[image: a5wBQVTqQNfix6HaLdjwtx9X.jpeg]
*Eos:  *The Dawn Goddess
No region of the mythological Universe went unpopulated.   One would find
attendant dryads nurturing the frailest saplings and grandest oaks just as
water spirits gathered in both encompassing seas and ribbon thin streams.
Demigods animated the faintest breezes, silvered the most distant clouds
and enlivened every hearth flame.  It was by ascribing all natural
phenomena to disparate, but always divine, agencies that they became both
explicable and enchanting.   That brings us neatly to Eos, the goddess of
dawn.  (The Romans called her "Aurora.") Eos was one of three children born
to Hyperion, the Titan deity of heavenly light and Theia, the Titan goddess
of ethereal light.  Eos' two siblings were Selene, the moon goddess, and
Helios, god of the Sun.   Prior to each sunrise, Eos' soft light suffused
the eastern sky, heralding Helios' ascent.      Initially, Eos was not only
beguilingly beautiful, but angelically good.  Her tresses were as strands
of pure sunlight nearly as bright as the golden tiara she wore on top of
them.    She was adorned in a diaphanous rose-tinted gown interlaced with
fresh flowers.  Her radiance shone gently over the world, scorching neither
land nor animal.   She took a few husbands, including, Astreus, the
handsome god of dusk.     Through these couplings she gave birth to the
four wind gods, Boreas  (north), Zephyrus (west), Notus (south) and Eurus
(east) as well as Eosphorous, the morning star, and the five Astra Planeta,
the five planets.       Of all the deities, she came closest to attaining
Universal adoration  by virtue of her tender beauty and benevolence.
However, Eos eventually developed a fierce passion for Ares, the god of war
and consort to Aphrodite, the goddess of love.    Eos and Ares often joined
together in secret until Aphrodite came to learn of these assignations.
 Although Eos discontinued the affair at once, Aphrodite punished her with
the dreaded curse of perpetual love.     Eos was condemned to be constantly
forlorn as she fell madly in love with many men, only to be rejected by
them all.   Only those familiar with the anguish of unrequited love will
know the extent of Eos' suffering.   For instance, one morning Eos saw and
fell in love with Cephalus, a prince of Phocis and the devoted husband to
Procris, daughter of the Athenian king Erechtheus.  Eos abducted Cephalus,
professed her love and pleaded with him to remain with her forever.  Yet,
despite the goddess' beauty, Cephalus scorned her advances.  He demanded to
be returned to Procris for he would love no other.    At last the miserable
Eos relented.  Although she tried to avenge the rejection by suggesting to
Cephalus that Procris might have proven unfaithful during her husband's
absence, Cephalus returned to Procris and they eventually resumed their
blissful marriage.    Eos also found similar heartbreak in her efforts to
entice Orion, who escaped her clutches despite her ardent efforts.
Having observed Eos' excruciating pain, Aphrodite ultimately removed the
curse, thereby permitting Eos to find  love with Trojan prince Tithonus.
 Although they spent many deliriously happy years together, Eos was pained
by the realization that her lover was mortal and therefore condemned to
die.   Eos prayed to Zeus to make Tithonus immortal so they could be
together forever. Although Zeus granted this wish, Eos neglected to ask him
to grant Tithonus eternal youth.  As time passed, Tithonus grew old and
enfeebled.   Eventually, he couldn't move or speak, but became everyday
weaker and more desiccated.    Though Eos was not powerful enough to
release Tithonus from his decrepitude, she was able to change his body.
She took him in her hands and transformed him into a cicada that every few
years loudly professes its deepest love for the goddess of dawn.

