Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / Four Worlds, One Sun; Plus, a Total Lunar Eclipse

Transcript

Four Worlds, One Sun; Plus, a Total Lunar Eclipse · Star Trails: From Backyard Astronomy to Cosmic Wonder

0:07
Howdy Star Gazers and welcome to this episode
0:09
of Star Trails. My name is Drew and I'll be your
0:13
guide to the night sky for the week of March
0:15
the 1st through the 7th. Believe it or not, this
0:19
is our 100th episode and over the past few months
0:23
we've traveled far. We've talked about stars
0:26
that will outlive our species. We've wandered
0:29
through globular clusters and nebula. We've stood
0:32
at the edge of galaxies and contemplated black
0:34
holes. but this month we're coming home. Every
0:38
object we'll discuss in March is right here in
0:41
our own solar system, not light years away. These
0:46
are worlds we can see with our own eyes, and
0:49
more than that, these are worlds we have visited.
0:52
Later in the show, we'll check in with this week's
0:55
sky, which features the only total lunar eclipse
0:58
of the year, and we'll take a quick look at electric
1:01
cars in space. Whether you're tuning in from
1:04
the backyard or the balcony, I'm glad you're
1:07
here. So grab a comfortable spot under the night
1:10
sky and let's get started. This month we're taking
1:14
a closer look at our solar system. We'll start
1:17
with the inner planets and move outward. Later
1:21
in the month we'll explore some of the wildest
1:23
moons of our system, venture into the mysterious
1:26
area beyond the outer planets, and we'll take
1:29
a special detour over to Pluto, the planet that
1:33
went on trial and lost. What I love about this
1:36
month's series is that humanity has orbited,
1:40
landed on, driven across, drifted into, and photographed
1:44
every planet we'll talk about this month. That's
1:48
stunning if you stop and think about it. So this
1:51
week we begin with the inner planets, Mercury,
1:54
Venus, Earth, and Mars. Four rocky worlds with
1:59
very different outcomes. Mercury is often overlooked.
2:09
It's tiny, it hugs the Sun, it never strays far
2:12
from the horizon, and it's notoriously difficult
2:16
to observe. But Mercury played a pivotal role
2:20
in one of the greatest scientific revolutions
2:22
in history. For decades in the 19th century,
2:27
astronomers noticed something odd about Mercury's
2:30
orbit. The point of closest approach to the Sun,
2:33
its perihelion, slowly shifted over time in a
2:37
way that Newton's laws couldn't fully explain.
2:40
The discrepancy was small, just 43 arc seconds
2:44
per century. Some astronomers proposed that an
2:47
unseen planet inside Mercury's orbit was tugging
2:51
on it gravitationally. They even gave this hypothetical
2:55
world a name, Vulcan. Searches were conducted,
3:00
observations were claimed, Vulcan sightings were
3:03
reported near the Sun's glare during eclipses,
3:06
but Vulcan didn't exist. Instead, in 1915 Albert
3:11
Einstein showed that Mercury's strange orbital
3:15
precession wasn't caused by an invisible planet.
3:19
It was caused by the curvature of space -time
3:21
itself. According to general relativity, massive
3:25
objects like the Sun warp the fabric of space
3:28
-time. Mercury, being so close to the Sun, moves
3:32
through that warped geometry. Its orbit isn't
3:36
simply a Newtonian ellipse, it's an ellipse slowly
3:39
turning within curved space -time. Mercury helped
3:43
prove that gravity isn't just a force, but rather
3:47
geometry. That's an extraordinary legacy for
3:50
a little planet most people struggle to find
3:53
in the twilight. But Mercury is weird in other
3:57
ways too. A year on Mercury, that's the time
4:01
it takes to orbit the sun, is 88 Earth days.
