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MARK HARTMAN: What if we
said that both of them

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00:00:32,689 --> 00:00:36,440
were the same
luminosity, but instead,

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00:00:36,440 --> 00:00:38,690
star 1 was way out here?

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00:00:43,990 --> 00:00:49,180
And now, d1 is greater than d2.

12
00:00:49,180 --> 00:00:53,674
Which one of these
stars, in the image,

13
00:00:53,674 --> 00:00:55,090
is going to have
a higher flux, is

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00:00:55,090 --> 00:00:58,330
going to look brighter when we
look at an image of that star?

15
00:00:58,330 --> 00:01:01,169
So talk with your groups, and
I'm going to do the same thing.

16
00:01:01,169 --> 00:01:02,710
I want you to then
be able to come up

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00:01:02,710 --> 00:01:07,510
and explain to us which
has the higher flux when

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00:01:07,510 --> 00:01:09,250
we measure from here on earth.

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00:01:14,650 --> 00:01:16,500
OK.

20
00:01:16,500 --> 00:01:18,500
Now, no changing your vote.

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00:01:18,500 --> 00:01:21,345
How many people
think that star 1 is

22
00:01:21,345 --> 00:01:22,595
going to have the higher flux?

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00:01:25,190 --> 00:01:26,470
So zero.

24
00:01:26,470 --> 00:01:31,670
How many people think star 2 is
going to have the higher flux?

25
00:01:31,670 --> 00:01:34,490
We have, like, five
or six hands shoot up,

26
00:01:34,490 --> 00:01:37,160
and then just a couple hands--

27
00:01:37,160 --> 00:01:37,760
yeah, I guess.

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00:01:37,760 --> 00:01:40,490
All right, now that I've seen
what everybody else has voted.

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00:01:40,490 --> 00:01:45,530
So let's say we had
10 votes for star 2.

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00:01:45,530 --> 00:01:47,375
Who would like to
come and explain why?

31
00:01:50,161 --> 00:01:50,660
Lauren?

32
00:01:55,240 --> 00:01:57,490
You don't have to write
anything if you don't want to,

33
00:01:57,490 --> 00:01:58,423
but go ahead.

34
00:01:58,423 --> 00:01:59,600
AUDIENCE: Well, if you--

35
00:01:59,600 --> 00:02:01,366
MARK HARTMAN: Use it to point.

36
00:02:01,366 --> 00:02:03,340
AUDIENCE: OK.

37
00:02:03,340 --> 00:02:08,460
So if it's the luminosity
divided by 4 pi,

38
00:02:08,460 --> 00:02:12,400
because this is squared, then
the luminosity's the same.

39
00:02:12,400 --> 00:02:14,045
This is the bigger
number than this is,

40
00:02:14,045 --> 00:02:15,910
so this would be an
even bigger number.

41
00:02:15,910 --> 00:02:21,090
And so then this would
be a bigger number

42
00:02:21,090 --> 00:02:23,980
for the first star than it
would be for the second.

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00:02:23,980 --> 00:02:26,910
And if you divide something
by a bigger number,

44
00:02:26,910 --> 00:02:31,013
then the answer will end
up being even smaller.

45
00:02:31,013 --> 00:02:34,450
I don't know if that
made sense or not.

46
00:02:34,450 --> 00:02:38,610
But so the bigger the
number you're dividing by,

47
00:02:38,610 --> 00:02:43,104
then the smaller the answer
will end up being, I guess.

48
00:02:43,104 --> 00:02:44,770
MARK HARTMAN: OK, so
who would like to--

49
00:02:44,770 --> 00:02:45,430
no, that was great.

50
00:02:45,430 --> 00:02:47,440
Who would like to take
what Lauren said and say it

51
00:02:47,440 --> 00:02:48,160
in their own words?

52
00:02:48,160 --> 00:02:48,868
Explain it again.

53
00:02:53,440 --> 00:02:55,410
You can only volunteer yourself.

54
00:02:55,410 --> 00:02:56,010
Sorry, Nikki.

55
00:02:56,010 --> 00:02:57,426
You can't volunteer
your teammate.

56
00:02:59,740 --> 00:03:00,750
Peter?

