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Subject: Giant Magellan Telescope (GMT) question/confusion rss

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Hammock Backpacker
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In 2020, a mega-telescope in Chile will make its first observations. It'll be the largest telescope ever built (the enclosure is 22 stories high), it'll be wicked-powerful (seven 20-ton mirrors are involved), and its resolution will beat the Hubble Space Telescope (it's projected to have 10x the Hubble's resolution). This, my friends, is the Giant Magellan Telescope (GMT), and it will be huge. In this short video, have a look at tons of renderings of what it will look like, and a peek at the mirror-manufacturing process already underway.

My favorite quote: "If we took this 27-foot mirror and then spread it out from coast to coast in the United States, east to west coast, the height of the tallest mountain on that mirror would be about half an inch. That's how smooth this mirror is." -Dr. Wendy Freedman.



Read the full text here: http://mentalfloss.com/article/53327/behold-giant-magellan-t...
--brought to you by mental_floss!


My question relates to the bolded text above. So are they saying that if they scaled up the mirror to a size that would stretch from the west to the east coast, that's how smooth it would be, or are they saying something else?
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"Scaled up" is my guess.

It reminds me of that piece of trivia where if you could scale the Earth down to the size of a billiard ball, it would feel as smooth as one. The disparity between the Mariana Trench and Mount Everest would be reduced to almost nothing at that scale, rendering it nice and smooth.

Now that I say that, though, if the Earth could be shrunk down to that size and have no appreciable difference in surface texture than that of a billiard ball, then why should I be impressed with that 27-foot mirror?
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Pete Goch
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Because, scaled up, the irregularities on the surface of the mirror produce only 1/2" high mountains instead of, say, 5-6 mile high mountains.
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Erik Henry
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Verkisto wrote:
. . . . if you could scale the Earth down to the size of a billiard ball, it would feel as smooth as one . . . .

Smoother, but not quite as round as a billiard ball.

http://blogs.discovermagazine.com/badastronomy/2008/09/08/te...


An interesting fact from this linked article: The Earth gains 20-40 tons of mass each day from all the space junk (e.g., meteors) we run into.


The article also has a link to a mapping tool you can use to easily see what's on the exact opposite side of the Earth from a given point:

http://www.freemaptools.com/tunnel-to-other-side-of-the-eart...
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Erik Henry
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So if I'm calculating it right, that means the surface imperfections on the actual-size mirror are less than 20 nanometers high. Pretty impressive.


Edit: And for comparison, the smallest particles of borosilicate glass (the mirror's material) ever made were 100-500 nanometers in diameter.
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Erik17 wrote:
Verkisto wrote:
. . . . if you could scale the Earth down to the size of a billiard ball, it would feel as smooth as one . . . .

Smoother, but not quite as round as a billiard ball.

http://blogs.discovermagazine.com/badastronomy/2008/09/08/te...


Which is interesting, when you think about all those massive oceans that are (to our impression) such a big deal to the planet - indeed, how we characterize it when looking at it (the 'pale blue dot').

You'd hardly be able to even FEEL them if you held a pool-ball-sized-Earth in your hand. It would feel a bit like you had picked it up after dropping it in a puddle - you'd have some sense that it had spots that were 'wet-ish', but it wouldn't change the overall characteristic of just being a very smooth rock in your hand.
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Maybe the earth really is that size and we're just really, really small...

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Andy Andersen
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I've got a splinter in my finger I can't see. Will they rent this thing out?
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Phil Sauer
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matthew.marquand wrote:
Maybe the earth really is that size and we're just really, really small...


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