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A Postcard to the Cosmos: Recreating the Arecibo Signal · Star Trails: From Backyard Astronomy to Cosmic Wonder

• 0:07
  Howdy stargazers and welcome to Star Trails.
• 0:10
  I'm Drew and I'll be your guide to the night
• 0:13
  sky for the week of November the 2nd through
• 0:15
  the 8th. This week we're talking about messages,
• 0:19
  the kind we send across the cosmos and the ones
• 0:22
  written in starlight. I'll share a quick observation
• 0:26
  report before we dive into what's happening overhead
• 0:28
  this week. Then in the second half of the show,
• 0:32
  we'll turn our gaze from the backyard to deep
• 0:35
  space to revisit the Arecibo message, the radio
• 0:39
  signal humanity beamed toward the stars more
• 0:42
  than 50 years ago. We'll break down what it said,
• 0:45
  how it worked, and whether anyone, human or otherwise,
• 0:49
  could ever decode it. Before we get into this
• 0:53
  week's night sky, I'd like to take a moment to
• 0:55
  report on the star party I attended last week.
• 0:59
  Last Saturday, my local club was holding their
• 1:02
  fall cookout at their dark sky site about an
• 1:05
  hour north of where I live. This year, I had
• 1:09
  high hopes to get in some serious stargazing.
• 1:12
  In particular, I wanted to get eyes on comet
• 1:14
  A6 Lemon and maybe even photograph it. We'd had
• 1:19
  cooler weather and clear blue skies all week,
• 1:22
  but as I made my way to the site Saturday afternoon,
• 1:26
  I noticed some ominous haze on the horizon and
• 1:29
  high -altitude clouds moving in. Just before
• 1:32
  6 p .m., I was welcomed by club president and
• 1:35
  friend of the podcast, Mike Roberts, occupying
• 1:39
  his important position at the grill. If nothing
• 1:42
  else, we'd have a good meal. And it turns out
• 1:45
  that may have been the highlight of the night.
• 1:48
  Just before 7 p .m. in the fading twilight, I
• 1:51
  scanned the sky for lemon with my 11 by 70 binoculars.
• 1:56
  Some low -lying clouds finally drifted away and
• 1:59
  the comet emerged in my field of view, resembling
• 2:02
  a small, very dim, hazy snowball. In the binoculars,
• 2:08
  I could detect a hint of a tail. If I hadn't
• 2:11
  been looking for it, I could have easily swept
• 2:13
  right past it. The only thing that gave it away
• 2:16
  was that it looked soft and fuzzy against the
• 2:19
  neighboring in focus stars. Having spotted lemon,
• 2:23
  I decided to try for a photo. Since I only had
• 2:26
  my camera and some normal lenses, it would have
• 2:29
  to be a wide field shot. At 70mm on a full frame
• 2:34
  camera, it was woefully small, but the coma and
• 2:37
  tail were visible enough. I stepped up to 200mm,
• 2:42
  and the results weren't much better on single
• 2:44
  exposure shots, so I won't be showing these off
• 2:48
  anywhere. By then, the clouds were rolling in
• 2:52
  around that portion of the sky, so I aimed higher,
• 2:55
  catching the Andromeda galaxy in binoculars,
• 2:59
  another fuzzy blob at this magnification. The
• 3:02
  Milky Way's dim river of light was crossing directly
• 3:06
  overhead, with Cygnus the Swan gliding along
• 3:09
  its path. We spotted numerous satellites drifting
• 3:14
  by, all of them starlings, of course. After about
• 3:18
  an hour, the atmospheric haze seemed to multiply
• 3:21
  and the sky was looking gray rather than black.