4:04
But a single solar day, from one sunrise to the
4:08
next, lasts 176 Earth days. If you stood on Mercury's
4:14
surface, you would watch the sun rise, pause,
4:18
reverse direction slightly, then continue its
4:20
path across the sky. The planet's 3 to 2 spin
4:25
orbit resonance creates one of the strangest
4:28
day -night cycles in the solar system. And despite
4:32
being the closest planet to the Sun, Mercury
4:35
has water ice. Not oceans, of course, but water
4:39
ice trapped in permanently shadowed craters near
4:42
its poles, where sunlight never reaches. So the
4:46
hottest world in the solar system harbors ice
4:49
in eternal darkness. As for exploration, Mercury
4:53
has only been visited by a handful of spacecraft.
4:57
NASA's Mariner 10 flew by in the 1970s. Decades
5:02
later, the MESSENGER mission orbited Mercury
5:05
from 2011 to 2015, mapping its surface in detail
5:10
and confirming the presence of that polar ice.
5:14
From Mercury, we venture out to Earth's twin,
5:17
Venus. Well, maybe it's more of a fraternal twin
5:20
than identical. Venus is nearly the same size
5:24
and mass as Earth. It's a rocky world wrapped
5:27
in clouds. For much of the 20th century, science
5:31
fiction writers imagined steaming jungles beneath
5:34
those clouds, swamps, oceans, maybe even life.
5:39
Instead, Venus turned out to be something far
5:42
more unsettling. It's a runaway greenhouse world.
5:46
Its thick atmosphere is composed mostly of carbon
5:49
dioxide. with surface pressures about 90 times
5:53
that of Earth. That's like being nearly a mile
5:57
underwater. The surface temperature hovers around
6:00
900 degrees Fahrenheit, and that's hot enough
6:04
to melt lead. As for those clouds, well, they're
6:08
made of sulfuric acid. Venus has a weird orbital
6:12
quirk in that it rotates backwards. While most
6:15
planets spin in the same direction they orbit
6:18
the Sun, Venus spins retrograde. That means on
6:22
Venus the Sun rises in the West and sets in the
6:25
East. Also, it rotates extremely slowly. A single
6:30
rotation of Venus takes about 243 Earth days.
6:35
That's longer than its year, which is about 225
6:39
Earth days. If you stood on its surface, ignoring
6:42
the fact that you'd be crushed and incinerated
6:45
almost instantly, you would experience one of
6:47
the strangest celestial rhythms imaginable. And
6:52
we've been there. The Soviet Union's Venera program
6:56
achieved one of the most remarkable feats in
6:58
planetary exploration. In the 1970s and early
7:02
80s, several Venera landers successfully reached
7:06
the surface of Venus. They transmitted data,
7:09
and in some cases images, before succumbing quickly
7:13
to the heat and pressure. The images they returned
7:16
are eerie. A flat, rock -strewn landscape beneath
7:20
a yellowish sky. The light filtered and distorted
7:24
by thick atmosphere. A suffocating alien stillness.
7:29
More recently, orbiters like NASA's Magellan
7:32
mission mapped Venus using radar. since visible
7:36
light can't penetrate the cloud deck. Radar revealed
7:40
a world shaped by volcanism, vast lava plains,
7:44
pancake domes, massive shield volcanoes. We're
7:49
still not entirely sure if Venus is volcanically
7:52
active today, but there have been hints. Sulfur
7:56
dioxide fluctuations, possible thermal anomalies.
8:00
Venus may still be reshaping itself beneath those
8:03
clouds. Scientists see Venus as a cautionary
8:07
tale for Earth. Two rocky planets born from the
8:11
same solar nebula, similar in size and composition,
8:15
and yet they diverged dramatically. One became
8:19
a world of oceans and life, the other became
8:22
a greenhouse gas furnace wrapped in acid clouds.
8:26
And yet, in our twilight sky, Venus remains the
8:30
brightest planet of all. Serene and beautiful
8:33
from a distance. Now we arrive at a planet we
8:38
think we know very well, Earth. But let's do
8:41
something unusual. Let's imagine we're not standing
8:44
on it. Let's imagine we're alien astronomers
8:47
observing this small blue world from dozens of
8:51
light years away. What would we see? First, we'd
8:55
notice the color. Earth is strikingly blue because
8:58
liquid water covers about 70 % of the surface.
