One of the most famous annual meteor showers is reaching its peak — the Leonids. These ultrafast meteors are due to crest overnight tonight and into early Tuesday morning (Nov. 16-17).
The Leonids are known for producing some of the most amazing meteor displays in the annals of astronomy. Most notable are meteor storms in 1799, 1833 and 1966, when meteor rates of tens of thousands per hour were observed. More recently, in 1999, 2001 and 2002, lesser Leonid displays of "only" a few thousand meteors per hour took place.
Unfortunately, those turn-of-the-century showers gave some skywatchers the impression that they could expect a similar occurrence of celestial fireworks from the Leonids every year. So, it is important to stress at the outset that any suggestion of a spectacular meteor Leonid display this year is, to put it mildly, overly optimistic.
If you're expecting a memorable sky show early on Tuesday morning, we're sorry to break this to you: The 2020 version of the Leonids is more than likely going to be a disappointment, since the shower will probably be weak and there likely will be long stretches when not a single one will be seen.
The Leonids received their moniker because the shower's emanation point — the spot from which the meteors seem to fan out — is located within the constellation of Leo, the Lion, from within the backward question mark pattern of stars known as "The Sickle."
The meteors are caused by Comet Tempel-Tuttle, which sweeps through the inner solar system every 33.3 years. Each time the comet passes closest to the sun, it leaves a "river of rubble" in its wake — a dense trail of dusty debris. A meteor storm is possible only if Earth passes directly through a fresh dust trail ejected by the comet over the past couple of centuries.
The lion's share (no pun intended) of comet dust can be found just ahead of and trailing behind Tempel-Tuttle. The comet last swept through the inner solar system in 1998. That's why spectacular meteor showers were seen in 1999, 2001 and 2002, with declining numbers thereafter.
In 2016, Tempel-Tuttle reached aphelion, the point in its orbit that's farthest from the sun —1.84 billion miles (2.96 billion kilometers). Now the comet is on its way back toward the inner solar system and will sweep closest to the sun again in May 2031.
Slim pickings in 2020
But it's also in the general vicinity of the comet where the heaviest concentrations of meteoroids are found as well. In contrast, at the point in the comet's orbit that Earth will be passing through on Tuesday morning, there's only a scattering of particles, bits of comet debris that crumbled off the comet's frozen nucleus perhaps a millennia or two ago.
So, the 2020 Leonids are expected to show only low activity this year. Mikhail Maslov, a highly regarded Russian expert in meteor shower predictions, forecasts a "plateau-like" level of maximum activity, which he suggests will stay approximately at the same level — about 15 per hour — during the period from 0300 GMT to 2000 GMT on Nov. 17 (10:00 p.m. to 3 p.m. EST on Nov. 16-17).
Canadian meteor forecasters Margaret Campbell-Brown and Peter Brown are a little more optimistic. In the 2020 "Observer's Handbook of the Royal Astronomical Society of Canada," the duo suggest rates of up to 20 per hour, with a maximum occurring at 1200 GMT (7 a.m. EST) on Nov. 17. That comes at or before sunrise throughout much of North America.
The International Meteor Organization forecasts rates of 10 to 20 per hour, with a peak at around 1100 GMT (6 a.m. EST) on Nov. 17. The moon is just past new and will pose no interference whatsoever. But whatever forecast you trust, be mindful that even at their very best, Leonids are expected to dart across your line of sight on an average of once every 3 to 6 minutes. And that's assuming you have a wide-open view of the entire sky and are blessed with dark, non-light polluted conditions.
How to observe and what to look for
Watching a meteor shower is a relatively straightforward pursuit. It consists of lying back, looking up at the sky and waiting. Keep in mind that any local light pollution or obstructions like tall trees or buildings will further reduce your chances of making a meteor sighting.
Leo does not start coming fully into view until the after-midnight hours, so that would be the best time to concentrate on looking for Leonids. As dawn is about to break at around 5 a.m. local time, The Sickle will have climbed more than two-thirds of the way up from the southeast horizon to the point directly overhead (called the zenith).
Also, because the Leonids are moving along in their orbit around the sun in a direction opposite to that of Earth, they slam into our atmosphere nearly head-on, resulting in the fastest meteor velocities possible: 45 miles (72 km) per second. Such speeds tend to produce bright meteors, which leave long-lasting streaks or vapor trains in their wake.
A mighty Leonid fireball can be quite spectacular, but such outstandingly bright meteors are likely to be very few and very far between this year (if any are seen at all).
A look ahead
The good news is that, as Comet Tempel-Tuttle draws closer to the sun, the Leonids are expected to slowly improve. According to Maslov, a greater preponderance of bright meteors is possible, especially in 2022 and 2025. But the truly spectacular Leonid shows will not start coming until 2033, when both Maslov and another well-known forecaster, the Frenchman Jeremie Vaubaillion, predict hourly rates of several hundred or more possible. And the very best years of the next Leonid cycle will likely be in 2034 and 2035.
In 2034, debris shed by Tempel-Tuttle from the year 1699 should lead to anywhere from 400 to 1600 Leonids per hour, followed some hours later by another surge of activity from material shed by the comet in 1767; 250 to 1000 Leonids per hour are possible. Finally, in 2035, 300 to 900 Leonids are possible from a dusty meteoroid trail dating back to 1633.
But if you can't wait until then, here's some good news: A prolific meteor shower is coming our way in less than a month: the December Geminids, now considered to be the best meteor shower of the year, producing over 100 per hour. They are expected to peak on the night of Dec 13. Space.com will provide you with all the details as we get closer to that date. So, stay tuned!
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.