Howdy Star Gazers 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 January
the 18th through the 24th. This week we'll continue
in our series aimed at new astronomers by exploring
how the universe moves, it's stranger than you
think, and we'll cover everything from the backward
motion of planets to the wobble that lets us
glimpse a bit of the far side of the moon from
time to time. Later in the show we'll take a
look at what you can expect to see in the night
sky this week, and we'll officially kick off
our Star Trails book club. 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. Step outside
on a clear night. Let the air settle. No wind,
no sound, no sense of movement at all. You're
standing perfectly still. But you're not. Because
right now, at this second, You're moving at about
a thousand miles per hour, because Earth is spinning.
If you're anywhere near the equator, you're riding
the fastest part of that spin. At the same time,
Earth is racing around the sun at roughly 67
,000 miles per hour. That's one full orbit every
year. An enormous curve traced through space
that you never feel. And the sun itself, the
anchor of our entire solar system, is orbiting
the center of the Milky Way at around half a
million miles per hour, carrying Earth, the moon,
and every planet along for the ride. And even
that isn't the end of it. The Milky Way itself
is moving through intergalactic space at well
over a million miles per hour, drawn by the gravity
of nearby galaxy groups. So, depending on how
you measure it, you can easily say you're moving
at more than a million miles per hour. You're
making Formula One champions like Lewis Hamilton
and Max Verstappen look slow, just by standing
still. Of course, it's all relative, because
everything in the universe is moving. The universe
doesn't feel fast, but it is. And once you understand
that, the movement of the night sky starts to
make a lot more sense. So let's start with the
motion you can actually see. Over the course
of an evening, stars rise in the east, arc across
the sky, and set in the west. Orion climbs higher.
Sirius flashes near the horizon. Everything seems
to drift westward together. That isn't the sky
moving, it's the earth turning. We're standing
on a rotating planet, and the sky is fixed far
beyond us. As Earth spins, our view changes.
If you sit outside long enough, you can actually
feel this motion intellectually. The stars aren't
sliding across the sky. You're being carried
beneath them. This is the most immediate motion
of the universe, and it's the one backyard astronomers
learn first. It's also the reason time matters
when you observe. Where something is at 8 p .m.
is not where it will be at midnight. We say this
frequently, the sky is a clock and it never stops
ticking. While the motion of the stars may seem
imperceptible at a glance, if you've ever used
a telescope, you've seen the motion firsthand.
While you're magnifying the view of a planet,
such as Jupiter, you're also magnifying the motion
of the sky. If you're using a telescope without
a motor drive, you've no doubt been frustrated
as you've watched your target planet speed out
of view, forcing you to reframe it. Even the
light from stars has to account for our motion.
As Earth moves through space, the direction starlight
appears to come from is shifted ever so slightly
in the direction we're traveling. This effect
is called aberration of starlight, and it's subtle,
only a tiny fraction of a degree. A useful way
to imagine it is walking through rain. Even if
the rain is falling straight down, you tilt your
umbrella forward because you are moving. Starlight
works the same way. The stars aren't changing
position, but because Earth is racing along its
orbit, the light reaches us at a slight angle.
What's remarkable is that this effect was measured
centuries ago, long before spacecraft or satellites.
Astronomers noticed that star positions shifted
in a way that could only be explained if Earth
was moving through space. In other words, the
sky isn't just telling us where things are, it's
quietly revealing how fast we're going. If Earth's
rotation explains the nightly motion, the moon
introduces complication. The moon doesn't rise
at the same time each night. It shifts eastward
by about 13 degrees every day, which means it
rises roughly 50 minutes later from one night
to the next. That's why it sometimes appears
in the evening sky, sometimes after midnight,
and sometimes not at all. Its phases are orbital
geometry. As the moon orbits Earth, we see different
portions of its sunlit half. That slow, steady
orbit shapes the rhythm of the month. And the
moon's orbit isn't perfectly circular. When a
full moon happens near its closest point to Earth,
it appears slightly larger and brighter. A so
-called supermoon. When it's farther away, it
looks smaller and dimmer, and we call that a
micro moon. One of the most common things people
hear about the moon is that we always see the
same face, as if the moon has chosen a side and
stubbornly refuses to turn around. But what's
actually happening is subtler and more elegant.
The moon does rotate, it just rotates at exactly
the same rate that it orbits Earth. This is called
tidal locking, and it's the result of gravity
acting over enormous stretches of time. Early
in its history, the moon likely spun faster.
Earth's gravity raised tides in the moon's interior,
not ocean tides, but solid body distortions.