9:03
That water absorbs red wavelengths and scatters
9:06
blue back into space. To a distant observer,
9:10
Earth's spectrum would show strong signatures
9:12
of water vapor in the atmosphere. That alone
9:16
would be interesting. But then the alien spectroscopist
9:20
would notice something even stranger. Oxygen.
9:23
Earth's atmosphere contains about 21 % molecular
9:27
oxygen, which is highly reactive. It doesn't
9:31
like to remain free in an atmosphere for long.
9:34
It bonds, oxidizes, and disappears into rocks.
9:38
For an atmosphere to maintain that much free
9:41
oxygen, something must be replenishing it continuously.
9:45
From a purely chemical perspective, Earth's atmosphere
9:49
is in disequilibrium. An alien observer might
9:52
detect methane alongside oxygen. Those two gases
9:57
should rapidly react and cancel each other out,
10:00
yet on Earth both persist. Of course, here on
10:04
Earth we know the explanation is biology. Photosynthesis
10:08
splits water molecules and releases oxygen as
10:12
waste. Microbes, plants, forests, and plankton
10:16
are all quietly altering the chemistry of an
10:19
entire planet. Then there's the reflectivity
10:23
problem. As Earth rotates, its brightness changes.
10:27
Oceans reflect differently than continents. Cloud
10:31
cover shifts. Seasonal variations alter albedo.
10:35
Ice caps grow and shrink. An alien observer tracking
10:39
the light curve might infer continents, weather
10:43
systems, polar ice caps. They'd even detect our
10:47
moon. Earth's unusually large moon stabilizes
10:51
the planet's axial tilt. That stabilizes climate
10:55
over long periods. From afar, the gravitational
10:59
dance between Earth and Moon would reveal itself
11:03
in subtle wobbles. And then there are the unnatural
11:07
signatures. Over the past century, Earth has
11:10
begun leaking radio signals into space, television
11:14
broadcasts, radar pulses, communications. a faint
11:18
expanding shell of electromagnetic noise roughly
11:22
100 light years in radius. And Earth has begun
11:26
sending objects away from itself. We've placed
11:30
satellites in orbit. We've sent probes to other
11:33
planets. We've launched spacecraft that have
11:35
exited the solar system entirely. And while an
11:39
alien astronomer wouldn't know about our culture,
11:42
our music, literature, or lifestyles, They'd
11:46
still see spectral lines, and if they're conducting
11:49
their own search for extraterrestrial intelligence,
11:52
maybe they'd hear our radio waves. The alien
11:56
observers would certainly notice our moon. Among
12:00
the inner planets, Earth is the only one with
12:02
a truly large, gravitationally significant moon.
12:07
Mars has two small, irregular moons, Phobos and
12:11
Deimos, which are likely captured asteroids.
12:14
But Earth's moon is enormous relative to its
12:18
planet. It's about one -quarter the diameter
12:21
of Earth and more than 1 % of Earth's mass. That
12:25
might not sound like much, but in planetary terms,
12:28
it's huge. In fact, some astronomers even describe
12:32
the Earth -Moon system as a double planet. The
12:36
barycenter, the shared center of mass around
12:39
which both Earth and the moon orbit, doesn't
12:42
sit at the exact center of Earth. It lies about
12:45
1700 kilometers beneath Earth's surface. Earth
12:49
itself wobbles around this point as the moon
12:53
orbits. Earth itself also does something subtle
12:56
but important. It spins once every 24 hours.
13:01
That rapid rotation helps generate a magnetic
13:04
field through the motion of molten iron at its
13:07
core. That magnetic field shields the atmosphere
13:11
from the solar wind, preventing it from being
13:13
stripped away over billions of years. And that
13:17
brings us to Mars, the red planet that wasn't
13:20
as lucky as Earth in regards to its atmosphere.
13:24
From a distance, Mars looks almost like Earth.
