September 2015 – Astronomy of the Renaissance

Heavens Above!

Heavens Above! is the astronomy section of the Sci@StAnd website, updated each month to highlight a particular phenomenon in this month’s night sky. Last month, we discussed the dwarf planet Pluto and the New Horizons spacecraft flyby. This month, we will profile three prominent astronomers of the Renaissance and their discoveries.

Fig 1. Painting of Renaissance Astronomy (Granger. Galileo Galilei 1564-1642)

Fig 1. Painting of Renaissance Astronomy (Granger. Galileo Galilei 1564-1642)

Although modern astronomy can trace its roots back to ancient times, the most prolific period of astronomical progress occurred during the Renaissance. In about the span of a human lifetime, we went from being centre of everything to a single planet amongst many others. For some the news was enlightening, but for many it was blasphemy.

In the late fifteenth century, scholars rediscovered the writings of the ancient Greeks. This was the beginning of the Renaissance, and of neoclassicism. Much of the forgotten knowledge brought light to a continent on the brink of destruction, purging the remaining shards of the medieval age. Along with this rediscovery came re-evaluations and criticisms of old knowledge. One such critic was a young clerk at a cathedral in Frombeck, Poland.

Fig 1. Potrait of Nicolaus Copernicus (public domain)

Fig 2. Portrait of Nicolaus Copernicus (public domain)

Nicolaus Copernicus suggested that rather than having the Earth at the centre of it all, perhaps the Sun should suit that position. This wasn’t merely a clerical proposal, but a deeply rooted scientific observation. Before taking up his place within the church, Copernicus was a student of mathematics and astronomy. After surveying the planets with his naked eye and tracking their motions, he calculated the necessary mathematics in order to support his theory. The physics that would be developed over the next century would prove his observations true.

He described his theory, called heliocentric or sun-centred, in a small manuscript called “Commentariolus” or the “Little Commentary”. He later developed his ideas into a more complete book titled “On the Revolutions of the Celestial Spheres”, and despite callings from the scientific community and elsewhere, Copernicus declined publication until on his deathbed in 1543. He was right to fear reprehension by the church, as Martin Luther had incited the protestant reformation only four years earlier. Thankfully, the theory had not yet gained mainstream interest. It was probably a good choice.

When Johannes Kepler was born in 1571, nearly everyone believed that all the planets and the sun orbited the Earth. He would become one of the greatest and most powerful defenders of the heliocentric model, using newly crafted mathematics to place the theory in the mainstream of scientific thought.

In 1596 Kepler wrote his first public oration on the heliocentric model, known at that point as the Copernican system. Searching for further instruction, he assumed the position of assistant to Tycho Brahe, who was then the most renowned astronomer in the world. Brahe’s state-of-the-art observatory in Prague collected information on the orbits of the planets and held the most accurate tables and charts at the time. When Brahe, who was reluctant to share the entire breath of his collections, died in 1601, Kepler gained access to all of the observations and saved them from being sold off.

Fig 2. Portrait of Johannes Kepler (public domain)

Fig 3. Portrait of Johannes Kepler (public domain)

Using these observations, Kepler formulated three of the most fundamental laws of celestial mechanics. His first law stated that all orbits are ellipses, not circles. This led to his second law, that planets travel more slowly at the furthest points in their orbits. These two laws helped to explain a series of previously unsolved mysteries in astronomy and gave direct evidence for a heliocentric universe. His third, and most powerful, law is purely observational. It says that if one can measure the period of an orbit, they can calculate the radius of that orbit. More specifically, the square of the period is equal to the cube of its radius. Newton would later amend this law to generalize it for all planetary and stellar systems.

Kepler summarized his work in several publications, most notably the “Astronomia Nova”, or “New Astronomy”. During his career he faced surprisingly minimal backlash from the church, likely due to his own connections with the clergy and academia. He died in 1630, upon returning from travels across Europe as a military adviser in the Thirty Years’ War.

The most revolutionary of the three profiles presented in this article is undoubtedly that of Galileo Galilei. Born in 1564 in Pisa, Italy, Galileo was a gifted student with visible intelligence. He began his career in mathematics at a teaching post at the University of Pisa, where he conducted experiments on motion and what would become known as gravity. He then moved to the University of Padua, where he gained fame from well-attended public lectures.

At the turn of the century, Galileo began work on military applications of physical principles such as hydrostatic balance and trajectories. This lead to his universal law of acceleration and vocal support for the Copernican system. Upon learning about recent developments in optics, Galileo constructed a simple telescope which allowed him to view the planets with unprecedented clarity.

Fig 3. Portrait of Galileo Galilei (public domain)

Fig 4. Portrait of Galileo Galilei (public domain)

He discovered that Jupiter had four orbiting stars, which we now know as moons. He also described the phases of Venus, similar to those seen of our moon. He also observed blemishes on the sun, which refuted the longstanding notion that the heavens are perfect bodies. This mounting body of evidence in favour of the Copernican system was brought to the attention of the church. Following the publication of a letter in which Galileo addressed his evidence in the context of scripture, the Inquisition ordered him to withhold all teachings of the Copernican system and reprimanded him for independently interpreting scripture without the consent of the church.

In 1623, Cardinal Maffeo Barberini, a close friend of Galileo, was elected Pope Urban VIII. Barberini encouraged Galileo to publish his work, which included the now famous “Dialogue Concerning the Two Chief World Systems” in 1632. Although he held close relations within the church, Galileo was summoned before the Inquisition and charged with heresy. He served his sentence under house arrest until his death in 1642, largely ignoring any restrictions placed on him by the church. During his final years, his works were privately published in France and Holland.

The contributions made by these three scientists has undoubtedly changed the world, fundamentally altering our view of ourselves. The next revolution of this magnitude wouldn’t be for another three hundred years, when Edwin Hubble discovered that we are only one galaxy amongst a sea of billions upon billions of others. Our understanding of the universe continues to evolve.

Next Month: The Mystery of Dark Energy

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