The year’s very best night to watch the sky? It’s this Sunday, the 13th. You’ll see the finest meteor shower of 2015. These are the Geminids, the sky’s “Old Faithful.” Their trustworthy one‑a‑minute frequency has created reliable December sparklers for the past century.
Someone at a deli recently asked, “What did you think of the Leonids?” Whoa, the Leonids, last month? They were a dud, a zero, just as we expected. You see, most meteor showers deliver just a few shooting stars per hour. Not worth our time. True, it was the Leonids that gave us the best shower of our lives in a predawn spectacle on November 18, 2021 that produced five brilliant meteors every minute. But the Leonids only do that a few times a century. They’re not expected to perform well again until 2099.
News media often carry headlines saying, “Watch meteors tonight!” But nearly all of those showers are hype. In truth, this year, when it comes to a solid, worthy spectacle, we had only the Perseids on August 12, and now the Geminids.
Geminids are much slower than those other showers because they don’t strike us head‑on. They come at Earth sideways. At 20 miles per second, they lope along at half the speed of the Perseids. It’s very appealing. Instead of sharp, brief zaps across the sky, we get leisurely streakers.
These meteors are also the most mysterious in the known universe. All other showers are debris from comets: skimpy stuff less dense than ice. Strangely, Geminid meteors are twice as dense, yet nonetheless a bit too lightweight to be bona fide metal/stone asteroid material. So what could they be?
There are other oddities, too. All other major meteor showers have been observed for centuries or millennia. But the Geminids were unseen as recently as the Civil War, when they started as a modest shower that delivered only 20 meteors per hour. Over time they’ve grown increasingly rich; now they deliver one to two a minute.
Despite decades of searching, the source of these strange fireworks was unknown until 1983, when NASA’s infrared‑detecting satellite IRAS found a small body moving in exactly the same path as the meteoroid swarm. Named Phaethon, it has a speedy orbit that carries it far within the orbit of Mercury and then out past Mars into the asteroid belt. Since Phaethon does not develop a cometlike tail nor shed material when approaching the Sun, it was assumed to be an asteroid, a rocky body.
Fine – except asteroids don’t disintegrate to produce meteor showers: curioser and curioser. Maybe Phaethon is a true rocky asteroid that suffered enough collisions to fill its lopsided orbit with debris. Or else, maybe Phaethon is an odd, unique has‑been comet, one that completely lost its icy outer covering and is at present just a comet‑core that has perhaps acquired a coating of interplanetary dust grains. Either way, the mystery material – which leaves no trails – puts on quite a show.
Also unlike the Perseids or Leonids, Geminids don’t ask you to wait until the hours before dawn. They’re well-seen all night long, although they’re particularly abundant around midnight. If that holds no appeal, no problem; you ought to see one every few minutes even if you venture outdoors at 8 p.m.
Try to get away from lights to a place with an open expanse of sky – not just breaks between trees. Bring a folding chair to be comfortable. Take in as much sky as possible.
This year the Moon is thin and harmless and conditions are perfect. Be patient and keep your eyes glued upward. If it’s clear Sunday night, you will see meteors.
Want to know more? To read Bob’s previous “Night Sky” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com.