13:27
It has polar caps, seasons, a 24 .6 hour day,
13:33
remarkably close to our own. A tilted axis produces
13:36
familiar rhythms of spring, summer, autumn, and
13:39
winter. Mars is a world that seems to have started
13:43
with potential. We see ancient river valleys
13:46
carved into its surface. Delta formations where
13:50
sediment once fanned outward into standing bodies
13:53
of water. Minerals that form only in the presence
13:56
of liquid water. Billions of years ago, Mars
14:00
almost certainly had flowing water on its surface.
14:04
It had a thicker atmosphere, a warmer climate,
14:07
and then something changed. Mars is only about
14:11
half the diameter of Earth. Smaller planets cool
14:14
faster. As its interior cooled, Mars likely lost
14:18
the dynamo effect that once generated a global
14:21
magnetic field. Without that magnetic shield,
14:25
the solar wind gradually stripped away much of
14:28
its atmosphere. The water didn't simply vanish,
14:32
some escaped to space, some froze underground,
14:36
and some remains locked in polar ice. What we're
14:40
left with today is a thin, cold atmosphere, less
14:43
than 1 % the pressure of Earth's, and a landscape
14:46
sculpted by wind and dust. Mars may be the most
14:50
explored inner planet after Earth. NASA's Spirit
14:55
and Opportunity rovers, solar -powered explorers,
14:58
lasted far beyond their expected lifetimes. Opportunity
15:03
operated for nearly 15 years. Curiosity and perseverance,
15:08
nuclear -powered rovers, continue to traverse
15:10
ancient lake beds and deltas, drilling into rocks
15:14
that may preserve chemical traces of past habitability.
15:18
We've flown a helicopter, ingenuity, in the thin
15:22
Martian air. That alone sounds like science fiction.
15:26
We haven't sent humans to Mars, but we're trying
15:29
to, and maybe one day we will. There's one more
15:33
reason Mars continues to grip our imagination,
15:36
the possibility that it once hosted life. We
15:40
know that early Mars had liquid water, and for
15:43
a period billions of years ago, Mars was likely
15:46
warmer and wetter. On Earth, life appears very
15:51
early in our geological record. almost as soon
15:54
as conditions allowed it. So scientists ask a
15:58
simple question. If life arose quickly here,
16:01
could it have arisen there? We haven't found
16:04
proof, but we found hints. In 1996, a meteorite
16:09
from Mars known as ALH84001 made headlines around
16:16
the world. Scientists announced that it contained
16:19
tiny structures resembling fossilized microbes.
16:23
along with chemical signatures suggestive of
16:26
biological activity. For a brief moment it seemed
16:29
possible that we had found evidence of past Martian
16:32
life. But over the following years further analysis
16:36
showed that those structures could be explained
16:38
by non -biological processes. The consensus today
16:43
is that the meteorite does not provide convincing
16:46
evidence of life. Since then, rovers have detected
16:50
organic molecules in Martian rocks. But organic
16:54
chemistry is not the same thing as biology. Methane
16:59
has also been detected in trace amounts in the
17:01
Martian atmosphere. Intriguing, but still inconclusive.
17:07
All four of these worlds formed from the same
17:10
protoplanetary disk four and a half billion years
17:13
ago. Same star, similar materials. But over billions
17:18
of years, tiny differences compounded. The inner
17:22
solar system is not a random assortment of rocks.
17:26
It's a long running experiment in planetary evolution.
17:30
Four test cases, one sun, and four very different
17:34
outcomes. If you want to understand how fragile
17:38
habitability is, you don't need to travel light
17:41
years away. You only need to look next door.
18:02
After a quick break, we'll be back with this
18:05
week's Night Sky Report and more. Stay with us.
18:21
Welcome back. I hope you don't mind if I take
18:25
a moment to meander and maybe nerd out a bit.
18:29
The last time I bought a car was almost 15 years
18:33
ago, and the hot tech of that era was built -in
18:36
GPS navigation, backup cameras, and Bluetooth.
18:41
These are things we just expect a new car to
18:44
have nowadays. My little economy hatchback had
18:48
none of that, although I did pack a few amateur
18:51
radio transceivers into it, earning it the nickname
18:54
The Hamster among my friends. Just as the universe
18:59
is fumbling toward entropy, so is my old car.