• 3:25
  The seeing tanked, so I packed up and headed
• 3:27
  home. Sometimes, it seems like these star parties
• 3:31
  are cursed, and then there are nights when the
• 3:34
  sky is so clear the stars seem to hover just
• 3:37
  feet above us. If nothing else, there's food,
• 3:40
  camaraderie, and an array of scopes to check
• 3:43
  out. If you've ever wondered what a star party
• 3:46
  is like, go back and listen to episode 41, where
• 3:50
  I combined the sights and sounds of a party into
• 3:53
  an immersive first -person report. This week
• 4:03
  the moon takes center stage. It begins the week
• 4:06
  as a waxing gibbous, bright and nearly full,
• 4:09
  and reaches its full phase on Wednesday, also
• 4:12
  known as the beaver moon. This one's also a super
• 4:16
  moon, appearing a touch larger and brighter than
• 4:19
  usual, as it makes one of its closest approaches
• 4:22
  to Earth this year. After that, the moon begins
• 4:25
  to wane, spending the weekend as a waning gibbous
• 4:28
  rising later each night. The moon will light
• 4:31
  up the sky all week, so it's not the best time
• 4:34
  for chasing faint nebula or galaxies. But if
• 4:37
  you're into lunar photography or moonlit landscapes,
• 4:41
  these bright nights are perfect. That high -contrast
• 4:44
  autumn air makes craters, mountains, and maria
• 4:48
  pop beautifully through binoculars or even a
• 4:51
  small telescope. As for the planets, Saturn hangs
• 4:55
  low in the southeastern sky just after sunset,
• 4:59
  shining with a steady golden light. It drifts
• 5:02
  southward throughout the evening, setting before
• 5:05
  midnight. Jupiter rises later in the night and
• 5:08
  commands the morning sky. You'll find it high
• 5:11
  in the east -southeast before dawn, bright and
• 5:15
  unmistakable. Through a telescope, its cloud
• 5:18
  bands and the four Galilean moons are always
• 5:21
  worth a look. Venus joins the morning show as
• 5:25
  well, the bright morning star gleaming low in
• 5:28
  the east before sunrise. It's slowly sinking
• 5:32
  toward the sun as November goes on, so catch
• 5:35
  it early while it's still prominent. Mercury
• 5:39
  is hiding too close to the sun this week and
• 5:42
  Mars remains faint and distant, but both will
• 5:45
  become more interesting later this year. The
• 5:48
  autumn zodiac still dominates the evening. Pisces,
• 5:52
  Aries, and Taurus spread out across the southern
• 5:55
  sky, while the great winter constellations are
• 5:59
  just starting to rise. If you stay up late, look
• 6:02
  towards the east and you'll see Orion beginning
• 6:05
  to climb above the horizon, a reassuring sign
• 6:08
  that the bright winter sky is around the corner.
• 6:13
  Coming up, we revisit the Arecibo signal, the
• 6:16
  message fired into space more than 50 years ago
• 6:19
  as a greeting to intelligent life. We'll take
• 6:23
  a look at the format of the message and investigate
• 6:26
  if an alien species could even figure out how
• 6:29
  to decode the message if they received it. To
• 6:32
  find out, we're going to generate our own version
• 6:35
  of the message and build our own decoder. That's
• 6:39
  after the break. Stay with us. Welcome back.
• 6:56
  In our last show, we examined the idea of the
• 6:59
  Fermi paradox, the idea that in a universe so
• 7:03
  vast, how is it possible we haven't communicated
• 7:07
  with any other species? And if you heard the
• 7:10
  episode, you might recall that we spent some
• 7:12
  time describing one of humankind's attempts to
• 7:16
  reach out to extraterrestrial life. Of course,
• 7:20
  I'm talking about the Arecibo message. a burst
• 7:23
  of binary code sent from Earth in 1974. It lasted
• 7:28
  just under three minutes, and though it was meant
• 7:31
  for ETs, I've often wondered if anyone could
• 7:34
  actually decode it if they received it. That's
• 7:38
  the subject of this half of the show. We're going
• 7:42
  to take the original binary message intended
• 7:45
  for the stars and turn it into audio. Then we're
• 7:48
  going to decode that audio in a modern way and
• 7:52
  see if we can reproduce the Arecibo signal the
• 7:54
  way in which it was intended to be seen. We may
• 7:58
  get into the weeds with some jargon along the
• 8:00
  way, but I promise I'll try and make it make
• 8:03
  sense. First, let's set the scene. The story
• 8:08
  begins at the Arecibo Observatory in Puerto Rico.
