Share our content. Why do meteors fly fast? Our expert Professor John Hearnshaw answered this question. Ask me a question Ask me a question Plastics in the Environment Understanding Aotearoa's plastics problem. Many scientists were skeptical that stones could fall from the clouds or the heavens, and often they simply didn't believe the accounts of people who claimed to have seen such things.
In , a fireball exploded over Connecticut, and several meteorites rained down. By then the first handful of asteroids had been discovered, and a new theory emerged suggesting meteorites were broken bits off asteroids or other planets.
A theory that still holds. The largest meteorite recovered in the United States fell in a wheat field in southern Nebraska in Witnesses saw a giant fireball in the afternoon that some said was brighter than the sun.
The meteorite was found buried 10 feet 3 meters deep in the ground. It weighed 2, lbs. The most famous meteorite crater in the United States is misnamed Meteor Crater. It's in Arizona, and it's huge. The rim rises feet 45 m from the surrounding plain, and the hole is feet m deep and nearly a mile wide.
It was the first crater that was proven to be caused by a meteorite impact, which occurred between 20, and 50, years ago. Meteors are often seen falling from the sky alone — one here, one there. But there are certain times in a year when dozens or even hundreds of meteors per hour will light up the sky, seemingly coming from one part of the sky, radiating in all directions, and falling toward Earth one after the other. There are several periodic meteor showers that astronomers and amateur observers wait for every year.
Meteor showers are named after the constellations from where the shower appears to be coming from. For example, the Orionids appear to originate from the mighty Orion constellation, while Perseid meteors seem to be coming from the Perseus constellation.
Leonids: The brightest and most impressive is the Leonid meteor shower , which can produce a meteor storm that showers the sky with thousands of meteors per minute at its peak. In fact, the term "meteor shower" was coined after astronomers' observed one of Leonids' most impressive displays in The Leonids occur every November, but the shower's most beautiful display happens at intervals of about 33 years, with the last one lighting Earth's sky in ; it is not expected to be repeated until Related: Amazing Leonid meteor shower photos.
Perseids: Another shower that is worth keeping awake for is the Perseid meteor shower , which is associated with the Comet Swift-Tuttle , which takes years to orbit the sun.
Home Archives About Contact. By William Orem Posted May 24, Media Player Error Update your browser or Flash plugin. What Is A Shooting Star? Orbits Take Control But there's another reason. It's like two cars passing in opposite directions. Faster Meteors In general, the fastest meteors to enter our atmosphere move at about 26 miles-per-second. These kinds burn up and are gone in less than one second. Thus, the Perseid meteor shower peaking about August 12 will appear to radiate from the constellation of Perseus, while the Leonid meteor shower peaking about November 18 will appear to radiate from the constellation Leo.
Meteor shower rates are highly variable, with the number of shower meteors seen following a curve of activity which usually lasts several days. Beginning at some level below the sporadic meteor background rate, the number of shower meteors seen will increase exponentially as the Earth approaches the densest portion of the stream.
The rate will then peak at some maximum level, followed by a decreasing exponential decay back below the normal sporadic level as the Earth leaves the stream. The duration of peak activity can vary widely between showers. Some meteor showers such as the Quadrantids have very sharp maximums, displaying their best rates for only a few hours each year. Other major showers such as the Taurids have a broader maximum, which can span across a few nights.
Meteor streams also vary greatly in strength between each other, depending upon such factors as the stream age, parent body composition, stream particle density and distribution, and how close the earth approaches to the stream core. Of the 10 major meteor showers, the low-rate showers such as the Taurids and April Lyrids will produce only about meteors per hour at their peak under good conditions, while the high-rate showers such as the Perseids or Geminids can produce up to meteors per hour at their peaks.
It is important to note that even the high rate showers will still produce only about 1 to 2 meteors each minute, with faster or slower periods occurring over time. Along with the major meteor showers, there are also a number of minor meteor showers which, while greater in number than the major streams, are difficult to detect above the background sporadic meteor rate.
These showers will generally yield only about meteors per hour at their maximums, with only a sprinkling of meteors produced on non-maximum nights.
It usually requires many hours of observing experience in order to correctly recognize and classify minor shower meteors. In addition, the Internet is a rapidly growing source for information on astronomical topics.
A few meteor shower observing guidelines are included below:. Plan your observing session as close to the time of shower maximum as possible. Meteor showers are usually quite disappointing under city and suburban conditions, so a dark observation site, far from city lights is preferred. Similarly, Meteor showers which occur near the time of gibbous or full moon usually do not perform well.
Many meteor shower radiants do not rise before midnight, making most meteor showers best between midnight and morning twilight. Once at the observation site, ample time should be allotted for your eyes to adjust to dark conditions, as this can take over an hour for full dark adaptation. No magnification devices will be necessary. The use of all lights should be minimized, with only dim, red pen-lights or flash-lights used sparingly. Most meteor observers observe from a reclining position, either in a lawn chair or sleeping bag, with their gaze directed about 45 degrees above the horizon, in the general direction of the shower radiant.
The best portion of the sky to watch is usually an area of sky about 30 degrees away from the radiant point for the shower. Due to the effect of perspective, shower meteors which appear very close to the radiant will be quite short in length, while those which appear some distance from the radiant can be quite long.
Members of the same shower, while varying greatly in brightness, will share common characteristics, such as speed, color range, and potential for leaving behind a train a glowing wake of air left behind after the meteor has passed.
It will also be noticed that the number of shower meteors seen will improve as the radiant gets higher in the sky. This is because meteors seen near the horizon are much farther away than those seen directly overhead, making them dimmer and harder to notice.
Also, the light from a meteor near the horizon must pass through much more atmosphere to reach the observer than for a meteor overhead, further attenuating the light from meteors at low elevation angles.
Perhaps the key work to remember in meteor observing is patience. Most meteor showers will not produce a spectacular display, but will instead produce a steady, reliable show — sometimes with a few surprises. Many publications which list meteor shower rates will often give a corrected value, called the Zenith hourly Rate ZHR which standardizes the shower rate to optimum observing conditions.
The shower rates listed are usually corrected for fully dark skies, and the meteor radiant point has been artificially located at the zenith, directly overhead.
0コメント