Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / Radio Astronomy: Listening to the Universe

Transcript

Radio Astronomy: Listening to the Universe · Star Trails: From Backyard Astronomy to Cosmic Wonder

• 0:07
  Howdy stargazers, and welcome to this episode
• 0:10
  of Star Trails. My name is Drew, and I'll be
• 0:13
  your guide to the night sky for the week of April
• 0:15
  the 12th through the 18th. This week we're talking
• 0:19
  about radio astronomy, and the processes that
• 0:22
  allow us to see everything from the afterglow
• 0:25
  of the Big Bang to the shape of black holes.
• 0:29
  Later in the show, I'll talk about some of the
• 0:31
  photography from the Artemis II mission, and
• 0:34
  we'll check in with this week's sky, which offers
• 0:37
  some gems for early risers. Whether you're tuning
• 0:41
  in from the backyard or the balcony, I'm glad
• 0:44
  you're here, so grab a comfortable spot under
• 0:46
  the night sky and let's get started. Hopefully
• 0:51
  you enjoyed the bonus episode I released last
• 0:54
  week about the David Bowie song, Space Oddity.
• 0:57
  I know that isn't everyone's cup of tea, which
• 1:01
  is why I didn't release it as part of the main
• 1:03
  sequence of shows. Anyway, I have news to report
• 1:07
  related to that episode. It looks like Bowie
• 1:10
  made it back into space. At the end of that bonus
• 1:14
  episode, I mentioned that I didn't know if the
• 1:17
  Artemis II astronauts were listening to Space
• 1:20
  Oddity. But, as it turns out, they did listen
• 1:23
  to a song featuring Bowie. One of the tracks
• 1:26
  on their so -called wake -up playlist was Under
• 1:30
  Pressure, the 1981 collaboration between Queen
• 1:34
  and Bowie. And here's another wild connection.
• 1:38
  Queen guitarist Sir Brian May has a doctorate
• 1:42
  in astrophysics. These songs are selected by
• 1:46
  mission control specialists and the wake -up
• 1:49
  songs are a tradition from the Apollo era. to
• 1:52
  help astronauts stay connected to humanity. Other
• 1:56
  artists featured on the Artemis playlist included
• 1:59
  Chappell Roan, John Legend, and more. The historic
• 2:04
  Artemis mission ended Friday after a successful
• 2:08
  splashdown in the Pacific. I'm looking forward
• 2:11
  to combing through the images they brought back.
• 2:14
  Later in the show, I'll talk about one particular
• 2:17
  image they've already shared. In the meantime,
• 2:20
  I'll include a link in the show notes to a playlist
• 2:23
  of their wake -up songs. Speaking of sounds in
• 2:29
  space, let's talk about radio astronomy. For
• 2:33
  most of human history, astronomy meant one thing,
• 2:37
  looking up. Watching the sky with our eyes, and
• 2:41
  later, with telescopes that extended those eyes,
• 2:45
  pulling distant light just a little closer. And
• 2:48
  through that simple act of looking, we've learned
• 2:51
  an extraordinary amount about the universe. Visual
• 2:55
  astronomy has given us the structure of the cosmos.
• 2:58
  It's how we mapped the stars, traced the motions
• 3:02
  of the planets, and discovered entire galaxies
• 3:05
  far beyond our own. It's how we study nebula,
• 3:10
  the birthplaces of stars, and the remnants of
• 3:13
  stellar death. And with techniques like spectroscopy,
• 3:18
  we've even learned what distant objects are made
• 3:20
  of, their temperatures, their velocities, and
• 3:24
  how fast they're moving away from us. Long exposure
• 3:29
  imaging pushed that even further. A camera left
• 3:32
  open to the sky for minutes or hours reveals
• 3:36
  structures so faint they're completely invisible
• 3:39
  to the human eye. Swirling gas clouds, distant
• 3:43
  galaxies, delicate filaments of cosmic structure.