Those tidal bulges created friction, and friction
drains energy. Over millions of years, that process
slowed the Moon's rotation until it reached a
stable state, one rotation for every orbit. The
result is synchronization. As the Moon goes once
around Earth, it turns once on its axis. From
our point of view, that means the same hemisphere
always faces us. And it's worth pausing on a
detail that often gets missed. Tidal locking
doesn't mean the moon doesn't spin. If it didn't
rotate at all, we would see every side over the
course of a month. The fact that we don't is
proof that it's rotating perfectly in step with
its orbit. Even then, the story isn't perfectly
tidy. Because the moon's orbit is slightly elliptical
and tilted, its rotation speed doesn't match
its orbital speed exactly at every point. That
mismatch produces Libration, a gentle rocking
that lets us glimpse a little beyond the Moon's
edge over time. That's why across months we can
see about 59 % of the Moon's surface, rather
than the 50 you might expect. So the Moon keeps
one face towards Earth, not because it's frozen
in place, but because it's locked in a gravitational
rhythm. rotating, orbiting, and wobbling just
enough to remind careful observers that even
the most familiar object in the night sky is
still very much in motion. Now let's zoom out.
Over weeks and months the entire night sky changes.
Orion dominates winter evenings, but by late
spring it slips away. Summer constellations take
its place. By autumn, the sky feels unfamiliar
again. The stars aren't leaving. We are. As Earth
orbits the sun, our nighttime view points in
different directions at different times of the
year. The stars behind the sun in July are not
the same stars behind it in January. Seasonal
skies are a consequence of perspective, not disappearance.
And once you see that pattern, the night sky
stops feeling like a puzzle and starts feeling
like a landscape. Some of the oddest behaviors
come from relative motion. Planets, for example,
usually drift eastward against the background
stars. But every so often, they slow down, stop,
and move backward for a time. This retrograde
motion baffled astronomers for centuries. The
planets aren't reversing course, we're just passing
them. Earth moves faster on an inner track, like
a car overtaking another on a highway. From our
moving viewpoint, the slower planet appears to
loop backward briefly before resuming its usual
direction. It's simply a matter of perspective.
Up until now, everything we've talked about happens
on human time scales. Hours, days, months, and
years. But the universe has slower motions too,
much slower. Earth's axis isn't fixed. It wobbles,
tracing a slow circle over about 26 ,000 years.
This motion, called precession, means the identity
of the North Star changes over time. Polaris
is only temporarily special. In the distant past,
other stars marked North. In the far future,
different ones will again. Even Earth's axial
wobble isn't perfectly smooth. On top of long
-term precession is a smaller motion called nutation,
a subtle nodding and jittering of Earth's axis
caused mostly by the Moon's changing gravitational
pull. As the Moon's orbit tilts and shifts, Earth
responds with a gentle shimmy layered over its
larger wobble. The key idea here is Earth doesn't
move in idealized curves, and it never has. Even
the Sun isn't standing still. Earth doesn't orbit
a perfectly fixed Sun. Instead, both Earth and
the Sun orbit a shared center of mass called
a barycenter, a point in space determined by
their combined gravity. Most of the time, that
point lies just outside the sun's surface, but
it shifts constantly as planets move. Add in
massive worlds like Jupiter and Saturn, and the
sun begins to wobble, subtly but measurably.
This means the solar system doesn't revolve around
a motionless center. Everything is responding
to everything else. All the stars we see are
also moving. They orbit the galaxy. drift relative
to one another, and slowly change position against
the background sky. This is called proper motion,
and while it's almost invisible over a single
lifetime, it becomes obvious across centuries
and millennia. If you want proof that stars themselves
are moving and not just in some abstract, academic
way, There's a quiet little red star in the constellation
Ophiuchus that tells the story better than any
diagram. It's called Bernard's star, and it holds
a remarkable record. It has the fastest known
proper motion of any star in the night sky. Bernard's
star drifts across the sky at about 10 arc seconds
per year. That doesn't sound like much, and visually
it isn't. But over a human lifetime, its position
shifts enough to be measured easily with modest
equipment. Over a few centuries, it noticeably
changes where it sits relative to neighboring
stars. Given enough time, it will wander completely
out of the familiar star patterns we use today.
What makes this especially striking is why it's
happening. Bernard's star isn't unusually fast
in an absolute sense, it's just close, only about
six light years away. Its proximity makes its
motion obvious. The stars are not fixed points,
they're travelers, and we're watching them in
the middle of their journeys. Constellations
feel eternal, but they aren't. They're temporary
patterns, snapshots taken during a brief moment
when star motions happen to line up in a familiar
way. The sky we know is not the sky our distant
descendants will see. All of this motion, spins,
orbits, wobbles, drifts, can feel overwhelming
when you list it out, but here's the quiet truth
at the center of it all. The sky looks stable
because we're moving with it. We share Earth's
rotation. We share the Sun's galactic orbit.
