WEBVTT 00:00:07.100 --> 00:00:10.019 Howdy Star Gazers and welcome to this episode 00:00:10.019 --> 00:00:13.580 of Star Trails. My name is Drew and I'll be your 00:00:13.580 --> 00:00:16.239 guide to the night sky for the week of February 00:00:16.239 --> 00:00:20.719 the 22nd to the 28th. This week we wrap up our 00:00:20.719 --> 00:00:24.160 month -long series on stars by exploring how 00:00:24.160 --> 00:00:28.480 they end their lives. For some it's a quiet process 00:00:28.480 --> 00:00:32.259 like embers cooling after a campfire. Others 00:00:32.259 --> 00:00:36.340 explode and some turn into black holes. destined 00:00:36.340 --> 00:00:39.200 to live the remainder of their lives like cosmic 00:00:39.200 --> 00:00:42.880 vampires facing eternity. Later in the show, 00:00:43.100 --> 00:00:45.259 we'll take a look at what you can see in the 00:00:45.259 --> 00:00:48.340 night sky this week. Whether you're tuning in 00:00:48.340 --> 00:00:51.060 from the backyard or the balcony, I'm glad you're 00:00:51.060 --> 00:00:53.520 here. So grab a comfortable spot under the night 00:00:53.520 --> 00:00:58.600 sky and let's get started. When I was a kid, 00:00:59.240 --> 00:01:01.920 I distinctly remember the night when I learned 00:01:01.920 --> 00:01:06.719 our son was at some point going to die. And to 00:01:06.719 --> 00:01:10.060 be honest, it wasn't a great feeling. Sitting 00:01:10.060 --> 00:01:12.780 on the floor in the den of my grandmother's house 00:01:12.780 --> 00:01:16.439 as twilight fell, I opened up my favorite astronomy 00:01:16.439 --> 00:01:20.329 tome, The Universe by National Geographic. and 00:01:20.329 --> 00:01:23.290 read a surprisingly long and detailed account 00:01:23.290 --> 00:01:27.530 of how in some five billion years our Sun would 00:01:27.530 --> 00:01:30.890 grow hotter, all life on Earth would be vaporized, 00:01:31.310 --> 00:01:35.250 and the Sun would expand into a red giant, enveloping 00:01:35.250 --> 00:01:39.629 Venus, Mercury, and the Earth. This was terrifying. 00:01:39.930 --> 00:01:42.489 It was the first realization that the Sun and 00:01:42.489 --> 00:01:45.780 Earth aren't permanent. Sure, I knew I wouldn't 00:01:45.780 --> 00:01:48.400 be around in five billion years to see the Sun 00:01:48.400 --> 00:01:51.099 collapse, but even as a seven or eight year old 00:01:51.099 --> 00:01:54.060 child, knowing that the end was approaching like 00:01:54.060 --> 00:01:57.719 a timer counting down, created a sense of existential 00:01:57.719 --> 00:02:01.719 dread and anxiety. So tonight, we're wrapping 00:02:01.719 --> 00:02:05.540 up our month -long theme about stars. We've talked 00:02:05.540 --> 00:02:08.280 about how they form, what they are, and what 00:02:08.280 --> 00:02:11.969 they do during their epic lifespans. We've done 00:02:11.969 --> 00:02:15.430 some statistical analysis related to star formation 00:02:15.430 --> 00:02:18.969 and what they leave behind. But now it's time 00:02:18.969 --> 00:02:22.389 to talk about how stars die, including the one 00:02:22.389 --> 00:02:26.969 that keeps us alive. The first thing to remember 00:02:26.969 --> 00:02:31.490 is most stars don't explode. Our imagination 00:02:31.490 --> 00:02:35.389 is filled with supernova. Stellar death is often 00:02:35.389 --> 00:02:38.699 portrayed as violent and spectacular. But the 00:02:38.699 --> 00:02:42.280 vast majority of stars don't end that way. As 00:02:42.280 --> 00:02:44.800 we've mentioned a few times this month, most 00:02:44.800 --> 00:02:48.039 stars in the universe are small red dwarfs that 00:02:48.039 --> 00:02:51.180 burn their hydrogen so slowly they will outlive 00:02:51.180 --> 00:02:54.520 the current age of the cosmos by orders of magnitude. 