Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / What a Star Is (and What It Isn’t)

Transcript

What a Star Is (and What It Isn’t) · Star Trails: From Backyard Astronomy to Cosmic Wonder

0:07
Howdy Star Gazers and welcome to this episode
0:10
of Star Trails. My name is Drew and I'll be your
0:13
guide to the night sky for the week of February
0:16
the 1st through the 7th. This month we're turning
0:20
our attention to the most familiar objects in
0:23
the sky and asking why they still surprise us.
0:27
Stars are the first objects we learn to recognize.
0:31
They feel simple, steady, almost obvious, but
0:35
they aren't. Over the next few episodes, we're
0:38
going to stay with stars long enough for those
0:41
assumptions to fall apart, and see what's left
0:44
when we stop treating them as scenery. Later
0:48
in this episode, we'll cover the night sky for
0:51
this week, and we kick off the discussion of
0:53
the first three chapters of Night Watch, a book
0:56
that makes an excellent companion to this podcast.
1:00
Whether you're tuning in from the backyard or
1:02
the balcony, I'm glad you're here. So grab a
1:05
comfortable spot under the night sky and let's
1:08
get started. So I can almost hear the groans
1:13
out there. Why stars and why multiple episodes
1:17
dedicated to them? Some of you may even remember
1:21
episode 48, which was all about stars. And in
1:24
fact, it's one of the shows I recommend to new
1:27
listeners. Our discussion tonight will cover
1:30
some similar but different ground. We're going
1:33
to challenge what you think you know about these
1:35
building blocks of the universe, or at least
1:38
reframe them in a way that encourages taking
1:41
a fresh look at them. Today's show will cover
1:44
what a star is and what it isn't, and over the
1:48
next few weeks we'll dig deeper into the lives
1:51
of stars, their connections to humanity, and
1:55
their fantastic deaths. And finally, we'll break
1:58
out data, statistics, and the random number generator
2:02
to simulate the birth of half a million stars
2:05
in our own little version of the Big Bang. Stars
2:10
are anything but boring. We owe our existence
2:13
to them. After all, and I'm quoting Carl Sagan
2:17
here, we are made of star stuff. When we talk
2:21
about stars, we usually start with a definition.
2:24
A star is a ball of gas. A star is powered by
2:28
nuclear fusion. A star shines because hydrogen
2:32
is being turned into helium in its core. And
2:36
all of that is true, but it's also an oversimplification.
2:40
A star isn't an object in the way we normally
2:43
mean that word. It's more like a process. A temporary
2:48
state. A long negotiation between forces that
2:52
would very much prefer a different outcome. At
2:56
its heart, a star begins with failure. In a stellar
3:00
nursery, gravity pulls matter inward relentlessly.
3:05
Gas collapses, compresses, and heats. In most
3:09
cases, that collapse never gets far enough to
3:12
matter. Clouds fragment, disperse, or drift back
3:16
into obscurity without ever becoming anything
3:18
we'd recognize as a star. But sometimes, rarely,
3:23
that collapse doesn't happen. Pressure rises,
3:27
temperatures climb. Long before fusion ignites,
3:30
a proto -star is born. Hot, dense, glowing, not
3:34
because it's burning fuel, but because it's falling
3:37
inward. That phase can last millions of years,
3:42
with gravity doing nearly all the work. Only
3:45
when the core reaches extreme temperatures does
3:48
hydrogen fusion finally begin. At that moment,
3:52
gravity is interrupted. Outward pressure pushes
3:55
back. The collapse slows not because it's failed,
4:00
but because it's been delayed. Fusion doesn't
4:03
create a star so much as it delays the inevitable.
4:07
A star is what happens when gravity is stopped
4:11
temporarily. That balance is everything. If fusion
4:15
weakens, gravity wins. If gravity is resisted
4:20
too strongly, the star swells, sheds mass, or
4:23
destabilizes. There's no permanent state here,
4:27
only equilibrium held for a while. And that's
4:31
what a star is. And it's important to say what
4:35
a star is not. A star is not stable. We imagine
4:41
stars as eternal, fixed points in the sky, but
4:45
that stability is an illusion created by human
4:48
lifetimes. Even the longest -lived stars are
4:52
burning through finite fuel. Some burn recklessly
4:56
fast. Others sip slowly, but none escape the
5:00
clock. We often describe stellar life cycles
5:04
as neat stages, and you've probably seen diagrams
5:08
of this in books. Birth, main sequence, giant,
5:12
and eventually remnant. It's as if stars politely
5:16
queue up in advance and order. But nature doesn't
5:20
respect our diagrams. Massive stars rotate violently.
