Exploring the full moon
A recent edition of this column discussed the phases of the moon. The full moon occurs on April 11. For several days before or after that date, the nearly-full moon will be visible for most of the night. This is the time when almost all of the near side of the moon will be visible to the naked eye.
Look up at the moon this month and you will see the most obvious features visible on the moon are the irregular splotches of light and dark areas. The human brain is very good at interpreting (or sometimes mis-interpreting) random patterns as more familiar objects, especially faces. This is why many people see the pattern of dark areas on the moon as a face in the form of “The Man in the Moon.” This phenomenon is known in psychology as “paredolia” and we see many other examples of it, such as the “Face on Mars” which some people see in images of some Martian hills taken by the Viking 1 orbiter and in the common children’s game of seeing faces, animals, and other familiar objects in the shapes of clouds. But many cultures have associated different images with the moon. The Aztecs, as well as many Asian cultures, see the outline of a rabbit on the face of the moon. This is one reason the Chinese lunar rover which landed on the moon in 2013 was named “Yutu”, which is Chinese for “Jade Rabbit.”
The indistinct lunar markings which are at the limit of visibility to the naked eye became clear when Galileo turned his newly-invented telescope to the moon for the first time in 1609. His telescope not only gave a better view of the moon; it also set into motion a revolution in human thought which changed the world and led to the our modern technological society as well as our concepts of democracy and liberty.
Before Galileo’s bold move, western cultures had followed the teachings of Aristotle for more than a thousand years. Aristotle taught that the earth was imperfect and corrupt but the heavens were perfect. The corrupt earth was at the center of the universe while heavenly objects were assumed to be perfect spheres moving around the earth in perfect circles. Therefore, Aristotle assumed the surface of the moon must be perfectly smooth and the patterns of light and darkness on its surface were due to some parts of the moon shining more brilliantly than others. But Galileo’s telescope revealed that the surface of the moon was a landscape much like the Earth with mountains, valleys, smooth plains and rugged craters. The idea that a heavenly object was not a perfect light in the sky but in reality a world with some of the same features as the imperfect Earth, lent support to the newly announced idea of Copernicus that the Earth was not the center of the universe but instead just one of several worlds orbiting the sun. This challenge to previously unquestionable authority became one part of the scientific revolution that led to The Enlightenment idea that reason, logic, and observation should determine our views of Nature and even our form of government. Thomas Jefferson was following in the footsteps of Galileo when he wrote in the Declaration of Independence that, “We hold these truths to be self-evident, that all men are created equal …”
Because his telescope revealed the darker areas of the moon to be smoother than the brighter areas, he called those darker areas “mare,” which is Latin for “sea,” making the analogy of a smooth sea beside rugged “highlands,” which is the term now applied to the brighter regions. Today, we know the mare are actually great plains produced by ancient lava flows. The relative smoothness of those plains made them an easier target than the rough terrain of the highlands for the first lunar landings. That is why the Sea of Tranquility was chosen as the landing site for Apollo 11 on July 20, 1969.
Despite the relative flatness of the plains on the Sea of Tranquility, there were enough craters and boulders present that Neil Armstrong and Buzz Aldrin had less than thirty seconds of fuel remaining when they finally found a safe spot to land. As NASA improved their equipment and crews gained more experience, the later Apollo missions ventured to more difficult landing sites. Just two years after Apollo 11, the Apollo 15 lunar module, Falcon, landed in the Apennine mountains of the moon. This challenging landing site was located several hundred miles northwest of the Sea of Tranquility, in the area that appears to be just above the nose of what we see as “The Man in the Moon.” Astronauts Dave Scott and Jim Irwin skimmed over the 15,000 foot peaks of the Apennines and guided their spacecraft to a precise landing at the foot of an 11,000 foot tall mountain located next to a 1,200 foot deep canyon known as Hadley Rille. Unlike canyons on Earth which are usually formed by water, Hadley Rille is the remnant of a river of molten lava which cut a channel 80 miles long and nearly a mile wide.
Scott and Irwin spent three days exploring the area around their landing site and returned hundreds of pounds of rocks for study, including one that caught their attention as appearing especially significant. This turned out to be the famous “Genesis Rock” which acquired that name because it was the oldest rock ever discovered and it helped to yield important clues to how that area of the moon had formed.
Only two more Apollo missions would land on the moon after Apollo 15, but the data returned by all of the Apollo missions would lead to a better understanding of the moon. We now know that the impact of a large asteroid with the moon shattered its crust 3.9 billion years ago and pushed up the Apennine mountains at the edge of the impact. The shattered crust was later covered by lava flows forming Mare Imbrium, also known as the Sea of Rains, which forms the right eye of “The Man in the Moon.” About 500 million years later, the weakened lunar crust was covered by lava flows which formed the smoother, darker surface of Mare Imbrium. Like the other “seas” of the moon, this area was covered by a smooth surface of dark lava after most of the large impacts had ended. Since then, there have been fewer impacts so the surface of the mare have fewer impact craters than the older highlands. Thanks to the efforts of all those who worked on the Apollo program, when you gaze upon the face of “The Man in the Moon” this month, you can know you are seeing the effect of billions of years of lunar history.
Gazing at the moon with your eyes is enjoyable, but seeing these features through a telescope can make this nearby world startlingly more real! The volunteers at the Adirondack Public Observatory are eager to show you. The Roll Off Roof Observatory (RORO) is open to the public on the first and third Fridays of each month until Memorial Day, approximately on half-hour after sunset.
Whether you’re an avid amateur astronomer or just starting out, come and view through our telescopes and learn about the Wilderness Above. For updates and notices, check out our website at adirondackpublicobservatory.org and our Facebook page. On our public observing days you can also call the RORO at 518-359-6317 to talk with one of our astronomers. Observing starts about one half hour past sunset.