Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / The Wolf Moon and Mars: Spooky Occultations & Planetary Oddities

Transcript

The Wolf Moon and Mars: Spooky Occultations & Planetary Oddities · Star Trails: From Backyard Astronomy to Cosmic Wonder

0:00
Howdy Stargazers and welcome to this episode of Star Trails.
0:12
I'm Drew and I'll be your guide to the night sky for the week starting January the 12th
0:18
through the 18th.
0:20
I'm really excited this week because a spooky phenomenon awaits us on January 13th.
0:27
The full, wolf moon will occult the planet Mars, causing it to disappear for about an
0:33
hour.
0:34
We'll explore why that happens and why we sometimes see eclipses and parades of planets.
0:41
It's all connected.
0:43
In the second half of the episode I'll share some facts about the solar system that you
0:48
may not have heard before.
0:50
For example, did you know Jupiter doesn't exactly orbit the sun like the other planets?
0:56
Click around and I'll tell you why.
0:59
This week is shaping up to be a fun one for stargazers, so let's get started.
1:06
The moon will be the main event this week as it waxes towards being full on January
1:11
13th.
1:12
This month's full moon is traditionally called the wolf moon.
1:17
In January's depths of winter, wolves were often heard howling outside villages, inspiring
1:23
this evocative name.
1:26
This luminous full moon will dominate the sky, making it a perfect companion for moon-lit
1:31
strolls.
1:34
Also on the 13th, a rare lunar occultation of Mars will occur, where the moon passes
1:40
in front of Mars, temporarily hiding it from view.
1:45
Observers on the east coast can expect to see Mars disappear between 9pm and 9.30pm,
1:51
reappearing about an hour later.
1:54
The west coast will see this event around 6pm.
1:58
Be sure to consult with a stargazing app like Stellarium or Sky Safari to learn the exact
2:04
time when you can see this phenomenon in your area.
2:09
By weeks end, the moon will have dwindled to nearly a third quarter moon with a little
2:13
more than half of the surface illuminated.
2:16
If Mars seems a little brighter this week, it's because the red planet reaches opposition
2:22
on January 15, meaning it will be at its brightest and most prominent size for the year.
2:29
Look for its reddish hue in the east in the constellation Gemini.
2:33
It's visible all night as it makes its way west before dawn.
2:39
Venus and Saturn will appear exceptionally close to each other on January 17 and 18,
2:44
a conjunction visible in the southwestern sky shortly after sunset.
2:50
Venus, the brighter of the two, will guide you to Saturn, just slightly to the left and
2:55
above Venus.
2:57
Jupiter is currently shining brightly in the constellation Taurus.
3:02
Look for it in the southeast sky between Orion and the Pleiades.
3:07
It will be the brightest object in that portion of the sky.
3:11
Mercury will be a morning star this week, but fairly elusive.
3:15
Look for it on the eastern horizon just before dawn.
3:25
In our last episode, I told you how to locate Orion by its three prominent belt stars, and
3:32
we journeyed through Taurus, home of the bright star Aldebaran and the Hyades star cluster.
3:39
Let's take a look at another constellation nearby, Gemini.
3:44
To the northeast of Orion, Gemini's twin stars, Castor and Pollux, are prominent.
3:50
The story of these twins is one of loyalty, love, and sacrifice.
3:56
According to mythology, Castor and Pollux were said to be the sons of Lita, a mortal
4:01
woman, and either her mortal husband, King Tendarius of Sparta, or the god Zeus, who
4:08
seduced Lita in the form of a swan.
4:12
Pollux was considered immortal because Zeus was his father, while Castor, being the son
4:17
of Tendarius, was mortal.
4:20
Despite their different parentage, Castor and Pollux were inseparable and renowned for their
4:25
adventures.
4:26
Together, they joined Jason and the Argonauts in their quest for the Golden Fleece.
4:31
They were also known for their strength, bravery, and skill in battle.
4:36
Their story takes a sorrowful turn when Castor, the mortal twin, is killed in a fight.
4:42
Pollux, stricken with grief, begged Zeus to let him share his immortality with his brother.
4:49
Zeus, moved by Pollux's devotion, grants his wish by transforming both brothers into
4:55
stars, placing them together in the sky as the constellation Gemini.
5:01
The constellation's two brightest stars represent the heads of the twins.
5:06
They sit close together in the sky, with their bodies outlined by dimmer stars.
5:12
Pollux is an orange giant star, slightly brighter than Castor, while Castor, a white star, is
5:19
actually a complex system of six stars bound by gravity.