• 3:47
  In many ways, visual astronomy is the foundation
• 3:51
  of everything we know. But it's only part of
• 3:55
  the story. Visible light is the tiny slice of
• 3:59
  the electromagnetic spectrum that our eyes can
• 4:02
  detect. And it's just that, a slice. The universe
• 4:07
  is constantly emitting energy across the vast
• 4:11
  range of wavelengths. from high -energy gamma
• 4:14
  rays to long, slow radio waves. And for most
• 4:19
  of human history, we were completely deaf to
• 4:22
  all of it. That changed in the 1930s, not in
• 4:26
  an observatory, but in a field in New Jersey.
• 4:30
  An engineer named Karl Jansky was working for
• 4:33
  Bell Telephone Laboratories, trying to track
• 4:37
  down sources of radio interference. He built
• 4:40
  an antenna that could sweep the sky. And at first,
• 4:44
  he found what he expected. Thunderstorms, distant
• 4:48
  noises, human -made signals. But then there was
• 4:52
  something else. A faint hiss that repeated not
• 4:55
  every 24 hours, but every 23 hours and 56 minutes.
• 5:01
  A sidereal day. That's the time it takes Earth
• 5:05
  to complete a rotation relative to distant stars.
• 5:10
  Jansky realized that signal wasn't coming from
• 5:13
  Earth at all. It was coming from the center of
• 5:16
  the Milky Way. For the first time in history,
• 5:19
  we had detected the universe not through light,
• 5:22
  but through radio waves. A few decades later,
• 5:26
  Arno Pinzias and Robert Wilson stumbled onto
• 5:30
  something even more profound. The cosmic microwave
• 5:33
  background. The faint afterglow of the Big Bang
• 5:37
  itself. This discovery is a cornerstone of modern
• 5:42
  cosmology. The cosmic microwave background is
• 5:46
  remarkably uniform, but not perfectly so. Tiny
• 5:50
  fluctuations in its temperature, variations of
• 5:53
  just a few millionths of a degree, encode information
• 5:57
  about the early universe. From those patterns,
• 6:01
  we've been able to determine the age of the universe,
• 6:05
  its composition, and even its large -scale geometry.
• 6:09
  The CMB is a snapshot of the universe when it
• 6:12
  was just 380 ,000 years old. And it still surrounds
• 6:17
  us today, filling all of space. At that point,
• 6:23
  astronomy changed forever. We were no longer
• 6:26
  just looking at the universe. We were beginning
• 6:29
  to listen to it. Radio astronomy is the study
• 6:32
  of the universe through radio waves. long wavelength
• 6:37
  electromagnetic radiation that behaves very differently
• 6:41
  from visible light. Instead of mirrors, radio
• 6:45
  telescopes use large dishes that collect and
• 6:48
  focus signals onto a receiver. These signals
• 6:52
  are incredibly faint, buried in noise, but they
• 6:56
  carry information that optical telescopes simply
• 6:59
  can't access. Radio waves pass through dust clouds
• 7:04
  that block visible light, allowing us to see
• 7:07
  star -forming regions and across the structure
• 7:10
  of our galaxy. They can be observed day or night,
• 7:14
  often through conditions that would make optical
• 7:16
  observation impossible. It reveals a hidden universe
• 7:21
  layered on top of the one we see. Facilities
• 7:25
  like the Arecibo Observatory, the Very Large
• 7:28
  Array, and the FAST telescope have allowed us
• 7:32
  to map hydrogen gas, discover pulsars first identified
• 7:37
  by Jocelyn Bell Burnell, and study the environments
• 7:41
  around black holes and distant galaxies. But
• 7:46
  the real story of radio astronomy is how we turn
• 7:49
  those signals into something we can understand.
• 7:53
  A radio telescope doesn't take pictures. It measures
• 7:57
  voltage over time. Tiny electrical fluctuations
• 8:02
  caused by incoming radio waves. When a signal
• 8:06
  reaches the dish, it's focused onto a receiver
• 8:09
  and converted into an electrical waveform. That
• 8:13
  signal is amplified using low -noise amplifiers,
• 8:17
  then digitized into a stream of numbers. At this
• 8:21
  point, we don't have an image. We have data.