57
00:03:00,750 --> 00:03:01,750
OK, go ahead.

58
00:03:08,470 --> 00:03:12,834
AUDIENCE: Flux is luminosity
over 4 pi times the distance

59
00:03:12,834 --> 00:03:14,117
squared.

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00:03:14,117 --> 00:03:16,736
Luminosity, for both
of the stars, is 10.

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00:03:16,736 --> 00:03:20,050
But star 1 has a
larger distance.

62
00:03:20,050 --> 00:03:24,406
So if it's 10 divided
by a large distance,

63
00:03:24,406 --> 00:03:26,320
then you're going
to get a small flux.

64
00:03:26,320 --> 00:03:28,660
But if it's luminosity
divided by a small distance,

65
00:03:28,660 --> 00:03:32,280
you're going to
get a bigger flux.

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00:03:32,280 --> 00:03:34,310
MARK HARTMAN: OK, that's good.

67
00:03:34,310 --> 00:03:38,030
So if something is further
away, if this distance is large,

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00:03:38,030 --> 00:03:41,900
this number, the surface area
of that imaginary sphere,

69
00:03:41,900 --> 00:03:43,670
gets a lot bigger.

70
00:03:43,670 --> 00:03:46,280
So we all said that
this star, which

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00:03:46,280 --> 00:03:50,840
is the same luminosity
but it's closer,

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00:03:50,840 --> 00:03:53,660
is going to have a higher flux.

73
00:03:53,660 --> 00:03:57,410
So what I'm going
to say now here

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00:03:57,410 --> 00:04:02,150
is 20 times the
luminosity of the sun.

75
00:04:02,150 --> 00:04:06,500
So star 1 is 20 times the
luminosity of the sun.

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00:04:06,500 --> 00:04:10,040
It's a certain distance
away, far distance.

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00:04:10,040 --> 00:04:15,590
Star 2 is less luminous, so
it's only 10 solar luminosities.

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00:04:15,590 --> 00:04:21,350
But the distance
is half as much.

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00:04:21,350 --> 00:04:25,920
So which one of those stars is
going to show up in our image?

80
00:04:25,920 --> 00:04:28,325
Which is going to
have a higher flux?

81
00:04:33,240 --> 00:04:34,320
So everybody decided?

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00:04:34,320 --> 00:04:35,060
AUDIENCE: Yes.

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00:04:35,060 --> 00:04:36,260
MARK HARTMAN: Yes, OK.

84
00:04:36,260 --> 00:04:39,800
How many people
think that star 1

85
00:04:39,800 --> 00:04:43,121
is going to have a higher flux?

86
00:04:43,121 --> 00:04:47,520
So I got one, two, three, four.

87
00:04:47,520 --> 00:04:51,180
How many people say that star 2
is going to have a higher flux?

88
00:04:51,180 --> 00:04:54,830
And you can't vote twice.

89
00:04:54,830 --> 00:04:56,420
No fair changing your vote.

90
00:04:56,420 --> 00:04:58,400
So we've got one, two, three.

91
00:04:58,400 --> 00:05:00,320
And you guys abstain?

92
00:05:00,320 --> 00:05:01,397
AUDIENCE: [INAUDIBLE]

93
00:05:01,397 --> 00:05:02,480
MARK HARTMAN: What's that?

94
00:05:02,480 --> 00:05:03,820
AUDIENCE: We said it
would be [? either. ?]

95
00:05:03,820 --> 00:05:04,528
MARK HARTMAN: OK.

96
00:05:04,528 --> 00:05:07,280
So we had one, two, three
who said that star 2 is

97
00:05:07,280 --> 00:05:08,155
going to be the same.

98
00:05:08,155 --> 00:05:10,321
And how many people think
it's going to be the same?

99
00:05:10,321 --> 00:05:11,610
AUDIENCE: I said [? either. ?]

100
00:05:11,610 --> 00:05:13,790
MARK HARTMAN: OK, I
have one, two, three.

101
00:05:13,790 --> 00:05:14,870
And you guys don't count.

102
00:05:14,870 --> 00:05:16,020
AUDIENCE: [? Even, ?]