00:02:55.120 --> 00:02:57.699 They won't explode, they'll simply fade away. 00:02:58.580 --> 00:03:01.979 Larger stars, like our sun, live for about 10 00:03:01.979 --> 00:03:05.139 billion years in what astronomers call the main 00:03:05.139 --> 00:03:09.419 sequence phase. During this time, hydrogen fuses 00:03:09.419 --> 00:03:13.039 into helium in the core. Fusion releases energy. 00:03:13.520 --> 00:03:16.800 That energy produces outward pressure. Gravity 00:03:16.800 --> 00:03:20.080 pulls inward and the two forces balance one another 00:03:20.080 --> 00:03:24.620 in what is called hydrostatic equilibrium. For 00:03:24.620 --> 00:03:27.759 billions of years, the Sun has existed in that 00:03:27.759 --> 00:03:31.960 quiet stalemate. But hydrogen in the core isn't 00:03:31.960 --> 00:03:34.520 infinite. And this is where the story becomes 00:03:34.520 --> 00:03:38.159 more subtle than most of us expect. Counter to 00:03:38.159 --> 00:03:41.259 what we might think as a star dies, some, like 00:03:41.259 --> 00:03:45.659 our sun, actually grow in size. When hydrogen 00:03:45.659 --> 00:03:48.520 in the sun's core is mostly depleted, fusion 00:03:48.520 --> 00:03:51.840 in the very center begins to slow. The outward 00:03:51.840 --> 00:03:54.780 pressure weakens. Gravity, which never takes 00:03:54.780 --> 00:03:58.620 a day off, begins to win. The core starts to 00:03:58.620 --> 00:04:02.150 contract. And here's the key piece. When gas 00:04:02.150 --> 00:04:06.229 is compressed, it heats up. Gravitational potential 00:04:06.229 --> 00:04:09.310 energy is converted into thermal energy as the 00:04:09.310 --> 00:04:13.270 core shrinks. Think about how a diesel engine 00:04:13.270 --> 00:04:17.110 works. Unlike a normal gas engine which uses 00:04:17.110 --> 00:04:20.490 spark plugs to touch off the combustion, a diesel 00:04:20.490 --> 00:04:23.209 engine compresses the air to ignite the fuel. 00:04:24.050 --> 00:04:26.870 Now imagine that process happening with half 00:04:26.870 --> 00:04:30.389 the mass of a star. It's not just a small contained 00:04:30.389 --> 00:04:34.569 explosion, it's nuclear fusion. As the core contracts, 00:04:34.810 --> 00:04:38.009 it becomes hotter and denser. Fusion in the center 00:04:38.009 --> 00:04:40.769 has largely ceased, but the rising temperature 00:04:40.769 --> 00:04:44.310 ignites hydrogen in a shell surrounding the inert 00:04:44.310 --> 00:04:48.509 helium core. Instead of fusion happening at the 00:04:48.509 --> 00:04:51.689 center, it now happens in a thin, intense layer 00:04:51.689 --> 00:04:55.660 around it. And that shell fusion is more energetic 00:04:55.660 --> 00:04:59.459 than the Sun's original core fusion was. The 00:04:59.459 --> 00:05:02.139 increased energy output pushes outward on the 00:05:02.139 --> 00:05:05.699 star's outer layers. Those layers respond by 00:05:05.699 --> 00:05:09.740 expanding dramatically. Our Sun will swell to 00:05:09.740 --> 00:05:12.360 perhaps a hundred times its current diameter, 00:05:12.959 --> 00:05:17.160 engulfing the inner planets. Paradoxically, gravity 00:05:17.160 --> 00:05:20.620 causes the expansion. Gravity compresses the 00:05:20.620 --> 00:05:23.959 core. Compression increases temperature. Higher 00:05:23.959 --> 00:05:28.000 temperature ignites shell fusion, and shell fusion 00:05:28.000 --> 00:05:31.620 increases energy output. Thus, the outer layers 00:05:31.620 --> 00:05:36.560 expand. As the Sun expands, its surface temperature 00:05:36.560 --> 00:05:40.160 drops. A larger surface area radiates energy 00:05:40.160 --> 00:05:43.000 more efficiently, so the outer layers cool to 00:05:43.000 --> 00:05:47.139 around 3 ,000 to 4 ,000 Kelvin. The Sun will 00:05:47.139 --> 00:05:50.490 appear redder and dimmer per unit area. even 00:05:50.490 --> 00:05:54.430 though its total luminosity increases. And this 00:05:54.430 --> 00:05:57.870 is the red giant phase. You can look up at the 00:05:57.870 --> 00:06:01.410 night sky right now and see some famous red giants. 