Comet Hale–Bopp
What is Comet Hale–Bopp?
Comets· Nucleus ~60 km. A great comet of the late 20th century. Its nucleus is far larger than Halley's; in spring 1997 it was visible to the naked eye even from cities, and it stayed visible without a telescope for a record 18 months.
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.
Hale–Bopp's third tail, made of sodium
Comet tails are usually described as two kinds. One is the blue ion tail, blown straight out by the stream of particles coming from the Sun. The other is the dust tail, which curves along the path the comet has travelled. In April 1997 a third tail was found on Hale–Bopp: a thin, straight tail made only of sodium atoms.
It could be seen only through telescopes fitted with a special filter that lets through just the yellow light given off by sodium. It stretched about 50 million km, roughly a third of the distance from Earth to the Sun, and was formed as sunlight pushed the sodium atoms away. Whether the sodium came from dust or straight from the nucleus is still debated. Sodium tails have since been seen in other bright comets as well.
The comet in depth
Comet Hale–Bopp was discovered on 23 July 1995 by Alan Hale and Thomas Bopp, working separately in the United States. At the time it was 7 AU away, beyond Jupiter's orbit, and being visible from so far meant it had to be very large. Its nucleus is estimated at 40 to 80 km across, more than five times the size of Halley's (about 11 km). It made its closest approach to the Sun on 1 April 1997.
Hale–Bopp was at its brightest in March and April 1997, nearly as bright as Sirius, the brightest star in the night sky, so it was easy to see even from cities. Photographs showed a straight blue tail and a curved white tail spreading apart. The blue tail is made of gas ions and the white tail of dust. It remained visible to the naked eye for about 18 months, a record.
A close pass by Jupiter in 1996 changed Hale–Bopp's orbit. Before, one lap took about 4,200 years; now it takes about 2,400, so it will next return in the 4380s. In the orbit view you can see its path stretching far past Neptune to about 370 AU. In the Sky view, go to the evening of 22 March 1997 (11:30 UTC) to see the comet's position in the north-western sky.
Frequently asked
- How close does Comet Hale–Bopp get to the Sun?
- The perihelion of Comet Hale–Bopp is 1997-04-01.
- How long is the orbital period of Comet Hale–Bopp?
- The period of Comet Hale–Bopp is ~2,400 yr (was 4,200).
- In one line, what is Comet Hale–Bopp?
- Comets — A great comet of the late 20th century.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.