103
00:05:16,020 --> 00:05:16,770
MARK HARTMAN: You
want to do even?

104
00:05:16,770 --> 00:05:17,395
AUDIENCE: Yeah.

105
00:05:17,395 --> 00:05:20,630
MARK HARTMAN: OK-- one, two,
three, four, five, say even.

106
00:05:20,630 --> 00:05:22,910
Five say same.

107
00:05:22,910 --> 00:05:27,000
And so then we'll take
two of you off there,

108
00:05:27,000 --> 00:05:30,020
and we'll go back to two.

109
00:05:30,020 --> 00:05:33,200
So who wants to try to
explain what they're thinking?

110
00:05:37,530 --> 00:05:39,752
Somebody who said that
the flux from star 1

111
00:05:39,752 --> 00:05:40,710
is going to be greater.

112
00:05:44,290 --> 00:05:45,975
I think you guys said
that, didn't you?

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00:05:45,975 --> 00:05:46,600
AUDIENCE: What?

114
00:05:46,600 --> 00:05:46,810
AUDIENCE: No.

115
00:05:46,810 --> 00:05:47,820
MARK HARTMAN: Didn't
you guys say that?

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00:05:47,820 --> 00:05:48,930
Who said that?

117
00:05:48,930 --> 00:05:50,370
AUDIENCE: He said that.

118
00:05:50,370 --> 00:05:51,930
MARK HARTMAN: Chris said that.

119
00:05:51,930 --> 00:05:52,530
AUDIENCE: No, I didn't/

120
00:05:52,530 --> 00:05:53,400
MARK HARTMAN: Yes, you did.

121
00:05:53,400 --> 00:05:54,702
AUDIENCE: I changed my answer.

122
00:05:54,702 --> 00:05:55,410
MARK HARTMAN: OK.

123
00:05:55,410 --> 00:05:56,550
Then what did you
change your answer to?

124
00:05:56,550 --> 00:05:58,470
AUDIENCE: The one
with the most people.

125
00:05:58,470 --> 00:06:00,220
MARK HARTMAN: No,
that's not how it works.

126
00:06:00,220 --> 00:06:01,800
I want you to come up,
and I want you to explain,

127
00:06:01,800 --> 00:06:03,424
because I heard a
couple of good things

128
00:06:03,424 --> 00:06:07,230
coming from you guys over
there about why this one would

129
00:06:07,230 --> 00:06:08,610
have a higher flux.

130
00:06:08,610 --> 00:06:10,010
So stand up.

131
00:06:10,010 --> 00:06:11,332
There you go.

132
00:06:11,332 --> 00:06:13,020
AUDIENCE: Why do I
need a marker for?

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00:06:13,020 --> 00:06:14,561
MARK HARTMAN: Just
in case, to point.

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00:06:14,561 --> 00:06:16,560
If you wanted to write
something, you can.

135
00:06:16,560 --> 00:06:19,650
Now, here's a tip.

136
00:06:19,650 --> 00:06:21,239
When you're up here
talking to people,

137
00:06:21,239 --> 00:06:23,280
you always want to make
sure that you turn around

138
00:06:23,280 --> 00:06:24,000
and look at them.

139
00:06:24,000 --> 00:06:29,542
If you need to, we'll do a thing
called touch, turn, and talk.

140
00:06:29,542 --> 00:06:31,500
So if you're talking
about this thing up there,

141
00:06:31,500 --> 00:06:33,990
you don't want to be like,
so then star 1 is up there,

142
00:06:33,990 --> 00:06:35,820
and there's another
thing down here.

143
00:06:35,820 --> 00:06:37,579
That's the worst
thing that you can do.

144
00:06:37,579 --> 00:06:39,370
You will run into that
if you go to college

145
00:06:39,370 --> 00:06:41,622
because some professors
will talk like this as they

146
00:06:41,622 --> 00:06:43,830
write on the board, and then
you can't hear anything.

147
00:06:43,830 --> 00:06:46,350
But I want you guys
to point to something,

148
00:06:46,350 --> 00:06:48,750
turn around, say what
you have to say about it.