THE SOUTHWORTH PLANETARIUM
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Founded January 1970
Julian Date: 2458973.16
2019-2020:  CXXXIX

THE DAILY ASTRONOMER
Monday, May 4, 2020
Remote Planetarium 26:  Space Weather

______________________________________
If you find Spaceweather intriguing, I would highly recommend consulting
the brilliant web-site   www.spaceweather.com.
__________________________________

Famed British astronomer Fred Hoyle (1915-2001) once said  "Space isn't
remote at all. It's only an hour's drive away if your car could go straight
upwards."  Indeed, the Karman Line, the  boundary separating Earth from
space, is merely 100 kilometers (62 miles) above sea level.     The
inconceivably vast region collectively known as "outer space" begins at
this demarcation.     Below and above we define the "space weather area,"
the high atmospheric layers within which those phenomena we call space
weather occur.

Although we'll be infiltrating the meteorological sphere by doing so, let's
begin today's class with a tour of Earth's atmosphere.

[image: 8f0c3606617eb0cd07c09dd22f46d58f.jpg]


   - *TROPOSPHERE    *Our true home, the troposphere is the lowest and
   thickest atmospheric layer.     The troposphere extends from the planetary
   boundary layer, the lowest region where frictional interactions with the
   planet's surface affects airflow, to the tropopause, the boundary
   separating the troposphere and the next layer, the stratosphere.  The
   altitude of the tropopause varies with latitude: 59,000 feet at the
   tropics; 56,000 feet at the mid latitudes and 20,000 feet in the polar
   regions.      As the troposphere contains seventy five percent of the
   atmosphere's mass, almost all weather phenomena occur within it.  We humans
   can only live within this layer which provides us with abundant oxygen and
   keeps us at the comparatively high atmospheric pressure to which our bodies
   have become accustomed.     Within the troposphere temperature and density
   decrease with increasing altitude.
   - *STRATOSPHERE *  The second major atmospheric layer extends up to an
   altitude of 50  kilometers above Earth's surface.  Along its lowest region
   one would find commercial aircraft and the tops of extremely high
   cumulonimbus clouds.    The stratosphere also contains the famous ozone
   layer.   Ozone is a molecule containing three oxygen atoms.   The molecular
   oxygen on which we rely consists only of two.      This ozone layer serves
   as a protective shield against most of the Sun's ultraviolet radiation.
    In the stratosphere, temperature increases with increasing altitude.
   - *MESOSPHERE.*   Deriving its name from the Greek word "mesos" for
   "middle", the mesosphere extends between 50 - 80 or 100 kilometers above
   Earth's surface, depending on the season and latitude.    Within the
   mesosphere temperatures decrease again with increasing altitude.   The
   Karman Line corresponds roughly to the mesopause, the boundary separating
   the Mesosphere and Thermosphere.      It is within the mesosphere that one
   would encounter *meteors.*
   - *THERMOSPHERE*   Here is where the ions are made by the solar
   photodissociation of molecules by ultraviolet light.  These ions scatter
   throughout the ionosphere, which extends from the upper mesosphere into the
   exosphere.    As the thermosphere extends above the Karman line, most of
   this atmospheric layer is technically in "outer space."  The upper levels
   of the thermosphere reach up to 500 kilometers.  This layer is called the
   "thermosphere" because of the high temperatures, such of which exceed 2,500
   degrees C.  However, one would still be cold in this layer because
   molecular collisions are so infrequent  It is within the thermosphere than
   *aurorae* occur.
   - *EXOSPHERE*   The uppermost atmospheric layer and the one about which
   scientists know little.   This highly rarefied region consists primarily of
   the lightest gases hydrogen and helium with trace amounts of carbon dioxide
   and oxygen.    There is no sharp boundary separating the upper exosphere
   and the region above it.


Today we'll discuss two main types of "Space weather:

   - *Meteor showers*
   - *Aurora Borealis*


Due to space constraints, we will be discussing potentially hazardous
asteroids at another time.

*METEOR SHOWERS*
Let's begin with three definitions.


