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The Hunter's Moon and Celestial Resonances · Star Trails: From Backyard Astronomy to Cosmic Wonder

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Howdy Star Gazers and welcome to this episode of Star Trails.
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I'm Drew and I'll be your guide to the night sky for the week starting October 13th to
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19th.
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This week brings a full moon and the possibility of a shimmering comet.
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We'll take a look at a minor constellation with a lonely star, and later in the episode
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we'll explore the orbital patterns that shape our planetary system, the gravitational interactions
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that create predictable patterns known as resonances.
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So grab a comfortable spot under the night sky and let's get started.
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First off, I hope many of you were able to catch the northern lights in some of the lower
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48 states this week.
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Following a massive geomagnetic storm in the wake of a coronal mass ejection, the skies
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lit up with aurora as far south as Mexico on October 11th.
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I know folks around my area saw and managed to photograph the aurora, but I wasn't so
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lucky.
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I thought I could spot some high altitude red or pink bands earlier in the evening from
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a photo taken in my backyard, so I ventured out into the countryside around 9pm and found
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a vast north-facing field.
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In the near total darkness, I saw absolutely nothing, so I suspect whatever folks saw in
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my area dissipated quickly.
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Since May, many states in lower latitudes have been fortunate to see the northern lights
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thanks to a very active solar cycle. While a solar storm can kill radio communications
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on some bands, overall, this solar cycle has been a boon for ham radio operators for the
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past year or more.
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A few years ago, solar activity, which plays a role in the propagation of radio waves,
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was at an all-time minimum, so operations in certain bands, like 10 meters, were very
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hit or miss.
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Anyway, space weather and amateur radio are topics for a future show, so let's get on
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with this week's exploration of the night sky.
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October 17th marks the full hunter's moon, which will also be the biggest and brightest
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supermoon of 2024.
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This supermoon will appear larger than usual due to the moon being at its closest point
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to Earth. You can start observing it on the evening of October 16th, and it will shine
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in the constellation Pisces.
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The hunter's moon has a rich lore rooted in the rhythms of rural life. The name originated
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from Native American and European traditions.
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After farmers brought in their crops under the bright harvest moon, which is the full
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moon nearest the autumnal equinox, the hunter's moon provided additional light for hunting
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game, which was then stored for winter.
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The bright moonlight allowed hunters to track animals at night, especially deer and other
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creatures.
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The hunter's moon is known for rising just after sunset, with the moonlight lasting throughout
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the night. This is because of the moon's shallow angle relative to the horizon during
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this time of year, which causes it to rise sooner than at other times.
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This creates an effect where the moonlight appears brighter and lasts longer in the sky,
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adding to its importance in ancient times.
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In modern times, the hunter's moon is also celebrated for its beauty, often appearing
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larger and more orange as it rises due to the atmospheric conditions when it's closer
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to the horizon.
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Elsewhere in the solar system, Saturn will be visible in the southeastern sky just after
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sunset and remain up for most of the night. On October 14th, it will be near the waxing
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gibbous moon, creating a striking conjunction.
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Jupiter will rise after 10pm, and in the early morning of October 19th, it will appear near
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the nearly full moon in the constellation Taurus. Look for Jupiter's bright presence
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in the eastern sky, especially after midnight.
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Mars rises near midnight. Its reddish hue will be noticeable in the pre-dawn hours as it
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climbs higher in the sky. Venus will be visible low in the west just after sunset. Although
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it sets soon after, you can catch it shining brightly early in the evening right now.
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And I've saved the best for last. From October 14th until the end of the month, Comet C2023A3
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should make a stunning appearance low on the western horizon after sunset.
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The best viewing window for this comet is from October 14th to the 24th, and is predicted
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to have a magnitude around zero. That means it's about the same brightness as Mars and
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will be easily visible to the naked eye. This comet has a long, curved tail, and images
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already captured of it have been stunning. Hopefully, you'll get a chance to see this
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icy visitor. The last time it visited Earth may have been around 80,000 years ago, in
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the era of the Neanderthals.