• 8:25
  To make sense of that data, astronomers use a
• 8:28
  process called the Fast Fourier Transform. The
• 8:32
  math behind the Fourier Transform dates back
• 8:35
  to Joseph Fourier in the early 1800s, who showed
• 8:39
  that complex signals can be broken down into
• 8:42
  simple sine and cosine waves. The modern fast
• 8:47
  Fourier transform developed in 1965 made this
• 8:52
  process dramatically faster and practical for
• 8:55
  real -time computing. Essentially, the FFT transforms
• 9:00
  a signal from the time domain into the frequency
• 9:03
  domain, revealing what frequencies are present
• 9:06
  and how strong they are. Without it, there would
• 9:10
  be no radio astronomy. It's essential because
• 9:14
  specific frequencies correspond to physical phenomena.
• 9:18
  One of the most important examples is the hydrogen
• 9:21
  line, at 1420 MHz. Neutral hydrogen atoms naturally
• 9:27
  emit radiation at this frequency, allowing astronomers
• 9:30
  to map vast clouds of gas across the galaxy.
• 9:35
  And thanks to the Doppler effect, shifts in that
• 9:38
  frequency reveal motion, rotation, expansion,
• 9:42
  and dynamics on a galactic scale. In fact, much
• 9:46
  of what we know about the structure of the Milky
• 9:49
  Way comes from this exact technique. By mapping
• 9:52
  hydrogen emissions across the sky and measuring
• 9:56
  how those signals shift, we've been able to trace
• 9:59
  out the spiral arms of our own galaxy, even though
• 10:02
  we're embedded inside it. But things get even
• 10:06
  more powerful when multiple telescopes are combined.
• 10:10
  In systems like the very large array, each antenna
• 10:14
  captures its own signal. These signals are aligned
• 10:18
  in time and combined through correlation, producing
• 10:22
  what are known as visibilities, the raw data
• 10:25
  of interferometry. From there, the process becomes
• 10:30
  even more computational. Using inverse Fourier
• 10:35
  transforms and deconvolution techniques, astronomers
• 10:39
  reconstruct an image from incomplete data. Let's
• 10:44
  pause there because that sounds complex, and
• 10:47
  it is. An inverse FFT is a process that lets
• 10:51
  us reconstruct a signal. So if the Fourier transform
• 10:55
  breaks a signal apart into its frequencies, the
• 10:59
  inverse transform puts it back together again.
• 11:03
  Deconvolution is a little harder to explain,
• 11:06
  but the idea is this. Imagine you've made a voice
• 11:10
  recording in a big concert hall, and the size
• 11:13
  of that space is creating a lot of reverb and
• 11:17
  echo. You can run your recording through a tool
• 11:20
  to strip out the reverb, which leaves the so
• 11:23
  -called dry signal. In radio astronomy, we need
• 11:27
  to subtract the distortion introduced by the
• 11:30
  so -called beam pattern of the radio telescope
• 11:34
  itself, and that's deconvolution. Basically,
• 11:38
  the telescope colors the signal it receives,
• 11:42
  and astronomers have to mathematically remove
• 11:44
  that effect to recover what's really out there.
• 11:48
  A process called windowing is used to smooth
• 11:51
  the edges of the signal and reduce artifacts
• 11:54
  introduced by the Fourier transform. Matched
• 11:58
  filtering helps detect extremely faint signals
• 12:01
  by comparing incoming data to known patterns.
• 12:06
  And a technology called beam forming allows arrays
• 12:10
  of antennas to electronically focus on a specific
• 12:14
  region of the sky without physically moving.
• 12:18
  And then there's the problem of interference.
• 12:21
  Radio frequency interference, or RFI, is everywhere.
• 12:25
  Signals from Earth -based technology can easily
• 12:29
  overwhelm the faint emissions from space. So,
• 12:33
  astronomers use a combination of hardware shielding,
• 12:36
  remote observatory locations, and sophisticated
• 12:40
  filtering algorithms to remove unwanted noise
• 12:43
  and isolate the signals they care about. And
• 12:48
  nowhere is all of this more dramatically demonstrated
• 12:51
  than in the first image of a black hole. In 2019,
• 12:56
  the Event Horizon Telescope linked radio telescopes
• 12:59
  across the globe using very long baseline interferometry,
• 13:05
  effectively turning Earth itself into a single
• 13:08
  telescope. The data was enormous, so large that
• 13:12
  it had to be stored on physical drives and shipped
• 13:15
  for processing. And just like everything we've
• 13:18
  discussed, the image wasn't directly observed.