00:06:02.170 --> 00:06:06.050 Betelgeuse in Orion is the classic example. It's 00:06:06.050 --> 00:06:09.370 already in its death throes, hundreds of times 00:06:09.370 --> 00:06:12.670 larger than the sun. If placed at the center 00:06:12.670 --> 00:06:15.810 of our solar system, it would extend past Mars. 00:06:16.110 --> 00:06:18.730 possibly even toward Jupiter, depending on how 00:06:18.730 --> 00:06:22.670 you measure its outer atmosphere. This star will 00:06:22.670 --> 00:06:26.050 not become a white dwarf. It will explode as 00:06:26.050 --> 00:06:28.610 a supernova within the next hundred thousand 00:06:28.610 --> 00:06:32.009 years or so, astronomically soon, though not 00:06:32.009 --> 00:06:36.250 calendar soon. Aldebaran is closer to the Sun's 00:06:36.250 --> 00:06:39.509 eventual fate. It's a red giant, not massive 00:06:39.509 --> 00:06:42.629 enough to explode, but expanded and cooling. 00:06:43.149 --> 00:06:46.110 This is a preview of what our Sun will look like 00:06:46.110 --> 00:06:50.069 in about 5 billion years. It's steady. It's not 00:06:50.069 --> 00:06:54.730 violent. It's just old. Eventually in our Sun 00:06:54.730 --> 00:06:57.949 the contracting helium core will become hot enough, 00:06:58.170 --> 00:07:02.490 about 100 million Kelvin, to ignite helium fusion 00:07:02.490 --> 00:07:06.050 into carbon and oxygen. This ignition happens 00:07:06.050 --> 00:07:09.740 in what astronomers call the helium flash. a 00:07:09.740 --> 00:07:12.560 rapid internal event that barely disturbs the 00:07:12.560 --> 00:07:16.519 outer star. After a brief period of renewed stability, 00:07:17.019 --> 00:07:19.720 fusion once again shifts outward into shells, 00:07:20.160 --> 00:07:23.120 and the outer layers grow increasingly unstable. 00:07:24.579 --> 00:07:27.920 Finally, the Sun will shed those layers entirely, 00:07:28.139 --> 00:07:31.839 creating a glowing planetary nebula, a delicate 00:07:31.839 --> 00:07:35.300 shell of gas expanding into space, and at the 00:07:35.300 --> 00:07:38.959 center remains the exposed core. And this is 00:07:38.959 --> 00:07:43.540 where the physics turns truly strange. What remains 00:07:43.540 --> 00:07:46.680 after the Sun sheds its outer layers is a white 00:07:46.680 --> 00:07:50.339 dwarf, roughly Earth -sized, containing about 00:07:50.339 --> 00:07:54.399 half the Sun's current mass. It no longer generates 00:07:54.399 --> 00:07:57.839 energy through fusion. It shines because it's 00:07:57.839 --> 00:08:01.879 hot, not because it's burning. The density inside 00:08:01.879 --> 00:08:05.439 a white dwarf is extraordinary. A teaspoon of 00:08:05.439 --> 00:08:08.860 its material would weigh several tons. At this 00:08:08.860 --> 00:08:12.339 stage, the matter is packed so tightly that classical 00:08:12.339 --> 00:08:15.500 physics alone cannot explain what holds it up. 00:08:16.040 --> 00:08:19.839 The answer lies in quantum mechanics. Electrons 00:08:19.839 --> 00:08:23.379 obey a rule known as the Pauli exclusion principle, 00:08:23.740 --> 00:08:26.720 which states no two electrons can occupy the 00:08:26.720 --> 00:08:30.529 same quantum state simultaneously. When gravity 00:08:30.529 --> 00:08:32.929 attempts to compress the white dwarf further, 00:08:33.450 --> 00:08:36.049 electrons are forced into higher energy states 00:08:36.049 --> 00:08:38.789 simply because there are no lower ones available. 