5:25
They lose material, they pulse, they interact
5:28
with companions. Some skip stages some reverse
5:33
course some collapse early many never follow
5:36
the standard path at all The life cycle we teach
5:41
is an average and most stars lives are messier
5:45
and more complicated Here's a wild fact most
5:49
stars are not alone Solitary stars like our Sun
5:54
are kind of unusual The majority of stars form
5:57
in pairs or groups, and their neighbors matter.
6:01
Companions exchange mass, distort orbits, and
6:05
alter fates. Some of the most dramatic, stellar
6:08
events we know about, certain supernova among
6:12
them, simply cannot happen unless a second star
6:15
is involved. A star's destiny is often shaped
6:19
not just by what it is, but by who it lives with.
6:23
Stars are social objects, yet we often regard
6:27
them as solitary. When a star does reach a relatively
6:32
stable phase, what we call the main sequence,
6:36
it sounds calm, ordinary, normal, but it isn't.
6:40
A star's life is that of contained violence,
6:44
internal turmoil, energy constantly trying to
6:47
shatter the grip of gravity. Inside a main sequence
6:51
star, hydrogen nuclei are constantly fusing into
6:55
helium under crushing pressure. Enormous amounts
6:59
of mass are converted directly into energy every
7:02
second. Gravity pushes inward. Fusion pushes
7:06
outward. What we experience as starlight begins
7:10
deep in the core, but it doesn't escape easily.
7:15
A photon created there doesn't travel straight
7:18
to the surface. It ricochets. It's absorbed and
7:21
re -emitted, bounced and scattered again and
7:24
again. That journey can take tens of thousands,
7:27
even millions of years. By the time that light
7:31
finally escapes into space, the conditions that
7:34
created it may no longer even exist. So a star's
7:39
glow is actually a slow leak. albeit the mechanism
7:43
that allows us to see them. Now let's talk about
7:47
color. We say stars are blue, white, yellow,
7:51
orange, or red as if color were a decoration.
7:55
But color is a diagnosis. A star's color tells
8:00
us its surface temperature. Blue stars burn hotter
8:03
and faster. Red stars burn cooler and often far
8:08
longer. or they are swollen giants nearing the
8:11
end of their balance. Human eyes are terrible
8:15
tools for measuring stellar color. In low light,
8:19
our color vision collapses. The atmosphere bends
8:22
and splits starlight. Near the horizon, stars
8:26
shimmer into rainbows. Sirius flashes blue, red,
8:30
and green, not because it's changing, but because
8:34
Earth won't hold still. Astrophotography has
8:38
trained us to expect color, but much of what
8:40
we see is interpretation layered atop reality,
8:44
calibration, enhancement, and long exposure,
8:48
revealing truths our eyes were never built to
8:51
perceive directly. The sky isn't lying, but it
8:54
isn't being entirely honest either. The same
8:58
is true for brightness. When we say a star is
9:02
bright, we're not describing the star itself.
9:04
We're describing a measurement. Astronomers use
9:08
a system called magnitude, a backward scale where
9:12
smaller numbers mean brighter objects and negative
9:15
numbers mark the brightest of all. It's an older
9:19
system refined mathematically but still rooted
9:22
in human perception. You'll often see stars categorized
9:26
by magnitude. Historically, ancient astronomers
9:30
catalogued stars down to about the sixth magnitude,
9:34
because that's where stars stop being reliably
9:37
visible to most people under natural skies. That's
9:41
why the original magnitude system ended there.
9:44
It was literally the edge of human perception.
9:47
In light -polluted skies, we might be able to
9:50
only see stars around magnitude 3. Binoculars
9:54
can draw in more light, often allowing us to
9:57
see stars at plus 9 or plus 10. Magnitude doesn't
10:02
tell us how powerful a star is, it tells us how
10:05
bright it appears from here on Earth. Brightness
10:10
is a collaboration between energy output and
10:13
distance, and we only experience the final result.
