In The History of the Kings of Britain, medieval chronicler Geoffrey of Monmouth tells the story of how a shooting star foretold the death of Ambrosius and the coming of King Arthur. Long ago, shooting stars were commonly thought to be omens, prophecies, or messages from the gods. Today, we know shooting stars aren’t really omens; they’re not even stars. They’re meteors.
When seen from Earth, a meteor looks like a star zooming across the sky in a blaze of white, so it’s natural to think that’s just what it is. But a meteor is actually something much less stellar. It’s a rock or a bit of sand or ice — space debris — that encounters Earth’s atmosphere. There’s lots of debris out there, and it’s moving incredibly fast, sometimes as fast as 100,000 miles per hour, says Cameron Hummels, a computational astrophysicist and research scientist at Caltech.
(Credit: Eliyahu Ungar-Sargon/Shutterstock)
When a fragment of debris collides with Earth’s atmosphere, it compresses the atmosphere in front of it as it hurtles through, a phenomenon known as bow shock. Hummels, who is also Caltech’s director of astrophysics outreach, compares this to the way water piles up in front of a speedboat as it zooms along a lake or river.
The compressed atmosphere heats up and, in turn, heats the object, which then emits radiation and light. So what we call a shooting star is actually “a bit of rock heating and ionizing the air it’s traveling through,” Hummels explains. First, the air and then the rock begins to glow.
Meteors can be very big. The one that caused the meteor crater in Arizona was about 150 feet across. But most, says Hummels, are somewhere between the size of a grain of sand and a small pebble.
It’s amazing that something as small as a pebble can create a streak of light so bright you can see it from the surface of the Earth. But Hummels reminds us that when we see a “shooting star” we’re seeing both the blazing hot object — the grain of sand or other debris — and the hot air around it.
The fact that it’s zipping along at such a high speed makes it brighter, too. The faster it goes, the more energy it has, Hummels explains, and the more energy it has, the brighter it is.
The debris causing those lovely flashes of light has several sources. Some of it is debris left over from the formation of planets. Fragments from asteroids that broke apart make up some of them, and some is debris shed by comets.
Comets are mostly ice, along with some dirt and dust; that’s why scientists often call them “dirty snowballs.” When comets pass through the inner part of the solar system, closer to the sun, they start to melt a little. As the ice burns away, the dust and bits of rock that were embedded in that ice are freed, and they trail off behind the comet. When Earth’s orbit and the comet’s orbit intersect, that debris encounters our atmosphere, often creating a light show that we call a meteor shower.
The terminology can be tricky. What’s the difference between a meteoroid, a meteor, and a meteorite? The difference is more a matter of what the object is doing than what it is.
Hummels compares these definitions to stages or transitions in life: child to adult to senior citizen. A meteoroid is a bit of orbiting space rock. When that meteoroid enters the atmosphere, it becomes a meteor. If it doesn’t burn up on entry (as most do) and makes it all the way to the ground, it becomes a meteorite. Same rock, different life stages.
To increase the odds of seeing a shooting star — or maybe lots of them — you need to find a dark place, as far from city lights as you can manage, away from trees or buildings that can block your view of the sky. Sit in a comfortable chair or on a towel on the ground. You want to have the widest possible view of the sky.
You don’t need a telescope. Hummels says they’re worthless for viewing meteor showers. He also recommends not looking at your phone; your eyes need to adjust to the dark, and the light from your phone will interfere with that. It may take 20 or 30 minutes for your eyes to adjust. Then, just relax, watch the sky, and try not to fall asleep.
There are several of what Hummels calls “premier” meteor showers that generate the most meteors per minute. The most active is the Geminids in December, but the most popular is probably the Perseids, which takes place in August when it’s warmer in the northern hemisphere. You can find more information about when, where, and how to see meteor showers in this guide by the American Meteor Society (AMS).
A shooting star is a meteor resulting from space debris, like rock, sand, or ice, entering Earth’s atmosphere and burning up. This creates a bright streak in the sky due to the phenomenon called bow shock, where the debris compresses and heats the atmosphere in front of it, making both the debris and air glow.
Chances are good on clear, dark nights away from city lights, with sightings possible every 10 to 15 minutes. During meteor showers, when Earth moves through comet debris trails, the frequency of shooting stars significantly increases.
They are bright streaks, typically white or blue, moving quickly across the sky. Their appearance, including brightness and color, varies with the debris’s composition and speed.
While once thought to be omens or messages from the gods, we now know shooting stars are meteors. Observing one is an opportunity to witness a natural celestial event.
Shooting stars occur when a meteor enters Earth’s atmosphere, causing a bow shock that heats and lights up both the debris and the surrounding air due to their high-speed collision.
It’s relatively common to see a shooting star, especially during meteor showers. There are better chances in areas free from light pollution and when Earth’s orbit intersects with dense debris fields.
No, a comet is not a shooting star. Comets are icy celestial bodies releasing debris that may cause meteor showers as they near the Sun, distinct from the meteors we see as shooting stars.
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