Understanding our Place in the Universe - Part I

Introduction: Making Sense of the Night Sky

Image Credit: Nathaniel J. Baskin, earthisaplanet.blogspot.com

Since the dawn of humanity, our species has gazed up at the night sky with a sense of wonder, eager to ponder the mysteries of the heavens above. It is only natural for us on Earth to yearn for a sense of connection with the ethereal, and for millennia, our most inquisitive minds have attempted to understand our place in the universe. In the tens of thousands of years that make up human history, however, it was not until the past few centuries that we fully grasped our present understanding that Earth is not the center, but one of many planets within the cosmos. Modern astronomy challenges our sense of significance to the core, and ultimately it is up to us to find meaning within the vast emptiness that surrounds us. As we look up at essentially the same sky tonight that our earliest ancestors saw in the past, it is important to remember that our modern understanding would not exist without the discoveries of curious minds throughout human history.

Under reasonable viewing conditions, even the most prehistoric observer who knew nothing of modern astronomy (who we shall refer to as Fred) would have been able to identify several prominent celestial features. The first would be thousands of twinkling points of light in all directions, some brighter than others, and some with a faint red or blue tinge. Fred would have also noticed a bright white orb that traversed the sky almost every night. He observed that the orb's shape varied predictably, from a sliver of a crescent to a full circle and back within a cycle of approximately 27 (Correction: 29.5) days. Occasionally, Fred may have spotted this orb in the early morning or evening hours when it was still light out. The final feature that our early human could easily identify was a faintly glowing band of patchy light stretching across the sky from end to end. These features would ultimately be referred to as the stars, the Moon, and the Milky Way, and are some of the defining characteristics of the night sky.

The more advanced human who had settled into an agricultural community (let's name her Mary) would have eventually noticed that all stars appeared to be fixed in position on a rotating celestial sphere. Mary identified constellations of stars that formed recognizable patterns, and observed that over the course of the evening, the sphere appeared to rotate around her. She also noticed that from day to day, the position of stars on the sphere appeared to be slightly shifted with respect to each previous evening. More peculiarly, this created a cycle that matched that of the seasons - at the beginning of each winter, the same constellations were visible at more or less the same location at the start of the evening. Additionally, the moon appeared to travel around the celestial sphere in a cycle related to its phases, roughly 12 times per seasonal cycle. This definitely came in handy for our early farmers, since the location of the constellations relative to the Moon and Sun could indicate when a new season was coming.

As the agricultural communities of Mary's time developed into larger, more permanent civilizations, their inhabitants identified five 'stars' that seemed to wander across the celestial sphere separately from the rest. Their motion was perplexing to early observers, with some even appearing to periodically switch directions. As a result of their peculiar paths, these 'wandering stars' became associated with the gods, and their positions were assumed to be tied to earthly events and to offer predictive power. Eventually, they would be referred to as the classic planets Mercury, Venus, Mars, Jupiter, and Saturn. For a long time, the Sun and Moon were also treated as planets, and the universe was viewed from a geocentric perspective, with the Earth at the center. It was not until the time of Copernicus when a heliocentric theory was proposed to better account for observations of the night sky. Under this new model, the Earth rotated about its axis once per day, the Moon orbited the Earth once per month,  and the Earth orbited the Sun as a planet once per year.

From our perspective at Earth's surface, it is not inherently obvious that we are standing on a planet like the ones we see in the sky, or that our planet is spherical like the rest. When Copernicus first introduced the heliocentric model of the Solar system, much of society had initially rejected the idea rather fervently because it conflicted with a deeply held sense of grand human importance. Individuals like Galileo Galilei who challenged the geocentric dogma faced substantial backlash before society ultimately accepted the new information. Nevertheless, our species' inherent curiosity has ultimately allowed us to develop a more accurate understanding of our place in the universe from observing the night sky and making sense of the stars and planets. In order to maintain perspective, it is imperative to continue looking up with curiosity lest we wish to sever our connection with the cosmos and retreat into isolation.