e.g. More stars than grains of sand on all the beaches on the world, or more stars in the Milky Way galaxy than grains of sand in just one particular beach. Some of these versions I think are probably people distorting the original statement.
So I think I can say fairly confidently the following:
i) There are more stars in the observable universe than there are grains of sand on the beaches (7*10^22 compared to about 10^19).
ii) However if you started including all the sand on the Earth's surface (not including sand below water) then the two numbers probably are about the same size; since our deserts aren't properly surveyed it's impossible to say which is bigger.
iii) Including all the sand under the ocean too, I think that you would find that there are many times more grains of sand on the earth than Stars in the Universe. Again, hard to say because so little of the ocean is mapped. But there's a lot of sand hidden from our view.
So in answer to the original question -- it probably depends on which grains of sand you are including. But you still have to make the calculations.
1. "What about it?" Was in answer to "what about Barry Island?" Your question was quite important and I wasn't meaning to be so blunt about that.
2. This "fact" tends to get stated in all sorts of ways, e.g. More stars than grains of sand on all the beaches on the world, or more stars in the Milky Way galaxy than grains of sand in just one particular beach. Some of these versions I think are probably people distorting the original statement.
So I think I can say fairly confidently the following:
i) There are more stars in the observable universe than there are grains of sand on the beaches (7*10^22 compared to about 10^19).
ii) However if you started including all the sand on the Earth's surface (not including sand below water) then the two numbers probably are about the same size; since our deserts aren't properly surveyed it's impossible to say which is bigger.
iii) Including all the sand under the ocean too, I think that you would find that there are many times more grains of sand on the earth than Stars in the Universe. Again, hard to say because so little of the ocean is mapped. But there's a lot of sand hidden from our view.
So in answer to the original question -- it probably depends on which grains of sand you are including. But you still have to make the calculations.
jake-the-peg gave some answer to that. Take an average Star like the sun and figure out its mass. You can then use various techniques to estimate the mass of a galaxy, by looking at some of its properties e.g. angular momentum. Then number of stars in that galaxy will be roughly given by mass/(mass of the sun).
Then you can estimate the number of galaxies by observing how many are in a particular region of the sky and multiplying that by the total sky area. This will at least give a ball-park figure, although with a few, sometimes fairly large, uncertainties along the way. Anyway, the answer comes to about 7*10^22, probably plus or minus about 10%.
Then you can estimate the number of galaxies by observing how many are in a particular region of the sky and multiplying that by the total sky area. This will at least give a ball-park figure, although with a few, sometimes fairly large, uncertainties along the way. Anyway, the answer comes to about 7*10^22, probably plus or minus about 10%.
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