10:17
This is where our intuition really breaks down.
10:21
The stars that dominate our night sky, the ones
10:24
we learn first, the ones with names, are not
10:28
typical stars. They're either unusually luminous,
10:32
unusually close, or both. They're giants, supergiants,
10:37
or nearby standouts. These account for about
10:41
99 % of the stars we see from Earth. The vast
10:45
majority of stars in the Milky Way are nothing
10:48
like them. Most stars in our galaxy are small,
10:52
cool, dim, red dwarves. They burn slowly. They
10:56
live for trillions of years. And from Earth,
11:00
almost all of them are completely invisible.
11:03
They don't announce themselves, they don't dominate
11:06
constellations, and they don't shape mythology.
11:09
If you could somehow turn down the brightness
11:11
bias of the sky, if you could see all stars equally,
11:15
regardless of distance, The familiar patterns
11:18
we know would dissolve. The night would be flooded
11:21
with faint, unassuming points of light. Not every
11:26
collapsing object even becomes a star as we know
11:30
them. Sometimes a cloud gathers enough mass to
11:33
heat up and glow faintly, but never enough to
11:36
sustain hydrogen fusion. These objects are called
11:40
brown dwarves. They're too massive to be planets
11:43
and too small to be stars. Some briefly fuse
11:48
a heavy form of hydrogen called deuterium, buying
11:51
them a short -lived glow. Then gravity resumes
11:54
its work, and they cool and fade. Brown dwarfs
11:58
are not stars that died. They are stars that
12:02
never quite lived. You'll sometimes hear Jupiter
12:05
called a failed star. It isn't, because Jupiter
12:09
never tried to ignite. Planets form differently,
12:14
assembling piece by piece in a disk around a
12:16
young star. Jupiter would need to be more than
12:19
70 times more massive to even approach fusion.
12:24
Brown dwarves remind us that star formation is
12:28
not guaranteed. The universe produces many more
12:31
almosts than successes. Here's another strange
12:36
fact. We can't actually observe stars directly.
12:40
Every star in the night sky, except one, is an
12:44
unresolved point of light, with no surface detail,
12:48
no texture, just photons collected and interpreted.
12:53
Our sun is the only star we can truly study.
12:57
We observe it from Earth and from space. We send
13:00
probes into its atmosphere. We watch its surface
13:03
churn, flare, ripple, and erupt. Then we take
13:08
what we learn from the sun and extend it, carefully,
13:11
to every other star in the universe. Stars are
13:15
not understood individually. They are understood
13:18
statistically. The sun is our Rosetta Stone.
13:23
Stars don't exist just to shine. They exist to
13:27
transform matter. Inside stars, simple elements
13:32
are rearranged into more complex ones. And when
13:35
stars die, sometimes gently, sometimes violently,
13:39
they return that processed material to the galaxy.
13:43
Every atom heavier than hydrogen and helium owes
13:47
its existence to stars that lived and failed
13:50
long before the sun was born. Stars are not the
13:54
universe's final products. They're its workshops.
13:59
And that leads to the most important thing a
14:01
star is not. A star is not the main character
14:05
of the universe. We build our stories around
14:09
stars because we orbit one, because they light
14:12
our nights, because they're visually generous.
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But stars are temporary fixtures in a universe
14:18
that prefers darkness, cold, and emptiness. They
14:23
are brief leaks of energy in a cosmos otherwise
14:26
content to coast. And that doesn't make them
14:29
insignificant. It makes them extraordinary. And,
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we happen to live during one of those pauses,
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on a planet warmed by a single star surrounded
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by thousands more, most of which we'll never
14:43
see, all of which will eventually fail. After
15:05
a quick break we'll return with this week's Night
15:08
Sky report and I'll share my thoughts on the
15:10
first three chapters of Night Watch. Stay with
15:13
us. Welcome back. I don't know about you, but
15:29
the weather here in my area has been pretty rough
15:31
for the past week, owing to winter storms, low
15:35
temperatures, ice, and snow. I think I managed
15:39
to see the moon and some stars just one evening
15:42
in the past week. I know a lot of folks are being
15:45
impacted by winter weather right now, and many
15:48
of you are iced in like Superman in the Fortress
15:51
of Solitude. So hopefully wherever you are, you're
15:55
at least staying warm. As we look at the sky
15:58
tonight through the seventh, one of the first
16:00
things you'll notice is the full moon, the snow
16:03
moon, shining high and bright early in the week.
