1 00:00:02,600 --> 00:00:04,710 Imagine that these 100 pennies 2 00:00:04,730 --> 00:00:09,590 represent the total energy input from the sun to Earth. 3 00:00:09,610 --> 00:00:11,600 That energy fluctuates over time. 4 00:00:11,620 --> 00:00:14,280 For a long time, scientists have known 5 00:00:14,300 --> 00:00:18,750 that the sun’s energy changes in a fairly regular “solar cycle”. 6 00:00:18,770 --> 00:00:20,530 The period from minimum to maximum 7 00:00:20,550 --> 00:00:23,600 and back to minimum is about eleven years, 8 00:00:23,620 --> 00:00:29,020 but even with those cycles, there’s very limited variation in total energy output. 9 00:00:29,040 --> 00:00:34,490 These are solar energy measurements collected by a variety of missions over the years. 10 00:00:34,510 --> 00:00:36,680 The question, however, is precisely— 11 00:00:36,700 --> 00:00:38,180 —precisely— 12 00:00:38,200 --> 00:00:41,650 —how much does the sun’s energy output change? 13 00:00:41,670 --> 00:00:44,260 Experts think the number is pretty small: 14 00:00:44,280 --> 00:00:47,130 perhaps just one tenth of one percent… 15 00:00:47,150 --> 00:00:49,470 …a tenth of a penny. 16 00:00:49,490 --> 00:00:55,470 But one tenth of one percent from the sun can have a profound influence on Earth. 17 00:00:55,490 --> 00:00:58,850 In terms of climate change research, scientists need to understand 18 00:00:58,870 --> 00:01:02,140 the balance between energy coming in from the Sun 19 00:01:02,160 --> 00:01:07,540 and energy radiating out from Earth, as modulated by Earth’s surface and atmosphere. 20 00:01:07,560 --> 00:01:10,190 That’s why NASA is launching TSIS, 21 00:01:10,210 --> 00:01:14,150 the Total and Spectral Solar Irradiance Sensor. 22 00:01:14,170 --> 00:01:15,770 An accurate solar energy measurement 23 00:01:15,790 --> 00:01:18,560 enables other influences on Earth’s energy balance 24 00:01:18,580 --> 00:01:21,270 to be isolated and more accurately quantified. 25 00:01:21,290 --> 00:01:23,370 That will pay big dividends 26 00:01:23,390 --> 00:01:35,391 in terms of understanding human and natural influences on Earth’s climate.