• 8:11
  It's November the 16th, 1974, and the telescope
• 8:16
  has just undergone a major upgrade. To celebrate,
• 8:21
  scientists Frank Drake and Carl Sagan wanted
• 8:24
  to do something audacious. So they decided to
• 8:27
  send a message to the stars. Arecibo was the
• 8:32
  most powerful radio telescope on Earth at that
• 8:35
  time. A 305 meter dish carved into a limestone
• 8:40
  valley. It could transmit a million watts at
• 8:44
  2380 megahertz, a frequency in the S band far
• 8:50
  above radio frequencies we generally listen to.
• 8:54
  To send a message into space, the team at Arecibo
• 8:58
  used a technique called phase modulation, essentially
• 9:02
  flipping the phase or rhythm of a radio wave
• 9:05
  back and forth to represent the ones and zeros
• 9:08
  of a binary message. We didn't transmit audio
• 9:13
  or spoken words into space, just pure data, and
• 9:18
  at that time it was the most powerful signal
• 9:21
  to leave Earth. The signal's final destination
• 9:25
  is the globular cluster M13 in the constellation
• 9:28
  Hercules, 25 ,000 light years away. M13 was selected
• 9:35
  because it was in the sky when the signal was
• 9:37
  scheduled to be sent. Crafted by Drake and Sagan,
• 9:42
  the message was a postcard to the cosmos that
• 9:44
  said, we're here. When decoded, the signal reveals
• 9:49
  quite a bit of information about the human experience,
• 9:53
  our science, our genetic makeup, where we are
• 9:56
  in the universe, and even more. But could anyone
• 9:59
  figure out how to convert the signal to meaningful
• 10:02
  data? To try and answer that question, let's
• 10:06
  look at what it takes to create such a signal
• 10:09
  and how we can use some relatively simple tools
• 10:12
  to crack the code. We'll start the investigation
• 10:16
  by learning a little more about the signal and
• 10:18
  its structure because the key to unraveling it
• 10:21
  lies in simple math. The message itself was exactly
• 10:25
  1679 bits long. When we refer to a bit, we're
• 10:31
  talking about a single on or off state, or in
• 10:35
  this case, a one or a zero binary. The number
• 10:40
  of bits in the message 1 ,679 was not chosen
• 10:45
  at random. It's the result of multiplying two
• 10:49
  prime numbers, 23 and 73, and that's the first
• 10:54
  key to unlocking the puzzle. If you arrange the
• 10:58
  sequence of 1s and 0s into a tall rectangle,
• 11:02
  23 columns across and 73 rows down, a picture
• 11:06
  emerges. The 0s represent a space, the 1s represent
• 11:11
  a graphical block. You could even use a spreadsheet
• 11:15
  or graph paper and plot the 1s and 0s into a
• 11:18
  23 by 73 grid and see the familiar pattern of
• 11:22
  the signal emerge. Any other combination results
• 11:26
  in a muddled message. Now let's break down the
• 11:30
  resulting image or pictograph from top to bottom.
• 11:34
  You've probably seen it in science books since
• 11:37
  the late 1970s. The sequence starts with a representation
• 11:42
  of the numbers 1 through 10 written in binary.
• 11:46
  Below that, the atomic numbers of hydrogen, carbon,
• 11:50
  nitrogen, oxygen, and phosphorus, the elements
• 11:53
  that form DNA. Then a diagram of DNA's double
• 11:59
  helix, with a number showing how many base pairs
• 12:02
  it contains. In the center, a little stick figure
• 12:06
  of a human next to a bar showing our height and
• 12:09
  a number indicating Earth's population in 1974.
