1 00:00:05,220 --> 00:00:08,340 An amazing phenomenon is happening today that won’t happen for another 13 years — Mercury is passing in front of the Sun! What exactly is going on? 2 00:00:08,480 --> 00:00:13,780 so it's very exciting day here on planet earth. Earth and all of the planets in 3 00:00:13,800 --> 00:00:18,810 our solar system are orbiting in a plain around the Sun and so what that means is 4 00:00:18,810 --> 00:00:22,800 that on very special days when the geometry is aligned perfectly 5 00:00:22,800 --> 00:00:27,029 we can watch the planets that are interior to us actually cross the face 6 00:00:27,029 --> 00:00:31,529 of the Sun just glide across the face of the Sun and today that's happening 7 00:00:31,529 --> 00:00:35,100 mercury is passing in front of the face of the Sun from the East Coast we can 8 00:00:35,100 --> 00:00:38,360 watch it pretty much all morning long. 9 00:00:38,380 --> 00:00:42,200 NASA uses events like this one to find planets around other stars. How does that work? 10 00:00:42,440 --> 00:00:46,550 so it's basically the exact same phenomenon that we're seeing here today 11 00:00:46,550 --> 00:00:51,820 with mercury passing in front of our Sun we can use that now to look for planets 12 00:00:51,820 --> 00:00:57,800 transiting across the face of their suns or stars. So when we look out at the 13 00:00:57,800 --> 00:01:01,280 nearby stars we're looking for transits and right now we h ave a mission in space 14 00:01:01,280 --> 00:01:06,350 called TESS, the transiting exoplanet survey satellite, measuring transits to 15 00:01:06,350 --> 00:01:11,210 discover planets around nearby bright stars and TESS is very capable of 16 00:01:11,210 --> 00:01:15,649 measuring just the tiniest dip in light from a star when a planet like the earth 17 00:01:15,649 --> 00:01:20,660 passes in front of a star like the Sun it's 84 parts per million fainter and so 18 00:01:20,660 --> 00:01:23,840 that's a really tough measurement to make but we have the technology now to 19 00:01:23,840 --> 00:01:27,040 do so and we're finding planets through this method. 20 00:01:27,040 --> 00:01:32,040 We’ve always been told not to look directly at the sun. So how can our viewers see today’s event? 21 00:01:32,220 --> 00:01:35,610 so it's very important not to look directly at the Sun even when exciting 22 00:01:35,610 --> 00:01:39,600 things like planets are transiting in front of the Sun but there are all kinds 23 00:01:39,600 --> 00:01:44,010 of ways that you can enjoy this event happening. One of the most amazing views 24 00:01:44,010 --> 00:01:49,230 you can get is on the internet. NASA will be showing a near live stream of this 25 00:01:49,230 --> 00:01:52,950 event from the Solar Dynamics Observatory and this is a solar 26 00:01:52,950 --> 00:01:57,600 telescope in orbit right now in space that is very powerful and as a solar 27 00:01:57,600 --> 00:02:01,800 observer and it's going to have a great view of mercury transiting. So tune in on 28 00:02:01,800 --> 00:02:05,310 the internet if you're lucky enough to live near a science museum or an 29 00:02:05,310 --> 00:02:08,760 astronomy club that is setting up telescopes to show you this in real time 30 00:02:08,760 --> 00:02:13,320 go online and see if you can be there in person for that as well. 31 00:02:13,800 --> 00:02:18,500 What do transits and eclipses teach us about our own solar system? 32 00:02:18,500 --> 00:02:23,300 so they've been so important historically in giving us a sense of 33 00:02:23,300 --> 00:02:28,490 what our solar system looks like and how big it is. It's easy to predict when 34 00:02:28,490 --> 00:02:33,170 transits happened because we understand the laws of nature that all the planets 35 00:02:33,170 --> 00:02:37,400 in our solar system follow in their movements. So for hundreds of years 36 00:02:37,400 --> 00:02:40,730 astronomers could predict transits of mercury, transits of Venus, and they would 37 00:02:40,730 --> 00:02:44,780 travel for hundreds of miles to observe these events was one of the first ways 38 00:02:44,780 --> 00:02:48,860 we started to really get a hold on the size of our solar system the Sun is 93 39 00:02:48,860 --> 00:02:53,630 million miles from Earth and the first measurements of that distance were made 40 00:02:53,630 --> 00:02:59,480 by measuring transits and working with the geometry to figure out our distance. 41 00:02:59,480 --> 00:03:04,220 Where can we learn more about stars and planets? 42 00:03:04,460 --> 00:03:08,820 so there's a huge amount of information online and growing all the time a great 43 00:03:08,820 --> 00:03:12,930 place to start for information about transits and tests would be in NASA at 44 00:03:12,930 --> 00:03:16,940 nasa sun or at nasa universe.