WEBVTT 00:00:07.710 --> 00:00:10.169 Howdy stargazers, and welcome to this episode 00:00:10.169 --> 00:00:13.269 of Star Trails. My name is Drew, and I'll be 00:00:13.269 --> 00:00:15.869 your guide to the night sky for the week of April 00:00:15.869 --> 00:00:19.730 the 12th through the 18th. This week we're talking 00:00:19.730 --> 00:00:22.969 about radio astronomy, and the processes that 00:00:22.969 --> 00:00:25.649 allow us to see everything from the afterglow 00:00:25.649 --> 00:00:28.589 of the Big Bang to the shape of black holes. 00:00:29.019 --> 00:00:31.739 Later in the show, I'll talk about some of the 00:00:31.739 --> 00:00:34.840 photography from the Artemis II mission, and 00:00:34.840 --> 00:00:37.979 we'll check in with this week's sky, which offers 00:00:37.979 --> 00:00:41.560 some gems for early risers. Whether you're tuning 00:00:41.560 --> 00:00:44.299 in from the backyard or the balcony, I'm glad 00:00:44.299 --> 00:00:46.799 you're here, so grab a comfortable spot under 00:00:46.799 --> 00:00:51.039 the night sky and let's get started. Hopefully 00:00:51.039 --> 00:00:54.200 you enjoyed the bonus episode I released last 00:00:54.200 --> 00:00:57.359 week about the David Bowie song, Space Oddity. 00:00:57.659 --> 00:01:01.100 I know that isn't everyone's cup of tea, which 00:01:01.100 --> 00:01:03.640 is why I didn't release it as part of the main 00:01:03.640 --> 00:01:07.680 sequence of shows. Anyway, I have news to report 00:01:07.680 --> 00:01:10.780 related to that episode. It looks like Bowie 00:01:10.780 --> 00:01:14.439 made it back into space. At the end of that bonus 00:01:14.439 --> 00:01:17.340 episode, I mentioned that I didn't know if the 00:01:17.340 --> 00:01:20.000 Artemis II astronauts were listening to Space 00:01:20.000 --> 00:01:23.299 Oddity. But, as it turns out, they did listen 00:01:23.299 --> 00:01:26.870 to a song featuring Bowie. One of the tracks 00:01:26.870 --> 00:01:30.290 on their so -called wake -up playlist was Under 00:01:30.290 --> 00:01:34.549 Pressure, the 1981 collaboration between Queen 00:01:34.549 --> 00:01:38.310 and Bowie. And here's another wild connection. 00:01:38.750 --> 00:01:42.870 Queen guitarist Sir Brian May has a doctorate 00:01:42.870 --> 00:01:46.849 in astrophysics. These songs are selected by 00:01:46.849 --> 00:01:49.549 mission control specialists and the wake -up 00:01:49.549 --> 00:01:52.849 songs are a tradition from the Apollo era. to 00:01:52.849 --> 00:01:56.930 help astronauts stay connected to humanity. Other 00:01:56.930 --> 00:01:59.890 artists featured on the Artemis playlist included 00:01:59.890 --> 00:02:04.709 Chappell Roan, John Legend, and more. The historic 00:02:04.709 --> 00:02:08.150 Artemis mission ended Friday after a successful 00:02:08.150 --> 00:02:11.430 splashdown in the Pacific. I'm looking forward 00:02:11.430 --> 00:02:14.110 to combing through the images they brought back. 00:02:14.729 --> 00:02:17.389 Later in the show, I'll talk about one particular 00:02:17.389 --> 00:02:20.400 image they've already shared. In the meantime, 00:02:20.659 --> 00:02:23.139 I'll include a link in the show notes to a playlist 00:02:23.139 --> 00:02:29.699 of their wake -up songs. Speaking of sounds in 00:02:29.699 --> 00:02:33.740 space, let's talk about radio astronomy. For 00:02:33.740 --> 00:02:37.099 most of human history, astronomy meant one thing, 00:02:37.340 --> 00:02:41.219 looking up. Watching the sky with our eyes, and 00:02:41.219 --> 00:02:44.719 later, with telescopes that extended those eyes, 00:02:45.099 --> 00:02:48.500 pulling distant light just a little closer. And 00:02:48.500 --> 00:02:51.159 through that simple act of looking, we've learned 00:02:51.159 --> 00:02:55.139 an extraordinary amount about the universe. Visual 00:02:55.139 --> 00:02:58.400 astronomy has given us the structure of the cosmos. 