WEBVTT 00:00:07.569 --> 00:00:10.109 Howdy Star Gazers and welcome to this episode 00:00:10.109 --> 00:00:13.449 of Star Trails. My name is Drew and I'll be your 00:00:13.449 --> 00:00:15.849 guide to the night sky for the week of March 00:00:15.849 --> 00:00:19.989 the 22nd to the 28th. This week we're continuing 00:00:19.989 --> 00:00:22.949 our exploration of our own cosmic neighborhood 00:00:22.949 --> 00:00:26.109 by taking a look at some of the most unique moons 00:00:26.109 --> 00:00:29.100 in the solar system. and which ones of those 00:00:29.100 --> 00:00:31.960 might have the right conditions to develop life. 00:00:32.759 --> 00:00:34.640 Later in the show, we'll take a look at this 00:00:34.640 --> 00:00:37.479 week's sky and pick up the next two chapters 00:00:37.479 --> 00:00:41.719 of our book club selection, Night Watch. Whether 00:00:41.719 --> 00:00:44.179 you're tuning in from the backyard or the balcony, 00:00:44.479 --> 00:00:47.200 I'm glad you're here. So grab a comfortable spot 00:00:47.200 --> 00:00:50.899 under the night sky and let's get started. I 00:00:50.899 --> 00:00:53.799 need to start this week's show by first thanking 00:00:53.799 --> 00:00:57.689 our listeners. I received some interesting feedback 00:00:57.689 --> 00:01:01.009 concerning last week's Pluto episode. Everything 00:01:01.009 --> 00:01:04.189 from a wonderful poem about Pluto sent in by 00:01:04.189 --> 00:01:06.810 a listener, to a handful of folks who mentioned 00:01:06.810 --> 00:01:10.049 Pluto as being their favorite planet. Some folks 00:01:10.049 --> 00:01:13.390 just enjoyed the story. At this point, I think 00:01:13.390 --> 00:01:16.349 it's safe to say Pluto is as much of a cultural 00:01:16.349 --> 00:01:19.890 object as it is an astronomical one. And we're 00:01:19.890 --> 00:01:22.930 not done with Pluto yet. More on that later in 00:01:22.930 --> 00:01:26.069 this show. And another listener who's currently 00:01:26.069 --> 00:01:29.629 vacationing in New Zealand sent me a slew of 00:01:29.629 --> 00:01:32.969 night sky images from Down Under, including one 00:01:32.969 --> 00:01:35.890 of my favorite objects, the Large Magellanic 00:01:35.890 --> 00:01:39.510 Cloud, plus a very bright image of the Milky 00:01:39.510 --> 00:01:43.709 Way's core, and an upside down rendition of Orion. 00:01:44.310 --> 00:01:47.530 It's kind of weird seeing Orion standing on his 00:01:47.530 --> 00:01:51.000 head. As always, if you want to contact me, just 00:01:51.000 --> 00:01:55.079 use the form over at StarTrails .Show. With that, 00:01:55.239 --> 00:01:59.560 let's get into our main topic this week. When 00:01:59.560 --> 00:02:02.120 most of us hear the word moon, we think of a 00:02:02.120 --> 00:02:06.579 very specific place. A gray, cratered world hanging 00:02:06.579 --> 00:02:11.840 quietly in our night sky. Airless, silent, unchanging. 00:02:12.340 --> 00:02:15.879 And for most of human history, that was our template. 00:02:16.300 --> 00:02:19.360 If you'd asked someone what a moon was, they 00:02:19.360 --> 00:02:21.860 would have described something very much like 00:02:21.860 --> 00:02:26.819 our own. And in many ways, our moon is extraordinary. 00:02:27.740 --> 00:02:31.419 It likely formed when a Mars -sized world slammed 00:02:31.419 --> 00:02:35.360 into early Earth, sending debris into orbit that 00:02:35.360 --> 00:02:39.479 eventually coalesced into the moon. It's unusually 00:02:39.479 --> 00:02:43.449 large for a rocky planet. so large that the Earth 00:02:43.449 --> 00:02:47.009 -Moon system almost behaves like a binary pair. 00:02:47.789 --> 00:02:51.250 Its gravity stabilizes Earth's tilt, helping 00:02:51.250 --> 00:02:54.129 keep our climate relatively steady over long 00:02:54.129 --> 00:02:57.590 periods of time. And, of course, it's the only 00:02:57.590 --> 00:03:00.689 world beyond Earth where human beings have ever 00:03:00.689 --> 00:03:04.490 set foot. But for all its importance, our Moon 00:03:04.490 --> 00:03:08.310 also gave us the wrong idea. Because when we 00:03:08.310 --> 00:03:11.229 finally began exploring the outer solar system, 00:03:11.389 --> 00:03:15.069 We discovered that moons are not all like ours, 00:03:15.370 --> 00:03:19.250 not even close. When the Voyager spacecraft flew 00:03:19.250 --> 00:03:22.229 past Jupiter and Saturn and sent back images, 00:03:22.590 --> 00:03:26.110 that changed everything. Suddenly, moons weren't 00:03:26.110 --> 00:03:29.750 just dead rocks orbiting distant planets. They 00:03:29.750 --> 00:03:32.889 were worlds, some of them violent, some of them 00:03:32.889 --> 00:03:36.889 dynamic, and some of them are possibly habitable. 