This month marks the return of the Orionid Meteor Shower, with its peak in the early morning hours of October 21. Up to 20 meteors per hour will be visible during this time.
Perhaps the best known of all comets is Halley. It is named after the 17th-18th century astronomer Edmond Halley (correctly pronounced so that it rhymes with rally, not daily). This familiar object is not only popular but also very reliable, visiting the inner solar system every 76 years.
Unfortunately, this is a long time to wait; Halley last came into view in 1985/1986 and won’t be back again until 2061. That means another 41 years of waiting for its reappearance. But thanks to the convenient interplay between Earth and Halley debris floating in space, sky watchers have another way to see at least small parts of this “dirty snowball,” in the form of the Orionid Meteor Shower.
Every time Halley nears the sun in its orbit, the comet warms up and discharges some of its gases and dust. Over time, these sand-sized grains of debris spread throughout the comet’s orbit. When the orbits of Earth and the debris intersect, many of the particles hurtle into Earth’s atmosphere and burn up, creating a shower of meteors.
The debris from Halley’s Comet meets up with Earth’s atmosphere twice a year, once in October to produce the Orionid Meteor Shower and again in May for the Eta Aquarid Meteor Shower. For this month’s Orionids, the fragments of Halley travel at speeds of about 41 miles/66 kilometers (that’s 148,000 miles per hour!). This makes them some of the fastest moving of any meteor shower.
While the Orionid Meteor Shower runs from October 2 through November 7, activity will peak during the early morning hours of October 21. Although many meteors may be seen during the preceding hours, the majority will be visible after midnight, when Earth is turning into the path of the oncoming debris. The waxing crescent Moon will already have set, so moonlight won’t wash out any of the expected 20 meteors-per-hour visible during the peak.
A meteor by any other name
Sky watchers through the years have used several terms in describing debris hurtling through space. Those most relevant here include meteoroid, meteor, and meteorite. Meteoroids are small, rocky or metal-rich bodies in space, usually remnants of asteroids or comets that have broken apart. If such bodies enter Earth’s atmosphere, they generally burn up in a glowing streak of light. These are called meteors. Any debris that survives this conflagration and hits Earth is called a meteorite.
A few meteors are visible on any given night when dust and other solar system junk sporadically enter Earth’s atmosphere and burn up. Meteor showers, on the other hand, are associated with a specific cloud of cometary remnants. The timing of their appearance is predictable and they display a concentration of meteors rather than a random few.
Meteors are often called shooting stars or falling stars but have nothing to do with stars. These misnomers go back to the days when the true nature of meteors was misunderstood, and they were believed to be the remnants of stars. In fact, the term meteor has been used to describe many objects in the sky, including not only “shooting stars”, but also clouds, raindrops (the term hydrometeor is still sometimes used to describe a raindrop) and more. A holdover of this concept is our modern term “meteorology,” which is not the study of “shooting stars” but rather the study of the weather.
Whatever we call these flashes of light, they are fun to watch, and October’s Orionid Meteor Shower may be especially enchanting because it connects us with one of history’s most fabled comets.
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