[ExI] New Hubble Deep Field Photos

spike at rainier66.com spike at rainier66.com
Mon Aug 20 16:14:24 UTC 2018

-----Original Message-----
From: spike at rainier66.com <spike at rainier66.com> 



>... square of area about 100 arc minutes would be 10 arc minutes on a side.  The moon (and sun) are about 30 arc minutes across, so it is an area about a tenth of a full moon...spike

We can make this work with only some minor brute force: a person can have a really really short arm (the T-Rex did) and imagine a really super huge grain of sand.  Sand is mostly quartz, and those can grow to arbitrary size methinks.  So just get a person with a short enough arm and a big enough grain of sand, and there you go.

But it has me thinking and pondering: why is it that when we use the terms grain of sand and grain of salt, most people can pretty well picture something somewhere in a range of perhaps a tenth of a millimeter to about a millimeter range?  I would estimate a typical grain of sand might be in the lower end of that range, and we already know it goes on down from there generally, but why don't we see really honking big grains of sand?  Or can we just call pea gravel really coarse sand? Why is it that when you go to the beach, most of the sand there is in that one decade range of size?

It would be interesting if some sharp high school student were to go out somewhere where there has never been any development, scoop up a shovel of whatever is down there, take it home, get a microscope, try to create a histogram of particle sizes she finds in there, see if it is kinda uniform across the size spectrum or if there is some kind of peak at the place where a lot of us think of the size of a grain of sand.


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