Comet Hale–Bopp perihelion
Naked-eye visible for a record 18 months, its twin ion and dust tails shone even over city lights.
The moment of Comet Hale–Bopp perihelion: https://nowsky.org/e/halebopp-1997 — opens at the right place and time, replayable, no login.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
Hale–Bopp was unusual from the moment of discovery. On 23 July 1995 Alan Hale and Thomas Bopp, unknown to each other, found it the same night from their own back yards, when it was 7 AU from the Sun — beyond Jupiter's orbit. Being visible that far out meant it was big: the nucleus is about 60 km across, four times Halley's.
Around perihelion on 1 April 1997 (0.91 AU) it brightened to nearly magnitude −1, the brightest object in the sky after Venus. The blue ion tail and white dust tail split visibly even from cities, and through March and April the comet hung in the north-western evening sky like a fixture, in the same place night after night.
Above all, its eighteen months of naked-eye visibility remain an unbroken record — from May 1996 to December 1997 the comet was in the night sky for a year and a half. Its next return is roughly 4,385 years away; the previous visit was around 2200 BC, in the time of Egypt's Old Kingdom.
The discovery story is a snapshot of amateur astronomy's golden age, and the rush to share comet photographs on the early internet is remembered as the start of online astronomy culture. The orbit view shows the immense ellipse and the sky view's comet replay brings back the spring sky of 1997.
Why it matters
Hale–Bopp is the textbook case of size making brightness. It never came within 1.3 AU of Earth, yet it became a great comet because its nucleus was enormous — the exact opposite of Hyakutake, which was small but close the year before.
Its scientific legacy includes a third tail: besides the ion and dust tails, a faint tail of sodium atoms was confirmed for the first time. Measurements of its deuterium ratio added evidence against the idea that Earth's oceans came from comets — a debate carried on by Rosetta's measurements at 67P.
It also left a shadow in popular culture. In March 1997 members of the Heaven's Gate group in the United States died in a mass suicide, believing a spacecraft followed the comet. The tragedy is still cited when the responsibilities of science communication are discussed.
How to watch
Hale–Bopp is now more than 50 AU from the Sun, but its nucleus is so large that big telescopes still track it — a rare comet seen to be active into the 2020s. Its next return is about 4,385 years away.
Choose Hale–Bopp in the sky view's event list to replay the evening of 1 April 1997 in the north-west — the comet and its twin tails hanging between Andromeda and Perseus. With Seoul as the location it stood some 20° above the horizon around 8 pm.
Select Hale–Bopp in the orbit view for its orbit, tilted nearly 89° to the ecliptic so that it pierces the solar system almost vertically; the event replay shows perihelion and the geometry with Earth.
See this for yourself — replay the moment in the orbit view
Background
The previous perihelion is computed at about 2215 BC; a close pass by Jupiter then shortened the period from 4,200 to 2,500 years, and this passage lengthened it again. Hale–Bopp's orbit changes from visit to visit with planetary perturbations.
Near perihelion the nucleus shed 250 tonnes of dust per second, and the coma grew larger than the Sun. Spiral jets from the nucleus, rotating every 11.3 hours, were photographed from the ground.
By rare coincidence Hale–Bopp stood beside the Sun during the total solar eclipse of 9 March 1997 over Mongolia and Siberia, and photographs survive of the comet and the corona in one frame under the darkened sky.
Twenty months passed between discovery and perihelion, and the brightness forecasts were revised several times along the way. Because it was already bright at great distance there was hope of a “comet of the century”, tempered by memories of Comet Kohoutek in 1973, which had been trumpeted as a great comet on the strength of its discovery brightness and fizzled — the byword for the uncertainty of comet predictions. Hale–Bopp did the opposite, brightening close to forecast, and left the lesson that comets with large nuclei are predictable.
FAQ
How long was it visible?
Eighteen months to the naked eye, from May 1996 to December 1997 — still the record.
How big is the nucleus?
About 60 km across, four times Halley's — which is why it was found beyond Jupiter's orbit.
When does it return?
In about 4,385 years; its last visit was around 2200 BC.
Who discovered it?
Alan Hale and Thomas Bopp, independently, 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.