00:02:58.939 --> 00:03:02.060 It's how we mapped the stars, traced the motions 00:03:02.060 --> 00:03:05.759 of the planets, and discovered entire galaxies 00:03:05.759 --> 00:03:09.719 far beyond our own. It's how we study nebula, 00:03:10.020 --> 00:03:13.520 the birthplaces of stars, and the remnants of 00:03:13.520 --> 00:03:18.139 stellar death. And with techniques like spectroscopy, 00:03:18.259 --> 00:03:20.919 we've even learned what distant objects are made 00:03:20.919 --> 00:03:24.340 of, their temperatures, their velocities, and 00:03:24.340 --> 00:03:29.139 how fast they're moving away from us. Long exposure 00:03:29.139 --> 00:03:32.699 imaging pushed that even further. A camera left 00:03:32.699 --> 00:03:36.340 open to the sky for minutes or hours reveals 00:03:36.340 --> 00:03:39.439 structures so faint they're completely invisible 00:03:39.439 --> 00:03:43.500 to the human eye. Swirling gas clouds, distant 00:03:43.500 --> 00:03:47.270 galaxies, delicate filaments of cosmic structure. 00:03:47.969 --> 00:03:51.129 In many ways, visual astronomy is the foundation 00:03:51.129 --> 00:03:55.069 of everything we know. But it's only part of 00:03:55.069 --> 00:03:59.650 the story. Visible light is the tiny slice of 00:03:59.650 --> 00:04:02.969 the electromagnetic spectrum that our eyes can 00:04:02.969 --> 00:04:07.530 detect. And it's just that, a slice. The universe 00:04:07.530 --> 00:04:11.009 is constantly emitting energy across the vast 00:04:11.009 --> 00:04:14.530 range of wavelengths. from high -energy gamma 00:04:14.530 --> 00:04:19.290 rays to long, slow radio waves. And for most 00:04:19.290 --> 00:04:22.069 of human history, we were completely deaf to 00:04:22.069 --> 00:04:26.569 all of it. That changed in the 1930s, not in 00:04:26.569 --> 00:04:29.769 an observatory, but in a field in New Jersey. 00:04:30.449 --> 00:04:33.949 An engineer named Karl Jansky was working for 00:04:33.949 --> 00:04:37.149 Bell Telephone Laboratories, trying to track 00:04:37.149 --> 00:04:40.779 down sources of radio interference. He built 00:04:40.779 --> 00:04:44.459 an antenna that could sweep the sky. And at first, 00:04:44.620 --> 00:04:48.360 he found what he expected. Thunderstorms, distant 00:04:48.360 --> 00:04:52.060 noises, human -made signals. But then there was 00:04:52.060 --> 00:04:55.699 something else. A faint hiss that repeated not 00:04:55.699 --> 00:05:01.019 every 24 hours, but every 23 hours and 56 minutes. 00:05:01.480 --> 00:05:05.399 A sidereal day. That's the time it takes Earth 00:05:05.399 --> 00:05:09.019 to complete a rotation relative to distant stars. 00:05:10.579 --> 00:05:13.759 Jansky realized that signal wasn't coming from 00:05:13.759 --> 00:05:16.579 Earth at all. It was coming from the center of 00:05:16.579 --> 00:05:19.540 the Milky Way. For the first time in history, 00:05:19.860 --> 00:05:22.519 we had detected the universe not through light, 00:05:22.819 --> 00:05:26.500 but through radio waves. A few decades later, 00:05:26.819 --> 00:05:30.160 Arno Pinzias and Robert Wilson stumbled onto 00:05:30.160 --> 00:05:33.920 something even more profound. The cosmic microwave 00:05:33.920 --> 00:05:37.660 background. The faint afterglow of the Big Bang 00:05:37.660 --> 00:05:42.339 itself. This discovery is a cornerstone of modern 00:05:42.339 --> 00:05:46.060 cosmology. The cosmic microwave background is 00:05:46.060 --> 00:05:50.519 remarkably uniform, but not perfectly so. Tiny 00:05:50.519 --> 00:05:53.899 fluctuations in its temperature, variations of 00:05:53.899 --> 00:05:57.899 just a few millionths of a degree, encode information 00:05:57.899 --> 00:06:01.740 about the early universe. From those patterns, 00:06:01.879 --> 00:06:04.660 we've been able to determine the age of the universe, 00:06:05.040 --> 00:06:08.920 its composition, and even its large -scale geometry. 