149
00:06:48,750 --> 00:06:51,240
And then point again
at something else,

150
00:06:51,240 --> 00:06:53,310
and then go from there.

151
00:06:53,310 --> 00:06:55,025
So Chris, you want
to model that for us?

152
00:06:55,025 --> 00:06:55,650
AUDIENCE: Sure.

153
00:06:55,650 --> 00:06:57,570
MARK HARTMAN: OK.

154
00:06:57,570 --> 00:06:59,820
AUDIENCE: I said that this
one was going to brighter--

155
00:06:59,820 --> 00:07:02,125
[? well, ?] get flux because--

156
00:07:02,125 --> 00:07:04,180
MARK HARTMAN: OK,
so you touched.

157
00:07:04,180 --> 00:07:05,640
Now turn around.

158
00:07:05,640 --> 00:07:06,440
Now talk to us.

159
00:07:06,440 --> 00:07:07,940
AUDIENCE: I said
that that was going

160
00:07:07,940 --> 00:07:11,070
to be brighter because
this one is twice

161
00:07:11,070 --> 00:07:13,010
as luminous as this one.

162
00:07:13,010 --> 00:07:16,500
And it's 1.5, you said, right?

163
00:07:16,500 --> 00:07:18,270
The distance is 1.5.

164
00:07:18,270 --> 00:07:20,010
MARK HARTMAN: It's
twice as far away.

165
00:07:20,010 --> 00:07:24,270
AUDIENCE: It's twice as far
away, but it's-- wait, what?

166
00:07:24,270 --> 00:07:26,518
You just messed me up.

167
00:07:26,518 --> 00:07:27,470
Wait.

168
00:07:27,470 --> 00:07:29,380
Hold on.

169
00:07:29,380 --> 00:07:31,630
What was the other thing?

170
00:07:31,630 --> 00:07:34,090
MARK HARTMAN: So this
one is twice as luminous,

171
00:07:34,090 --> 00:07:35,680
but it's also twice as far away.

172
00:07:35,680 --> 00:07:36,790
AUDIENCE: That's it?

173
00:07:36,790 --> 00:07:37,030
MARK HARTMAN: Yeah.

174
00:07:37,030 --> 00:07:39,113
AUDIENCE: Well, then they're
going to be the same.

175
00:07:39,113 --> 00:07:40,550
MARK HARTMAN: OK.

176
00:07:40,550 --> 00:07:42,475
So let's hear why
you think they're

177
00:07:42,475 --> 00:07:44,350
going to be the same,
because a lot of people

178
00:07:44,350 --> 00:07:45,850
said they were going
to be the same.

179
00:07:45,850 --> 00:07:49,930
AUDIENCE: Well,
if this one's half

180
00:07:49,930 --> 00:07:52,265
as luminous as that
one, and then this one's

181
00:07:52,265 --> 00:07:56,550
twice as far as that one, if you
divide both of those factors,

182
00:07:56,550 --> 00:07:59,290
then it would be--

183
00:07:59,290 --> 00:08:02,350
2 divided by 2 is 1,
and 1 divided by 1 is 1.

184
00:08:02,350 --> 00:08:05,120
So they're both 1.

185
00:08:05,120 --> 00:08:06,129
MARK HARTMAN: OK.

186
00:08:06,129 --> 00:08:07,420
I can kind of see some of that.

187
00:08:07,420 --> 00:08:09,711
Who else said that it was
the same who wants to come up

188
00:08:09,711 --> 00:08:10,540
and say that?

189
00:08:10,540 --> 00:08:12,090
That was good.

190
00:08:12,090 --> 00:08:14,586
And it did the touch,
turn, and talk.

191
00:08:14,586 --> 00:08:16,210
Somebody else who
said it was the same.

192
00:08:22,424 --> 00:08:23,760
Peter already did one.

193
00:08:23,760 --> 00:08:24,920
Anybody else want a chance?

194
00:08:29,260 --> 00:08:29,900
OK.

195
00:08:29,900 --> 00:08:30,566
Peter, go ahead.

196
00:08:33,374 --> 00:08:41,980
AUDIENCE: [INAUDIBLE]
I basically

197
00:08:41,980 --> 00:08:46,180
did the same thing Chris did.

