The sky is falling… twice!
Two of the most interesting. meteor showers will occur as the year comes to an end: the Leonid and Geminid showers, which put on a great show. Better yet, for both showers, the thin crescent moon will slip below the horizon shortly after sunset, giving way to darker nights for better viewing.
To see the Leonids, you need to hurry a little because they will reach their peak on the night of November 17, that is, tonight. Although you can go out tomorrow and continue seeing them. The Geminids will peak on December 14, so you still have time. Anyway, the Geminid meteor shower is better. The Leonids can be seen at a rate of between 10 and 15 meteors per hour, while the Geminids are more ostentatious: up to 150 meteors per hour fly through our atmosphere during that shower!
Sometimes, however, on a scale of one to 10, the Leonids spin up to 11—at least metaphorically. Historically, its peak has shown enormous upward variation, and there have been reliable reports of Leonid meteorite “storms” reaching more than 100,000 meteors per hour! That’s about 30 per second, which would be both very exciting and extremely disturbing. It really would seem like the sky is falling.
The cause of these storms dates back to the origin of the Leonids themselves: Comet 55P/Tempel-Tuttle. The comet takes about 33 years to orbit the Sun following a highly elliptical path that takes it up to three billion kilometers (approximately the same distance as Uranus from the Sun) into the interior of the solar system, to approximately the orbital distance of Earth.
Comets are a mixture of ice and rock., and as Tempel-Tuttle approaches the sun, the heat from sunlight vaporizes the ice at its core. As this vapor escapes into space, it takes with it a fraction of the comet’s material, mainly in the form of small grains of rock and dust, but also in the form of sizable pebbles, up to about a centimeter in diameter. All of this debris also orbits the sun, roughly following the Tempel-Tuttle orbital path.
However, that “more or less” is important because it summarizes several peculiarities that can make any year’s Leonids extra prodigious, or just ordinary.
Every year, in mid-November, the Earth passes by these cosmic remains.. When it does, some of Tempel-Tuttle’s debris crashes into our atmosphere at hypersonic speeds, heating up to glow briefly but brightly in the sky.
These striking flashes through Earth’s atmosphere are standard for most meteors., but some things about the Leonids make their show special. One is that Tempel-Tuttle orbits the Sun in a so-called retrograde manner: it moves in the opposite direction to that of the planets. That means we hit the Leonids head-on, which in turn means their relative speed as they pass through the atmosphere is much greater than that of most other meteors, averaging around 70 km per second. The brightness of a meteor depends mainly on its mass and speed, so such high speeds make the Leonids brighter than meteors from many other showers.
As for the famous Leonid meteor storms, each time Tempel-Tuttle approaches the sun it releases a new batch of meteorites (the term for fragments of space debris that later become “meteorites” by entering and burning up in a planet’s atmosphere). The pressure of sunlight and the gravitational pull of the planets act on these streams of meteorites, pulling them away from the comet into slightly different orbits. Sometimes the Earth passes through a particularly dense stream, which dramatically increases the number of meteors. The last major storm from such a stream occurred in the early 2000s, and the next one is predicted to occur in 2033. Many hundreds of meteors per hour could light up Earth’s skies then.
So this year’s Leonids aren’t expected to be especially stormy, but there could still be surprising spikes in activity. The best thing you can do is go out and look!
The December Geminids are also unusual because, unlike the meteors of almost all other annual showers, their parent body is not a comet but an asteroid. In this case it is 3200 Phaethon, a rock about 6 km in diameter. Its orbit takes it past Mars but drops it a scorching 21 million kilometers from the sun, closer than Mercury’s orbit.
Experts assumed for many years that the intense heat of that narrow passage vaporized the rock on Phaeton’s surface and that this was the source of the Geminid meteoroids. Research published just this year in the Planetary Science Magazine, however, it has a different conclusion. Scientists modeled how the particles would leave Phaethon if they were produced by solar heating and found that the subsequent orbit they would take does not match what is actually observed.
However, when the paper’s authors assumed that a small asteroid hit Phaethon in the past, the resulting violent rock ejection matched the Geminids’ orbits much better. In fact, two other asteroids, called Year 1999 and 2005 UDBoth have orbits very similar to Phaethonimplying that all three were formed when a larger asteroid broke up in a large collision.
If true, this means that every Geminid meteor you see is a small piece of shrapnel from two asteroids that collided with each other a long time ago. That’s really cool.
The Geminids orbit the Sun in the same general direction as the Earth does., so they overtook us at a more majestic speed of 35 kilometers per second, still dozens of times faster than a rifle bullet. The meteor shower is also known for having larger chunks, so in addition to offering more meteors per hour, it can also be very bright.
What do you need to do to see these two heavenly performances?? Unlike many other events in the sky, for the Leonid and Geminid showers (and all other meteor showers), you don’t need binoculars or a telescope. In fact, I suggest you don’t use them at all because meteors cross the sky so fast that if you’re leaning over an eyepiece, you probably won’t see them.
Instead, find a location away from lights and artificial objects that obscure the sky, such as buildings and trees. The darker and clearer your view, the better, because meteors can appear anywhere in the sky. A blanket or lounger is best for resting; you want to be comfortable. Dress warmly, of course! I think hot chocolate makes the night even better.
The best time in general to see rain is after midnight local time, which is when you are on the part of the Earth that faces our planet’s direction of travel. (This is like riding in a car in the rain; raindrops mainly hit the front windshield and not the rear.) The Leonid shower is known for its Earth-grazing meteorites, which enter the atmosphere at a very low angle, and which can shine brightly. burns all over the sky. These Earthgrazers are best when Leo (the place in the sky from which meteors appear to radiate, called the shower’s “radiant”) rises above the horizon around 11 p.m. local time.
Meteor showers are a great excuse to get out into the night sky, and they’re even better in the company of friends and family. I used to wake up my daughter when she was very little so we could go out and see them, and I still cherish those memories. If you can, spend some time observing fragments of asteroids and comets on their final journey through our sky and make your own memories.