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For those of you looking to spot something a little off the beaten path this October,
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take a look at Pisces Austrinus, the southern fish. It's a lesser known but still interesting
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constellation that rises in the southern sky during the fall. While it may not be as famous
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as some of its neighboring constellations, such as Aquarius, Pisces Austrinus holds a
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special place in the sky. In fact, it's home to one of the brightest stars you can see
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this time of year, Fomalot. Fomalot shines at magnitude 1.16, making it one of the brightest
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stars in the night sky, and the brightest star in its immediate region. It's often
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called the Lonely Star, because it stands alone in a relatively empty patch of sky, away
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from other bright stars. You'll notice its clear, solitary presence in the southern
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sky, especially on dark autumn nights. Fomalot also has some modern significance. Astronomers
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have discovered an exoplanet orbiting this star, known as Fomalot B, or Dagon. This makes
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Pisces Austrinus an exciting target for those interested in the ongoing search for planets
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beyond our solar system. In ancient Greek stories, Pisces Austrinus represents the great
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fish that swallowed water from the floods sent by Zeus. Some myths also associate it
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with the fish that saved Aphrodite and her son Eros when they were transformed to escape
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the monstrous Typhon. This tale is also tied to the neighboring constellation Pisces, representing
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two fish swimming together. Today, we're going to explore one of the
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more fascinating aspects of orbital dynamics in our solar system, resonances. These are
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relationships between orbiting bodies where their gravitational interactions cause them
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to establish predictable, repeating patterns. In simple terms, a resonance occurs when two
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or more orbiting objects exert a regular periodic gravitational influence on each other, usually
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because their orbital periods are a similar ratio. For example, if one planet takes exactly
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twice as long to orbit the sun as another, we call that a 2 to 1 resonance. Resonances
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can occur between planets, moons, or even small objects like asteroids, and these orbital
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relationships play a key role in the stability of our solar system. Our understanding of
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orbital resonances goes back centuries to the early days of celestial mechanics. One
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of the key figures in this field was the French mathematician and physicist Pierre Simon
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Laplace. In the late 18th century, Laplace developed a mathematical framework for understanding
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how gravitational forces shape the motion of celestial bodies. His work extended and
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built upon the laws of motion first formulated by Isaac Newton, and he laid the foundation
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for modern orbital mechanics. Laplace was the first to describe the Laplace resonance,
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a three-body orbital resonance that we observe today among the moons of Jupiter, Io, Europa,
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and Ganymede. These moons follow a 1 to 2 to 4 resonance, meaning for every four orbits
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Io makes around Jupiter, Europa makes 2, and Ganymede makes 1. This resonance affects
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the physical conditions of these moons, particularly Io. The constant gravitational tug from the
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other moons causes significant tidal forces, which heat Io's interior, leading to the
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extreme volcanic activity we observe there. In the centuries following Laplace, astronomers
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began to realize that these resonant patterns weren't just an abstract mathematical curiosity,
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they were a key to unlocking new discoveries. For instance, the discovery of Neptune was
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the result of the study of resonances. In the early 19th century, astronomers noticed
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that Uranus wasn't moving as expected. Its orbit showed small deviations, suggesting
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that another planet was influencing it through gravitational interactions, likely a resonance
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effect. Using these discrepancies, French mathematician
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Urbain Le Verrier and British astronomer John Couch Adams independently calculated the position
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of this unseen planet. In 1846, astronomers pointed their telescopes to the predicted
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coordinates and Neptune was found, exactly where the calculations had indicated. This
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marked the first time a planet was discovered through mathematical prediction, an extraordinary
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triumph for celestial mechanics and gravitational theory.
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And speaking of Neptune, let's explore the resonance between it and Pluto. Despite the
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fact that Pluto's orbit crosses inside Neptune's, the two will never collide because they're
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locked in a 3-2 resonance. This means that for every 3 orbits Neptune completes around
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the Sun, Pluto completes 2. This resonance ensures that they're never at the same point
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in their orbits at the same time, which stabilizes their otherwise intersecting paths.
