Meteors from Halley's Comet
May 5, 2015: As May of 2015 unfolds, Halley's Comet is more than 5 billion kilometers from Earth, receding into the inky blackness of the outer solar system, where its looping orbit takes it every 76 years. Dim and distant, history's most famous comet won't be back until sometime in 2061.
Can’t wait? You can see a piece of Halley's Comet this week.
In early May, Earth passes through a stream of comet dust left behind by Halley many years ago. The encounter will cause a meteor shower called the “Eta Aquariids” visible from both hemispheres of Earth.
"Each Eta Aquariid meteoroid is a piece of Halley's Comet doing a dive into the atmosphere," explains Bill Cooke of NASA’s Meteoroid Environment Office. "Many people have never seen this famous comet, but on the morning of May 6th they can watch bits of it leave fiery trails across the sky."
Each time Halley’s Comet swings by the sun, intense solar heat vaporizes about 6 meters of ice and rock from the comet’s nucleus. Dusty debris particles, about the size of sand grains, spread along the comet's orbit, filling it with tiny meteoroids.
"Halley treats us to a meteor shower twice a year as our planet passes by the debris cloud," says Cooke. "In May we have the Eta Aquariids, and in October the Orionids."
If astronomers named meteor showers after their parent comets, these displays would be called “Halley-ids.” Instead, meteor showers are named after their radiant—that is, the point in the sky from which the meteors emerge. In May, Halley’s meteors are called Eta Aquariids because they radiate away from the vicinity of the star Eta Aquarii. In October, Halley’s meteors are called Orionids because they seem to fly out of the constellation Orion.
“Whatever you call them, they are beautiful,” says Cooke.
You won't need binoculars or a telescope to observe Eta Aquariid meteors. The naked eye does just fine.
"Eta Aquariids are fast, moving at 66 km/s (148,000 mph!), and often trace long bright paths across the sky,” he continues. "In the northern hemisphere, depending on your latitude [the closer to the equator the better], you should see from 10 to 40 meteors at the shower’s peak."
Although Eta Aquariid meteors can appear anywhere overhead, their trails always point back toward the radiant in Aquarius. The link to Aquarius lets you know that you’ve seen a piece of Halley, and not a random meteoroid from another comet.
Cook advises a visit to the countryside, if possible. This year’s Eta Aquariids will already be competing with glare from the gibbous moon only 2 days past full. City lights will only make the situation worse.
No matter where you live, the best time to look is during the hours before local sunrise on May 6th. Wake up early and enjoy the show.
Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit: Science@NASA