00:03:37.449 --> 00:03:41.550 A moon is simply a natural satellite, anything 00:03:41.550 --> 00:03:45.150 that orbits a planet or a dwarf planet, but maybe 00:03:45.150 --> 00:03:48.330 that's a little too straightforward. Some moons 00:03:48.330 --> 00:03:52.289 are bigger than planets. For example, Ganymede 00:03:52.289 --> 00:03:55.830 and Titan are both larger than the planet Mercury. 00:03:56.569 --> 00:03:59.710 Some systems behave like binary worlds, think 00:03:59.710 --> 00:04:03.449 Pluto and Charon. Some moons may have formed 00:04:03.449 --> 00:04:06.729 like planets, just in orbit around another world. 00:04:06.939 --> 00:04:10.520 while others were wanderers captured by gravity. 00:04:11.139 --> 00:04:15.180 Rings and moons are related. Inside a certain 00:04:15.180 --> 00:04:18.540 distance, known as the Roche limit, material 00:04:18.540 --> 00:04:21.560 can't clump together into a moon, so it forms 00:04:21.560 --> 00:04:25.560 rings instead. In fact, if an object goes beyond 00:04:25.560 --> 00:04:28.079 that limit, it's likely going to break apart 00:04:28.079 --> 00:04:31.500 because of the planet's gravity. Saturn is the 00:04:31.500 --> 00:04:34.759 king of the rings, of course, but Jupiter, Uranus, 00:04:34.980 --> 00:04:39.120 and Neptune all have wispy ring systems. And 00:04:39.120 --> 00:04:41.579 there are shepherd moons around these systems 00:04:41.579 --> 00:04:44.759 that gravitationally keep the ring systems in 00:04:44.759 --> 00:04:48.899 check. Outside the Roche limit, rings can eventually 00:04:48.899 --> 00:04:52.959 coalesce into moons. So in a sense, rings are 00:04:52.959 --> 00:04:56.500 moons that never formed, and nearby moons are 00:04:56.500 --> 00:05:00.519 rings that finish the job. There's a great diversity 00:05:00.519 --> 00:05:04.540 in moon types just in our solar system. Take 00:05:04.540 --> 00:05:08.920 Io, one of Jupiter's moons. It's the most volcanically 00:05:08.920 --> 00:05:12.740 active world in the entire solar system. Its 00:05:12.740 --> 00:05:16.439 surface is constantly being reshaped by eruptions, 00:05:16.860 --> 00:05:20.500 lava flows, sulfur plumes, and landscapes that 00:05:20.500 --> 00:05:23.339 look more like a fever dream than a place in 00:05:23.339 --> 00:05:28.399 space. And the reason is gravity. Jupiter's immense 00:05:28.399 --> 00:05:32.279 pull stretches and squeezes Io over and over 00:05:32.279 --> 00:05:35.829 again. generating heat inside the moon. That 00:05:35.829 --> 00:05:40.529 process is called tidal heating. That same process 00:05:40.529 --> 00:05:44.009 leads us to something even more remarkable. Because 00:05:44.009 --> 00:05:47.370 if tidal forces can generate heat, they can melt 00:05:47.370 --> 00:05:50.829 ice. And if they can melt ice, they can create 00:05:50.829 --> 00:05:55.430 oceans. Hidden ones. Europa, another of Jupiter's 00:05:55.430 --> 00:05:58.959 moons, looks like a frozen world. Its surface 00:05:58.959 --> 00:06:02.279 is smooth, bright, and criss -crossed with long 00:06:02.279 --> 00:06:06.199 fractures that resemble sea ice on Earth. But 00:06:06.199 --> 00:06:09.519 beneath that icy shell, scientists believe there's 00:06:09.519 --> 00:06:13.519 a global ocean, possibly deeper than all of Earth's 00:06:13.519 --> 00:06:17.980 oceans combined. We haven't seen that ocean directly. 