1 00:00:07,050 --> 00:00:04,010 Bell Tone 2 00:00:07,070 --> 00:00:10,100 Music 3 00:00:10,120 --> 00:00:13,210 Narrator: When we look up at the sun from Earth, it seems calm and unchanging. 4 00:00:13,230 --> 00:00:17,240 The truth is quite different. 5 00:00:29,420 --> 00:00:21,300 Music 6 00:00:29,440 --> 00:00:33,510 In addition to these abrupt changes in activity, the sun also has long 7 00:00:33,530 --> 00:00:37,540 term, more regular pattern of change. This pattern is called the sunspot 8 00:00:37,560 --> 00:00:41,580 cycle and a single cycle lasts for about 11 years, although it can be as short 9 00:00:41,600 --> 00:00:45,620 as 8 or as long as 14 and it can vary dramatically in intensity. 10 00:00:45,640 --> 00:00:49,640 During one cycle, the number of sunspots, a good indicator of 11 00:00:49,660 --> 00:00:53,660 solar activity, goes from low to high and back down to low. 12 00:00:53,680 --> 00:00:57,680 Solar minimum represents a time when sunspot numbers are relatively low, 13 00:00:57,700 --> 00:01:01,770 and solar maximum represents a period when sunspot numbers are relatively high. 14 00:01:01,790 --> 00:01:05,790 During this cycle, the location of the sunspots also 15 00:01:05,810 --> 00:01:09,810 changes. They are at middle latitudes during solar maximum, and move 16 00:01:09,830 --> 00:01:13,830 closer to the equator as the sun approaches solar minimum. At solar minimum, 17 00:01:13,850 --> 00:01:17,860 there are sometimes no sunspots to observe. At solar maximum there can be many 18 00:01:17,880 --> 00:01:21,900 at the same time. The number of sunspots is important 19 00:01:21,920 --> 00:01:25,940 because sunspots are the visual markers of where powerful magnetic fields have emerged 20 00:01:25,960 --> 00:01:29,960 from the sun's interior. These magnetic fields power solar flares and 21 00:01:29,980 --> 00:01:34,000 coronal mass ejections, which can affect Earth and other objects in the solar system. 22 00:01:34,020 --> 00:01:38,020 As the sunspots increase, so does the frequency and severity 23 00:01:38,040 --> 00:01:42,110 of flares and CMEs. The sun's 11-year 24 00:01:42,130 --> 00:01:46,140 cycle is a symptom of a longer, 22-year-cycle called the solar cycle, 25 00:01:46,160 --> 00:01:50,170 or Hale Cycle, which affects the sun's magnetic fields. 26 00:01:50,190 --> 00:01:54,200 Every 11 years, the sun's poles flip--north becomes south and south 27 00:01:54,220 --> 00:01:58,230 becomes north, so every 22 years, the poles return to the position 28 00:01:58,250 --> 00:02:02,270 where they started the cycle. The flip is due to the complex movement of 29 00:02:02,290 --> 00:02:06,310 magnetic fields inside the sun that are constantly stretching, twisting, and 30 00:02:06,330 --> 00:02:10,350 crossing as solar material bubbles up from the sun's core. But the exact 31 00:02:10,370 --> 00:02:14,470 pattern of movements is not yet mapped out. Because the sunspot 32 00:02:14,490 --> 00:02:18,530 cycle follows a similar pattern regardless of the orientation of the poles, 33 00:02:18,550 --> 00:02:22,560 it only takes half as long as the solar cycle. The two cycles are different, 34 00:02:22,580 --> 00:02:26,580 but the 11-year sunspot cycle is often referred to as the solar cycle, 35 00:02:26,600 --> 00:02:30,610 which can be a little confusing. Right now the 36 00:02:30,630 --> 00:02:34,710 sun is approaching solar maximum, so flares and CMEs are more common than 37 00:02:34,730 --> 00:02:38,730 they were a few years ago. This cycle may peak in 2013, or 38 00:02:38,750 --> 00:02:42,750 early 2014, and should reach its minimum around 2020 39 00:02:42,770 --> 00:02:46,790 although predictions about the sun are still uncertain. The slower 40 00:02:46,810 --> 00:02:50,830 than expected progress of this sunspot cycle has led some to speculate 41 00:02:50,850 --> 00:02:54,990 that the next sunspot cycle might be very minimal, with few sunspots even at 42 00:02:55,010 --> 00:02:59,020 solar maximum. It is still far too early to know, but even if this is 43 00:02:59,040 --> 00:03:03,060 the case, it has happened before and isn't something to worry about, it just means 44 00:03:03,080 --> 00:03:07,100 that the sun would briefly be a little closer to the unchanging orb it looks like from 45 00:03:07,120 --> 00:03:08,120 the ground.