|Discovered by||prehistoric (observation); Edmond Halley
(recognition of periodicity) (17 February 1994) (9 December
2023) last perihelion: 9 February 1986 next perihelion: 28 July
2061 |Semi-major axis||17.8 AU| |Orbital period||75.3 a|
|Dimensions||15×8 km, 11 km (mean)| |Mass||2.2 × 1014 kg| |Mean
density||0.6 (estimates range from 0.2 to 1.5 g/cm3)| |2.2 d
(52.8 h) (?)| |Apparent magnitude||28.2 (in 2003)| Halley's
Comet or Comet Halley (officially designated 1P/Halley) is the
best-known of the short-period comets, and is visible from Earth
every 75 to 76 years. Halley is the only short-period comet that
is clearly visible to the naked eye from Earth, and thus the
only naked-eye comet that might appear twice in a human
lifetime. Other naked-eye comets may be brighter and more
spectacular, but will appear only once in thousands of years.
Halley's returns to the inner Solar System have been observed by
astronomers since at least 240 BC, and recorded by Chinese,
Babylonian, and medieval European chroniclers,