00:06:18.360 --> 00:06:21.240 Instead, we've detected it through a kind of 00:06:21.240 --> 00:06:24.980 cosmic detective work. The surface geology suggests 00:06:24.980 --> 00:06:28.569 movement. Magnetic measurements from the Galileo 00:06:28.569 --> 00:06:32.470 spacecraft indicate a conductive, likely salty, 00:06:32.670 --> 00:06:36.209 layer beneath the ice. Models of tidal heating 00:06:36.209 --> 00:06:39.189 show there's enough energy to keep water liquid, 00:06:39.629 --> 00:06:43.930 so all signs point to an ocean in the dark. And 00:06:43.930 --> 00:06:48.509 Europa isn't alone. At Saturn, a tiny moon called 00:06:48.509 --> 00:06:51.649 Enceladus shocked scientists when the Cassini 00:06:51.649 --> 00:06:55.250 spacecraft discovered geysers erupting from its 00:06:55.250 --> 00:06:59.269 south pole, jets of water vapor and ice blasting 00:06:59.269 --> 00:07:03.069 into space. Cassini flew through those plumes 00:07:03.069 --> 00:07:07.129 and detected salts, organic molecules, even hydrogen, 00:07:07.930 --> 00:07:09.970 evidence that this water has been in contact 00:07:09.970 --> 00:07:13.610 with rock deep below the surface. In other words, 00:07:13.810 --> 00:07:17.029 Enceladus has an ocean, and it's leaking into 00:07:17.029 --> 00:07:21.639 space. Then there's Titan. Titan is something 00:07:21.639 --> 00:07:25.160 else entirely. It's larger than the planet Mercury 00:07:25.160 --> 00:07:28.779 and has a thick nitrogen atmosphere, denser than 00:07:28.779 --> 00:07:32.180 Earth's in some ways, and a surface shaped by 00:07:32.180 --> 00:07:36.600 weather, clouds, rain, rivers, and lakes. But 00:07:36.600 --> 00:07:40.939 the liquid isn't water. It's methane and ethane. 00:07:41.459 --> 00:07:44.600 Titan is a world where it rains hydrocarbons 00:07:44.600 --> 00:07:48.160 and rivers carve through landscapes of ice as 00:07:48.160 --> 00:07:52.500 hard as rock. And we've been there. In 2005, 00:07:52.920 --> 00:07:56.120 the Huygens probe parachuted through Titan's 00:07:56.120 --> 00:07:59.459 orange sky and landed on its surface, the most 00:07:59.459 --> 00:08:03.060 distant landing humanity has ever achieved. It 00:08:03.060 --> 00:08:06.459 sent back images of an eerie landscape, rounded 00:08:06.459 --> 00:08:09.519 stones of water ice scattered across what looked 00:08:09.519 --> 00:08:13.680 like a dried riverbed. And beneath Titan's crust, 00:08:14.000 --> 00:08:18.009 there may be yet another hidden ocean. Back at 00:08:18.009 --> 00:08:20.930 Jupiter, Ganymede is the biggest moon in the 00:08:20.930 --> 00:08:24.370 solar system. If it and Titan were orbiting the 00:08:24.370 --> 00:08:27.470 Sun instead of gas giants, we'd be calling them 00:08:27.470 --> 00:08:31.310 planets. Ganymede has its own magnetic field, 00:08:31.750 --> 00:08:34.590 and it's the only moon we know of that does. 00:08:35.230 --> 00:08:38.009 Beneath its surface may lie multiple layers of 00:08:38.009 --> 00:08:41.649 ocean, stacked between sheets of ice like a planetary 00:08:41.649 --> 00:08:46.299 layer cake. Callisto, also a Jovian moon, is 00:08:46.299 --> 00:08:50.200 heavily cratered and ancient. It too may also 00:08:50.200 --> 00:08:53.200 hide a deep ocean beneath its battered exterior. 00:08:54.019 --> 00:08:57.720 And farther out orbiting Neptune is Triton, a 00:08:57.720 --> 00:09:01.620 strange icy world that likely didn't form around 00:09:01.620 --> 00:09:04.940 Neptune at all. It was probably captured from 00:09:04.940 --> 00:09:08.480 the Kuiper Belt. It orbits backward against the 00:09:08.480 --> 00:09:11.889 rotation of the planet. And Voyager 2 observed 00:09:11.889 --> 00:09:15.710 nitrogen geysers erupting from its surface. Even 00:09:15.710 --> 00:09:18.330 at the edge of the solar system, these moons 00:09:18.330 --> 00:09:21.990 are active. And then there are the quieter, lesser 00:09:21.990 --> 00:09:25.769 -known worlds. Mimas, a small moon of Saturn, 00:09:25.990 --> 00:09:29.129 looks like the Death Star from Star Wars. It's 00:09:29.129 --> 00:09:32.990 dominated by a massive impact crater. But recent 00:09:32.990 --> 00:09:36.210 evidence suggests that it may have a, guess what, 00:09:36.429 --> 00:09:40.649 a hidden ocean beneath its icy shell. Iepidus 00:09:40.649 --> 00:09:43.889 is split dramatically in two, one hemisphere 00:09:43.889 --> 00:09:47.649 bright as snow, the other dark as coal, creating 00:09:47.649 --> 00:09:50.830 one of the starkest contrasts in the solar system. 