00:08:39.350 --> 00:08:42.870 This creates a pressure called electron degeneracy 00:08:42.870 --> 00:08:45.669 pressure that doesn't depend on temperature. 00:08:46.830 --> 00:08:49.909 The white dwarf isn't supported by heat. It's 00:08:49.909 --> 00:08:52.409 supported by the structure of quantum reality 00:08:52.409 --> 00:08:56.320 itself. Afterwards, it will simply cool over 00:08:56.320 --> 00:08:59.840 trillions of years, fading gradually into darkness. 00:09:01.259 --> 00:09:03.960 There are planetary nebulae you can see right 00:09:03.960 --> 00:09:06.720 now that represent what the sun's far future 00:09:06.720 --> 00:09:11.539 could look like. The ring nebula, M57, is the 00:09:11.539 --> 00:09:14.779 exposed outer layers of a sun -like star that 00:09:14.779 --> 00:09:18.340 died thousands of years ago. At its center is 00:09:18.340 --> 00:09:22.840 a white dwarf, the compressed remnant core. The 00:09:22.840 --> 00:09:25.960 Dumbbell Nebula is larger and easier to observe 00:09:25.960 --> 00:09:29.000 in small telescopes than the Ring Nebula. It's 00:09:29.000 --> 00:09:31.799 another Sun -like star shedding its atmosphere. 00:09:33.019 --> 00:09:35.480 And while you aren't likely to be able to spot 00:09:35.480 --> 00:09:38.419 it, we know of another fairly close white dwarf. 00:09:39.220 --> 00:09:42.000 Sirius, the brightest star in our sky, has a 00:09:42.000 --> 00:09:46.200 tiny companion, Sirius B. A white dwarf about 00:09:46.200 --> 00:09:49.379 the size of Earth, but nearly as massive as the 00:09:49.379 --> 00:09:53.179 Sun. It's difficult to see visually because it's 00:09:53.179 --> 00:09:56.399 overwhelmed by the glare of Sirius A, but it's 00:09:56.399 --> 00:09:59.200 been imaged and studied exclusively by Hubble 00:09:59.200 --> 00:10:03.639 and X -ray telescopes. That tiny dot represents 00:10:03.639 --> 00:10:08.100 quantum mechanics holding up half a star. If 00:10:08.100 --> 00:10:11.039 a star begins its life more massive than the 00:10:11.039 --> 00:10:15.179 Sun, the ending changes dramatically. Massive 00:10:15.179 --> 00:10:18.309 stars burn through their fuel quickly. fusing 00:10:18.309 --> 00:10:20.809 heavier and heavier elements in their cores. 00:10:21.649 --> 00:10:24.789 Hydrogen becomes helium, helium becomes carbon, 00:10:25.129 --> 00:10:28.850 carbon becomes oxygen, and so on, building an 00:10:28.850 --> 00:10:31.970 onion -like structure of nested fusion layers. 00:10:32.710 --> 00:10:35.750 This process continues until iron accumulates 00:10:35.750 --> 00:10:40.210 in the core. But iron is a dead end because fusing 00:10:40.210 --> 00:10:43.409 iron consumes energy instead of releasing it. 00:10:43.950 --> 00:10:47.309 When the core becomes iron -rich, fusion can 00:10:47.309 --> 00:10:50.509 no longer support it, and gravity wins completely. 00:10:51.149 --> 00:10:54.929 The core collapses in less than a second. Electrons 00:10:54.929 --> 00:10:58.330 are crushed into protons forming neutrons and 00:10:58.330 --> 00:11:01.889 releasing an enormous burst of neutrinos. The 00:11:01.889 --> 00:11:04.710 collapsing core rebounds, driving a supernova 00:11:04.710 --> 00:11:08.269 explosion that briefly outshines entire galaxies. 