Chaucer saw Halley's Comet?

Chaucer did see Halley's Comet. It wasn't called Halley's then, but astronomers, calculating backward, noted details of appearances of a comet (Latin, cometa, long-haired star) at 70-75 year intervals since at least 240 BC. Many chronicles tell of multiple tails, or a tail that stretched 60 degrees across the sky, or a star whose light was greater than the brilliance of the moon. It is claimed that there is no mention of the 1378 apparition. But Chaucer may have left one.
     What do we know about comets? They appear, stay a while among the stars, then vanish. They have long tails and can be visible to the naked eye. In the Middle Ages they were believed to be portentous, usually disastrous. A chronicler in 1066 rants, "You've came, have you? . . .  you source of tears to many mothers, you evil. I hate you."
     Chaucer could have read about these intruders into the orderliness of the heavens. He surely saw one firsthand in 1378. The poet's Canon, sudden intruder on the Canterbury journey, has all the characteristics of a comet among the celestial pilgrims.
     The narrator draws attention to the meeting about to take place.
          Before we had ridden fully five miles, 
          At Boghtoun under Blee we began to be overtaken
          By a man clothed in black clothes,
          And underneath he had a white surplice.
          His hackney, that was all dappled grey,
          So sweat that it was a wonder to see.
The narrator is captivated by the amount of sweat produced by the advancing figure.
          About the breastplate the foam stood very high,
          He was all flecked with foam and looked like a magpie.
Froth is heaped on the harness and spatters the rest of the horse's body, looking like white splotches on an otherwise black bird.
          But it was a joy to see him sweat!
          His forehead dripped like part of a distillery
Perspiration creates an aura surrounding the rider--a very workable depiction of a comet.
     Besides the sweat, the Canon's "garments" become part of this trailing image.
          In my heart I began to wonder
          What he was, until I understood
          How his cloak was sewed to his hood;
          For which, when I had thought a while,
          I judged him to be some sort of canon.
A canon is a type of clergyman. (We'll have reason to expand on that later.) Wonderment ceases when it's understood how the cloak and hood were joined. That doesn't help understand "what he was," but it fits the comet game.
     A hat is added for good measure.
          His hat hung by a cord down his back.
The connection is tenuous. The narrator describes how it's possible for cloak, hood and hat to stay together in spite of the pace at which the Canon travels.
     Speed of a comet, compared to the movement of the rest of the heavens, is the topic when,
          It seemed he had pricked (spurred), for three miles.
He's prodding his mount to close the gap between the pilgrims and himself. Chaucer's "it seemed" indicates "but not really." The distance is an imaginative approximation.
          For he had ridden at more than a trot or pace;
          He had spurred (sped), as if he were a madman.
     The Canon/comet will be in their presence for a little over 100 lines. Then, as expected, he "fled away" and was gone forever.
     So far, we've seen the insubstantial train of the comet and its speed. Visibility is also part of its spectacle. Here, using word-play with "lite," which means both light and little, the game continues.
          It seemed he carried "lite" array  (little clothing).
          All light for the summer rode this worthy man.
He carried little clothing is the usual reading. But, as our comet, the words tell of his luminous quality as well, his lighted participation among the arranged figures in the night sky.
     It's curious that the Canon is prepared for summer if the pilgrims had set out one April morning. The words "lite array" for the "somer," that is, "Light for all of the summer," provide a reasonable time span for a comet's visibility.
     When the Host comments on the tattered condition of the clergyman's clothing the term lite is used once again. And, for the last time, lite accompanies the circumstances of his departure.
     When the narrator first notes the Canon's approach, a brief mention is made of a male (in Middle English, either a male human being or a bag, pouch) on the hind-quarters of the "horse." We'll take that up next time.