We share our local neighborhood of stars. And
even at the largest scales, motion never disappears.
The Milky Way is not a rigid disk frozen in space.
It flexes and stretches under the gravitational
influence of nearby galaxies. especially the
Andromeda galaxy, which is slowly approaching
us. These galactic tides gently reshape stellar
orbits over hundreds of millions of years. The
same gravity that raises tides on Earth and locks
the moon to our planet also sculpts galaxies.
There's one last wrinkle in this motion. When
you look at the sky, you're never seeing things
as they are right now. Moonlight is about one
second old. Sunlight left eight minutes ago.
The stars of Orion shine from hundreds or thousands
of years in the past. So all the motion we're
talking about, you're watching it slightly delayed,
stitched together from different moments in time.
Astronomy isn't just the study of where things
are, it's the study of where things were and
how their motion reaches us across distance.
The night sky isn't still, and once you understand
that, every observation starts to feel less like
confusion and more like choreography. After a
quick break, we'll return with this week's night
sky report and the first reading assignment for
our book club. Stay with us. Welcome back! Tonight
and over the coming week, a nearly absent moon
will make for some of the best dark sky observing
many of us get all winter. We reach New Moon
tonight, which means the moon will be nearly
invisible in the sky for several evenings around
this date. With virtually no lunar glow to wash
out faint objects, this is an ideal time to explore
galaxies, nebula, and star clusters with binoculars
or a telescope. With the moon out of the way
early in the week, the planet Jupiter continues
to dominate the night sky. Earlier in January,
Jupiter reached opposition, meaning Earth passed
directly between it and the Sun, and it will
remain bright and prominent through late January.
The gas giant rises around sunset and stays visible
all night. Climbing into the south and shining
is one of the brightest objects in the sky. Even
small telescopes and good binoculars can reveal
its four largest moons, and under stable seeing,
hints of cloud bands on its disk. Not far behind
Jupiter in the evening sky is Saturn, visible
after sunset in the southwest. Through a small
telescope, Saturn's rings continue to be a delightful
sight, though it will be lower in the sky than
Jupiter. On January 23, an attractive pairing
awaits observers. The thin, waxing crescent moon
will appear close to Saturn and Neptune in the
western sky after sunset. Saturn is, of course,
bright enough to see with the unaided eye, and
Neptune, much fainter, can be pulled out with
binoculars or a telescope if you know where to
look. An app like Stellarium can help you locate
it precisely. This grouping makes a nice target
for early evening observation as the moon's crescent
returns. This week also offers the chance to
revisit some deep sky favorites. The Beehive
Cluster in Cancer is well placed in the eastern
sky after dusk. This open cluster, also cataloged
as Messier 44, is a beautiful sight in binoculars
or a wide field telescope. appearing as a misty
patch of dozens of stars. Also this week, if
you're using telescopes with tracking or a good
star chart, you can enjoy fainter wanderers.
Uranus remains a binocular object tucked near
the Pleiades cluster, and Neptune will be easier
to spot during the Moon -Saturn close approach
on the 23rd, though both require optical aid
and some patience. Finally, take a moment to
step back from specific targets and enjoy the
winter Milky Way sprawling across the sky from
Orion through Gemini and into Auriga and Perseus.
With few nights this dark all month, the winter
constellations and the rich patches of interstellar
dust and star -birth regions around them are
especially satisfying even through binoculars.
That's a snapshot of what's up this week. Bundle
up, step outside early in the evening, and let
your eyes adjust. The dark skies this week are
a gift. Okay folks, the Star Trails book club
is finally happening. If you want to follow along,
you're going to need a copy of Night Watch by
Terrence Dickinson. Make sure you get the 5th
edition for the most up -to -date information,
although I'm reading the 4th edition, which is
accurate to 2025. I don't think the stars on
the included charts will have moved that much
to make a difference. In our first show in February,
two weeks from now, I'm going to talk about my
favorite portions of the first three chapters.
Chapter 1, Discovering the Cosmos, is a broad
survey of the goals of the book. Chapter 2, The
Universe in 11 Steps, sets up a fascinating discussion
on the scale of the universe. And Chapter 3,
Backyard Astronomy, really matches up well with
the Star Trails philosophy, and it's full of
useful tips for navigating the sky. I'll offer
up my thoughts in more detail on these sections,
and if you've read Nightwatch, I'd love to hear
your reflections also. Feel free to comment over
at StarTrails .Show. 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. It 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!