00:11:09.029 --> 00:11:13.019 What remains depends on the core's mass. If the 00:11:13.019 --> 00:11:15.899 remnant core is between roughly one and a half 00:11:15.899 --> 00:11:19.240 and about two or three solar masses, collapse 00:11:19.240 --> 00:11:23.159 halts at an even more extreme stage. Electrons 00:11:23.159 --> 00:11:27.720 and protons merge into neutrons. The result is 00:11:27.720 --> 00:11:30.860 a neutron star, typically about 20 kilometers 00:11:30.860 --> 00:11:34.000 across, yet containing more mass than the Sun. 00:11:34.740 --> 00:11:38.340 Its density is so extreme that a sugar cube -sized 00:11:38.340 --> 00:11:42.080 piece would outweigh a mountain. Once again, 00:11:42.600 --> 00:11:45.919 quantum mechanics intervenes. Neutron degeneracy 00:11:45.919 --> 00:11:48.700 pressure, the same exclusion principle applied 00:11:48.700 --> 00:11:52.879 to neutrons, presents further collapse. Inside, 00:11:53.159 --> 00:11:56.860 matter may exist as a superfluid, possibly containing 00:11:56.860 --> 00:12:00.799 exotic particles or even free quarks. We're still 00:12:00.799 --> 00:12:03.379 probing this frontier with gravitational wave 00:12:03.379 --> 00:12:06.240 observations and nuclear physics experiments. 00:12:07.340 --> 00:12:11.820 Some neutron stars spin rapidly and emit beams 00:12:11.820 --> 00:12:16.080 of radiation, appearing to us as pulsars. The 00:12:16.080 --> 00:12:19.779 Crab Nebula, M1, is the remnant of a supernova 00:12:19.779 --> 00:12:25.419 observed in 1054 AD. At its center lies a neutron 00:12:25.419 --> 00:12:29.480 star, the Crab Pulsar, spinning about 30 times 00:12:29.480 --> 00:12:33.639 per second. Other neutron stars possess magnetic 00:12:33.639 --> 00:12:37.649 fields so intense they defy comprehension. These 00:12:37.649 --> 00:12:41.769 are magnetars, neutron stars with extraordinarily 00:12:41.769 --> 00:12:45.590 amplified magnetic fields, trillions of times 00:12:45.590 --> 00:12:48.570 stronger than Earth's. The leading explanation 00:12:48.570 --> 00:12:52.149 is that rapid rotation during collapse amplifies 00:12:52.149 --> 00:12:55.870 magnetic fields like a dynamo. The result is 00:12:55.870 --> 00:12:58.669 an object capable of releasing immense bursts 00:12:58.669 --> 00:13:03.269 of X -rays and gamma rays. They are rare and 00:13:03.269 --> 00:13:06.529 violent, but still the product of stellar collapse. 00:13:06.720 --> 00:13:11.340 And that finally brings us to black holes. If 00:13:11.340 --> 00:13:14.759 the collapsing core exceeds the mass that neutron 00:13:14.759 --> 00:13:18.279 degeneracy pressure can support, no known force 00:13:18.279 --> 00:13:22.519 can halt the implosion. Gravity overwhelms every 00:13:22.519 --> 00:13:26.179 resistance. The core continues collapsing until 00:13:26.179 --> 00:13:30.039 an event horizon forms. That's a boundary beyond 00:13:30.039 --> 00:13:33.919 which even light cannot escape. A black hole 00:13:33.919 --> 00:13:37.220 isn't a cosmic vacuum cleaner. It's a region 00:13:37.220 --> 00:13:40.740 of spacetime so curved that all future paths 00:13:40.740 --> 00:13:45.039 point inward. At its center, classical general 00:13:45.039 --> 00:13:48.740 relativity predicts a singularity, a point of 00:13:48.740 --> 00:13:52.799 infinite density and zero volume. But infinities 00:13:52.799 --> 00:13:55.440 in physics are usually a sign that the theory 00:13:55.440 --> 00:13:59.070 has been pushed beyond its valid domain. Most 00:13:59.070 --> 00:14:02.169 physicists suspect that a future theory of quantum 00:14:02.169 --> 00:14:05.450 gravity will replace the singularity with something 00:14:05.450 --> 00:14:09.649 finite, though we