00:09:51.889 --> 00:09:55.009 Miranda, a moon of Uranus, looks like it was 00:09:55.009 --> 00:09:57.870 shattered and reassembled with cliffs and terrain 00:09:57.870 --> 00:10:02.330 so bizarre that it defies easy explanation. And 00:10:02.330 --> 00:10:06.570 out at Pluto, Charon, or is it pronounced Cairon, 00:10:06.809 --> 00:10:10.529 is so large relative to Pluto that the two orbit 00:10:10.529 --> 00:10:14.190 a point in space between them. The New Horizons 00:10:14.190 --> 00:10:18.570 flyby in 2015 revealed vast canyons and signs 00:10:18.570 --> 00:10:22.549 of ancient geological activity. In addition to 00:10:22.549 --> 00:10:26.129 Charon, Pluto has four irregular tiny moons, 00:10:26.549 --> 00:10:30.610 making it a complex six -body system. They don't 00:10:30.610 --> 00:10:34.070 behave like our moon or even like most of the 00:10:34.070 --> 00:10:37.200 large moons of Jupiter and Saturn. Instead of 00:10:37.200 --> 00:10:40.940 being tidally locked, some of them tumble unpredictably. 00:10:41.500 --> 00:10:44.519 Their rotations are influenced by the constantly 00:10:44.519 --> 00:10:47.940 shifting gravitational pull of both Pluto and 00:10:47.940 --> 00:10:52.659 Charon. It's a dynamically messy system. We've 00:10:52.659 --> 00:10:55.120 talked about some of the most well -known moons 00:10:55.120 --> 00:10:58.320 in this episode, but here are a couple of really 00:10:58.320 --> 00:11:02.159 weird ones you might not know about. Hyperion 00:11:02.159 --> 00:11:05.759 orbits Saturn and resembles a sponge or a piece 00:11:05.759 --> 00:11:09.039 of coral drifting through space. Its surface 00:11:09.039 --> 00:11:11.799 is covered in deep, sharp -edged craters giving 00:11:11.799 --> 00:11:14.980 it a porous appearance. But the truly strange 00:11:14.980 --> 00:11:18.360 part is its motion, and this is a trait it shares 00:11:18.360 --> 00:11:22.440 with some of Pluto's moons. Hyperion isn't tidally 00:11:22.440 --> 00:11:25.700 locked, and it tumbles around Saturn in an unpredictable 00:11:25.700 --> 00:11:29.159 way. If you were standing on Hyperion, which 00:11:29.159 --> 00:11:32.600 would be complicated, Saturn wouldn't rise and 00:11:32.600 --> 00:11:36.100 set in a regular way. It would drift unpredictably 00:11:36.100 --> 00:11:39.960 across the sky. Another excellent oddball is 00:11:39.960 --> 00:11:43.120 Phoebe, also a moon of Saturn. I'm beginning 00:11:43.120 --> 00:11:45.679 to think Saturn is probably the most fun place 00:11:45.679 --> 00:11:47.940 to be in the solar system. It has everything. 00:11:48.139 --> 00:11:52.580 Rings, weird moons, and more. Anyway, Phoebe 00:11:52.580 --> 00:11:55.879 orbits Saturn backward, much like Triton does 00:11:55.879 --> 00:11:59.200 around Neptune. So it didn't form with Saturn, 00:11:59.460 --> 00:12:02.340 and like Triton, it's possibly a relic from the 00:12:02.340 --> 00:12:05.980 Kuiper Belt. It's dark, irregular, and ancient. 00:12:06.440 --> 00:12:09.460 A fossil from the early solar system just hanging 00:12:09.460 --> 00:12:13.200 out in Saturn's orbit. Before we drift away from 00:12:13.200 --> 00:12:17.299 Saturn, I also have to mention Janus and Epimetheus. 00:12:17.899 --> 00:12:21.059 These two moons share nearly the same orbit, 00:12:21.440 --> 00:12:24.000 and every few years when they get near each other, 00:12:24.279 --> 00:12:27.769 they effectively swap places. These are called 00:12:27.769 --> 00:12:31.750 co -orbital moons. And what I mean by swapping 00:12:31.750 --> 00:12:35.669 places is this. One moon orbits closer to the 00:12:35.669 --> 00:12:38.149 planet than the other. When they approach one 00:12:38.149 --> 00:12:41.350 another, a gravitational dance takes place between 00:12:41.350 --> 00:12:44.549 the two, and one assumes the closer inner orbit, 00:12:45.029 --> 00:12:47.889 trading places with the other, now pushed to 00:12:47.889 --> 00:12:50.870 the outer track. And they do this repeatedly. 