19:03
With many systems failing, I finally had to retire
19:06
it last week. In the 15 years since the hamster
19:10
rolled off the assembly line, a lot has changed.
19:13
In 2011, there were maybe three consumer electric
19:17
cars, and only society's elite or extreme early
19:21
adopters drove them. Now they're everywhere,
19:25
and charging points are peppered throughout cities
19:27
and along highways. Electric is just another
19:31
choice in the sea of automobiles. In recent years,
19:34
they've become surprisingly affordable, particularly
19:37
in the used market, where they currently represent
19:40
some of the best value in the industry. So I
19:43
decided my next ride would be powered by electrons,
19:47
and I've been in full -on geek mode ever since.
19:50
For my new car, I chose a color similar to Neil
19:54
Armstrong's Marina Blue Corvette Stingray, and
19:58
yes, that was absolutely on purpose. My new hatchback
20:02
on steroids is fun to drive, but because a large
20:06
part of the car is a high -voltage battery, you
20:08
can also do some very practical things with it,
20:11
like power equipment. Imagine being at a dark
20:15
sky site with your imaging rig plugged straight
20:18
into your electric car. Maybe it gets cold, so
20:21
you plug in a small space heater. Maybe you get
20:24
sleepy, so you power up a coffee maker. Meanwhile,
20:28
a laptop hums quietly, guiding a telescope that's
20:32
tracking a galaxy millions of light years away.
20:35
No marine batteries, power inverters, or noisy
20:38
generators. Just stored energy in silence. This
20:43
is my Observatory on Wheels. And it dawned on
20:47
me that electric cars have been part of space
20:49
travel for more than half a century. The first
20:53
vehicles humans ever drove on another world were
20:56
electric. During the Apollo missions beginning
20:59
with Apollo 15 in 1971, astronauts unfolded the
21:05
lunar roving vehicle from the side of the lunar
21:08
module like some kind of cosmic origami. It ran
21:12
on non -rechargeable silver -zinc -potassium
21:15
-hydroxide batteries with four independent electric
21:19
motors, one in each wheel. Top speed? 8 miles
21:23
per hour. In this case, electricity was required
21:27
because it couldn't have burned fuel even if
21:29
it wanted to. There's no oxygen on the moon.
21:33
Lunar astronauts logged nearly 60 miles on the
21:36
lunar surface with their rovers. They collected
21:39
samples, explored craters, and dramatically increased
21:42
the scientific return of the missions. And when
21:45
they left, they parked the rovers there. There
21:48
are still three electric vehicles sitting quietly
21:52
on the moon. Then there are the Mars rovers,
21:55
which we've already mentioned earlier in this
21:57
episode. While they weren't made to carry humans,
22:00
they are, in every meaningful way, electric cars
22:04
operating on a different planet. And, of course,
22:07
there's the slightly absurd case of the Tesla
22:11
Roadster launched into space in 2018, during
22:14
the first flight of SpaceX's Falcon Heavy rocket.
22:18
Instead of a dummy payload, they bolted a production
22:21
electric sports car to the upper stage and sent
22:24
it into orbit around the sun. On the dashboard,
22:28
a sign read, don't panic, a nod to writer Douglas
22:32
Adams. David Bowie's Space Oddity blasted through
22:36
the speakers on a loop into the soundless vacuum
22:39
of the cosmos. There's a mannequin in a space
22:42
suit in the driver's seat, nicknamed Starman,
22:46
and the roadster is still orbiting the sun to
22:49
this day. You can track its location on websites
22:52
like Heavens Above, and it may wander the inner
22:55
solar system for millions of years. That means
22:58
the first production car to leave Earth was electric.