don't yet know what. We tend 00:14:09.649 --> 00:14:12.529 to group black holes into categories based on 00:14:12.529 --> 00:14:16.690 mass. Stellar mass black holes form from collapsing 00:14:16.690 --> 00:14:19.929 massive stars. These typically range from about 00:14:19.929 --> 00:14:23.870 3 to perhaps 50 times the mass of the Sun. But 00:14:23.870 --> 00:14:27.029 these objects are only tens of kilometers across, 00:14:27.429 --> 00:14:31.409 and that's astonishingly compact. Then there 00:14:31.409 --> 00:14:34.549 are intermediate -mass black holes, which likely 00:14:34.549 --> 00:14:37.429 range from hundreds to hundreds of thousands 00:14:37.429 --> 00:14:41.009 of solar masses. Evidence for these is still 00:14:41.009 --> 00:14:44.149 emerging, but gravitational wave detections and 00:14:44.149 --> 00:14:47.230 observations of dense star clusters do suggest 00:14:47.230 --> 00:14:51.370 they exist. And finally, there are supermassive 00:14:51.370 --> 00:14:54.700 black holes. Every large galaxy we've studied 00:14:54.700 --> 00:14:58.100 appears to host one at its center. The one in 00:14:58.100 --> 00:15:02.019 our galaxy, Sagittarius A, has a mass of about 00:15:02.019 --> 00:15:06.519 4 million suns. In the far future of the universe, 00:15:06.840 --> 00:15:09.759 after stars have burned out, after white dwarfs 00:15:09.759 --> 00:15:13.419 have cooled, and after neutron stars have decayed 00:15:13.419 --> 00:15:17.000 or collapsed, black holes may be the last major 00:15:17.000 --> 00:15:20.799 structures left. This hypothetical scenario is 00:15:20.799 --> 00:15:24.200 sometimes called the black hole era of the universe. 00:15:24.820 --> 00:15:27.279 And it's so far in the future that it makes the 00:15:27.279 --> 00:15:30.720 sun's 5 billion remaining years look like a brief 00:15:30.720 --> 00:15:35.100 candle flicker. At some point, even black holes 00:15:35.100 --> 00:15:38.740 sputter out. In the weird quantum fields of a 00:15:38.740 --> 00:15:41.659 black hole, some particles manage to escape. 00:15:42.299 --> 00:15:45.179 You've maybe heard this term before. Hawking 00:15:45.179 --> 00:15:48.669 radiation. because it was in fact theorized by 00:15:48.669 --> 00:15:52.549 physicist Stephen Hawking. Over time, and I do 00:15:52.549 --> 00:15:55.730 mean a very long time, the black hole will slowly 00:15:55.730 --> 00:15:59.629 lose mass. We're talking time scales that are 00:15:59.629 --> 00:16:03.169 slow even by astronomical standards. We need 00:16:03.169 --> 00:16:05.990 to shift our perspective by powers of 10 for 00:16:05.990 --> 00:16:10.230 it to even make sense. For example, the evaporation 00:16:10.230 --> 00:16:13.350 of a stellar mass black hole could take years 00:16:13.350 --> 00:16:17.649 on the order of 10 to the 67th power. That's 00:16:17.649 --> 00:16:22.909 a 1 with 67 zeros behind it. A supermassive black 00:16:22.909 --> 00:16:26.809 hole may take 10 to the 100 years or more to 00:16:26.809 --> 00:16:30.210 die. By comparison, the current age of the universe 00:16:30.210 --> 00:16:34.090 in years is only about 10 to the 10th power. 