• 12:14
  It was about four billion people. Beneath that,
• 12:18
  a row of nine dots representing the planets of
• 12:21
  our solar system, with the third one offset.
• 12:24
  That's Earth. And yep, Pluto was still considered
• 12:28
  a planet back then. Finally, at the bottom, there's
• 12:32
  a representation of the Arecibo telescope itself,
• 12:35
  with a coded version of its diameter. The signal
• 12:39
  was designed to be so universal that it didn't
• 12:42
  require spoken language to read it, just logic
• 12:45
  and math. If you've ever read or seen the movie
• 12:49
  Contact, which was written by Sagan, you might
• 12:52
  recall prime numbers were also used there to
• 12:55
  decode a message from the stars. Primes are useful
• 12:59
  in this field because they're mathematically
• 13:01
  special, not likely to occur naturally as arranged
• 13:05
  signals or patterns in nature. Sagan used them
• 13:09
  as the logical bearer of meaning before words
• 13:13
  or images. Fortunately, we know this going into
• 13:16
  our experiment. To see how readable the signal
• 13:20
  really is, I decided to recreate it using modern
• 13:23
  tools. My weapon of choice is the general purpose
• 13:27
  programming language of Python. It's a language
• 13:30
  I have some experience with, and the high level
• 13:33
  nature of Python means coders have access to
• 13:36
  some really advanced functions, such as modules
• 13:40
  that do the heavy lifting of signal generation
• 13:43
  and analysis. Basically, I set out to create
• 13:47
  a software modem to modulate and demodulate the
• 13:52
  Arecibo signal. With some lines of Python, I
• 13:56
  took the original binary sequence from Wikipedia.
• 13:59
  all 1679 bits, and I mapped it to sound. I decided
• 14:06
  to use a protocol inspired by my ham radio experience,
• 14:10
  frequency shifted keying, or FSK. With this technique,
• 14:15
  I assigned specific audio frequencies to the
• 14:18
  ones and zeros. In this case, 1200 and 1800 hertz.
• 14:26
  It's essentially the same principle ham radio
• 14:29
  operators used in digital modes like radio teletype.
• 14:34
  To match the data rate of Arecibo, we're encoding
• 14:37
  at 10 bits per second, which results in a transmission
• 14:41
  of just under three minutes in length. Finally,
• 14:45
  the script outputs the binary stream as a WAV
• 14:48
  audio file that can be played on just about any
• 14:50
  device. At this point, our result is similar
• 14:55
  to the signal sent from Arecibo with a couple
• 14:58
  major differences. Since we're shifting between
• 15:01
  two audible frequencies, we've essentially sonified
• 15:05
  the raw data so that we can now hear it. Remember,
• 15:09
  the Arecibo message simply shifted the phase
• 15:12
  of a carrier wave to represent the data, so there
• 15:16
  wasn't much to actually listen to in the original
• 15:18
  transmission. For fun, I recreated the phase
• 15:22
  shifted version and it basically just sounds
• 15:25
  like one continuous tone. But to hear that tone,
• 15:29
  I had to lower the frequency by magnitudes. The
• 15:32
  Arecibo signal was sent at a frequency that is
• 15:35
  millions of times, no joke, millions, higher
• 15:39
  than what we can hear as humans. To explain it
• 15:43
  another way, for any musicians out there, check
• 15:45
  this out. To make the original Arecibo signal
• 15:49
  audible, we're reducing it in pitch by about
• 15:52
  1 .2 million octaves to bring it into the range
• 15:56
  of human hearing. As a result, our version sounds
• 16:01
  like a stream of robotic chirps and pulses. I
• 16:04
  could actually send it out into the ether with
• 16:07
  my ham radio transceiver if I wanted to, and
• 16:10
  someone could, in theory, decode it. They would
• 16:14
  need to understand the protocol, in other words,
• 16:17
  my data rate and how the data is structured once
• 16:20
  received. Essentially that 23 by 73 grid that
• 16:25
  I've mentioned. So to complete the circle, let's
• 16:31
  decode the message using another Python script
• 16:34
  and see if we can translate the audio data into
• 16:37
  the familiar visual of the Arecibo pictograph.