00:06:09.680 --> 00:06:12.699 The CMB is a snapshot of the universe when it 00:06:12.699 --> 00:06:17.980 was just 380 ,000 years old. And it still surrounds 00:06:17.980 --> 00:06:23.480 us today, filling all of space. At that point, 00:06:23.720 --> 00:06:26.500 astronomy changed forever. We were no longer 00:06:26.500 --> 00:06:29.000 just looking at the universe. We were beginning 00:06:29.000 --> 00:06:32.899 to listen to it. Radio astronomy is the study 00:06:32.899 --> 00:06:37.129 of the universe through radio waves. long wavelength 00:06:37.129 --> 00:06:41.529 electromagnetic radiation that behaves very differently 00:06:41.529 --> 00:06:45.829 from visible light. Instead of mirrors, radio 00:06:45.829 --> 00:06:48.829 telescopes use large dishes that collect and 00:06:48.829 --> 00:06:52.670 focus signals onto a receiver. These signals 00:06:52.670 --> 00:06:56.129 are incredibly faint, buried in noise, but they 00:06:56.129 --> 00:06:59.250 carry information that optical telescopes simply 00:06:59.250 --> 00:07:04.189 can't access. Radio waves pass through dust clouds 00:07:04.189 --> 00:07:07.250 that block visible light, allowing us to see 00:07:07.250 --> 00:07:10.430 star -forming regions and across the structure 00:07:10.430 --> 00:07:14.129 of our galaxy. They can be observed day or night, 00:07:14.529 --> 00:07:16.910 often through conditions that would make optical 00:07:16.910 --> 00:07:21.110 observation impossible. It reveals a hidden universe 00:07:21.110 --> 00:07:25.019 layered on top of the one we see. Facilities 00:07:25.019 --> 00:07:28.839 like the Arecibo Observatory, the Very Large 00:07:28.839 --> 00:07:32.420 Array, and the FAST telescope have allowed us 00:07:32.420 --> 00:07:37.139 to map hydrogen gas, discover pulsars first identified 00:07:37.139 --> 00:07:41.399 by Jocelyn Bell Burnell, and study the environments 00:07:41.399 --> 00:07:46.339 around black holes and distant galaxies. But 00:07:46.339 --> 00:07:49.500 the real story of radio astronomy is how we turn 00:07:49.500 --> 00:07:53.060 those signals into something we can understand. 00:07:53.839 --> 00:07:57.819 A radio telescope doesn't take pictures. It measures 00:07:57.819 --> 00:08:02.180 voltage over time. Tiny electrical fluctuations 00:08:02.180 --> 00:08:06.560 caused by incoming radio waves. When a signal 00:08:06.560 --> 00:08:09.519 reaches the dish, it's focused onto a receiver 00:08:09.519 --> 00:08:13.579 and converted into an electrical waveform. That 00:08:13.579 --> 00:08:17.139 signal is amplified using low -noise amplifiers, 00:08:17.699 --> 00:08:21.730 then digitized into a stream of numbers. At this 00:08:21.730 --> 00:08:24.569 point, we don't have an image. We have data. 00:08:25.269 --> 00:08:28.250 To make sense of that data, astronomers use a 00:08:28.250 --> 00:08:32.289 process called the Fast Fourier Transform. The 00:08:32.289 --> 00:08:35.169 math behind the Fourier Transform dates back 00:08:35.169 --> 00:08:39.690 to Joseph Fourier in the early 1800s, who showed 00:08:39.690 --> 00:08:42.769 that complex signals can be broken down into 00:08:42.769 --> 00:08:47.919 simple sine and cosine waves. The modern fast 00:08:47.919 --> 00:08:52.279 Fourier transform developed in 1965 made this 00:08:52.279 --> 00:08:55.500 process dramatically faster and practical for 00:08:55.500 --> 00:09:00.360 real -time computing. Essentially, the FFT transforms 00:09:00.360 --> 00:09:03.559 a signal from the time domain into the frequency 00:09:03.559 --> 00:09:06.740 domain, revealing what frequencies are present 00:09:06.740 --> 00:09:10.019 and how strong they are. Without it, there would 00:09:10.019 --> 00:09:14.220 be no radio astronomy. It's essential because 00:09:14.220 --> 00:09:17.700 specific frequencies correspond to physical phenomena. 00:09:18.600 --> 00:09:21.480 One of the most important examples is the hydrogen 00:09:21.480 --> 00:09:27.039 line, at 1420 MHz. Neutral hydrogen atoms naturally 00:09:27.039 --> 00:09:30.679 emit radiation at this frequency, allowing astronomers 00:09:30.679 --> 00:09:34.340 to map vast clouds of gas across the galaxy. 