Comet Hale–Bopp perihelion
This great comet rounded the Sun on 1 April 1997. It stayed visible to the naked eye for about 18 months, a record, and its twin tails could be seen even from cities.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
Comet Hale–Bopp was discovered separately by two people on the same night, 23 July 1995. Alan Hale was observing from his driveway in New Mexico, and Thomas Bopp was looking through a telescope in the Arizona desert. At that time the comet was 7.2 AU from the Sun, between the orbits of Jupiter and Saturn. Being visible that far away meant it had to be very large.
In fact its nucleus is estimated to be about 60 km across, roughly six times the size of Halley's Comet. A large nucleus releases a lot of gas and dust when the Sun warms it. That is why Hale–Bopp looked very bright even though it never came closer to Earth than 1.3 AU.
On 1 April 1997 the comet passed 0.91 AU from the Sun. Around then it brightened to about magnitude −1, and among the stars in the night sky only Sirius was brighter. Its blue ion tail and white dust tail could be seen splitting apart even from cities, and throughout March and April it stayed in the same part of the north-western evening sky.
Above all, it stayed visible to the naked eye for a long time, about 18 months. From May 1996 to December 1997 it was in the night sky for a year and a half, twice as long as the previous record holder, the Great Comet of 1811, at about nine months. Its next visit will be around the year 4385, and its last visit was around 2215 BC.
When and where to see it
Because its nucleus is so large, Hale–Bopp was tracked long after it left. In 2022 the James Webb Space Telescope photographed it 46.2 AU from the Sun. It is even farther away now, and its next return will be around the year 4385.
Choose Hale–Bopp in the sky view's event list to replay the north-western sky on an early April evening in 1997. The comet hangs between the constellations Andromeda and Perseus, with its two tails pointing upward. Move the date backward and forward to see how it stayed in the evening sky for weeks.
Select Hale–Bopp in the orbit view to see its orbit, tilted about 89 degrees to the plane of the planets. The comet seems to plunge through the solar system from top to bottom. The event replay shows the moment it rounded the Sun together with Earth's position at that time.
See this for yourself — replay the moment in the orbit view
Past returns and history
Hale–Bopp's orbit changed during this visit. In April 1996 the comet passed 0.77 AU from Jupiter, and Jupiter's gravity pulled on its orbit. One trip around the Sun had taken about 4,200 years since its visit around 2215 BC, but now it takes only about 2,400 years.
Near the Sun, Hale–Bopp was extremely active. At its peak it is estimated to have thrown off about 2,000 tonnes of dust every second. The nucleus spun about once every eleven and a half hours, and ground-based telescopes photographed jets of gas curling into spiral patterns because of that rotation.
On 9 March 1997 a total solar eclipse was seen from northern China, Mongolia and eastern Siberia. While the Moon covered the Sun and the sky grew dark, Hale–Bopp was visible near the Sun at the same time. This created the rare chance to capture the eclipse's corona and the comet in one photograph.
Twenty months passed between discovery and the comet's closest approach to the Sun, and the brightness forecasts changed several times along the way. People were cautious because in 1973 Comet Kohoutek had been expected to become a great comet and turned out faint. Hale–Bopp, however, brightened close to what had been predicted.
Why it matters
Hale–Bopp is a classic example of a comet that was bright because it was big, even though it stayed far away. Comet Hyakutake, a year earlier, was small but came very close to Earth. Hale–Bopp was the opposite case, and together the two comets show that brightness depends on both size and distance.
It also led to scientific discoveries. Besides the ion and dust tails, a faint third tail made of sodium atoms was confirmed. Measurements also showed that the share of heavy hydrogen, called deuterium, in the comet's water was about twice that in Earth's oceans. This suggested that comets could not be the only source of Earth's water, and the question was later taken up again by the Rosetta spacecraft.
There was also a sad event. In March 1997, 39 members of a religious group in the United States called Heaven's Gate took their own lives, believing that a spacecraft was following the comet. The event is often mentioned as an example of what can happen when false beliefs spread alongside science news.
FAQ
How long was it visible?
About 18 months to the naked eye, from May 1996 to December 1997, twice the previous record.
How big is the nucleus?
It is estimated at about 60 km across, roughly six times the size of Halley's Comet. That is why it could be found beyond Jupiter's orbit.
When will it return?
Around the year 4385. Its last visit was around 2215 BC.
Who discovered it?
Alan Hale and Thomas Bopp, separately, on the same night: 23 July 1995.
Related
- Comet Hyakutake sweeps past Earth
- Comet NEOWISE — the great comet of 2020
- Halley's Comet perihelion (1986)
- Jupiter — object index
- The Sun — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.