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The full phase occurs tonight. In much of the
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Northern Hemisphere, February is among the snowiest
16:14
months of the year, so cultures from Native American
16:17
tribes to colonial settlers use this snow moon
16:21
as kind of a natural calendar marker. It's also
16:24
been called the hungry moon, the Bear Moon, the
16:27
Ice Moon, and other names rooted in the seasons
16:31
and the challenges winter brings. This full moon
16:34
means faint deep sky objects will be washed out
16:38
early in the week. That said, bright targets
16:40
like open clusters and contrasty stellar fields
16:44
still hold up beautifully, and the moon's presence
16:47
itself becomes part of the story. An interesting
16:51
moment coming right at the start of the observation
16:53
window is the moon's close association with the
16:56
bright star Regulus in Leo. Tonight and into
17:01
the second, the moon sits near Regulus, so close
17:04
that from some parts of North America, it will
17:07
even occult Regulus on the second. Be sure to
17:11
check in with an app like Stellarium to determine
17:13
the exact time of the occultation. For instance,
17:17
at my location, the right limb of the moon will
17:20
just barely graze Regulus around 9pm on that
17:23
date. As the week progresses, the moon wanes
17:27
to gibbous, which means later nights after moonset
17:30
give cleaner views of star clusters and the subtler
17:34
features in the winter sky. Planets this week
17:37
are not the main attraction, but there are a
17:40
couple worth noting. Jupiter is still visible
17:43
in the early evening, shining brightly before
17:46
it sinks toward the west. It's past its best
17:49
opposition views, but it's still unmistakable
17:52
and makes a good anchor point in the sky. Saturn
17:55
is much fainter and lower and really requires
17:58
binoculars or a telescope to appreciate, but
18:02
it's there for patient observers. Now let's talk
18:05
about stars and clusters, especially the ones
18:08
people tend to overlook. High in the sky this
18:12
week, you'll find the faint constellation Cancer.
18:16
Cancer doesn't have any bright stars to announce
18:18
itself, but it hides two excellent clusters that
18:21
reward a slower look. The first is the Beehive
18:26
cluster, also known as Messier 44. To the naked
18:30
eye under darker skies, it appears as a soft
18:33
patch of light. In binoculars, it explodes into
18:36
dozens of stars scattered across a wide field.
18:40
This is one of those objects that feels more
18:42
natural in binoculars than in a telescope, and
18:46
it's especially satisfying once the moon has
18:49
dipped lower in the sky. Nearby is Messier 67,
18:53
a very different kind of cluster. M67 is older,
18:58
tighter, and more subdued. It doesn't jump out
19:02
at you, but once you settle in, it feels dense
19:04
and deliberate. almost like a fossil record of
19:08
an earlier generation of stars. It's an excellent
19:11
contrast to the beehive, and a reminder that
19:14
not all clusters tell the same story. If you're
19:18
willing to move your gaze a little farther south,
19:20
look toward Monoceros, the unicorn. This is one
19:24
of the most underappreciated winter constellations,
19:27
largely because it's faint and doesn't resemble
19:30
much of anything at a first glance. But Monoceros
19:33
is rich in star clusters. One standout here is
19:37
NGC 2244, the central cluster of the Rosette
19:42
region. Even if the surrounding nebula is washed
19:45
out by moonlight, the cluster itself is visible
19:48
in binoculars or a small scope as a loose grouping
19:52
of young stars. This is a great object to revisit
19:56
later in the month under darker skies, but it's
19:58
still worth finding now. Back in Orion, but away
20:03
from the famous nebula, there's a small charming
20:06
cluster called NGC 2169. Through binoculars or
20:11
a low -power telescope, its stars form a pattern
20:14
that looks like the number 37. It's subtle and
20:18
a little whimsical. This is also a good week
20:21
to simply wander star fields, spend some time
20:24
around Procyon and Canis Minor, or scan the regions
20:28
between Orion and Gemini. These areas don't have
20:32
marquee objects, but they're full of subtle patterns,