198
00:08:46,180 --> 00:08:49,164
l1 is-- the distance
is twice as long as l2.

199
00:08:49,164 --> 00:08:52,900
So it's times 2.

200
00:08:52,900 --> 00:08:58,401
But then-- so l2 is
only half as luminous.

201
00:08:58,401 --> 00:09:02,240
I mean, l1 is two times
as luminous as l2.

202
00:09:02,240 --> 00:09:04,190
So that's also times 2.

203
00:09:04,190 --> 00:09:06,610
And it cancels out to equal 1.

204
00:09:06,610 --> 00:09:07,340
MARK HARTMAN: OK.

205
00:09:07,340 --> 00:09:11,535
So the first time, you said
l1 is twice as luminous.

206
00:09:11,535 --> 00:09:13,410
But then what did you
say about the distance?

207
00:09:13,410 --> 00:09:15,076
Because I think you
said luminous again.

208
00:09:15,076 --> 00:09:15,694
AUDIENCE: Oh.

209
00:09:15,694 --> 00:09:18,129
The distance for the
first one is twice

210
00:09:18,129 --> 00:09:19,712
that of the second one.

211
00:09:19,712 --> 00:09:20,420
MARK HARTMAN: OK.

212
00:09:20,420 --> 00:09:23,232
So if your distance
gets bigger, what's

213
00:09:23,232 --> 00:09:24,440
going to happen to your flux?

214
00:09:24,440 --> 00:09:26,462
AUDIENCE: It will decrease.

215
00:09:26,462 --> 00:09:27,170
MARK HARTMAN: OK.

216
00:09:27,170 --> 00:09:31,760
So you're saying because on the
top, l1 is twice as luminous,

217
00:09:31,760 --> 00:09:34,350
but then it's going
to be twice as far.

218
00:09:34,350 --> 00:09:36,920
So you divide by 2 down here.

219
00:09:36,920 --> 00:09:39,450
So they kind of cancel out.

220
00:09:39,450 --> 00:09:41,720
OK.

221
00:09:41,720 --> 00:09:44,180
What about somebody
who said that f2

222
00:09:44,180 --> 00:09:48,830
was going to be larger, that
star 2 was going to be more

223
00:09:48,830 --> 00:09:49,910
luminous?

224
00:09:49,910 --> 00:09:51,830
Why would you say that?

225
00:09:51,830 --> 00:09:54,126
One of those three people.

226
00:09:54,126 --> 00:09:55,250
AUDIENCE: I think that now.

227
00:09:58,370 --> 00:10:00,920
MARK HARTMAN: You already got
to change your answer twice.

228
00:10:00,920 --> 00:10:02,878
Let's think about who
was one of the people who

229
00:10:02,878 --> 00:10:05,190
voted for f2 right away?

230
00:10:05,190 --> 00:10:06,350
You guys?

231
00:10:06,350 --> 00:10:08,824
Bianca?

232
00:10:08,824 --> 00:10:10,132
AUDIENCE: Well, because you--

233
00:10:10,132 --> 00:10:11,590
MARK HARTMAN: Turn,
turn, and talk.

234
00:10:11,590 --> 00:10:13,844
AUDIENCE: Because even
though this is 2 times

235
00:10:13,844 --> 00:10:16,052
and it looks like it would
cancel out, you square it.

236
00:10:16,052 --> 00:10:18,035
So it's really 4, not 2.

237
00:10:18,035 --> 00:10:25,702
So then if you do it out, so
it's 20 [INAUDIBLE] divided

238
00:10:25,702 --> 00:10:30,690
by [? 4 ?] d squared--

239
00:10:30,690 --> 00:10:34,160
MARK HARTMAN: If we rewrite
and we just say that this is d,

240
00:10:34,160 --> 00:10:36,241
and this is 2d--

241
00:10:36,241 --> 00:10:36,740
right?

242
00:10:36,740 --> 00:10:37,573
That's what we said.

243
00:10:37,573 --> 00:10:38,480
AUDIENCE: Oh, yeah.

244
00:10:38,480 --> 00:10:39,563
MARK HARTMAN: That's fine.

