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PROFESSOR: Because
there was a point when

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you could start to read.

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Behind that point, you
couldn't read it anymore,

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00:00:29,110 --> 00:00:30,960
and in front of that
point you could.

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So when you were at
a large distance--

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when the text was at a large
distance from your eyes,

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what do the text look like?

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I saw a couple of
different explanations.

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So what did the
text look like when

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you were a large distance away?

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What did it look like?

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00:00:45,510 --> 00:00:48,750
Black lines.

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Anyone else have another
description they want to use?

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Black lines.

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Blurry.

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I like that.

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What did you say?

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00:00:59,070 --> 00:00:59,911
Chinese characters?

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00:00:59,911 --> 00:01:01,410
It looked like a
different language.

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00:01:01,410 --> 00:01:02,610
You couldn't read it.

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00:01:02,610 --> 00:01:05,459
You could tell that there was
some difference between them,

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right?

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00:01:06,225 --> 00:01:07,933
Like, you could tell
that there was maybe

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a vertical line or something,
but you couldn't recognize it.

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You couldn't decide what it was.

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00:01:14,280 --> 00:01:15,000
OK, I like that.

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00:01:15,000 --> 00:01:16,875
So maybe it looked like
a different alphabet.

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00:01:19,610 --> 00:01:25,400
Different alphabet, nice.

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I like that.

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That's good.

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00:01:27,480 --> 00:01:31,770
What about when you were
a small distance away,

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what did it look like?

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00:01:34,530 --> 00:01:42,040
Actual words, real
writing, you could read it.

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You can see details
about those letters,

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and we're going to call that--

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we're going to say that
you can see details,

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but I really like Juan's
different alphabet there.

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Because you can
see that it's not

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a Chinese character, or
a Cyrillic character,

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or a different alphabet
that you're not used to.

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00:02:02,780 --> 00:02:06,560
But you could read
the characters.

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00:02:10,022 --> 00:02:11,980
Now just because you are
standing farther back,

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does that mean the
letters weren't actually

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there like they changed into
some other mysterious language?

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No, they're still there.

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You just can't read
the characters.

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You can't see detail.

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You could read the characters.

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You can see details.

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Here, you cannot see details.

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How would you say
the angular size

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of that text would compare when
you are a large distance away

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versus when you're a
small distance away?

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In your camera-- when you
have these two cameras here,

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you take an image, and that gets
transferred back to your brain.

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When you're far
from the text, what

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is the angular
size of that text?

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It's what?

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It's smaller, right?

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So let's do this.

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We have small angular size.

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What about when you're close?

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It gets large.

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You get a large angular size.

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And you can get closer,
and closer, and closer,

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and closer until
each of those letters

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00:03:36,550 --> 00:03:39,070
actually looks pretty
big, so the angular size

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of those letters is big, and
you can easily see the details.

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00:03:43,180 --> 00:03:48,550
So there was some point in
between where you could first,

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as you got closer,
start to see details.

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You could first start
to read the characters.

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You could first tell that
they were words in writing.

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And we call that the
smallest angular size, you

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or your detector--

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your detector-- can resolve.

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So when astronomers talk
about resolving things,

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that means they're talking
about seeing details.

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00:04:28,010 --> 00:04:31,780
So for each of your eyes,
there is a smallest angular

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00:04:31,780 --> 00:04:34,750
size that your
detector can resolve,

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and for people,
that size-- we're

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actually going to
calculate this,

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00:04:38,800 --> 00:04:41,260
but we're running out of
time a little bit today.

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00:04:41,260 --> 00:04:44,910
So for a person, your
smallest angular size--

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I'm just going to write
this down over here--

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00:04:47,720 --> 00:04:49,810
for a person, the
smallest angular size

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00:04:49,810 --> 00:04:55,000
is equal to about 3 times
10 to the minus 4 radians.

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00:04:58,550 --> 00:05:00,950
All right, that doesn't
mean a whole lot.

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00:05:00,950 --> 00:05:03,520
What that means is when you're
about a meter or so away,

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00:05:03,520 --> 00:05:08,650
you can read text that's a
couple of millimeters tall.

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00:05:08,650 --> 00:05:11,980
For different telescopes,
they can actually

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00:05:11,980 --> 00:05:15,760
resolve details that are
much smaller than that

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00:05:15,760 --> 00:05:18,660
in terms of angular size.

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00:05:18,660 --> 00:05:31,970
For the micro
observatory telescopes,

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00:05:31,970 --> 00:05:37,130
we've got an angular
size of about 7 times 10

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00:05:37,130 --> 00:05:41,150
to the minus 5 radians.

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00:05:41,150 --> 00:05:44,090
And for the Chandra
X-ray telescope,

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00:05:44,090 --> 00:05:50,390
the one that we're
going to use, we

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00:05:50,390 --> 00:05:53,390
are going to see that it's
resolution, or the smallest

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00:05:53,390 --> 00:05:58,460
angle that it can see
details, is 5 times 10

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00:05:58,460 --> 00:06:01,650
to the minus 6 radians.

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00:06:04,340 --> 00:06:06,980
Which one of these detectors
has the smallest angle

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00:06:06,980 --> 00:06:07,860
that it can see?

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00:06:11,270 --> 00:06:13,685
Which one of these
numbers is the smallest?

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00:06:17,210 --> 00:06:17,900
OK.

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00:06:17,900 --> 00:06:26,240
Because remember this is
0.0003 radians, so 3 times 10

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to the minus 4.

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00:06:27,990 --> 00:06:32,930
We move the decimal point over
one, two, three, four places,

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00:06:32,930 --> 00:06:35,660
and we get 0.0003.

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00:06:35,660 --> 00:06:45,530
This one is 0.00007, so
smaller, and this one is 5--

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or I'm sorry.

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0.000005 radians, so
this number is smaller.

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So if you guys
can only see this,

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that means that other telescopes
could be farther away,

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and they could
still see details.

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Or they can see smaller
details than we can see.