00:12:51.629 --> 00:12:55.490 I didn't forget about Mars. It has Phobos and 00:12:55.490 --> 00:12:58.990 Deimos, two little rocky potatoes that were likely 00:12:58.990 --> 00:13:02.049 captured by the Martian gravity. In other words, 00:13:02.230 --> 00:13:05.470 they didn't form alongside Mars the way our moon 00:13:05.470 --> 00:13:09.389 formed alongside Earth. Our moon is the only 00:13:09.389 --> 00:13:12.690 large moon of the inner solar system, which makes 00:13:12.690 --> 00:13:17.470 us quite an outlier. The outer planets are moon 00:13:17.470 --> 00:13:21.299 machines. Jupiter now has more than 90 known 00:13:21.299 --> 00:13:26.600 moons, Saturn more than 140, and Uranus and Neptune 00:13:26.600 --> 00:13:30.519 both have dozens. Astronomers think the difference 00:13:30.519 --> 00:13:33.019 in numbers between the outer and inner planets 00:13:33.019 --> 00:13:35.759 is similar to why the outer planets are so much 00:13:35.759 --> 00:13:38.940 larger. The inner solar system was hotter when 00:13:38.940 --> 00:13:41.919 it formed. Close to the sun, lighter materials 00:13:41.919 --> 00:13:44.919 like water, ice, and gases couldn't condense 00:13:44.919 --> 00:13:49.279 easily. that left mostly rock and metal. Out 00:13:49.279 --> 00:13:52.940 beyond the frost line, ices could form, and ice 00:13:52.940 --> 00:13:56.759 is abundant. That gave the outer planets far 00:13:56.759 --> 00:13:59.659 more raw material to build not just planets, 00:14:00.019 --> 00:14:04.039 but entire systems of moons. Also, since the 00:14:04.039 --> 00:14:06.860 outer planets are all enormous, their gravity 00:14:06.860 --> 00:14:09.960 is strong enough to capture passing objects and 00:14:09.960 --> 00:14:13.759 hold on to large numbers of moons. None of that 00:14:13.759 --> 00:14:17.059 explains why Pluto, smaller than even our moon, 00:14:17.460 --> 00:14:21.059 somehow has five moons of its own. Well, the 00:14:21.059 --> 00:14:24.440 moons of Pluto and Earth may actually share an 00:14:24.440 --> 00:14:27.740 origin story. Earth's moon is likely the result 00:14:27.740 --> 00:14:31.039 of a giant impact, which is a rare and chaotic 00:14:31.039 --> 00:14:34.820 event. Pluto's moons may have also formed from 00:14:34.820 --> 00:14:38.240 such an impact. A collision early in Pluto's 00:14:38.240 --> 00:14:40.740 history would have thrown debris into orbit, 00:14:41.059 --> 00:14:44.039 which later coalesced into Charon and the smaller 00:14:44.039 --> 00:14:48.600 moons. Mercury and Venus may have once had moons, 00:14:48.820 --> 00:14:51.919 but over billions of years, gravitational interactions 00:14:51.919 --> 00:14:55.580 with the sun could have destabilized those systems, 00:14:56.179 --> 00:14:58.620 causing moons to either crash into the planet 00:14:58.620 --> 00:15:02.620 or escape. So the outer solar system ends up 00:15:02.620 --> 00:15:05.440 looking like kind of a miniature solar system 00:15:05.440 --> 00:15:08.779 factory. with planets surrounded by their own 00:15:08.779 --> 00:15:11.519 collections of worlds, while the inner solar 00:15:11.519 --> 00:15:15.259 system is comparatively sparse. I remember reading 00:15:15.259 --> 00:15:18.679 in Carl Sagan's Cosmos years ago that there could 00:15:18.679 --> 00:15:22.259 be multiple places to sustain life in our solar 00:15:22.259 --> 00:15:26.720 system, not just Earth and Mars. Of course, Sagan 00:15:26.720 --> 00:15:29.240 was including many of the moons in the outer 00:15:29.240 --> 00:15:31.799 solar system that had been recently discovered. 00:15:32.139 --> 00:15:34.860 The possibility that some of these moons might 00:15:34.860 --> 00:15:37.740 be habitable, not on the surface or in sunlight, 00:15:38.279 --> 00:15:41.879 but beneath the ice, is a fascinating one. On 00:15:41.879 --> 00:15:45.100 Earth, we've discovered ecosystems thriving in 00:15:45.100 --> 00:15:48.139 complete darkness, deep in the ocean, powered 00:15:48.139 --> 00:15:51.379 not by sunlight, but by chemical energy from 00:15:51.379 --> 00:15:55.740 hydrothermal vents. If similar environments exist 00:15:55.740 --> 00:15:59.360 on Europa or Enceladus, liquid water, energy, 00:15:59.580 --> 00:16:03.100 chemistry, then the basic