00:16:34.940 --> 00:16:38.860 Black holes aren't eternal, but for all practical 00:16:38.860 --> 00:16:41.840 astrophysical purposes they might as well be. 00:16:42.259 --> 00:16:44.919 As they lose mass their temperature increases 00:16:44.919 --> 00:16:48.080 and near the very end of their evaporation they 00:16:48.080 --> 00:16:51.120 would radiate intensely and vanish in a final 00:16:51.120 --> 00:16:55.399 burst of high energy radiation. This final phase 00:16:55.399 --> 00:16:58.279 has of course never been observed and remains 00:16:58.279 --> 00:17:01.480 theoretical. This brings me back around to where 00:17:01.480 --> 00:17:04.740 we started this episode. pondering the dread 00:17:04.740 --> 00:17:09.319 of our own sun's death. Our sun feels foundational, 00:17:09.480 --> 00:17:13.259 yet it is temporary. But its transformation lies 00:17:13.259 --> 00:17:15.819 so far in the future that it functions more as 00:17:15.819 --> 00:17:19.259 a philosophical boundary than an impending event. 00:17:20.200 --> 00:17:23.200 Humanity has only existed for a tiny fraction 00:17:23.200 --> 00:17:27.359 of the sun's lifespan. If the sun were a 70 -year 00:17:27.359 --> 00:17:30.319 -old human, our entire species would have only 00:17:30.319 --> 00:17:34.140 appeared a few hours ago. When its time comes, 00:17:34.319 --> 00:17:37.920 the Sun will not rage. It will compress, ignite 00:17:37.920 --> 00:17:41.839 new layers, expand, shed, and settle into a dense 00:17:41.839 --> 00:17:45.019 white ember held together by the quantum rules 00:17:45.019 --> 00:17:48.000 that make the universe coherent at its smallest 00:17:48.000 --> 00:17:51.859 scales. In the meantime, it's humbling to realize 00:17:51.859 --> 00:17:55.079 that everything heavier than helium in your body 00:17:55.079 --> 00:17:58.319 was forged in stars that lived and died before 00:17:58.319 --> 00:18:02.460 ours was even born. Stellar deaths made rocky 00:18:02.460 --> 00:18:05.740 planets possible. It made chemistry complex. 00:18:06.160 --> 00:18:24.799 And it made us. After a quick break, we'll be 00:18:24.799 --> 00:18:27.980 back with this week's Sky Report. Stay with us. 00:18:40.379 --> 00:18:44.839 Welcome back. This week's sky offers a rich mix 00:18:44.839 --> 00:18:48.140 of wandering worlds and familiar lunar phases, 00:18:48.640 --> 00:18:51.819 perfect for both binocular stargazers and people 00:18:51.819 --> 00:18:55.619 simply stepping outside after dinner. As the 00:18:55.619 --> 00:18:58.819 sun sets, start by finding the moon. This week 00:18:58.819 --> 00:19:01.980 it's rotating into view as a thin waxing crescent 00:19:01.980 --> 00:19:05.640 early in the week. By February 24th, the moon 00:19:05.640 --> 00:19:08.740 reaches first quarter. appearing half illuminated 00:19:08.740 --> 00:19:11.859 and hanging high in the southern sky around sunset. 00:19:12.660 --> 00:19:15.640 By week's end, it grows into a bright, waxing 00:19:15.640 --> 00:19:18.759 gibbous rising earlier each evening and dominating 00:19:18.759 --> 00:19:22.000 the early night. This week is especially good 00:19:22.000 --> 00:19:25.079 for planets because a slow -building planetary 00:19:25.079 --> 00:19:29.279 parade is unfolding in the evening sky. Six planets, 00:19:29.680 --> 00:19:33.900 Mercury, Venus, Jupiter, Saturn, Uranus, and 00:19:33.900 --> 00:19:36.779 Neptune, will appear along the same stretch of 00:19:36.779 --> 00:19:40.779 sky shortly after sunset. From Earth's perspective, 00:19:40.980 --> 00:19:43.940 they trace a broad arc along the ecliptic that 00:19:43.940 --> 00:19:46.819 can be seen in a single sweep with dark skies 00:19:46.819 --> 00:19:51.160 and clear horizons. Start your evening soon after 00:19:51.160 --> 00:19:54.500 sunset by looking low toward the western horizon. 00:19:55.140 --> 00:19:57.900 There, Venus shines brightest among the inner 00:19:57.900 --> 00:20:01.259 planets, a brilliant beacon just above the horizon. 