245
00:10:39,563 --> 00:10:40,090
Keep going.

246
00:10:40,090 --> 00:10:45,391
AUDIENCE: And this would
be 10 [? L7 ?] over 4 pi,

247
00:10:45,391 --> 00:10:48,410
and just d squared
because there's no 2.

248
00:10:48,410 --> 00:10:49,743
It's not twice the length.

249
00:10:49,743 --> 00:10:51,910
So then this would
cancel out to be 5.

250
00:10:51,910 --> 00:10:55,418
And then since the bottoms
are the same, [? you can ?]

251
00:10:55,418 --> 00:11:01,270
see 5 is [INAUDIBLE]

252
00:11:01,270 --> 00:11:03,400
MARK HARTMAN: OK.

253
00:11:03,400 --> 00:11:06,160
So does that convince anybody?

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00:11:06,160 --> 00:11:07,537
Somebody else want to say that?

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AUDIENCE: It [? convinced ?] me.

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MARK HARTMAN: It convinced you?

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AUDIENCE: [? Well-- ?]

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MARK HARTMAN: OK,
Chris, do you want

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to come back up here and
explain why you think?

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AUDIENCE: No, I didn't think
because of the same way

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she did.

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I was just thinking
because you said

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that if it was a farther
distance-- not today,

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but Thursday or Wednesday,
you said that the energy,

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it loses particles.

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And they become
weaker as they travel.

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So I thought even though
the distance was only half,

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it wouldn't get actually half
of the amount as the other one.

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[? That would ?] get less
than half because [INAUDIBLE]..

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MARK HARTMAN: Oh, OK.

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That's actually important.

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On Thursday, we didn't say
that the particles got weaker,

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necessarily.

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The particles are
always the same.

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They don't change.

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It's just that as they
get further away from you,

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they spread out because they're
going on straight lines,

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and those straight lines
diverge from each other.

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So as you go further out, yeah,
the luminosity of this one

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is bigger.

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But every time that you
double the distance away,

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the amount of flux that
you get doesn't just

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drop by a factor of 2.

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It doesn't drop in half.

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00:12:21,430 --> 00:12:25,480
It drops to one quarter
of what the original was.

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00:12:25,480 --> 00:12:28,750
Because if you think about
it, the area, if I had--

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00:12:28,750 --> 00:12:30,820
say that Bianca was
holding a light bulb.

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00:12:30,820 --> 00:12:33,040
Pretend like you're
holding a light bulb.

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00:12:33,040 --> 00:12:38,410
If I'm up here, I'm collecting
this area of particles.

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00:12:38,410 --> 00:12:43,270
As I go further back, those
particles all spread out.

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00:12:43,270 --> 00:12:45,700
If I go twice as
far away, it's not

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that I'm just collecting
twice fewer particles.

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00:12:48,340 --> 00:12:51,580
I'm actually collecting
four times fewer particles

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00:12:51,580 --> 00:12:54,010
because this factor has
to do with 4 pi times

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00:12:54,010 --> 00:12:56,650
the distance to
the object squared.

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00:12:56,650 --> 00:13:00,430
So even though we've doubled our
luminosity between these two,

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00:13:00,430 --> 00:13:03,010
distance always wins.

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00:13:03,010 --> 00:13:05,680
When you've got something
that's really far away,

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00:13:05,680 --> 00:13:08,690
it's always going
to get overpowered.

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00:13:08,690 --> 00:13:14,620
This flux is always going to
be overpowered by the distance.

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00:13:14,620 --> 00:13:18,190
So based on what we just said--
so the [? actual ?] what you

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00:13:18,190 --> 00:13:23,230
would see is that the flux from
the second [? star, ?] even

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00:13:23,230 --> 00:13:27,990
though the other one
is twice as luminous,

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00:13:27,990 --> 00:13:30,610
the flux from the second star
is still going to be more.

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00:13:30,610 --> 00:13:33,400
You're still going
to get more counts.

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00:13:33,400 --> 00:13:36,340
So here is my
question to you guys.

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00:13:36,340 --> 00:13:41,070
What would I have
to do to star 1?