ingredients for life 00:16:03.100 --> 00:16:06.820 may be present. And here's the part that changes 00:16:06.820 --> 00:16:09.700 how we think about the universe. When we search 00:16:09.700 --> 00:16:12.600 for habitable worlds, we tend to look for planets 00:16:12.600 --> 00:16:15.840 like Earth, rocky, sitting at just the right 00:16:15.840 --> 00:16:19.480 distance from their star. But our own solar system 00:16:19.480 --> 00:16:23.600 is telling us something surprising. Moons warmed 00:16:23.600 --> 00:16:27.120 by gravity instead of sunlight, oceans hidden 00:16:27.120 --> 00:16:30.940 beneath ice, small distant worlds orbiting giant 00:16:30.940 --> 00:16:34.120 planets, their oceans circulating quietly in 00:16:34.120 --> 00:16:37.759 the dark. These moons are intriguing areas for 00:16:37.759 --> 00:16:40.960 future exploration. Remember, many of these moons 00:16:40.960 --> 00:16:44.279 have only been seen once during the Voyager flybys 00:16:44.279 --> 00:16:49.000 of the 1980s. There's a lot more science to learn. 00:16:49.399 --> 00:16:52.500 Future missions such as Europa Clipper, which 00:16:52.500 --> 00:16:56.019 was launched in 2024, is designed to study the 00:16:56.019 --> 00:16:59.960 subsurface ocean of Europa. And Dragonfly is 00:16:59.960 --> 00:17:03.460 expected to launch in 2028 on a mission to Titan. 00:17:04.039 --> 00:17:07.220 It's a robotic helicopter designed to fly on 00:17:07.220 --> 00:17:10.480 Titan where it will study habitability and chemistry. 00:17:10.940 --> 00:17:14.720 And, of course, NASA is making plans to return 00:17:14.720 --> 00:17:18.180 to our moon with the Artemis program, with a 00:17:18.180 --> 00:17:22.920 landing scheduled for 2027. We have one more 00:17:22.920 --> 00:17:26.259 episode about our solar system to close out March. 00:17:26.720 --> 00:17:29.720 Next week, we journey into the Kuiper Belt and 00:17:29.720 --> 00:17:45.980 beyond. After a quick break, we'll be back to 00:17:45.980 --> 00:18:01.859 cover this week's night sky. Stay with us. Welcome 00:18:01.859 --> 00:18:05.559 back. Let's step outside now and take a look 00:18:05.559 --> 00:18:08.819 at this week's sky. We're coming off of a new 00:18:08.819 --> 00:18:11.240 moon, which means this is one of the best weeks 00:18:11.240 --> 00:18:14.349 of the month for deep sky observing. As the week 00:18:14.349 --> 00:18:17.630 begins, a delicate, waxing crescent moon hangs 00:18:17.630 --> 00:18:21.329 low in the western sky just after sunset, growing 00:18:21.329 --> 00:18:24.650 a little fuller each night. By mid -week, the 00:18:24.650 --> 00:18:27.750 moon reaches first quarter, appearing half -lit, 00:18:28.150 --> 00:18:31.630 and on the evening of March 26th, it forms a 00:18:31.630 --> 00:18:34.269 nice pairing with Jupiter in the constellation 00:18:34.269 --> 00:18:38.009 Gemini. This is a great time to notice something 00:18:38.009 --> 00:18:42.079 subtle, earth -shine. That faint glow illuminating 00:18:42.079 --> 00:18:45.119 the dark portion of the crescent moon is actually 00:18:45.119 --> 00:18:49.140 sunlight reflected off of Earth. Now let's talk 00:18:49.140 --> 00:18:53.480 planets. The standout this week is Venus, blazing 00:18:53.480 --> 00:18:57.440 in the western sky just after sunset. It's reemerged 00:18:57.440 --> 00:19:00.460 as the evening star, shining brighter than anything 00:19:00.460 --> 00:19:03.859 else in the night sky except the moon. You'll 00:19:03.859 --> 00:19:06.660 find it low in the west, lingering for more than 00:19:06.660 --> 00:19:09.869 an hour after sunset. If you catch it with a 00:19:09.869 --> 00:19:12.289 small telescope you may even notice it showing 00:19:12.289 --> 00:19:15.609 a crescent phase, much like a tiny version of 00:19:15.609 --> 00:19:18.529 the moon. I've been seeing Venus on my evening 00:19:18.529 --> 00:19:21.609 walks lately and its brightness is so startling 00:19:21.609 --> 00:19:24.269 I have a hard time looking away. It's really 00:19:24.269 --> 00:19:27.930 one of my favorite sights in the night sky. Higher 00:19:27.930 --> 00:19:31.730 up dominating the evening is Jupiter. It's bright, 00:19:32.029 --> 00:19:35.660 steady, and unmistakable. Look at it in a telescope 00:19:35.660 --> 00:19:37.859 and you'll see it flanked by the moons we've 00:19:37.859 --> 00:19:42.180 been discussing, Io, Europa, Ganymede, and Callisto. 