WEBVTT FILE

1
00:00:00.000 --> 00:00:03.990
Our sun's steady heat and light

2
00:00:04.010 --> 00:00:08.000
makes life on Earth possible, but instruments operating above

3
00:00:08.020 --> 00:00:12.000
our atmosphere see a more dynamic star. Magnetic

4
00:00:12.020 --> 00:00:16.010
activity associated with sunspots can fire off torrents of

5
00:00:16.030 --> 00:00:20.020
high-energy radiation and launch billion-ton clouds of plasma--

6
00:00:20.040 --> 00:00:24.060
called coronal mass ejection--into space.

7
00:00:24.080 --> 00:00:28.060
NASA's Fermi Gamma-ray Space Telescope orbits Earth and monitors the entire

8
00:00:28.080 --> 00:00:32.070
sky for gamma rays, the highest-energy light there is.

9
00:00:32.090 --> 00:00:36.080
Most of the time, the sun is merely a faint source of gamma rays,

10
00:00:36.100 --> 00:00:40.080
which are produced when high-energy particles called cosmic rays

11
00:00:40.100 --> 00:00:44.090
interact with either its surface gas or its lower-energy light.

12
00:00:44.110 --> 00:00:48.110
Occasionally, tangled magnetic fields near

13
00:00:48.130 --> 00:00:52.120
sunspots suddenly release their pent-up energy.

14
00:00:52.140 --> 00:00:56.120
This produces an explosion that rapidly accelerates charged particles to near

15
00:00:56.140 --> 00:01:00.130
the speed of light. Confined by magnetic fields,

16
00:01:00.150 --> 00:01:04.130
some of these particles toward the sun and excite gamma-ray emission.

17
00:01:04.150 --> 00:01:08.140
Suddenly, the sun may become the brightest object

18
00:01:08.160 --> 00:01:12.150
in Fermi's sky.

19
00:01:12.170 --> 00:01:16.150
Now, scientists say Fermi has caught gamma rays from solar storms located on the

20
00:01:16.170 --> 00:01:20.160
opposite side of the sun, where the spacecraft shouldn't be able to see them at all.

21
00:01:20.180 --> 00:01:24.190
Here's one of them.

22
00:01:24.210 --> 00:01:28.200
NASA's STEREO B spacecraft has a clear view of the solar flare, but

23
00:01:28.220 --> 00:01:32.220
the eruption cannot be seen by NASA's Solar Dynamics Observatory,

24
00:01:32.240 --> 00:01:36.220
which views the sun from the same direction as Earth and Fermi. Yet Fermi's

25
00:01:36.240 --> 00:01:40.230
Large Area Telescope detected gamma rays associated with this flare

26
00:01:40.250 --> 00:01:44.230
for nearly two hours. Here's what's going on.

27
00:01:44.250 --> 00:01:48.240
Magnetic field lines extend high above each active region on the sun

28
00:01:48.260 --> 00:01:52.240
and charged particles must travel along them.

29
00:01:52.260 --> 00:01:56.250
Some particles accelerated at the leading edge of a coronal mass ejection can

30
00:01:56.270 --> 00:02:00.260
follow these lines and strike the opposite side of the sun, traveling

31
00:02:00.280 --> 00:02:04.260
about 300,000 miles in less than five minutes.

32
00:02:04.280 --> 00:02:08.270
So far, Fermi has observed two additional

33
00:02:08.290 --> 00:02:12.280
farside flares, doubling the number of these rare detections.

34
00:02:12.300 --> 00:02:16.280
These observations will help scientists better understand how particles

35
00:02:16.300 --> 00:02:20.290
accelerate, travel, and interact to produce gamma rays

36
00:02:20.310 --> 00:02:24.290
during solar storms.

37
00:02:24.310 --> 00:02:28.310
[Music]

38
00:02:28.330 --> 00:02:32.320
[Beeping]

39
00:02:32.340 --> 00:02:38.038
[Beeping]