00:09:35.399 --> 00:09:38.519 And thanks to the Doppler effect, shifts in that 00:09:38.519 --> 00:09:41.990 frequency reveal motion, rotation, expansion, 00:09:42.450 --> 00:09:46.889 and dynamics on a galactic scale. In fact, much 00:09:46.889 --> 00:09:49.070 of what we know about the structure of the Milky 00:09:49.070 --> 00:09:52.769 Way comes from this exact technique. By mapping 00:09:52.769 --> 00:09:56.110 hydrogen emissions across the sky and measuring 00:09:56.110 --> 00:09:59.190 how those signals shift, we've been able to trace 00:09:59.190 --> 00:10:02.629 out the spiral arms of our own galaxy, even though 00:10:02.629 --> 00:10:06.809 we're embedded inside it. But things get even 00:10:06.809 --> 00:10:10.250 more powerful when multiple telescopes are combined. 00:10:10.639 --> 00:10:14.440 In systems like the very large array, each antenna 00:10:14.440 --> 00:10:18.679 captures its own signal. These signals are aligned 00:10:18.679 --> 00:10:22.620 in time and combined through correlation, producing 00:10:22.620 --> 00:10:25.899 what are known as visibilities, the raw data 00:10:25.899 --> 00:10:30.460 of interferometry. From there, the process becomes 00:10:30.460 --> 00:10:35.059 even more computational. Using inverse Fourier 00:10:35.059 --> 00:10:39.450 transforms and deconvolution techniques, astronomers 00:10:39.450 --> 00:10:44.090 reconstruct an image from incomplete data. Let's 00:10:44.090 --> 00:10:47.250 pause there because that sounds complex, and 00:10:47.250 --> 00:10:51.350 it is. An inverse FFT is a process that lets 00:10:51.350 --> 00:10:55.710 us reconstruct a signal. So if the Fourier transform 00:10:55.710 --> 00:10:59.149 breaks a signal apart into its frequencies, the 00:10:59.149 --> 00:11:02.210 inverse transform puts it back together again. 00:11:03.960 --> 00:11:06.639 Deconvolution is a little harder to explain, 00:11:06.879 --> 00:11:10.580 but the idea is this. Imagine you've made a voice 00:11:10.580 --> 00:11:13.980 recording in a big concert hall, and the size 00:11:13.980 --> 00:11:17.379 of that space is creating a lot of reverb and 00:11:17.379 --> 00:11:20.480 echo. You can run your recording through a tool 00:11:20.480 --> 00:11:23.720 to strip out the reverb, which leaves the so 00:11:23.720 --> 00:11:27.580 -called dry signal. In radio astronomy, we need 00:11:27.580 --> 00:11:30.820 to subtract the distortion introduced by the 00:11:30.820 --> 00:11:34.360 so -called beam pattern of the radio telescope 00:11:34.360 --> 00:11:38.600 itself, and that's deconvolution. Basically, 00:11:38.860 --> 00:11:41.779 the telescope colors the signal it receives, 00:11:42.360 --> 00:11:44.720 and astronomers have to mathematically remove 00:11:44.720 --> 00:11:47.659 that effect to recover what's really out there. 00:11:48.519 --> 00:11:51.799 A process called windowing is used to smooth 00:11:51.799 --> 00:11:54.759 the edges of the signal and reduce artifacts 00:11:54.759 --> 00:11:58.399 introduced by the Fourier transform. Matched 00:11:58.399 --> 00:12:01.840 filtering helps detect extremely faint signals 00:12:01.840 --> 00:12:05.240 by comparing incoming data to known patterns. 00:12:06.419 --> 00:12:10.580 And a technology called beam forming allows arrays 00:12:10.580 --> 00:12:14.000 of antennas to electronically focus on a specific 00:12:14.000 --> 00:12:16.899 region of the sky without physically moving. 00:12:18.059 --> 00:12:20.600 And then there's the problem of interference. 00:12:21.419 --> 00:12:25.379 Radio frequency interference, or RFI, is everywhere. 00:12:25.740 --> 00:12:29.039 Signals from Earth -based technology can easily 00:12:29.039 --> 00:12:33.019 overwhelm the faint emissions from space. So, 00:12:33.279 --> 00:12:36.440 astronomers use a combination of hardware shielding, 00:12:36.600 --> 00:12:40.100 remote observatory locations, and sophisticated 00:12:40.100 --> 00:12:43.960 filtering algorithms to remove unwanted noise 00:12:43.960 --> 00:12:48.200 and isolate the signals they care about. And 00:12:48.200 --> 00:12:51.500 nowhere is all of this more dramatically demonstrated 00:12:51.500 --> 00:12:55.929 than in the first image of a black hole. In 2019, 00:12:56.269 --> 00:12:59.870 the Event Horizon Telescope linked radio telescopes 00:12:59.870 --> 00:13:04.590 across the globe using very long baseline interferometry, 00:13:05.309 --> 00:13:08.149 effectively turning Earth itself into a single 00:13:08.149 --> 00:13:12.470 telescope. The data was enormous, so large that 00:13:12.470 --> 00:13:15.529 it had to be stored on physical drives and shipped 00:13:15.529 --> 00:13:18.950 for processing. And just like everything we've 00:13:18.950 --> 00:13:21.809 discussed, the image wasn't directly observed. 