00:19:42.880 --> 00:19:45.140 You'll see them change position from night to 00:19:45.140 --> 00:19:48.079 night, and sometimes they render shadows on the 00:19:48.079 --> 00:19:51.420 Jovian surface. If you're up early, there's a 00:19:51.420 --> 00:19:54.339 more subtle challenge waiting for you. Late in 00:19:54.339 --> 00:19:57.240 the week, Mercury begins to peek into the pre 00:19:57.240 --> 00:20:01.099 -dawn sky, very low on the horizon before sunrise. 00:20:01.440 --> 00:20:04.299 It's not an easy target, but if you have a clear 00:20:04.299 --> 00:20:07.380 eastern horizon and a bit of patience, you might 00:20:07.380 --> 00:20:10.400 catch it briefly before the sun washes it away. 00:20:11.079 --> 00:20:13.960 Now this is the time of year astronomers quietly 00:20:13.960 --> 00:20:17.259 get excited about. Spring brings what's known 00:20:17.259 --> 00:20:21.440 as galaxy season. As the Milky Way dips below 00:20:21.440 --> 00:20:23.880 the horizon in the evening, we're able to look 00:20:23.880 --> 00:20:27.539 past the plane of our galaxy into deep space. 00:20:27.819 --> 00:20:31.450 And that means galaxies and lots of them. In 00:20:31.450 --> 00:20:34.869 the constellation Leo, you can find the Leo Triplet, 00:20:35.329 --> 00:20:38.190 three galaxies interacting with each other across 00:20:38.190 --> 00:20:42.269 millions of light years. In Ursa Major, near 00:20:42.269 --> 00:20:47.529 the Big Dipper, look for M81 and M82, a pair 00:20:47.529 --> 00:20:51.170 of galaxies, one graceful and spiral, the other 00:20:51.170 --> 00:20:55.480 ragged and explosive. And if you sweep your telescope 00:20:55.480 --> 00:20:58.880 toward Virgo and Coma Berenices, you'll begin 00:20:58.880 --> 00:21:02.579 to encounter entire fields of galaxies. Faint 00:21:02.579 --> 00:21:06.319 smudges of light, each one a vast island universe. 00:21:07.380 --> 00:21:09.779 For something a little more low -key, try tracking 00:21:09.779 --> 00:21:13.339 down the Coma star cluster in Coma Berenices, 00:21:13.740 --> 00:21:16.559 a loose, delicate scattering of stars that's 00:21:16.559 --> 00:21:20.430 best seen with binoculars under dark skies. Or, 00:21:20.450 --> 00:21:23.369 if you're feeling ambitious, hunt down the Ghost 00:21:23.369 --> 00:21:27.470 of Jupiter Nebula in Hydra, a faint planetary 00:21:27.470 --> 00:21:31.549 nebula that resembles a pale ghostly disk. And 00:21:31.549 --> 00:21:34.009 finally, take a moment this week to simply look 00:21:34.009 --> 00:21:37.710 up without a plan. Find Orion setting in the 00:21:37.710 --> 00:21:41.529 west, slowly leaving our evening skies. Look 00:21:41.529 --> 00:21:44.750 overhead to Gemini, with Jupiter shining among 00:21:44.750 --> 00:21:48.829 the twin stars Castor and Pollux. And rising 00:21:48.829 --> 00:21:51.329 in the east, you'll begin to see the constellations 00:21:51.329 --> 00:21:55.789 of Spring, Leo, Virgo, and Boötes taking their 00:21:55.789 --> 00:22:04.849 place. We're slowly creeping towards the end 00:22:04.849 --> 00:22:08.289 of our book club selection, Night Watch, and 00:22:08.289 --> 00:22:11.509 there are just a few chapters left. Chapters 00:22:11.509 --> 00:22:14.650 8 and 9 bring us back to something familiar. 00:22:14.880 --> 00:22:18.720 our own moon and its relationship with the Sun. 00:22:19.359 --> 00:22:22.319 These are two very short chapters, and I'm not 00:22:22.319 --> 00:22:25.039 sure if they offer much to experienced observers, 00:22:25.599 --> 00:22:27.980 but since our topic this week was all about the 00:22:27.980 --> 00:22:30.700 moons of our solar system, it seemed appropriate 00:22:30.700 --> 00:22:33.950 to talk about them in this episode. Chapter 8 00:22:33.950 --> 00:22:37.289 is all about observing the Moon and Sun. These 00:22:37.289 --> 00:22:40.150 two familiar objects are easy to take for granted, 00:22:40.329 --> 00:22:43.089 but endlessly rewarding if you spend a little 00:22:43.089 --> 00:22:47.049 time with them at the eyepiece. The Moon, especially, 00:22:47.190 --> 00:22:49.809 is one of the best targets for backyard astronomy. 