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