• 16:42
  We need to first load up the audio file for analysis,
• 16:46
  and fortunately Python contains libraries that
• 16:49
  do just that. Knowing the data rate of 10 bits
• 16:53
  per second, we segment the audio into windows
• 16:56
  of one -tenth of a second. For each window, we
• 16:59
  measure the energy of those two tones. Whichever
• 17:02
  frequency is stronger, either 1200 or 1800 Hz,
• 17:06
  becomes that bit's value, a 1 or a 0. Presumably,
• 17:12
  an alien species could analyze the message and
• 17:15
  see there is patterned information that appears
• 17:17
  in regular intervals. If you load up our wave
• 17:20
  file into an audio editor like Audacity, you
• 17:24
  can zoom into the waveforms and actually see
• 17:26
  the alternating tones. When you string these
• 17:30
  bits back together, you get the same binary sequence
• 17:34
  that left Earth in 1974. Using a graphic library
• 17:38
  in Python, we can plot the binary values into
• 17:42
  that 23 by 73 grid and pop out the resulting
• 17:46
  image as a PNG file. And there it is, the Arecibo
• 17:51
  message with its familiar DNA helix, stick figure,
• 17:55
  and radio dish perfectly recreated. If you'd
• 17:59
  like to try this for yourself, I'll make my code,
• 18:02
  WAV file, and resulting graphics available in
• 18:05
  the show notes. You'll need Python installed
• 18:08
  on whatever computer you're using. I'm using
• 18:11
  Linux, but Python runs on everything from Windows
• 18:14
  to Mac OS to systems on chip like the Raspberry
• 18:18
  Pi. So encoding and decoding the Arecibo signal
• 18:23
  is actually somewhat straightforward, but only
• 18:26
  because we already knew how it was constructed.
• 18:30
  Assuming an intelligent civilization made it
• 18:32
  this far, would they even understand what they're
• 18:35
  looking at? Can we as humans even understand
• 18:38
  it? A viewer would see the geometric shapes,
• 18:42
  stripes, dots, the stick figure of a human, but
• 18:45
  would you recognize the bar next to the human
• 18:48
  indicates its height in binary? Would you recognize
• 18:51
  that those five lines of dots are atomic numbers?
• 18:56
  Would you know the twin spirals are DNA? Even
• 19:00
  for us, the meaning only emerges because we already
• 19:03
  basically know the story. We know what DNA looks
• 19:07
  like. We know what a solar system looks like.
• 19:09
  We know what a human is. Maybe some folks even
• 19:13
  know how to convert binary to the familiar numbers
• 19:15
  of a base -10 system. An alien species wouldn't
• 19:20
  share those references. They might not even perceive
• 19:23
  visual patterns the way we do. Maybe they'd interpret
• 19:27
  the entire thing as a mathematical proof or a
• 19:30
  piece of music or a coordinate map. Or maybe
• 19:33
  they wouldn't recognize it as a message at all.
• 19:37
  The Arecibo pictograph looks self -explanatory
• 19:40
  to us because it is us, and that's the trap.
• 19:44
  It's anthropocentric. It's written in the language
• 19:48
  of human experience, dressed in the symbols of
• 19:51
  universal truth, yes or no, on or off. So imagine
• 19:57
  you're the one receiving it. an alien scientist
• 20:00
  staring at a stream of data from the sky. How
• 20:03
  would you even begin? Maybe you notice a repeating
• 20:07
  pattern of phase shifts. Okay, maybe that means
• 20:10
  it's digital. You count 1679 bits. You somehow
• 20:16
  realize that's 23 times 73, both prime numbers.