00:22:50.369 --> 00:22:53.230 Even a small telescope will reveal an incredible 00:22:53.230 --> 00:22:57.130 landscape of craters, mountain ranges, and vast 00:22:57.130 --> 00:23:00.960 lava plains known as maria. One of the best times 00:23:00.960 --> 00:23:03.680 to observe is along the line between light and 00:23:03.680 --> 00:23:07.119 dark, called the Terminator, where shadows stretch 00:23:07.119 --> 00:23:09.680 across the surface and give those features depth 00:23:09.680 --> 00:23:12.920 and texture. This chapter also includes some 00:23:12.920 --> 00:23:17.500 nice maps of the moon's surface. Chapter 8 also 00:23:17.500 --> 00:23:20.200 encourages something we don't talk about often, 00:23:20.660 --> 00:23:24.460 observing the sun. Now, this comes with an important 00:23:24.460 --> 00:23:28.509 caveat. You must use proper solar filters. But 00:23:28.509 --> 00:23:31.630 when you do, even a modest telescope can reveal 00:23:31.630 --> 00:23:35.349 sunspots, those dark shifting regions tied to 00:23:35.349 --> 00:23:38.849 the sun's magnetic activity. With specialized 00:23:38.849 --> 00:23:41.750 equipment, you can even see solar prominences, 00:23:42.450 --> 00:23:45.710 massive arcs of plasma rising from the sun's 00:23:45.710 --> 00:23:50.089 surface. Then in chapter 9, we move into eclipses. 00:23:50.529 --> 00:23:52.869 These are the moments when the sun, earth, and 00:23:52.869 --> 00:23:56.589 moon align just right to create something extraordinary. 00:23:57.069 --> 00:24:00.049 A solar eclipse happens when the Moon passes 00:24:00.049 --> 00:24:02.890 in front of the Sun, casting its shadow on Earth. 00:24:03.710 --> 00:24:06.549 A lunar eclipse occurs when Earth moves between 00:24:06.549 --> 00:24:09.609 the Sun and the Moon, and our shadow darkens 00:24:09.609 --> 00:24:13.930 the lunar surface. Total solar eclipses, in particular, 00:24:14.150 --> 00:24:17.109 have captivated people throughout history. In 00:24:17.109 --> 00:24:20.789 fact, the book describes so -called eclipse cults. 00:24:20.809 --> 00:24:22.990 These are people who travel across the globe 00:24:22.990 --> 00:24:26.150 to stand in the narrow path of totality where 00:24:26.150 --> 00:24:29.710 day briefly turns to night. Lunar eclipses are 00:24:29.710 --> 00:24:33.089 more common and a bit more forgiving. You don't 00:24:33.089 --> 00:24:35.829 need special equipment to enjoy them and they 00:24:35.829 --> 00:24:39.609 often turn the moon a deep coppery red as Earth's 00:24:39.609 --> 00:24:42.349 atmosphere filters sunlight into the shadow. 00:24:42.829 --> 00:24:45.730 You can refer to the tables in this chapter to 00:24:45.730 --> 00:24:48.210 discover when the next eclipses are happening. 00:24:49.109 --> 00:24:51.170 We'll wrap up our discussion on the remaining 00:24:51.170 --> 00:24:54.769 chapters of Night Watch in two weeks. We're almost 00:24:54.769 --> 00:24:57.789 done. If you're a newer observer and you've made 00:24:57.789 --> 00:24:59.710 it this far in the book, then your knowledge 00:24:59.710 --> 00:25:02.970 of the night sky and how to view it has increased 00:25:02.970 --> 00:25:11.130 exponentially since we began this journey. That's 00:25:11.130 --> 00:25:13.390 going to do it for this week. If you found this 00:25:13.390 --> 00:25:15.690 episode interesting, please share it with a friend 00:25:15.690 --> 00:25:18.670 who might enjoy it. The easiest way to do that 00:25:18.670 --> 00:25:22.230 is by sending folks to our website, StarTrails 00:25:22.230 --> 00:25:25.809 .Show. And if you want to support the show, use 00:25:25.809 --> 00:25:28.349 the link on the site to buy me a coffee. That 00:25:28.349 --> 00:25:31.549 really helps. Be sure to follow Star Trails on 00:25:31.549 --> 00:25:35.009 Blue Sky and YouTube. Links are in the show notes. 00:25:35.529 --> 00:25:38.250 Until we meet again beneath the stars, clear 00:25:38.250 --> 00:25:39.150 skies everyone.