THE SOUTHWORTH PLANETARIUM
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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

[image: QbiZg5ZoP24vMFBZtZXgluVmkEfLOnCeYffSHpgebmo.jpg]
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.
_____________________________________________
*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
__________________________________________________
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.)

__________________________________________________
*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
__________________________________________________

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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