00:13:21.990 --> 00:13:26.139 It was reconstructed. Using Fourier transforms, 00:13:26.320 --> 00:13:30.220 correlation, and deconvolution algorithms, scientists 00:13:30.220 --> 00:13:32.980 assembled an image of the black hole's shadow 00:13:32.980 --> 00:13:38.139 in the galaxy M87. Multiple independent teams 00:13:38.139 --> 00:13:41.460 used different reconstruction methods and all 00:13:41.460 --> 00:13:44.580 arrived at the same fundamental structure, a 00:13:44.580 --> 00:13:48.320 bright ring surrounding a dark center. There 00:13:48.320 --> 00:13:51.460 was discussion about how much of that image was 00:13:51.460 --> 00:13:55.360 real versus algorithmic, but that's the nature 00:13:55.360 --> 00:13:59.120 of this kind of science. The structure is strongly 00:13:59.120 --> 00:14:02.340 supported by the data, even if the fine details 00:14:02.340 --> 00:14:05.480 vary. In other words, we didn't take a picture 00:14:05.480 --> 00:14:10.820 of a black hole, we solved for it. More recently, 00:14:11.279 --> 00:14:13.799 radio telescopes have uncovered something even 00:14:13.799 --> 00:14:17.669 stranger. brief, intense flashes of energy known 00:14:17.669 --> 00:14:22.470 as fast radio bursts. These signals last just 00:14:22.470 --> 00:14:26.009 milliseconds, yet release enormous amounts of 00:14:26.009 --> 00:14:28.830 energy, often from galaxies billions of light 00:14:28.830 --> 00:14:31.889 years away. They're one of the most mysterious 00:14:31.889 --> 00:14:34.970 phenomena in modern astronomy, and we're still 00:14:34.970 --> 00:14:38.509 working to understand what causes them. Radio 00:14:38.509 --> 00:14:41.250 astronomy is the foundation for the search for 00:14:41.250 --> 00:14:45.360 extraterrestrial intelligence program. It's also 00:14:45.360 --> 00:14:49.279 currently being used to study exoplanet magnetospheres, 00:14:49.399 --> 00:14:52.460 and we've used it to discover wild phenomena 00:14:52.460 --> 00:14:57.200 like quasar jets. Sometimes the most intriguing 00:14:57.200 --> 00:15:00.139 discoveries in astronomy don't look like galaxies 00:15:00.139 --> 00:15:03.419 or nebula. They look like numbers on a page. 00:15:04.659 --> 00:15:09.299 In 1977, a signal detected by the Big Ear radio 00:15:09.299 --> 00:15:12.299 telescope stood out so clearly from the background 00:15:12.299 --> 00:15:16.240 noise, that astronomer Jerry Amon circled it 00:15:16.240 --> 00:15:20.700 and wrote a single word beside it, wow. This 00:15:20.700 --> 00:15:24.340 was, of course, dubbed the wow signal, and it 00:15:24.340 --> 00:15:27.019 was simply a string of characters on a printout 00:15:27.019 --> 00:15:30.580 representing signal intensity over time. The 00:15:30.580 --> 00:15:33.899 data indicated it was a very strong narrow -band 00:15:33.899 --> 00:15:37.600 signal near the hydrogen line, rising and falling 00:15:37.600 --> 00:15:41.470 over about 72 seconds. which is what you'd expect 00:15:41.470 --> 00:15:44.409 from a fixed telescope as the Earth rotates. 