Comet Hale–Bopp
What is Comet Hale–Bopp?
Comets· Nucleus ~60 km. The great comet of the 20th century — a nucleus five times Halley's, whose twin blue ion and white dust tails shone over city lights in spring 1997 and stayed naked-eye visible for a record 18 months. Replay its long orbit, and the March 1997 sky, in the simulators.
Where Comet Hale–Bopp is in your sky right now: https://nowsky.org/solar/sky?sel=comet:halebopp9&loc=seoul&sd=1997-03-22T11:30Z — location and time set automatically, no login.
Past visits and the next return
Orbit and period
| Nucleus | ~40–80 km |
|---|---|
| Perihelion | 1997-04-01 |
| Period | ~2,400 yr (was 4,200) |
| Record | 18 months naked-eye — a record |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- How close does Comet Hale–Bopp get to the Sun?
- 1997-04-01.
- How long is the orbital period of Comet Hale–Bopp?
- ~2,400 yr (was 4,200).
- In one line, what is Comet Hale–Bopp?
- Comets — The great comet of the 20th century — a nucleus five times Halley's, whose twin blue ion and white dust tails shone over city lights in spring 1997 and stayed naked-eye visible for a record 18 months.
- Where is Comet Hale–Bopp in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
The third tail, drawn in sodium
Comet tails come in two kinds, or so the textbooks said — the blue ion tail streaming straight out on the solar wind, and the yellow dust tail curving along the orbit. In April 1997 Hale–Bopp showed a third. A thin, straight tail made only of sodium atoms, visible solely through telescopes fitted with a sodium D-line filter, it reached 50 million km, pushed out by the pressure of sunlight at an angle between the other two.
Where the sodium came from is still argued — released as dust grains broke down in sunlight, or evaporated straight from the nucleus. Hale–Bopp was large enough for the third tail to be caught for the first time, but sodium tails have since been confirmed in other bright comets, and the phenomenon is now filed as common but usually too faint to see. It counts among the most unexpected of Hale–Bopp's observational legacies.
The comet in depth
Comet Hale–Bopp was discovered independently on 23 July 1995 by Alan Hale and Thomas Bopp. It was already visible at 7 AU, beyond Jupiter's orbit — a sign of an unusually large comet, and expectations of a great comet followed. Its nucleus is estimated at 40–80 km across, more than five times Halley's 11 km, and it reached perihelion at 0.91 AU on 1 April 1997.
At its peak in March and April 1997 it shone at magnitude −1, easily seen from cities, with a blue ion tail and a yellowish dust tail fanning apart in countless photographs. Scientifically it delivered the first detection of a sodium tail, and its deuterium ratio fed the debate over the origin of Earth's oceans. A 1996 pass near Jupiter shortened its period from about 4,200 to 2,400 years, so it returns in the mid-2400s.
Track Hale–Bopp in the orbit view to see an orbit that stretches far past Neptune, out to 370 AU. In the Sky view, move to Seoul on the evening of 22 March 1997 to replay the comet hanging in the northwestern sky.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.