23:02
EVs may or may not be the future depending on
23:05
who you ask, but the truth is they were humanity's
23:08
first off -world transportation dating back to
23:11
the Apollo era. And so here I am driving what
23:15
feels like a spaceship on pavement during a week
23:18
when the moon takes center stage. So let's get
23:21
into it. This month kicks off with a headline
23:25
event, a total lunar eclipse. The moon begins
23:29
the week waxing toward full. By the night of
23:32
March 2, into the early hours of March 3, it
23:35
reaches full moon, traditionally known as the
23:38
worm moon, named for the time of year when the
23:42
ground softens and life begins to stir beneath
23:44
the surface. But this year that full moon won't
23:48
stay bright for long. In the early morning hours
23:51
of March 3, the earth will move directly between
23:54
the sun and the moon, casting its shadow across
23:57
the lunar surface. This is a total lunar eclipse,
24:01
and it's the only one in 2026 visible to much
24:05
of North America and the Pacific region. A lunar
24:08
eclipse unfolds gradually. First, the moon slips
24:12
into the Earth's penumbra, a subtle shading that
24:15
many observers won't even notice. Then comes
24:18
the umbra, the darker central shadow, and you'll
24:22
begin to see a distinct bite taken from the lunar
24:25
disk. Over the course of a couple hours, that
24:28
bite grows until the moon is fully engulfed.
24:31
Totality lasts just under an hour, about 58 minutes.
24:35
Instead of disappearing, the moon turns coppery
24:38
red. This effect is caused by a sunlight passing
24:42
through Earth's atmosphere, where it gets filtered
24:44
and bent. Blue light scatters away, while the
24:48
longer red wavelengths continue on, curving into
24:51
Earth's shadow and softly illuminating the moon.
24:55
The exact shade of red can vary. If Earth's atmosphere
24:59
is especially dusty, perhaps from volcanic eruptions
25:03
or heavy pollution, the moon can appear darker,
25:06
even brick red. On a particularly clear year,
25:09
it may glow more orange or copper. You won't
25:13
need a telescope. In fact, lunar eclipses are
25:16
best enjoyed with your own eyes. Binoculars can
25:19
enhance the color contrast, but this is a naked
25:22
eye event. Once this eclipse passes, we won't
25:26
see another total lunar eclipse in North America
25:28
until late 2028 or early 2029. So if skies are
25:34
clear, this is one to check out. You'll want
25:36
to use an app like Stellarium to track where
25:39
the eclipse occurs in your area. Here in the
25:42
southeast U .S., where I'm located, the eclipse
25:44
begins around 5 a .m. on the morning of the 3rd.
25:48
Very low on the western horizon, so it's going
25:51
to be a tough one for some of us to spot. Now
25:54
while the moon steals the spotlight this week,
25:57
the planets are still putting on their quiet
25:59
show. Jupiter shines brightly in the evening
26:02
sky, still positioned among the stars of Gemini.
26:06
It's one of the brightest objects overhead after
26:08
sunset, outshining nearby stars Castor and Pollux.
26:13
Low in the western twilight, Mercury lingers,
26:16
but it's a fleeting target. Around March 7th,
26:20
it reaches inferior conjunction, passing between
26:23
Earth and the Sun, which means it will be extremely
26:26
difficult to see by week's end. Catch it early
26:29
in the week if you have a very clear western
26:31
horizon. Venus also glows in the dusk. Near the
26:36
end of the week it draws close to Neptune in
26:38
a conjunction, though Neptune itself will require
26:41
binoculars and very steady skies to glimpse.
26:46
I'd plan to get into the next two chapters of
26:48
Night Watch in this episode, but let's hold off
26:51
on that discussion until next week. We'll be
26:54
discussing the outer planets in the next episode,
26:56
so the chapter about the planets should fit nicely
26:59
into our discussion. That's going to do it for
27:05
this week. If you found this episode interesting,
27:08
please share it with a friend who might enjoy
27:10
it. The easiest way to do that is by sending
27:12
folks to our website, StarTrails .Show. And if
27:16
you want to support the show, use the link on
27:18
the site to buy me a coffee. That really helps.
27:22
Be sure to follow Star Trails on Blue Sky and
27:25
YouTube. Links are in the show notes. Until we
27:28
meet again beneath the stars, clear skies everyone.