• 13:21
  It was reconstructed. Using Fourier transforms,
• 13:26
  correlation, and deconvolution algorithms, scientists
• 13:30
  assembled an image of the black hole's shadow
• 13:32
  in the galaxy M87. Multiple independent teams
• 13:38
  used different reconstruction methods and all
• 13:41
  arrived at the same fundamental structure, a
• 13:44
  bright ring surrounding a dark center. There
• 13:48
  was discussion about how much of that image was
• 13:51
  real versus algorithmic, but that's the nature
• 13:55
  of this kind of science. The structure is strongly
• 13:59
  supported by the data, even if the fine details
• 14:02
  vary. In other words, we didn't take a picture
• 14:05
  of a black hole, we solved for it. More recently,
• 14:11
  radio telescopes have uncovered something even
• 14:13
  stranger. brief, intense flashes of energy known
• 14:17
  as fast radio bursts. These signals last just
• 14:22
  milliseconds, yet release enormous amounts of
• 14:26
  energy, often from galaxies billions of light
• 14:28
  years away. They're one of the most mysterious
• 14:31
  phenomena in modern astronomy, and we're still
• 14:34
  working to understand what causes them. Radio
• 14:38
  astronomy is the foundation for the search for
• 14:41
  extraterrestrial intelligence program. It's also
• 14:45
  currently being used to study exoplanet magnetospheres,
• 14:49
  and we've used it to discover wild phenomena
• 14:52
  like quasar jets. Sometimes the most intriguing
• 14:57
  discoveries in astronomy don't look like galaxies
• 15:00
  or nebula. They look like numbers on a page.
• 15:04
  In 1977, a signal detected by the Big Ear radio
• 15:09
  telescope stood out so clearly from the background
• 15:12
  noise, that astronomer Jerry Amon circled it
• 15:16
  and wrote a single word beside it, wow. This
• 15:20
  was, of course, dubbed the wow signal, and it
• 15:24
  was simply a string of characters on a printout
• 15:27
  representing signal intensity over time. The
• 15:30
  data indicated it was a very strong narrow -band
• 15:33
  signal near the hydrogen line, rising and falling
• 15:37
  over about 72 seconds. which is what you'd expect
• 15:41
  from a fixed telescope as the Earth rotates.
• 15:45
  To this day, we still don't know what that signal
• 15:48
  was, but it's never been confirmed as extraterrestrial,
• 15:52
  and it's never been heard again. Behind every
• 15:56
  radio image is a pipeline of processing, filtering
• 16:00
  noise, correcting for Earth's rotation, compensating
• 16:03
  for atmospheric effects, and assembling a coherent
• 16:06
  picture from fragments of a signal. It's less
• 16:10
  like taking a photograph and more like assembling
• 16:13
  a picture from echoes. And here's the part that
• 16:17
  might surprise you. The same fundamental techniques
• 16:21
  that make radio astronomy possible are quietly
• 16:24
  at work in your everyday life. The amplification
• 16:28
  and digitization of signals, the use of Fourier
• 16:32
  transforms to break complex signals into frequencies,
• 16:36
  the filtering of noise, And even techniques like
• 16:39
  beamforming are built into the devices you use
• 16:43
  every day. Your phone relies on them to maintain
• 16:46
  a clear connection. Your Wi -Fi router uses beamforming
• 16:51
  to direct signals towards your devices. Your
• 16:55
  noise -cancelling headphones filter out noise
• 16:57
  to isolate what you want to hear. Voice recognition
• 17:01
  is much like matched filtering. Even the music
• 17:06
  you stream every day has been broken down into
• 17:09
  frequencies and rebuilt again, using the same
• 17:12
  kind of math astronomers use to study the universe.