00:15:45.269 --> 00:15:48.029 To this day, we still don't know what that signal 00:15:48.029 --> 00:15:51.809 was, but it's never been confirmed as extraterrestrial, 00:15:52.129 --> 00:15:56.169 and it's never been heard again. Behind every 00:15:56.169 --> 00:16:00.070 radio image is a pipeline of processing, filtering 00:16:00.070 --> 00:16:03.750 noise, correcting for Earth's rotation, compensating 00:16:03.750 --> 00:16:06.990 for atmospheric effects, and assembling a coherent 00:16:06.990 --> 00:16:10.899 picture from fragments of a signal. It's less 00:16:10.899 --> 00:16:13.779 like taking a photograph and more like assembling 00:16:13.779 --> 00:16:17.620 a picture from echoes. And here's the part that 00:16:17.620 --> 00:16:21.059 might surprise you. The same fundamental techniques 00:16:21.059 --> 00:16:24.379 that make radio astronomy possible are quietly 00:16:24.379 --> 00:16:28.639 at work in your everyday life. The amplification 00:16:28.639 --> 00:16:32.059 and digitization of signals, the use of Fourier 00:16:32.059 --> 00:16:35.639 transforms to break complex signals into frequencies, 00:16:36.240 --> 00:16:39.470 the filtering of noise, And even techniques like 00:16:39.470 --> 00:16:43.210 beamforming are built into the devices you use 00:16:43.210 --> 00:16:46.970 every day. Your phone relies on them to maintain 00:16:46.970 --> 00:16:51.490 a clear connection. Your Wi -Fi router uses beamforming 00:16:51.490 --> 00:16:55.070 to direct signals towards your devices. Your 00:16:55.070 --> 00:16:57.990 noise -cancelling headphones filter out noise 00:16:57.990 --> 00:17:01.929 to isolate what you want to hear. Voice recognition 00:17:01.929 --> 00:17:06.420 is much like matched filtering. Even the music 00:17:06.420 --> 00:17:09.200 you stream every day has been broken down into 00:17:09.200 --> 00:17:12.400 frequencies and rebuilt again, using the same 00:17:12.400 --> 00:17:15.680 kind of math astronomers use to study the universe. 00:17:16.660 --> 00:17:19.940 In fact, every time I edit a podcast, I'm using 00:17:19.940 --> 00:17:23.420 a fast Fourier transform, perhaps a thousand 00:17:23.420 --> 00:17:26.599 times a second or more, depending on how many 00:17:26.599 --> 00:17:30.220 tracks and audio processors I'm using. The efficiency 00:17:30.220 --> 00:17:32.839 of modern computers is incredible when you think 00:17:32.839 --> 00:17:36.710 about it. We'll explore the computational side 00:17:36.710 --> 00:17:39.930 of astronomy in more detail in a future episode, 00:17:40.029 --> 00:17:43.829 but for now it's enough to say this. Radio astronomy 00:17:43.829 --> 00:17:47.089 doesn't just expand what we can observe, it changes 00:17:47.089 --> 00:17:51.509 how we think about observing. The night sky isn't 00:17:51.509 --> 00:17:54.789 silent, it's alive with signals that are ancient, 00:17:55.130 --> 00:17:58.809 energetic, and constant. For most of human history, 00:17:59.009 --> 00:18:01.470 we simply didn't have the tools to detect them. 00:18:01.970 --> 00:18:04.920 But now we're listening. and what we're hearing 00:18:04.920 --> 00:18:08.140 is a universe far richer than anything we could 00:18:08.140 --> 00:18:29.069 ever see with our eyes alone. After a quick break, 00:18:29.250 --> 00:18:31.869 we'll be back to cover this week's sky and talk 00:18:31.869 --> 00:18:34.470 about a photograph from the Artemis II mission. 00:18:34.710 --> 00:18:50.269 Stay with us. Welcome back. You know, there's 00:18:50.269 --> 00:18:53.430 something about the infamous dark side of Earth 00:18:53.430 --> 00:18:55.970 image from the Artemis II mission that's had 00:18:55.970 --> 00:19:00.410 me thinking a lot about perspective. The ever 00:19:00.410 --> 00:19:03.329 -prickly internet photography community was in 00:19:03.329 --> 00:19:06.430 a tizzy last week over this image, focusing on 00:19:06.430 --> 00:19:09.910 the camera used and its settings, the lens choice, 00:19:10.210 --> 00:19:14.250 the ISO, and so on. As a photographer, these 00:19:14.250 --> 00:19:17.210 factors interested me too, but ultimately what 00:19:17.210 --> 00:19:21.140 matters is something much simpler. For the first 00:19:21.140 --> 00:19:24.259 time in a long time, we're seeing the entire 00:19:24.259 --> 00:19:27.900 Earth as a complete sphere, just hanging there 00:19:27.900 --> 00:19:31.180 in space. And here's the part that didn't really 00:19:31.180 --> 00:19:34.859 dawn on me until recently. Most astronauts never 00:19:34.859 --> 00:19:39.180 actually see that. When you're in low Earth orbit, 00:19:39.380 --> 00:19:41.920 like the crews aboard the International Space 00:19:41.920 --> 00:19:46.869 Station, you're only about 250 miles up. That 00:19:46.869 --> 00:19:50.150 sounds high, but on a planetary scale, it's nothing. 