5:25
Mars will become part of this constellation during the week, adding a bright, reddish,
5:30
and negative 1.4 magnitude guest star to the twins.
5:41
If you pay attention to the positions of the planets, the moon, and the sun, you might
5:46
notice something peculiar.
5:48
They all follow a similar path across the sky.
5:52
For example, right now the moon, Saturn, and Venus are roughly lined up in one part of
5:57
the sky.
5:59
If you were to draw a line through them, that line would arc across the sky to the opposite
6:04
horizon, passing near Jupiter and Mars.
6:08
The line that the planets follow is the ecliptic plane.
6:13
Our solar system is actually a relatively flat disk, with the planets orbiting the sun
6:19
on a conceptual plane, called the ecliptic.
6:23
Earth and the other planets' orbits are roughly aligned to the ecliptic plane.
6:28
When we look up at the night sky, the ecliptic appears as a curved line tracing across the
6:33
celestial sphere, marking the sun's apparent path over the course of a year.
6:40
The planets formed from a rotating disk of gas and dust billions of years ago.
6:46
This protoplanetary disk flattened out owing to the conservation of angular momentum, leading
6:52
to the alignment of planetary orbits.
6:55
While their orbits aren't perfectly aligned, each has a slight tilt, they all stay close
7:01
to the ecliptic.
7:03
The sun's path across the sky follows the ecliptic, as does the moon, although its orbit
7:08
is slightly tilted relative to the ecliptic.
7:12
When the moon and sun's apparent paths intersect, it creates a point called a node.
7:18
These are points where solar and lunar eclipses can occur.
7:22
As planets and the moon hover near the ecliptic, their apparent paths often intersect.
7:28
This is why events like the Venus and Saturn conjunction, or the Mars occultation by the
7:33
moon, occur.
7:35
They're all traveling along the same general path in the sky.
7:40
The idea of the ecliptic simplifies the study of celestial motions and provides a framework
7:46
for understanding alignments and events in the sky.
7:50
For backyard astronomers, it's a celestial highway guiding you to the planets and even
7:55
the occasional surprise like a comet or asteroid.
8:05
Now let's look at some weird facts related to a few of the planets in our solar system.
8:12
Did you know a day on Mercury is longer than its year?
8:17
Mercury takes about 88 Earth days to complete one orbit around the sun.
8:23
That's its year.
8:24
However, it also spins on its axis very slowly, taking about 59 Earth days to make one full
8:32
rotation.
8:34
This rotational period is called a sidereal day, and it's a bit different from a solar
8:40
day which features a sunrise and sunset.
8:45
Because of this interplay between orbit and rotation, from the perspective of someone
8:49
standing on Mercury's surface, the time from one sunrise to the next is roughly 176 Earth
8:57
days long.
8:59
In other words, one solar day on Mercury lasts almost twice as long as a Mercuryan year.
9:07
This odd scheduling is due to something called a spin orbit resonance.
9:13
Mercury is in a 3-2 resonance, meaning it rotates exactly three times about its axis
9:18
for every two orbits around the sun.
9:22
Spin orbit resonances happen because tidal forces from the sun lock the planet's rotation
9:28
rate in a precise ratio to its orbital period.
9:32
Mercury is close enough to the sun that it experiences powerful gravitational pulls,
9:38
ensuring its spin and orbit remain locked in this unusual pattern.
9:43
Now, let's cruise over to Venus, the hottest planet in the solar system, and one with another
9:50
rotational quirk.
9:53
Most planets in the solar system rotate on their axes in the same direction they orbit
9:58
the sun, which is counterclockwise if viewed from above the sun's north pole.
10:05
Venus, however, spins in the opposite direction.
10:09
This is called retrograde rotation, and it means that on Venus, the sun would appear
10:14
to rise in the west and set in the east, if you could survive long enough under its harsh
10:21
atmospheric conditions to watch a sunset.
10:25
No one is entirely sure why Venus rotates backward, but the leading hypotheses involve
10:31
ancient collisions with large protoplanetary bodies, or gravitational interactions with
10:38
the sun and other planets.
10:40
Whatever caused this backward spin, the slow retrograde rotation of Venus contributes to
10:46
its extreme atmospheric dynamics and bizarre day-night cycles.
10:53
A sidereal day on Venus is 243 Earth days, making it longer than its year, which is around
11:00
225 Earth days.
11:04
Venus boasts the highest temperatures of any planet in our solar system, with surface temperatures
11:10
around 860 degrees Fahrenheit.
11:14
This extreme heat is largely due to a runaway greenhouse effect driven by its dense carbon
11:20
dioxide atmosphere.
