Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / Light and Darkness: From the Harvest Moon to the Far Side
Transcript
- Howdy stargazers, 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 starting September 15 to the 21st. On today’s episode we’ll explore the dichotomy of the Moon. This week we’ll experience its bright full phase, but behind the luminous lunar face we can see from Earth, unseen by most, there is a dark side. Later in the show, we’ll journey there and attempt to uncover its mysteries. So grab your observational instrument of choice, a comfortable chair, and let’s get started. This week we’re in for some spectacular lunar viewing. The highlight of the week is the Full Harvest Moon on September 17. The Harvest Moon is the full moon closest to the autumnal equinox, and it has historically been significant for farmers. Before the advent of artificial lighting, the bright light of the Harvest Moon allowed farmers to work late into the night, bringing in their crops under the extended twilight. This moon is often larger and more orange when it rises, adding to its dramatic appearance. And there’s more. This Full Harvest Moon is also a supermoon, the second of four in a row this year. A Supermoon occurs when the full moon coincides with its closest approach to Earth in its orbit, known as perigee. This makes the moon appear slightly larger and brighter than a typical full moon. If that isn’t enough, the Americas, Europe and Africa will experience a partial lunar eclipse on the night of the Harvest Moon. The event starts around 8:45 a.m. EST on the 17th, and the eclipse peaks around 10:45 p.m. During the peak the Moon will pass through Earth’s umbra – that’s the darker center portion of Earth’s shadow regions during an eclipse. The effect will be subtle, with only a slight darkening near the top of the Moon, as it’s grazed by the Earth’s shadow. While all this is happening, be sure to look to the right of the Moon to catch Saturn as a bright point of light in nearby Aquarius. As the week progresses, the moon transitions into the Waning Gibbous phase. During this phase, the moon will start to rise later each night, shining brightly in the late evening and early morning hours. We’ll have a good chance to see Mercury this week. Now a morning star, Mercury will be visible at a decently bright magnitude of -1.3 just before dawn after 6 a.m. in the eastern sky, but it will creep back into the Sun’s glare later in the month. There’s also a good viewing window for Venus this week as it lingers in the western sky for an hour after sunset. Clocking in at a very bright -3.8 magnitude, it’s the brightest object in the sky apart from the Moon. Jupiter remains in Taurus, visible after midnight. Mars follows several hours later, rising in Gemini. Look to the east for both. As we continue this week’s journey, we’re going to venture into one of the most mysterious and enigmatic places in our local celestial neighborhood – the dark side of the Moon. This hidden half has been the subject of myths, legends, and even a few conspiracy theories. First, let’s clear up a common misconception. When we talk about the “dark side” of the Moon, we’re really referring to the far side of the Moon – the hemisphere that always faces away from Earth. The term “dark side” is a bit of a misnomer because this side of the Moon isn’t actually in perpetual darkness. In fact, it experiences day and night cycles just like the near side we see from Earth. The reason the far side is hidden from us is due to something called synchronous rotation. This means that the Moon takes the same amount of time to rotate on its axis as it does to orbit Earth – about 27.3 days. As a result, one hemisphere of the Moon is always facing us, while the other remains out of view. The far side of the Moon has long captured the imagination, partly because it’s a place we can never see with our own eyes from Earth. This mystery has given rise to all sorts of stories and speculations. For example, in ancient cultures, the Moon itself was often associated with deities and supernatural events. The unseen far side, shrouded in mystery, became a symbol of the unknown. Some cultures believed it was a place where gods or spirits resided, hidden away from mortal eyes. In modern times, the far side has been the subject of conspiracy theories – perhaps most famously the idea that alien bases or secret government installations might be hidden there. These ideas, while intriguing for science fiction, have no basis in reality. For centuries, no one knew for sure what was on the far side of the Moon. It wasn’t until 1959, when the Soviet Luna 3 spacecraft took the first photographs, that humanity got its first glimpse. The images revealed a rugged, cratered landscape very different from the near side’s familiar maria, or “seas.” As there have been Moon missions as recently as this year – and some have failed spectacularly – I’m fascinated by the fact that a probe viewed the far side as early as 1959, just two years after the launch of Sputnik. One of the most striking features on the far side is the South Pole-Aitken Basin, one of the largest and oldest impact craters in the entire solar system. This colossal basin stretches about 2,500 kilometers and is several kilometers deep. Studying this region has provided scientists with valuable insights into the Moon’s history and the early solar system. In recent years, missions like China’s Chang’e program have further explored the far side. In 2019, Chang’e 4 became the first spacecraft to land on the far side of the Moon, specifically in the Von Kármán crater within the South Pole-Aitken Basin. This mission has been conducting groundbreaking research, including studying the Moon’s geology and testing the feasibility of growing plants in lunar soil. There are still unanswered questions about the far side’s geology, the history of impacts that have shaped its surface, and how its environment might differ from the near side. For instance, the far side’s crust is thicker, and it has far fewer maria – those dark, basaltic plains formed by ancient volcanic activity – compared to the near side. And we don’t really have an explanation for why these hemispheres are so different. One of the intriguing aspects of the Moon’s far side is the presence of localized magnetic fields, which are stronger in certain regions than those found on the near side. This has puzzled scientists because the Moon as a whole lacks a global magnetic field, unlike Earth. The origin of these magnetic anomalies is still not fully understood, but they are thought to be remnants of ancient magnetic activity within the Moon's core, possibly linked to the intense impacts that created the large basins on the far side. The far side also holds potential resources that could be vital for future lunar exploration. One of the most significant is water ice, believed to exist in permanently shadowed craters near the lunar poles. These areas, which never receive sunlight, could harbor substantial amounts of ice, a crucial resource for sustaining human presence on the Moon. Water can be used not only for drinking and growing food but also for producing oxygen and hydrogen, which are essential for life support and rocket fuel. Establishing a sustainable outpost on the Moon might depend on the ability to locate, extract, and utilize these resources. The far side is also an ideal location for certain types of scientific research, particularly radio astronomy. Because it’s shielded from Earth’s radio noise, the far side offers a pristine environment for listening to the faint signals from the distant universe. Future missions might establish observatories there to study the cosmos in ways we simply can’t do from Earth or even from the near side of the Moon. I wasn’t entirely accurate when I mentioned earlier that we never see the far side. Because of lunar libration – which we talked about back in episode 32 – we can actually catch glimpses of the far side from Earth. Up to about 18% of the far side becomes visible over time. And I can’t end the show without mentioning this – For all the Pink Floyd fans out there, while the band’s iconic album “The Dark Side of the Moon” is more about mental states and human experience, its title has undoubtedly contributed to the mystique surrounding this unseen half of our nearest celestial neighbor. That's it for today’s episode of Star Trails. Before you go, I invite you to check out our weekly e-mail newsletter on Substack. It’s completely free, and a great supplement to the podcast. We’re also on Mastodon @star_trails. If you get a chance, stop by and say hello. I’ll include links to both services in the show notes. Also, remember our website, startrails.show, where you can find all our episodes, including transcripts and night sky maps. Until next time, keep looking up and exploring the night sky. Clear skies, everyone!