20:36
faint companions, and gentle color contrasts
20:39
that are easy to miss when you're always chasing
20:41
famous targets. Because the moon is bright early
20:44
in the week, think about timing rather than fighting
20:47
conditions. Step outside before moonrise or stay
20:51
out after it sets. Use binoculars, let your eyes
20:55
adapt, and don't rush. It's finally time to discuss
21:05
our first book club selection, Night Watch, by
21:09
Terence Dickinson. I chose this book because
21:12
it's often recommended as a good starting point
21:15
for beginner stargazers. That doesn't mean seasoned
21:18
observers can't enjoy it. Every time I open it,
21:22
I learn something new, and I've mentioned it
21:24
before, but this book could be an accompanying
21:27
text for this podcast because it's really aimed
21:29
at backyard binocular observers. Before we go
21:33
any further, it's worth talking briefly about
21:36
editions, because Nightwatch has been updated
21:39
several times over the years, and you may not
21:43
all be reading the same one. I'm personally working
21:47
from the 4th edition, which technically only
21:49
carries star charts through 2025. That's still
21:54
completely fine for what we're doing here. The
21:57
fundamentals haven't changed, the sky hasn't
21:59
rearranged itself, and everything in these early
22:02
chapters remains solid and relevant. There is
22:06
a new fifth edition, and if you're using that
22:09
one, you'll notice a few meaningful upgrades.
22:12
The photography throughout the book is more modern,
22:15
with newer astrophotography replacing some of
22:18
the older images, many of which, in earlier editions,
22:21
were taken by Dickinson himself, and definitely
22:24
show their age. The fifth edition also expands
22:27
coverage of the southern sky, which is valuable
22:30
in general, even if we don't spend much time
22:33
there on this podcast. There's also more material
22:36
related to modern observing and imaging techniques,
22:40
including astrophotography. That said, for our
22:44
purposes, especially these opening chapters focused
22:47
on orientation, scale, and backyard observing,
22:51
the fourth and fifth editions are philosophically
22:53
identical. The words still land the same, the
22:57
guidance still works, and the sky they describe
23:00
is the same one above your head tonight. So if
23:03
you've got the fifth edition, great. If you're
23:06
working from the fourth, don't worry, you're
23:08
not behind and you're not missing anything essential
23:11
for this discussion. This opening chapter, Discovering
23:15
the Cosmos, is brief, but it's doing something
23:17
important. Dickinson makes it very clear that
23:21
astronomy doesn't begin with equations or equipment.
23:24
It begins with attention. He frames astronomy
23:27
as something you can do with your eyes alone,
23:30
then gradually expands that to binoculars and
23:33
telescopes without ever making the naked eye
23:36
feel like a lesser option. One line of thinking
23:39
that really resonated with me is his idea that
23:42
we're all celestial tourists, and just like traveling
23:46
somewhere new on Earth, the experience gets richer
23:49
when you understand a little about where you
23:51
are and what you're looking at. You don't need
23:54
to be an expert, but knowing the lay of the land
23:57
changes everything. That philosophy should feel
24:00
very familiar to listeners of this podcast. The
24:04
goal isn't to pile on jargon or technical baggage.
24:07
It's to untangle it just enough so the sky starts
24:11
feeling accessible. If Chapter 1 is an invitation,
24:16
Chapter 2 is perspective therapy. This chapter,
24:20
The Universe in Eleven Steps, walks outward from
24:24
Earth in steps, each one expanding the scale
24:27
by factors of a hundred, until you're suddenly
24:30
dealing with distances and sizes that stop making
24:33
intuitive sense. And that's the point. Dickinson
24:37
is taking an honest look at the problem of scale
24:40
in our universe and how to begin to comprehend
24:43
its vastness. What really stands out here is
24:47
how visual this chapter is. Even if you're familiar
24:50
with the structure of the solar system, the Milky
24:52
Way, and beyond, seeing it laid out this way
24:56
reminds you just how strange our situation is.
