THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian date: 2458751.5
2019-2020: XVIII
"Someday I hope math grows up and stops expecting everyone else to solve its problems."
-Anonymous
THE DAILY ASTRONOMER
Thursday, September 26, 2019
Morning Meteor Mystery
Morning Meteor Mystery
A Perseid meteor streaks through the pre-dawn sky on August 11th. Notice the
constellation Orion to the right of the image. Although we associate Orion with the
winter sky, it emerges in the pre-dawn sky in early to mid August.
Meteors are not objects. They are, instead, the rapid flickers of light produced when meteoroids infiltrate the atmosphere at an altitude between 50 - 75 miles above Earth's surface. These meteoroids move so rapidly, between 25,000 - 160,000 miles per hour, that they burn up in the atmosphere and excite the atoms along their descending path. (They tend to move faster in the pre-dawn than early evening.) This excitation elevates the electrons within these atoms to higher energy states. When the electrons revert back to their original energy levels, they emit visible light photons we perceive as the meteor.
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METEOR
the light emitted when a meteoroid descends through the atmosphere
METEOROID
a fragment of a comet or -less frequently- an asteroid that moves through outer space until it encounters a planet. Meteoroids tend to be the size of sand grains or small pebbles.
METEORITE
a remnant of a meteoroid that survives the descent through the atmosphere. Most meteorites that land on Earth are virtually impossible to find as they tend to fall into the ocean. When they fall on land, they are often concealed by vegetation or blend in with nearby debris, such as micrometeorites in sand. For this reason, many meteorites are discovered in Antarctica, which is largely frozen and will preserve the meteorite
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One can see a meteor about every six to ten minutes on average. We refer to these lights as "sporadic meteors," as they can occur at anytime and are caused by any of the myriad meteoroids currently milling about through space. At other times, we'll experience a meteor shower, when Earth ploughs through a stream of meteoroids. During a meteor shower peak, one can often observe as many as 50 - 150 meteors an hour, depending on the density of the meteoroid stream through which Earth is moving. Whereas sporadic meteors can appear anywhere, meteors associated with meteor showers originate from a specific region, called a "radiant." The shower, itself, is most often named for the constellation region that contains this radiant, such as the Perseids (August), Orionids (October) or Geminids (December). These meteoroids tend to move at varying speeds and leave trails that are sometimes fleeting and at other times persistant. (They tend to move faster in the pre-dawn than early evening.)
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MAJOR METEOR SHOWERS
QUADRANTIDS (From a region once designated as Quadrans Muralis, an
obsolete constellation in an area now occupied by the Big Dipper and Bootes)
peak January 3/4
LYRIDS (Lyra the Harp)
peak April 22/23
ETA AQUARIDS (within the constellation Aquarius)
peak May 7/8
DELTA AQUARIDS (within the constellation Aquarius)
peak July 29/30
PERSEIDS (Perseus the Warrior)
peak August 11/12
ORIOINDS (Orion the Hunter)
peak October 22/23
LEONIDS (Leo the Lion)
peak November 17/18
GEMINIDS (Gemini the Twins)
peak December 13/14
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Now, one can venture outside on any night to ob.....
Wait a second!!
Why do meteors tend to move faster in the pre-dawn sky than in the evening sky? The time of day would seem to make little difference, wouldn't it?
Well, it would if Earth were a stationary target. In fact, Earth is moving around the Sun at about 66,000 miles an hour.* In the evening, the meteoroid is "catching up" to Earth and therefore tends to move more slowly. In the morning, the meteoroid is moving toward Earth and infiltrates the atmosphere much more rapidly. Analogously, think of a person trying to run after a moving car as another one runs toward it: when reaching the car, the first person will appear to the passengers to be moving more slowly than the second one.
Although we feel as though we're observing the Universe from an immobile point, we are actually moving rapidly through space. The apparently static night sky does offer us subtle hints that we are watching moving objects from a moving platform: such as stellar aberration, the apparent displacement of stars from their actual positions, and the varying speeds of meteors. It was these subtle hints that ultimately induced humans to understand our place in an ever changing cosmos.
*Yes, faster in the winter when Earth is slightly closer to the Sun than in the summer, when Earth is slightly farther away.
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