Timeline of UFO belief in Christianity

This article is an exerpt from Daniel O'Connor's monumental book "Only Man Bears his Image" (Used with permission)

Timeline of Alien Belief
Date Event
Before Christ Alien belief is espoused by many pre-Christian Pagan thinkers—particularly by way of the atheistic materialist “atomist” philosophy of Democritus and hedonistic philosophy of Epicurus—but is condemned by Socrates, Plato, Aristotle, and others. (ET belief is also common in Eastern religions such as Hinduism and Buddhism)
0-500 A.D. Alien belief is condemned by all of the Fathers of the Church who opined on it (except Origen.)
543 A.D. At the Synod of Constantinople, the Church condemns Origen for many heresies, taking note of his belief in aliens (this condemnation was ratified at the Fifth Ecumenical Council, in 553, also at Constantinople)
748 A.D. Pope Zachary condemns the alien belief of Virgil
1459 A.D. Pope Pius II condemns the alien belief of Zaninus de Solcia 1400s Breaking from a millennium and a half of Sacred Tradition, Nicholas of Cusa becomes the first ever non-condemned Catholic thinker to espouse belief in aliens. Despite his enormous popularity, this teaching of his is almost universally ignored by the faithful for centuries.
1500s No Christian thinker other than Giordano Bruno promotes Cusa’s belief. 1600 A.D. Giordano Bruno is executed for heresy; with alien belief featuring prominently in the trial.
1500s-1600s The Protestant Reformation takes place. For the first time, Christendom begins to question even unanimous consensuses held throughout Sacred Tradition’s history.
1600s – 1700s The “Copernican Revolution” takes place (well after the life of Copernicus himself). The planets are observed in some detail for the first time ever with telescopes following Galileo, and thinkers (mostly secular, but some religious) increasingly insist that such planets “must” harbor life as ours does.
1700s “The Enlightenment” takes place, which seeks to overthrow Divine Authority and replace it with rationalism. The heretical “Principle of Plenitude” quickly becomes one of its main tenets, and this Principle serves as the ideological catalyst for alien belief.
1793 A.D. The Deist, Thomas Paine, publishes a blistering attack against Christianity based upon the secular world’s then near-unanimous assumption that aliens exist, in his work The Age of Reason, which becomes wildly popular and solicits countless responses for a century thereafter.
1800s Secular academia de-facto declares alien belief (“plurality doctrine”)—which had now been established as a “pillar of enlightenment optimism”—one of the requisite beliefs for scholars. The few who dissent are castigated, and acceptance of the existence of extraterrestrials becomes an unquestioned premise upon which scholarly discourse is built. Therefore, even some Catholic thinkers choose to defend the Faith (e.g., against Paine’s attack) by way of focusing not on refuting aliens—which then appeared too difficult—but rather on insisting aliens do not overthrow Christianity. Despite the total dominance of alien belief among scholars in this era, no writers venerated by the Church espoused it, no Popes supported it, and no evidence exists that the ordinary faithful ever by-and-large adopted the view. Only evidence to the contrary can be found, and even Magisterium promulgated in this period (e.g., Leo XIII’s Arcanum) implicitly rules out aliens. Later in this century, some scientists begin realizing the illogical nature of alien belief and begin writing against it.
1900s Alien belief remains common among establishment academics until improvements in astronomy and technological advancements in telescopes (and, eventually, space flights), successively refute each one of the 19th-century conjectures that had been used to justify alien belief. Eventually, academia’s pendulum swings toward the opposite direction, and most academics appear not to believe in aliens.
1947 A.D. The Roswell Incident & the Kenneth Arnold UFO Sighting. A radically new phase in the alien belief debate begins. No longer is it a “merely academic” question, it becomes a matter with massive, immediate, concrete consequences. A government device crashed in Roswell, New Mexico, but it was treated by many as an alien-piloted craft. From this moment forward, the “UFO” craze began, and steadily increased in fervor to the present day.

Note: This article is a work in progress. More to come. Check back for final edits in a few weeks.