The Moon
The Moon, also known as Luna, is Earth’s only natural satellite and is the most prominent feature of the night sky. The Moon has had many profound impacts on Earth and its inhabitants, controlling the tides, inspiring art and literature, serving as a tool for ancient civilizations, and standing as a significant milestone for human exploration!
The Formation and Lunar Environment
The prevailing theory for the formation of the Moon is the Theia Impact hypothesis. This theory suggests that a roughly Mars-sized celestial body collided with the Earth around four and a half billion years ago. This collision ejected debris from both celestial bodies and over time it came together to form a unified satellite over Earth, the Moon.
Credit: NASA's Ames Research Center
Luna is the fifth largest moon in the entire solar system, with a diameter of around 3500 kilometers. The Moon may seem pretty large, but it still has a relatively small mass compared to Earth, meaning gravity on the Moon is only about a fifth of what we experience here. Our Moon exhibits something known as synchronous rotation. As the Moon orbits the Earth it rotates on its axis at the same rate, meaning that the same side of the Moon is always facing us! This is where the idea of “the dark side of the Moon” came from: we never see the other side from our perspective, so it is “dark” to our eyes. However, it is important to note that the other side of the Moon is not dark in the literal sense, and has days and nights just as the rest of the Moon does.
The Moon lacks a magnetosphere and has a very thin atmosphere known as an exosphere. Combined, the Moon is left incredibly vulnerable to meteor impact, temperature swings, solar wind, coronal mass ejections (CMEs), and galactic cosmic rays (GCRs). The unshielded bombardment of meteors is why the Moon appears covered in craters, unlike the Earth or other atmospheric planets/moons. Additionally, micrometeoroid impacts are constantly altering the lunar surface, dredging up new soil. The lack of a strong atmosphere also contributes to significant temperature variance throughout Luna’s day/night cycle. The surface temperature can reach up to 130 degrees Celsius in the day, and down to -175 degrees Celsius at night. Solar wind and CMEs bring charged particles to the surface of the Moon causing lunar dust to be electrostatically charged, which can be a major design challenge for ground equipment.
The Moon's impact on earth
Luna may not be as massive as the Earth, but its gravity still has a profound effect on our planet. Oceanic tides are caused by the gravitational pull of the Moon! The Moon’s gravity pulls at all points on our planet causing the oceans to “squeeze” around the globe. This creates a bulge facing towards the Moon, and another bulge facing opposite to the Moon. The changing tides are then caused by the Earth rotating through these bulges, although to us it may seem like the ocean itself is retreating and returning. It is worth noting that the Sun plays a role in the Earth’s tides as well, although less significantly. The main observed phenomenon occurs when the Moon and the Sun are inline with one another, causing an ultra-high tide known as a Spring tide. When the Sun and the Moon are perpendicular, a lower than normal high tide is observed known as a Neap tide.
Eclipses are another notable astronomical phenomenon caused by the Moon. There are two different types of eclipses, solar eclipses (when the Moon blocks out the Sun from our perspective on Earth) and lunar eclipses (when the Earth blocks out the Sun from the Moon’s perspective). Each eclipse type can occur either as a partial eclipse or a total eclipse, depending on if the entirety of the sun’s light is blocked out or not. During a total solar eclipse here on Earth, the sky darkens significantly and a ring of light can be seen illuminating the edges of the Moon. It is truly one of the most magnificent events one can experience!
Over time, the Moon has also slowed down Earth’s rotation, and in the process is gradually moving into higher orbits. Evidence from photosynthetic bacteria layers (stromatolites) suggest that 850 million years ago, one day on earth was only about 21 hours! Presently, the Moon moves away from us by about five centimeters per year.
Luna has been a target for the human eye since the dawn of humanity itself. The Moon has made its way into myth, legend, and historical accounts across all cultures. Observation of the Moon has also been critical to the success of humankind: allowing for more precise timekeeping and the creation of calendars, and serving as a guide to agricultural planning. Luna has also been a major artistic, literary, and musical inspiration for many works. Appearing in Vincent Van Gogh’s Starry Night, and Ludwig van Beethoven’s Moonlight Sonata.
Earth’s Moon has served
as a goal for explorers and the curious for quite some time.
In 1969, NASA made history as the first humans successfully landed on the Moon’s surface in the Apollo program. The Apollo missions were an enormous step forward for their time, but unfortunately, no one has returned to the Moon since the last Apollo mission (Apollo 17) in 1972. This is changing though as NASA has once again made plans to return to the Moon with the Artemis campaign! The Artemis missions aim to not only return humans to the Moon but also establish a long-term presence. The missions will provide valuable experience with long-term space exploration, and will pave the way for future missions to Mars and beyond!
We only achieve these great aspirations through the imaginations from people all over our globe and the collective dogged determination to reach goals that otherwise would be unattainable alone.