00:20:01.660 --> 00:20:04.799 Not far below it is Mercury, still a challenge 00:20:04.799 --> 00:20:07.500 because it sits low and close to the Sun's glare, 00:20:07.940 --> 00:20:10.500 but visible if you can catch it while the sky 00:20:10.500 --> 00:20:14.619 is still dusky and the horizon is clear. Saturn 00:20:14.619 --> 00:20:17.759 also lingers in this direction, a softer yellow 00:20:17.759 --> 00:20:20.759 point that will benefit from binoculars or a 00:20:20.759 --> 00:20:23.359 small telescope to cut through the twilight. 00:20:24.140 --> 00:20:26.839 Toward the east and southeast as night deepens, 00:20:26.940 --> 00:20:29.480 you'll see Jupiter, the brightest star in the 00:20:29.480 --> 00:20:33.079 evening sky this month. It rises early and stays 00:20:33.079 --> 00:20:36.099 high well into the night, far easier to spot 00:20:36.099 --> 00:20:40.079 than Mercury, Venus, or even Saturn. In a telescope, 00:20:40.400 --> 00:20:43.059 Jupiter's cloud bands and its large moons make 00:20:43.059 --> 00:20:46.880 for stunning details if the air is steady. The 00:20:46.880 --> 00:20:50.700 outer ice giants, Uranus and Neptune are also 00:20:50.700 --> 00:20:53.759 part of this extended parade, located between 00:20:53.759 --> 00:20:56.869 the brighter worlds. They're too faint to see 00:20:56.869 --> 00:20:59.609 with the naked eye. Binoculars or a telescope 00:20:59.609 --> 00:21:01.829 will help you tease them out against the star 00:21:01.829 --> 00:21:05.710 fields. The best collective view of this six 00:21:05.710 --> 00:21:09.069 -planet parade builds toward February 28th, when 00:21:09.069 --> 00:21:11.890 all six planets are visible in the same post 00:21:11.890 --> 00:21:15.609 -sunset window roughly 30 to 90 minutes after 00:21:15.609 --> 00:21:19.269 sundown. Start with the western horizon for Venus, 00:21:19.410 --> 00:21:22.730 Mercury, and Saturn, then sweep eastward to catch 00:21:22.730 --> 00:21:26.059 Jupiter higher in the sky. Uranus and Neptune 00:21:26.059 --> 00:21:30.180 will be between them, subtle, but there. Finally, 00:21:30.279 --> 00:21:32.740 even with the moon brightening later in the week, 00:21:32.839 --> 00:21:35.500 don't miss a couple of quieter sky -watching 00:21:35.500 --> 00:21:38.720 opportunities earlier in the period. On the evening 00:21:38.720 --> 00:21:42.019 of February 23, the moon moves through the northern 00:21:42.019 --> 00:21:46.160 part of the Pleiades star cluster, subtly occulting 00:21:46.160 --> 00:21:50.000 stars as it passes. It makes a fine pairing for 00:21:50.000 --> 00:21:53.980 binoculars or a wide -field telescope. Next week 00:21:53.980 --> 00:21:56.859 we'll return to our book club covering chapters 00:21:56.859 --> 00:22:01.099 6 and 7 in Nightwatch. These chapters cover deep 00:22:01.099 --> 00:22:04.099 sky objects and the planets of our solar system. 00:22:04.539 --> 00:22:07.099 And like the previous chapters, make excellent 00:22:07.099 --> 00:22:14.279 companion readings for this podcast. That's going 00:22:14.279 --> 00:22:16.839 to do it for this week. If you found this episode 00:22:16.839 --> 00:22:18.960 interesting, please share it with a friend who 00:22:18.960 --> 00:22:21.730 might enjoy it. The easiest way to do that is 00:22:21.730 --> 00:22:25.750 by sending folks to our website, StarTrails .Show. 00:22:26.309 --> 00:22:28.890 And if you'd like to support the show, use the 00:22:28.890 --> 00:22:31.529 link on the site to buy me a coffee. That really 00:22:31.529 --> 00:22:35.029 helps. Be sure to follow Star Trails on Blue 00:22:35.029 --> 00:22:38.210 Sky and YouTube. Links are in the show notes. 00:22:38.829 --> 00:22:41.630 Until we meet again beneath the stars, clear 00:22:41.630 --> 00:22:42.450 skies everyone.