24:59
We're not at the center of anything. We're not
25:02
special in location. We're riding along in a
25:06
galaxy that's one among billions. By the time
25:10
this chapter ends, you have a much better sense
25:12
of where the night sky fits into the larger universe.
25:16
Now, this is where Night Watch really starts
25:19
to feel like a companion to this podcast. Chapter
25:23
3, Backyard Astronomy, is densely packed, but
25:27
it's written with a light touch. It covers how
25:30
the sky moves, while stars appear to rotate around
25:34
Polaris. and how Earth's rotation creates that
25:38
slow celestial swirl we talked about earlier
25:41
this year on the show. One of my favorite sections
25:45
is Dickinson's discussion of measuring the sky
25:48
using your hands, how a fist held at arm's length
25:52
spans about 10 degrees, and how your fingers
25:56
can become a built -in ruler. This is such a
25:59
simple idea, but it's incredibly empowering once
26:02
you start using it. Suddenly, the sky feels measurable,
26:06
navigable, and less abstract. He also does a
26:10
nice job showing how familiar constellations
26:13
act as signposts. Using the Big Dipper to find
26:16
stars like Arcturus, Vega, Deneb, and Regulus
26:21
turns the sky into a map instead of a guessing
26:24
game. There's also a subtle but important discussion
26:28
of star brightness that ties directly into something
26:31
we talked about earlier in this episode. Most
26:34
of the stars we can see from Earth are not typical
26:37
stars. They're larger and more luminous than
26:40
our Sun, and yet the Sun itself is brighter and
26:44
larger than more than 90 % of the stars in the
26:48
Milky Way. This chapter also introduces constellations,
26:52
explains why they're named the way they are,
26:55
and even includes a pronunciation guide, and
26:58
I'll admit, that was humbling. There are a few
27:01
names in here that I've been confidently mispronouncing
27:04
for years. Finally, Dickinson touches on the
27:08
stuff that moves, such as satellites, rocket
27:11
bodies, and space stations, and reminds us that
27:15
not everything crossing the sky is ancient or
27:17
distant. Some of it is very much ours. What I
27:21
appreciate most about these opening chapters
27:24
is they don't assume you're starting from zero,
27:26
but they're easy to understand even if you are.
27:30
I also want to take a moment to say something
27:32
in defense of books themselves. Like many of
27:36
you, I tend to read books on a device these days,
27:39
like a Kindle. Nightwatch is not available as
27:43
a download, and that's not a bad thing. Astronomy
27:47
is a field that moves quickly in some ways and
27:50
incredibly slow in others, and books like Night
27:53
Watch sit right at that intersection. The technology
27:57
changes, the photography improves, the charts
28:00
get updated, but the sky doesn't reinvent itself
28:03
every year. There's something uniquely valuable
28:07
about a well -designed astronomy book. It invites
28:11
you to slow down, flip a few pages, and let ideas
28:15
settle. That's why Nightwatch feels like such
28:18
a natural fit for this show. It's trying to teach
28:22
you how to look, how to think, and how to stay
28:25
curious. It's exactly the right tool for the
28:29
kind of astronomy we're practicing here. We'll
28:32
discuss the next two chapters two weeks from
28:35
now. Chapter four is all about stars, which aligns
28:39
nicely with this month's theme. Chapter five
28:43
is a discussion about stargazing equipment. and
28:46
includes an honest and eye -opening discussion
28:49
about the nature of telescopes. I think you'll
28:52
enjoy both sections. Also, the Nightwatch website,
28:57
nightwatchbook .com, contains additional content
29:01
such as videos and links to online resources
29:04
that complement the book. Check that out if you
29:07
get a chance. And I don't have any homework to
29:10
give out or anything, but if you want to share
29:13
your thoughts on the book, Feel free to send
29:15
me a note via the show website. That's going
29:21
to do it for this week. If you found this episode
29:23
interesting, please share it with a friend who
29:26
might enjoy it. The easiest way to do that is
29:29
by sending folks to our website, StarTrails .Show.
29:34
And if you want to support the show, use the
29:36
link on the site to buy me a coffee. That really
29:39
helps. Be sure to follow Star Trails on Blue
29:43
Sky and YouTube. Links are in the show notes.
29:47
Until we meet again beneath the stars, clear
29:49
skies everyone.