• 20:21
  You try arranging the bits. Maybe you find the
• 20:24
  right orientation and maybe not. And if you do,
• 20:27
  you're still faced with a puzzle made by a species
• 20:30
  you've never met, living on a world you've never
• 20:33
  seen, with no shared biology or shared reference
• 20:37
  frames. It's like solving a crossword puzzle
• 20:40
  in a language that doesn't exist. And maybe this
• 20:45
  works both ways. Maybe we've already received
• 20:49
  messages like this and we didn't recognize them.
• 20:52
  We've detected fleeting, unexplained radio bursts,
• 20:56
  like the famous wow signal, and fast radio bursts
• 21:00
  that repeat and vanish. Maybe those are natural,
• 21:04
  or maybe they're messages encoded in forms we
• 21:07
  can't yet decipher. SETI scientist Paul Davies
• 21:12
  once said that an alien transmission might be,
• 21:15
  quote, hidden in plain sight, a pattern so subtle
• 21:19
  we mistake it for noise. And Jill Tarter reminded
• 21:23
  us that if the universe is speaking to us, we
• 21:26
  might not recognize the language. The Arecibo
• 21:30
  message was meant to say something about who
• 21:33
  we were and what we could do. It was an act of
• 21:36
  optimism, a beacon of math and meaning beamed
• 21:40
  into the dark. Even now, more than 50 years later,
• 21:44
  that signal is still traveling outward at the
• 21:47
  speed of light, racing across the space between
• 21:50
  stars. Long after our voices fade, that signal
• 21:54
  will keep going, like a perfectly preserved artifact
• 21:58
  of curiosity and intelligence. Maybe someday
• 22:02
  someone will catch it, maybe they'll rearrange
• 22:05
  the bits and see the shape of a human, and maybe
• 22:08
  they'll wonder who we were. or maybe they'll
• 22:10
  see nothing at all. The Arecibo message was just
• 22:14
  the beginning. Since 1974, we've sent a handful
• 22:18
  of others, each one a new experiment in interstellar
• 22:21
  communication. In 1983, Japan's message to Altair
• 22:27
  carried digital greetings toward a nearby bright
• 22:29
  star. In 1999 and 2003, the Cosmic Call 1 &2
• 22:35
  projects transmitted more elaborate self -describing
• 22:39
  data sets toward multiple Sun -like stars. Later
• 22:44
  came the Teenage Message in 2001, a musical broadcast
• 22:49
  created by Russian students, and NASA's 2008
• 22:53
  Across the Universe signal, which beamed a Beatles
• 22:56
  song toward Polaris. That same year and into
• 23:10
  2009, messages such as a message from Earth and
• 23:14
  hello from Earth targeted the potentially habitable
• 23:17
  world Gliese 581c, carrying thousands of short
• 23:22
  notes from people around the globe. Each attempt
• 23:26
  has been part scientific demonstration and part
• 23:30
  act of faith. Whether these signals ever reach
• 23:33
  another mind is unknown, but together they form
• 23:36
  a faint chorus of intent. Evidence that at least
• 23:40
  once and then again and again a small species
• 23:44
  on a small planet looked up and tried to say
• 23:47
  hello to the universe. It's funny how the things
• 24:08
  we love sometimes circle back and meet each other.
• 24:13
  For me, astronomy, ham radio, and music always
• 24:17
  felt like separate pursuits. One is about the
• 24:20
  stars, one is about radio waves, and one is about
• 24:24
  sound. But when you start listening closely,
• 24:27
  you realize they're all part of the same language.
• 24:31
  I had a lot of fun making this one, but producing
• 24:34
  episodes like this requires a good bit of time
• 24:36
  and even more caffeine. If you found it interesting,
• 24:40
  please share it with a friend who might enjoy
• 24:42
  it. The easiest way to do that is by sending
• 24:45
  folks to our website, StarTrails .Show. And if
• 24:49
  you want to support the show, use the link on
• 24:52
  the site to buy me a coffee. It really helps.
• 24:55
  Be sure to follow us on Blue Sky and YouTube.
• 24:59
  Links are in the show notes. Until we meet again
• 25:02
  beneath the stars, clear skies everyone.