WEBVTT 1 00:00:00.000 --> 00:00:02.710 [upbeat music] 2 00:00:02.710 --> 00:00:04.730 What's Up for September? 3 00:00:04.730 --> 00:00:07.820 Moving fast in the cosmos with planet Mercury 4 00:00:07.820 --> 00:00:11.270 and stars Arcturus and Altair. 5 00:00:11.270 --> 00:00:12.420 You'll have to be quick 6 00:00:12.420 --> 00:00:14.670 to catch a glimpse of Mercury this month, 7 00:00:14.670 --> 00:00:17.200 as the innermost and fastest-moving planet, 8 00:00:17.200 --> 00:00:20.120 namesake of the fleet-footed mythological messenger, 9 00:00:20.120 --> 00:00:24.070 appears low in the west for a short time following sunset. 10 00:00:24.070 --> 00:00:26.500 But those with a clear view toward the horizon 11 00:00:26.500 --> 00:00:28.970 will be rewarded with some nice planetary groupings 12 00:00:28.970 --> 00:00:31.160 for the first week and a half of September. 13 00:00:31.160 --> 00:00:33.050 line:15% You'll find Mercury just a few degrees 14 00:00:33.050 --> 00:00:34.280 line:15% above the western horizon 15 00:00:34.280 --> 00:00:36.690 line:15% about half an hour after the sun sets, 16 00:00:36.690 --> 00:00:38.490 line:15% with much brighter Venus higher 17 00:00:38.490 --> 00:00:40.720 line:15% and slightly farther to the south. 18 00:00:40.720 --> 00:00:41.790 line:15% On the ninth and tenth, 19 00:00:41.790 --> 00:00:44.690 line:15% look for the pair to be joined by the crescent Moon. 20 00:00:44.690 --> 00:00:47.650 line:15% In between the two planets is the bright star Spica, 21 00:00:47.650 --> 00:00:50.010 line:15% which is actually two stars orbiting each other 22 00:00:50.010 --> 00:00:51.970 at a distance three times closer 23 00:00:51.970 --> 00:00:54.290 than Mercury orbits our sun. 24 00:00:54.290 --> 00:00:55.910 Mercury should be visible for you 25 00:00:55.910 --> 00:00:58.490 from the mid-northern latitudes on south. 26 00:00:58.490 --> 00:00:59.770 The farther south you are, 27 00:00:59.770 --> 00:01:02.250 the longer Mercury will be above the horizon for you 28 00:01:02.250 --> 00:01:03.442 before it sets. 29 00:01:03.442 --> 00:01:04.580 [meteor swishes] 30 00:01:04.580 --> 00:01:07.280 In addition to Spica, two other bright stars 31 00:01:07.280 --> 00:01:10.170 you can easily spot early in the evening in September 32 00:01:10.170 --> 00:01:13.130 are Arcturus and Altair. 33 00:01:13.130 --> 00:01:16.410 Arcturus is the brightest star in the northern sky. 34 00:01:16.410 --> 00:01:18.440 It owes this status largely to the fact 35 00:01:18.440 --> 00:01:20.030 that it's relatively close by, 36 00:01:20.030 --> 00:01:23.070 at about 37 light years from our solar system. 37 00:01:23.070 --> 00:01:24.750 line:15% You can find Arcturus in the west 38 00:01:24.750 --> 00:01:27.620 line:15% in the first couple of hours after it gets dark. 39 00:01:27.620 --> 00:01:28.820 line:15% Look for the Big Dipper, 40 00:01:28.820 --> 00:01:30.920 line:15% and follow its handle over toward the south 41 00:01:30.920 --> 00:01:33.300 line:15% about the width of an outstretched hand. 42 00:01:33.300 --> 00:01:37.720 line:15% It's easy to remember with the phrase "arc to Arcturus." 43 00:01:37.720 --> 00:01:39.760 line:15% One interesting thing about Arcturus 44 00:01:39.760 --> 00:01:41.270 line:15% is that compared to other stars, 45 00:01:41.270 --> 00:01:45.180 it's moving extremely fast with respect to our solar system. 46 00:01:45.180 --> 00:01:47.390 In fact, the discovery of the star's motion 47 00:01:47.390 --> 00:01:49.710 was a huge moment in astronomy. 48 00:01:49.710 --> 00:01:51.630 Before that, the positions of the stars were thought 49 00:01:51.630 --> 00:01:53.970 to be fixed and unchanging. 50 00:01:53.970 --> 00:01:56.970 After Edmund Halley's discovery, the understanding 51 00:01:56.970 --> 00:01:59.300 that the stars move around as independent objects 52 00:01:59.300 --> 00:02:00.860 began to take hold. 53 00:02:00.860 --> 00:02:03.350 After you've found orange-colored Arcturus, 54 00:02:03.350 --> 00:02:05.830 spin yourself around toward the south-southeast 55 00:02:05.830 --> 00:02:07.830 to find Altair. 56 00:02:07.830 --> 00:02:10.870 line:15% You'll spy it hanging right above Saturn all month. 57 00:02:10.870 --> 00:02:13.050 line:15% In fact, it's about as high above Saturn 58 00:02:13.050 --> 00:02:15.310 line:15% as Saturn is from the horizon. 59 00:02:15.310 --> 00:02:17.570 Altair is a bright white-colored star, 60 00:02:17.570 --> 00:02:20.360 which makes for a nice color comparison with Arcturus 61 00:02:20.360 --> 00:02:22.270 and nearby Antares. 62 00:02:22.270 --> 00:02:23.920 At just 17 light years away, 63 00:02:23.920 --> 00:02:26.280 it's definitely one of the closest bright stars 64 00:02:26.280 --> 00:02:27.830 to our solar system. 65 00:02:27.830 --> 00:02:30.230 line:15% One of the coolest things about Altair is that it rotates 66 00:02:30.230 --> 00:02:33.570 line:15% so fast that it's flattened into an oval shape. 67 00:02:33.570 --> 00:02:36.540 Since it's so close by, astronomers have actually been able 68 00:02:36.540 --> 00:02:41.030 to image this fast spinner's flattened shape directly. 69 00:02:41.030 --> 00:02:45.230 So look for Altair and Arcturus in the September sky, 70 00:02:45.230 --> 00:02:48.500 two bright nearby stars that, along with Mercury, 71 00:02:48.500 --> 00:02:52.554 each have their own spin on what it means to be fast. 72 00:02:52.554 --> 00:02:53.690 [meteor swishes] 73 00:02:53.690 --> 00:02:56.253 Here are the phases of the Moon for September. 74 00:02:58.520 --> 00:03:00.550 You can catch up on all of NASA's missions 75 00:03:00.550 --> 00:03:03.870 to explore the solar system and beyond at nasa.gov. 76 00:03:03.870 --> 00:03:06.870 I'm Preston Dyches from NASA's Jet Propulsion Laboratory, 77 00:03:06.870 --> 00:03:09.274 and that's What's Up for this month. 78 00:03:09.274 --> 00:03:11.691 [soft music]