Each time one of these large balls of rock and ice swings close to the Sun it loses a little more of its material in a stream of vapor, releasing the dust and grit trapped inside. Since the majority of meteors seen in a meteor shower come from the same stream of particles, they all seem to rain down from one corner of the sky.
The constellation that appears closest to where the meteor shower appears to be coming from when it's at its peak gives the annual event its name. Astronomers use the term Zenithal Hourly Rate ZHR to describe the peak density of meteors that can be observed in an hour under perfect conditions. While meteor showers are a predictable part of the astronomical time table, nature isn't always on our side. Not only can clouds ruin a good viewing, but a bright Moon, or even the timing of the rising and setting of the meteor shower's celestial coordinates can make them hard to see.
Variations in the density of the stream of dust we might happen to be passing through will also determine how many meteors we see each hour. The nature of the rock that left this trail of debris is a bit odd, thought to be a 'rock comet' that orbits the Sun every five and a half years.
The meteors that appear during a meteor shower seem to radiate from one point in the sky. This illusion is an effect of perspective, just as a roadway seems to converge in the distance. Usually, meteor showers take the name of the constellation from which the meteors appear to radiate. For example, during the Perseid shower in August, meteors seem to streak from a point in the constellation Perseus. The science of meteor astronomy began in , when a storm of 60, meteors an hour shocked the world.
By the s, it had become clear that many meteor showers were annual — including the normally placid Leonids, which produced the big storm — and that they were somehow related to comets. Astronomers now consider comets to be "dirty snowballs" consisting of a mixture of dust and frozen gases. A comet becomes visible only during its closest approach to the Sun, when areas on the comet's icy surface become warm enough to evaporate.
The resulting jets of evaporating gases carry with them any solid matter mixed with the original ice. At each pass near the Sun, the comet ejects a stream of material.
The particles composing the stream orbit the Sun in slightly different paths than the source comet. Each particle receives small accelerations from forces other than gravity, and these orbits become increasingly modified over time. The ejected streams become more diffuse with age and lose their individual identities. Concentrated initially near the comet, the debris diffuses along each stream's orbit and eventually forms a thin band of material that Earth encounters every year.
A meteor shower occurs on the date in the year when Earth passes nearest to the band of material associated with a comet's orbit.
Most of the meteors seen during one of the annual showers arise from fluffy particles not much larger than sand grains. As a particle enters Earth's atmosphere, it collides with gas atoms and molecules. The particle becomes wrapped in a glowing sheath of heated air and vaporized material boiled off its own surface. Meteors become visible at altitudes between 50 and 75 miles 80 and kilometers , with faster particles typically shining at greater heights.
Many of the faster, brighter meteors may leave behind a train — a dimly glowing trail that persists for many seconds or, more rarely, minutes. Larger debris may create a fireball — a spectacular meteor bright enough to outshine even Venus. Occasionally, a fireball will fragment; this event is accompanied by bright flares and even "sparks" thrown a short distance from the meteor's main trail.
Such a fireball is called a bolide. The best way to enjoy a meteor shower is to dress warmly, set down a blanket or lawn chair at a dark site, get comfortable, and watch the stars. On any night of the year, meteors appear faster, brighter, and more numerous after midnight. That's when your location has turned into Earth's direction of motion around the Sun and plows into meteor particles nearly head-on, rather than having them catch up from behind.
The peak activity of a meteor shower occurs in the hours when Earth passes closest to the orbit of the shower particles. The ideal circumstance for any observer is for the shower to peak at a time when its radiant is highest in the sky during the morning hours; most of the year's best showers have the potential to meet these criteria.
A brief summary of the year's best meteor showers follows. For many northern locations, the Quadrantid radiant is above the horizon all night long, but observing is best after local midnight. Generally visible between December 28 and January 6, the Quadrantids have a sharp activity peak around January 3. Typical rates vary between 40 and per hour; about 5 percent leave trains. When the shower was first recognized as annual in , the radiant occurred in a constellation no longer recognized — Quadrans Muralis Wall Quadrant.
The cold nights of northern winters and typically faint meteors keep this shower from being truly popular. Until late , this was the only major meteor shower whose parent body remained unknown. But that year astronomers found a near-Earth asteroid named EH1. When astronomers estimated the theoretical speed and radiant for a hypothetical meteor shower caused by particles from EH1, the results fell squarely in the middle of those measured for the Quadrantids by meteor observers. In the case of a meteor shower, the glowing streaks may appear anywhere in the sky, but their "tails" all seem to point back to the same spot in the sky.
That's because all the meteors are coming at us at the same angle, and as they get closer to Earth the effect of perspective makes them seem to get farther apart. It's like standing in the middle of railroad tracks and seeing how the two tracks come together in the distance.
Meteor showers are named for the constellation where the meteors appear to be coming from. So, for example, the Orionids Meteor Shower, which occurs in October each year, appear to be originating near the constellation Orion the Hunter. Here are dates of major meteor showers. Peak viewing times will vary by a day or two each year. Keep in mind: If the moon is full or near full, you may not see many meteors. Some years are better than others for numbers of meteors per hour.
Bring blankets, a sleeping bag, and a thermos of something warm to drink. The Orionid shower happens every October and can last for a week, treating patient observers to a show of 50 to 70 shooting stars per hour at its peak. Related: Orionid meteor shower sparks bright fireballs video. Quadrantids: The Quadrantid meteor shower comes from the debris of an asteroid called EH1, which some astronomers think was part of a comet that broke apart centuries ago.
The debris enters Earth's atmosphere in early January and offers astronomers and other observers a brief show. Related: Spectacular Quadrantid meteor photos. Geminids: Like the Quadrantids, the Geminid meteor shower also came from dust particles of an asteroid, this time a near-earth asteroid called Phaeton.
Meteor showers are mostly from comets, so having an asteroid as parents make the Quadrantids and Geminids different from other meteor showers. The Geminids happen in December and spray up to 40 meteors per hour out of the Gemini constellation at its peak. Other meteor showers to watch out for are the Eta Aquarids , also remnants of Halley's comet, in May; and the Lyrids , which have been chronicled for more than 2, years, in late April.
People living in the Northern Hemisphere are in the best position to observe the most beautiful meteor showers. For example, North America is right below the region of the sky where the January Quadrantids shower appears. A bright moon can dim the prospect of seeing a good meteor shower, drowning out all but the brightest meteors. Local light pollution dampens prospects, too, so the best place to view a meteor shower is from out in a rural location.
Most meteor showers are best viewed in the pre-dawn hours, when the part of Earth you are standing on is facing the direction of Earth's orbit. It's like bugs hitting a car's windshield. In the late evening hours, on the other hand, the meteors are less frequent — loosely akin to bugs hitting a car's rear bumper. Meteor showers can be seen at different times of the year depending on when Earth is going to pass through the comet's or asteroid's path.
Some meteor showers happen annually; others only appear over a period of several years, while some of the best shows — meteor storms — happen just once or twice in a lifetime. Weather can also hamper a good view of meteor showers. A clear sky is a gift to night gazers, which is why meteor showers during the summer are more anticipated than those that fall in the winter months. If you want to try and capture a meteor shower yourself, we have a guide to the best cameras for astrophotography and the best lenses for astrophotography , to get you all started.
This article was updated on Sept.
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