00:19:50.869 --> 00:19:53.450 From that distance, you see curvature. You see 00:19:53.450 --> 00:19:56.650 oceans, continents, weather systems, stretching 00:19:56.650 --> 00:20:00.009 across thousands of miles. But you don't see 00:20:00.009 --> 00:20:04.009 the whole Earth. You're too close. If you want 00:20:04.009 --> 00:20:07.390 to see an entire sphere, you have to be far enough 00:20:07.390 --> 00:20:09.730 away that it fits inside your field of view. 00:20:10.069 --> 00:20:13.990 This is a no -brainer. For Earth, that distance 00:20:13.990 --> 00:20:17.289 turns out to be surprisingly large. In a low 00:20:17.289 --> 00:20:20.230 orbit, Earth fills your entire frame and then 00:20:20.230 --> 00:20:23.329 some. To step back far enough to see the full 00:20:23.329 --> 00:20:26.269 disk, you need to be not hundreds of miles away, 00:20:26.690 --> 00:20:29.970 but thousands. Roughly speaking, you need to 00:20:29.970 --> 00:20:33.769 get out to 6 ,000 miles or more before the entire 00:20:33.769 --> 00:20:36.930 Earth can comfortably fit into view as a complete 00:20:36.930 --> 00:20:40.869 circle. And that's exactly what the Artemis mission 00:20:40.869 --> 00:20:44.079 did. They headed out toward the moon, tens of 00:20:44.079 --> 00:20:47.200 thousands of miles away, finally giving us the 00:20:47.200 --> 00:20:50.180 distance needed to see our planet as a whole. 00:20:50.940 --> 00:20:54.200 When you're close, Earth feels endless. It fills 00:20:54.200 --> 00:20:57.279 your vision. It's where you are. But when you 00:20:57.279 --> 00:21:00.119 step back far enough, it becomes something else 00:21:00.119 --> 00:21:04.779 entirely, a finite object, a sphere of oceans, 00:21:05.059 --> 00:21:09.559 clouds, and life suspended in black space. We've 00:21:09.559 --> 00:21:12.259 seen this before, of course. Images from the 00:21:12.259 --> 00:21:16.259 Apollo 17 mission, the famous blue marble, gave 00:21:16.259 --> 00:21:19.319 us that same perspective more than 50 years ago. 00:21:19.559 --> 00:21:23.019 But for a long time, that view hasn't been something 00:21:23.019 --> 00:21:27.500 we could experience in real time. The infamous 00:21:27.500 --> 00:21:31.700 pale blue dot image does something similar. It's 00:21:31.700 --> 00:21:35.019 not technically a great photo, just a blue pixel 00:21:35.019 --> 00:21:38.579 in a dark void. But it offers up something more 00:21:38.579 --> 00:21:43.279 valuable. Scale, perspective, and humility. And 00:21:43.279 --> 00:21:46.119 that's why this new image matters. Not because 00:21:46.119 --> 00:21:49.259 it was shot with a 10 year old Nikon camera. 00:21:49.779 --> 00:21:52.480 Not because it has some sensor noise or that 00:21:52.480 --> 00:21:55.220 it could have been sharper. Not because some 00:21:55.220 --> 00:21:57.400 goof on the internet thinks they could have shot 00:21:57.400 --> 00:22:00.500 it better. But because it reminds us of something 00:22:00.500 --> 00:22:04.119 easy to forget. You can't see the whole earth 00:22:04.119 --> 00:22:13.829 until you leave it. And now, let's step outside. 00:22:14.890 --> 00:22:17.609 This week offers one of the best observing windows 00:22:17.609 --> 00:22:20.390 of the month, and it comes down to one simple 00:22:20.390 --> 00:22:24.069 thing. Darkness. We're moving into a new moon 00:22:24.069 --> 00:22:27.150 on April 17th, which means for much of this week 00:22:27.150 --> 00:22:30.750 the sky will be free of bright moonlight. In 00:22:30.750 --> 00:22:33.029 fact, early in the week you'll catch a waning 00:22:33.029 --> 00:22:36.269 crescent moon just before sunrise, hanging low 00:22:36.269 --> 00:22:39.589 in the southeastern sky. It's a beautiful sight, 00:22:39.809 --> 00:22:42.769 especially if you look for Earthshine, the faint 00:22:42.769 --> 00:22:45.950 glow on the dark portion of the moon caused by 00:22:45.950 --> 00:22:49.569 sunlight reflecting off Earth. By the end of 00:22:49.569 --> 00:22:52.089 the week, the moon disappears entirely into the 00:22:52.089 --> 00:22:55.630 sun's glare, reaching new phase on the 17th. 00:22:55.690 --> 00:22:59.250 And then just a day later, on the 18th, a razor 00:22:59.250 --> 00:23:02.150 -thin, waxing crescent returns to the evening 00:23:02.150 --> 00:23:07.380 sky, only about 1 % illuminated. This is prime 00:23:07.380 --> 00:23:11.460 time for deep sky observing. April marks the 00:23:11.460 --> 00:23:14.619 heart of what astronomers often call galaxy season. 