Songfacts®:

• "Halley's Comet" is a short-period comet that orbits the Sun and is visible from Earth every 75–76 years. It is named after English astronomer Edmund Halley, who calculated its orbit in 1682.
  
  Billie Eilish uses the galactic spectacle to illustrate her reluctance to give her heart to a boy. She says she "comes around" even less than the once-in-a-lifetime visit of Halley's Comet.
• Though Eilish rarely falls in love, this song finds her absolutely smitten - hook, line and sinker. She struggles to sleep and when the singer does drift off, the guy often features in her dreams. Eilish said in a Spotify commentary: "'Halley's Comet' is just about falling in love and feeling a feeling of euphoria, like you're floating. Love is a crazy, crazy thing. 'Halley's Comet' is a sweet, romantic song."
• Eilish's love interest presumably lives in the Eastern Time Zone, which is three hours ahead of the pop star's Los Angeles' Pacific Time. This links to her 2019 track "I Love You," where she sings about being with her boyfriend in New York City.
  
  We fall apart as it gets dark
  I'm in your arms in Central Park
  
  Eilish also talks on both tracks about her reluctance to fall for her beau as she's worried about becoming emotionally vulnerable. This begs the question: Are the two songs about the same guy?
• Eilish co-wrote the track with its producer, her brother Finneas O'Connell. Finneas starts the song as a piano ballad as Billie hesitantly confesses to falling in love. By the end he is distorting his sister's famous breathy vocals to capture her complex thoughts about potentially finding "the one."
• "Halley's Comet" appeared lastly in 1986 and will reappear in mid-2061. Here are a few more fun facts about the celestial body:
  
  The first recorded perihelion passage of Halley's Comet was in 240 BC.
  
  Halley's Comet and Earth experienced their closest approach to one another in 837 AD when their separating distance equaled 0.0342 AU (3.2 million miles).
  
  In 1066, Halley's Comet appeared shortly before William the Conqueror invaded England. The Norman king took it as a good omen; his battle cry became "A new star, a new king."
  
  The pictures on the Bayeux tapestry tell the story of events from 1064 to 1066, culminating in the Battle of Hastings. One scene features the first known depiction of Halley's Comet.
  
  On the night before the 1910 funeral of King Edward VII of the UK, near panic gripped Londoners as the Earth passed through the tail of Halley's Comet.
  
  Humorist Mark Twain was born on and died on days when Halley's Comet could be seen.