• 17:16
  In fact, every time I edit a podcast, I'm using
• 17:19
  a fast Fourier transform, perhaps a thousand
• 17:23
  times a second or more, depending on how many
• 17:26
  tracks and audio processors I'm using. The efficiency
• 17:30
  of modern computers is incredible when you think
• 17:32
  about it. We'll explore the computational side
• 17:36
  of astronomy in more detail in a future episode,
• 17:40
  but for now it's enough to say this. Radio astronomy
• 17:43
  doesn't just expand what we can observe, it changes
• 17:47
  how we think about observing. The night sky isn't
• 17:51
  silent, it's alive with signals that are ancient,
• 17:55
  energetic, and constant. For most of human history,
• 17:59
  we simply didn't have the tools to detect them.
• 18:01
  But now we're listening. and what we're hearing
• 18:04
  is a universe far richer than anything we could
• 18:08
  ever see with our eyes alone. After a quick break,
• 18:29
  we'll be back to cover this week's sky and talk
• 18:31
  about a photograph from the Artemis II mission.
• 18:34
  Stay with us. Welcome back. You know, there's
• 18:50
  something about the infamous dark side of Earth
• 18:53
  image from the Artemis II mission that's had
• 18:55
  me thinking a lot about perspective. The ever
• 19:00
  -prickly internet photography community was in
• 19:03
  a tizzy last week over this image, focusing on
• 19:06
  the camera used and its settings, the lens choice,
• 19:10
  the ISO, and so on. As a photographer, these
• 19:14
  factors interested me too, but ultimately what
• 19:17
  matters is something much simpler. For the first
• 19:21
  time in a long time, we're seeing the entire
• 19:24
  Earth as a complete sphere, just hanging there
• 19:27
  in space. And here's the part that didn't really
• 19:31
  dawn on me until recently. Most astronauts never
• 19:34
  actually see that. When you're in low Earth orbit,
• 19:39
  like the crews aboard the International Space
• 19:41
  Station, you're only about 250 miles up. That
• 19:46
  sounds high, but on a planetary scale, it's nothing.
• 19:50
  From that distance, you see curvature. You see
• 19:53
  oceans, continents, weather systems, stretching
• 19:56
  across thousands of miles. But you don't see
• 20:00
  the whole Earth. You're too close. If you want
• 20:04
  to see an entire sphere, you have to be far enough
• 20:07
  away that it fits inside your field of view.
• 20:10
  This is a no -brainer. For Earth, that distance
• 20:13
  turns out to be surprisingly large. In a low
• 20:17
  orbit, Earth fills your entire frame and then
• 20:20
  some. To step back far enough to see the full
• 20:23
  disk, you need to be not hundreds of miles away,
• 20:26
  but thousands. Roughly speaking, you need to
• 20:29
  get out to 6 ,000 miles or more before the entire
• 20:33
  Earth can comfortably fit into view as a complete
• 20:36
  circle. And that's exactly what the Artemis mission
• 20:40
  did. They headed out toward the moon, tens of
• 20:44
  thousands of miles away, finally giving us the
• 20:47
  distance needed to see our planet as a whole.
• 20:50
  When you're close, Earth feels endless. It fills
• 20:54
  your vision. It's where you are. But when you
• 20:57
  step back far enough, it becomes something else
• 21:00
  entirely, a finite object, a sphere of oceans,
• 21:05
  clouds, and life suspended in black space. We've
• 21:09
  seen this before, of course. Images from the
• 21:12
  Apollo 17 mission, the famous blue marble, gave
• 21:16
  us that same perspective more than 50 years ago.
• 21:19
  But for a long time, that view hasn't been something
• 21:23
  we could experience in real time. The infamous
• 21:27
  pale blue dot image does something similar. It's
• 21:31
  not technically a great photo, just a blue pixel
• 21:35
  in a dark void. But it offers up something more
• 21:38
  valuable. Scale, perspective, and humility. And
• 21:43
  that's why this new image matters. Not because
• 21:46
  it was shot with a 10 year old Nikon camera.
