Halley's Comet makes its closest approach to Earth at a distance equal to 0.0342 AU (5.1 million kilometres/3.2 million miles).

Halley's Comet is the only known short-period comet that is consistently visible to the naked eye from Earth, appearing every 72–80 years, though with the majority of recorded apparitions occurring after 75–77 years. It last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061. Officially designated 1P/Halley, it is also commonly called Comet Halley, or sometimes simply Halley.

The astronomical unit is a unit of length defined to be exactly equal to 149597870700 m. Historically, the astronomical unit was conceived as the average Earth-Sun distance, before its modern redefinition in 2012.

April 10 is the 100th day of the year in the Gregorian calendar; 265 days remain until the end of the year.