11:23
The thick cloud layers trap heat very efficiently, allowing sunlight in but preventing infrared
11:30
radiation from escaping back into space.
11:34
Venus' clouds are filled with sulfuric acid droplets, and the resulting chemical and thermal
11:40
environment is incredibly hostile.
11:44
Probes that have landed on Venus, like the Soviet Venera missions, survived only a short
11:49
time on the order of minutes to a couple of hours before succumbing to the crushing pressure
11:55
and corrosive heat.
11:57
Yet, this very harshness makes Venus a key laboratory for understanding the limits of
12:03
planetary habitability and the power of greenhouse gases.
12:08
Let's make a jump out to Jupiter, our largest planet, and an outlier for several other reasons.
12:17
Jupiter's great red spot is an enormous storm system big enough to swallow multiple Earths.
12:23
It's been observed continuously since at least the 1600s, making it perhaps the longest
12:29
lived storm we know.
12:32
While the great red spot has shrunk somewhat over recent decades, it remains a swirling
12:37
anti-cyclone with winds topping hundreds of kilometers per hour.
12:43
Scientists still debate why it's so stable and why it's red.
12:48
Possible explanations range from the storm dredging up chemicals from deep in Jupiter's
12:53
atmosphere that turn red when exposed to sunlight, to complex interactions of ammonia
13:00
and other compounds.
13:02
Juno spacecraft data continues to shed new light on the storm's depth and structure,
13:08
but the great red spot remains a powerhouse of planetary meteorology, illustrating how
13:13
different weather can be on a gas giant compared to Earth.
13:17
Here's a strange but true tidbit.
13:21
Jupiter doesn't orbit the Sun's center.
13:24
It orbits a shared center of mass, the Berry Center, that actually lies outside the Sun's
13:31
surface.
13:32
Despite Jupiter being only a fraction of the Sun's mass, it's still so massive compared
13:38
to the other planets that its gravitational pull is significant enough to yank the Sun
13:43
ever so slightly off-center.
13:46
When two bodies orbit each other, say Jupiter and the Sun, they both revolve around their
13:51
combined center of mass, not just one body around the other.
13:57
Because Jupiter is by far the heaviest planet in the Solar System, more than twice as massive
14:02
as all other planets combined, the Sun-Jupiter Berry Center ends up sitting about one to
14:08
two solar radii above the Sun's actual center.
14:13
This might sound small on the scale of the entire Solar System, but it's enormous compared
14:18
to how the other, lighter planets affect the Sun.
14:21
So when you visualize Jupiter orbiting the Sun, remember that the Sun is also wobbling
14:27
around a point in space, paying its gravitational dues to the Solar System's most massive
14:33
planet.
14:36
Jupiter's massive gravity doesn't just pull the Sun off-center, it also orchestrates
14:40
a host of other dance moves throughout the Solar System.
14:44
For instance, many astronomers refer to Jupiter as the Solar System's cosmic vacuum cleaner,
14:50
because it deflects or captures numerous comets and asteroids that might otherwise threaten
14:55
the inner planets.
14:58
When a comet from the distant Kuiper Belt or O-Ork cloud ventures inward, Jupiter's strong
15:04
gravitational field can alter the comet's trajectory significantly, sometimes flinging
15:09
it back out of the Solar System or steering it into a collision course with itself, as
15:15
with comet Shoemaker-Levy-9 in 1994.
15:20
In this way, Jupiter acts as a partial shield for Earth, though it can hurl objects onto
15:26
potentially hazardous paths, depending on the geometry of the encounter.
15:32
Another lesser-known effect is Jupiter's role in creating gaps in the asteroid belt.
15:37
We mentioned this in our last episode.
15:40
Asteroids whose orbits resonate strongly with Jupiter's, for example those completing exactly
15:46
three orbits for every one of Jupiter's, can get their orbits destabilized over time.
15:53
This gravitational nudging carves out the so-called Kirkwood gaps, which are underpopulated
15:58
zones in the asteroid belt.
16:02
There are a lot more fun facts we could discuss about these and other planets, but we'll save
16:07
those for future episodes.
16:09
Be sure to get out this week and watch the moon occult Mars.
16:13
And while we do have a bright moon washing out all those fainter deep-sky objects, it's
16:18
still a great time for looking at Jupiter and Saturn through a nice telescope.
16:26
If you found this episode helpful, let me know and feel free to send in your questions
16:31
and observations.
16:33
The easiest way to do that is by visiting our website, startrails.show.
16:39
This is also a great way to share the show with friends.
16:43
Until next time, keep looking up and exploring the night sky.
16:47
Clear skies, everyone.