• 21:49
  Not because it has some sensor noise or that
• 21:52
  it could have been sharper. Not because some
• 21:55
  goof on the internet thinks they could have shot
• 21:57
  it better. But because it reminds us of something
• 22:00
  easy to forget. You can't see the whole earth
• 22:04
  until you leave it. And now, let's step outside.
• 22:14
  This week offers one of the best observing windows
• 22:17
  of the month, and it comes down to one simple
• 22:20
  thing. Darkness. We're moving into a new moon
• 22:24
  on April 17th, which means for much of this week
• 22:27
  the sky will be free of bright moonlight. In
• 22:30
  fact, early in the week you'll catch a waning
• 22:33
  crescent moon just before sunrise, hanging low
• 22:36
  in the southeastern sky. It's a beautiful sight,
• 22:39
  especially if you look for Earthshine, the faint
• 22:42
  glow on the dark portion of the moon caused by
• 22:45
  sunlight reflecting off Earth. By the end of
• 22:49
  the week, the moon disappears entirely into the
• 22:52
  sun's glare, reaching new phase on the 17th.
• 22:55
  And then just a day later, on the 18th, a razor
• 22:59
  -thin, waxing crescent returns to the evening
• 23:02
  sky, only about 1 % illuminated. This is prime
• 23:07
  time for deep sky observing. April marks the
• 23:11
  heart of what astronomers often call galaxy season.
• 23:15
  With the Milky Way dipping lower in the evening
• 23:17
  sky, we're looking outward, away from the dense
• 23:21
  star fields and into the vast expanse of intergalactic
• 23:24
  space. Look toward the constellation Leo, now
• 23:29
  high in the evening sky, where you'll find the
• 23:31
  Leo triplet. three galaxies interacting with
• 23:35
  one another, appearing as faint smudges of ancient
• 23:38
  light. Nearby in Ursa Major, you'll find Messier
• 23:43
  81 and 82, two striking galaxies often seen together
• 23:48
  in the same field of view. These are not bright
• 23:51
  objects. You're seeing light that has traveled
• 23:54
  millions of years to reach your eyes. The planets
• 23:58
  are putting on a show this week, but you'll need
• 24:00
  to be an early riser to catch some of them. On
• 24:04
  the morning of April 18th, a rare alignment unfolds
• 24:07
  low on the eastern horizon. Mercury, Mars, and
• 24:12
  Saturn gather together in a tight grouping, with
• 24:15
  Neptune nearby for those with binoculars or a
• 24:18
  telescope. This planet parade will be subtle,
• 24:22
  and you'll need a clear, unobstructed horizon
• 24:24
  and a bit of patience. Venus continues to dominate
• 24:28
  the early evening sky, shining brilliantly in
• 24:31
  the west just after sunset. It's unmistakable,
• 24:35
  the brightest object in the sky after the sun
• 24:38
  and moon. Jupiter is still visible in the evening,
• 24:41
  high in the sky. And finally, while it won't
• 24:44
  peak until next week, the Lyrid meteor shower
• 24:47
  is beginning to ramp up. Active from around April
• 24:51
  16th and onward, You may catch a few early meteors
• 24:55
  streaking across the sky in the pre -dawn hours.
• 24:59
  With the moon out of the way, the conditions
• 25:01
  are ideal. The Lyrids are associated with debris
• 25:05
  from Comet Thatcher and are known for their bright
• 25:08
  meteors, fireballs, and visible smoke trails.
• 25:12
  They're expected to peak on the 22nd. That's
• 25:20
  going to do it for this week. If you found this
• 25:22
  episode interesting, please share it with a friend
• 25:25
  who might enjoy it. The easiest way to do that
• 25:28
  is by sending folks to our website, StarTrails
• 25:31
  .Show. And if you want to support the show, use
• 25:35
  the link on the site to buy me a coffee. That
• 25:37
  really helps. Be sure to follow Star Trails on
• 25:41
  Blue Sky and YouTube. Links are in the show notes.
• 25:45
  Until we meet again beneath the stars, clear
• 25:48
  skies everyone!