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Saturn's moons and rings provide several examples of resonance-driven dynamics. One
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prominent case involves the moons Mimas and Tethys, which are in a 2-1 resonance. Each
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time Tethys completes one orbit around Saturn, Mimas completes two. This interaction has
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played a role in shaping Saturn's rings, particularly the Cassini division, a gap in
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the rings. Mimas exerts gravitational forces on the particles and the rings, preventing
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material from accumulating in this region.
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There's also a fascinating resonance between the Earth and the Moon. This is a 1-1 spin
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orbit resonance, more commonly referred to as synchronous rotation. It means that the
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Moon rotates on its axis in the same amount of time it takes to orbit the Earth, about
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27.3 days. As a result, the same side of the Moon is always facing Earth. That's why we
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never see the far side of the Moon from our vantage point.
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This synchronous rotation is the result of tidal forces between the Earth and the Moon.
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In the early history of our planet, the Moon rotated faster. Over millions of years, Earth's
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gravitational pull created tidal friction on the Moon, gradually slowing its rotation
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until it became locked in this resonance. Now, the Moon's spin is perfectly matched
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to its orbital period, and it's been that way for a very long time.
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There is a reciprocal effect to this interaction. The Moon, of course, exerts tidal forces here
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on Earth, which is why we experience tides in the oceans. Over time, these forces are
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also slowing Earth's rotation. Every century, Earth's day gets a tiny bit longer, about
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1.7 milliseconds per century. As Earth's rotation slows, the Moon is gradually moving farther
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away from us, by about 3.8 centimeters per year. This means the resonance between Earth
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and the Moon will continue to evolve over millions of years.
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You may recall in our last episode, I mentioned that Earth recently captured a new Moon, a
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small asteroid about the size of a school bus. This isn't the first time this has happened.
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Here Earth asteroid 3753 Crueenye has in the past been called Earth's second Moon. Crueenye
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isn't a true Moon but shares a one-to-one resonance with Earth. Instead of orbiting
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Earth directly, Crueenye follows a unique, horseshoe-shaped path around the Sun that
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keeps it in sync with Earth. This resonance prevents Crueenye from ever coming too close
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to Earth while keeping it in a gravitational dance with our planet.
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Resonances are not limited to just these major moons and planets. There are several
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other interesting examples throughout our solar system.
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Jupiter plays a key role in shaping the asteroid belt through a series of resonances. These
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are called Kirkwood gaps, named after astronomer Daniel Kirkwood, who discovered them in the
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19th century. The Kirkwood gaps are regions in the asteroid belt where there are fewer
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asteroids because their orbital periods would have been in resonance with Jupiter, causing
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gravitational disturbances that ejected the asteroids from these orbits. For instance,
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there's a three-to-one resonance gap where an asteroid would orbit the Sun three times
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for every one orbit of Jupiter. Over time, these resonances either push asteroids into
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new orbits or eject them from the belt altogether.
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Resonances also occur in the distant Kuiper Belt, where objects like Pluto and its fellow
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dwarf planets preside. Many Kuiper Belt objects are in resonance with Neptune. For instance,
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there are KBOs in two to three resonances with Neptune, meaning that for every two orbits
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Neptune makes around the Sun, these objects complete three orbits. This stabilizes the
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orbits of these small bodies despite their proximity to Neptune's much stronger gravitational
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influence.
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While not part of our solar system, it's worth noting that resonances are observed in
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exoplanetary systems as well. Several multi-planet systems discovered by astronomers show planets
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in tight, resonant orbits, providing evidence that resonance is a common feature in planetary
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systems across the galaxy.
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Resonances are important because they help maintain the stability of our solar system
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over long timescales. By preventing chaotic interactions between orbiting bodies, resonances
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help keep their orbits predictable and stable. In some cases, resonances can also destabilize
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certain orbits as we see with asteroids in the Kirkwood gaps. The existence of resonances
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suggests that the solar system has undergone a delicate process of gravitational balancing
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that has shaped its current structure.
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That's it for today's episode of Star Trails. If you found this episode informative or
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entertaining, please share it with a friend. The easiest way to do that is by visiting
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our website, startrails.show, where you can find all of our episodes including transcripts,
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night sky maps, and more.
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Until next time, keep looking up and exploring the night sky. Clear skies, everyone!