00:23:15.059 --> 00:23:17.640 With the Milky Way dipping lower in the evening 00:23:17.640 --> 00:23:21.079 sky, we're looking outward, away from the dense 00:23:21.079 --> 00:23:24.759 star fields and into the vast expanse of intergalactic 00:23:24.759 --> 00:23:29.019 space. Look toward the constellation Leo, now 00:23:29.019 --> 00:23:31.880 high in the evening sky, where you'll find the 00:23:31.880 --> 00:23:35.400 Leo triplet. three galaxies interacting with 00:23:35.400 --> 00:23:38.940 one another, appearing as faint smudges of ancient 00:23:38.940 --> 00:23:43.359 light. Nearby in Ursa Major, you'll find Messier 00:23:43.359 --> 00:23:48.779 81 and 82, two striking galaxies often seen together 00:23:48.779 --> 00:23:51.880 in the same field of view. These are not bright 00:23:51.880 --> 00:23:54.460 objects. You're seeing light that has traveled 00:23:54.460 --> 00:23:58.500 millions of years to reach your eyes. The planets 00:23:58.500 --> 00:24:00.640 are putting on a show this week, but you'll need 00:24:00.640 --> 00:24:04.000 to be an early riser to catch some of them. On 00:24:04.000 --> 00:24:07.660 the morning of April 18th, a rare alignment unfolds 00:24:07.660 --> 00:24:12.000 low on the eastern horizon. Mercury, Mars, and 00:24:12.000 --> 00:24:15.319 Saturn gather together in a tight grouping, with 00:24:15.319 --> 00:24:18.339 Neptune nearby for those with binoculars or a 00:24:18.339 --> 00:24:22.059 telescope. This planet parade will be subtle, 00:24:22.220 --> 00:24:24.799 and you'll need a clear, unobstructed horizon 00:24:24.799 --> 00:24:28.890 and a bit of patience. Venus continues to dominate 00:24:28.890 --> 00:24:31.869 the early evening sky, shining brilliantly in 00:24:31.869 --> 00:24:35.430 the west just after sunset. It's unmistakable, 00:24:35.650 --> 00:24:38.150 the brightest object in the sky after the sun 00:24:38.150 --> 00:24:41.529 and moon. Jupiter is still visible in the evening, 00:24:41.789 --> 00:24:44.789 high in the sky. And finally, while it won't 00:24:44.789 --> 00:24:47.710 peak until next week, the Lyrid meteor shower 00:24:47.710 --> 00:24:51.369 is beginning to ramp up. Active from around April 00:24:51.369 --> 00:24:55.319 16th and onward, You may catch a few early meteors 00:24:55.319 --> 00:24:58.319 streaking across the sky in the pre -dawn hours. 00:24:59.039 --> 00:25:01.140 With the moon out of the way, the conditions 00:25:01.140 --> 00:25:05.200 are ideal. The Lyrids are associated with debris 00:25:05.200 --> 00:25:08.680 from Comet Thatcher and are known for their bright 00:25:08.680 --> 00:25:12.019 meteors, fireballs, and visible smoke trails. 00:25:12.660 --> 00:25:20.710 They're expected to peak on the 22nd. That's 00:25:20.710 --> 00:25:22.950 going to do it for this week. If you found this 00:25:22.950 --> 00:25:25.269 episode interesting, please share it with a friend 00:25:25.269 --> 00:25:28.069 who might enjoy it. The easiest way to do that 00:25:28.069 --> 00:25:31.329 is by sending folks to our website, StarTrails 00:25:31.329 --> 00:25:35.069 .Show. And if you want to support the show, use 00:25:35.069 --> 00:25:37.769 the link on the site to buy me a coffee. That 00:25:37.769 --> 00:25:41.190 really helps. Be sure to follow Star Trails on 00:25:41.190 --> 00:25:44.710 Blue Sky and YouTube. Links are in the show notes. 00:25:45.329 --> 00:25:48.250 Until we meet again beneath the stars, clear 00:25:48.250 --> 00:25:49.069 skies everyone!