Halley's Comet Won't Be Back Until 2061 — But Its Debris Lights Up the Sky This Week

Halley's Comet is not back. The most famous comet in history is currently far too faint to be seen from Earth and will not return to the inner solar system until 2061. But this week, Earth is passing through the trail of dust and debris the comet left behind on its previous laps around the Sun — and that is worth stepping outside for.

The annual Orionid meteor shower peaks during the night of October 21–22, when tiny particles shed by Halley's Comet slam into Earth's atmosphere at roughly 66 kilometres per second. The friction heats the surrounding air and produces the brief streaks of light known as meteors. Under ideal dark-sky conditions, observers can expect between 10 and 20 Orionids per hour.

This year, conditions are not ideal for much of the night. A bright waxing gibbous Moon will drown out the fainter meteors for hours. The window improves significantly after moonset — around 3 a.m. local time — leaving a stretch of darker sky before dawn, just as the constellation Orion climbs high. The shower gets its name from Orion because the meteors appear to radiate from a point near that constellation, but individual streaks can flash across any part of the sky, so a wide, unobstructed view is more useful than staring at any single spot.

Even at peak rates, patience is required. Twenty meteors per hour averages to roughly one every three minutes, and they do not arrive on a schedule — several may streak across the sky in quick succession, followed by a longer lull. Skywatchers should allow at least 15 minutes for their eyes to adjust to the dark and avoid looking at phone screens or other bright lights during that time.

The Orionids are one of two meteor showers produced by Halley's debris. The other, the Eta Aquariids, occurs each May when Earth crosses a different part of the same debris trail.

Halley's Comet — officially designated 1P/Halley — is the only known short-period comet that reliably becomes visible to the naked eye from Earth, appearing roughly every 74 to 79 years. Its periodic returns have been observed and recorded since at least 240 BC, but it was not until 1705 that English astronomer Edmond Halley recognized that sightings from 1531, 1607, and 1682 were all the same object. He predicted its return for 1758; it arrived on Christmas Day that year, seen first by German amateur astronomer Johann Georg Palitzsch. The comet has been named after Halley ever since.

The comet's most recent visit, in 1986, became two very different stories. For the public, it was widely remembered as a disappointment — heavily promoted as a once-in-a-lifetime spectacle, it brightened only to third magnitude and was difficult to see from the Northern Hemisphere. The 1986 apparition was described as the comet's worst in 2,000 years, according to Space.com. Light pollution had increased dramatically since Halley's previous pass in 1910, and at its closest approach to Earth on April 10, 1986, the comet was nearly three times farther away than it had been at its minimum distance in 1910.

Those who came for the comet saw the comet — the cynics didn't — but it was there.— Henry J. Stern, New York City Parks Commissioner

For astronomers, however, 1986 was a scientific windfall. The European Space Agency's Giotto mission became the first spacecraft to observe a comet in detail, returning the first direct data on the structure of a comet nucleus. The mission supported Fred Whipple's 'dirty snowball' model — the idea that comets are composed of a mixture of volatile ices and dust — while also revealing that Halley's surface is largely made up of dusty, non-volatile materials, with only a small portion being icy. The Soviet Vega 1 and Vega 2 spacecraft also flew past, coming within roughly 8,890 km and 8,030 km respectively, and returning data on the comet's dimensions, shape, temperature, and surface properties.

The comet's next perihelion is expected around mid-2061. Anyone who wants to see the comet itself, rather than its leavings, will need to wait nearly four more decades.

Why it matters — The Orionid shower is one of the few times each year that the average person can witness a direct physical trace of Halley's Comet — the most storied object in astronomical history — without any equipment, making this week's peak a rare accessible connection to a comet that won't be seen again until 2061.

Reported by theskylive.com, theguardian.com, nightsky.jpl.nasa.gov, en.wikipedia.org, space.com, duplos.cl, newsbreak.com, sciencedaily.com