   - *Meteoroids:*  particles in outer space flaked off from comets or
   asteroids.  These are meteoroids when suspended in outer space.
   - *Meteors:*  the lights we see when meteoroids infiltrate the upper
   atmosphere (between 250,000 - 330,000 feet)
   - *Meteorites:  *fragments of meteoroids that survived the descent
   through the atmosphere and are found on Earth's surface


Meteors are not exactly rare.  Millions of meteoroids descend through the
atmosphere each day.    Due to atmospheric light scattering, only those
meteors that appear at night are visible.  On any given night one can see a
meteor every 6 - 10 minutes on average.  During certain times of year,
however, we will experience meteor showers.  These showers occur when Earth
passes through a stream of meteoroids generally cast off from comets.
While these showers can last for weeks, they each have a peak date on which
the greatest number of meteors will be visible.        We can estimate this
number based on a value called the Zenithal Hourly Rate (ZHR). This value
refers to the number of meteors a seasoned observer would see in a
completely dark sky if the *radiant *were at the zenith.


   - *radiant: *  the apparent point from which meteors appear to originate
   - *zenith*:  point directly overhead


As the amount of atmospheric gases between an observer and outer space is
minimum at the zenith, obscuration is also at a minimum at this location.
  As most observers will not see the radiant at the zenith or in a
completely dark sky, the number of meteors one might observe per hour can
be significantly less than the ZHR value.

[image: greatshowpre.jpg]

Meteor showers are generally named for the constellation (or sometimes the
star) from which the associated meteors appear to originate.
The major meteor showers:

   - *Quadrantids: *  named for the now obscure constellation Quadrans
   Muralis, the Quadrantids appear to emanate out of the region around the
   boundary connecting Bootes and the Big Dipper.      The peak occurs around
   early January, but generally produces about 20 - 25 meteors an hour on peak
   night,    The parent object, defined as the object which produces the
   associated meteoroids, is unknown.  It might be Comet C/1385 U1
   - *Lyrids:* appearing to emanate from the constellation Lyra the Harp,
   the Lyrids peak in late April.    Produced by remnants of Comet Thatcher,
   the Lyrid shower is slightly more active than the Quadrantids with an
   hourly peak rate of 30 - 35.
   - *Perseids: * peaking in mid August, the Perseids appear to emanate
   from the constellation Perseus.     This is one of the year's most active
   showers with an hourly rate exceeding 60.   The parent comet is Swift Tuttle
   - *Orionids.* The late October shower.  Appearing to originate in the
   constellation Orion, the Orionids produce 30 - 40 meteors an hour.  Perhaps
   the most interesting aspect of this shower is that its parent body is the
   famous Comet Halley.
   - *Leonids *The  mid November shower.    These particles emitted from
   the Comet Tempel-Tuttle appear to originate from the constellation Leo the
   Lion.    As the parent comet follows a 33 year orbit, this shower can flare
   into a storm or a very active shower every 33 years.   We're not expecting
   such a flare up anytime soon as the late once occurred in 2001. Can produce
   80 - 100 meteors an hour
   - *Geminid*s.  The mid December shower.  This shower is unusual in that
   its parent body might by the minor planet 3200 Phaeton, as opposed to a
   comet.    This shower produces 30 - 50 meteors at peak and appears to
   emanate from the constellation Gemini,


*Note:*   these emanation directions are illusory.    Meteors travel in
parallel paths relative to Earth.

*Second note:*   It is best to watch for meteors after midnight, the time
at which our part of the planet is moving into the meteoroid stream.

*AURORA BOREALIS:*
Though it was Galileo himself who coined the term "aurora borealis,"
meaning "northern dawn," he was unable to explain why glowing lights
occasionally appeared in the northern sky.       We now know that charged
solar particles produce this light by interactions with atmospheric atoms.
These ejections produce copious outflows of plasma from the Sun's outermost
layers.   Once reaching Earth, these charged particles encounter Earth's
magnetosphere which directs them toward the magnetic poles.

[image: nasa_northern_lights_afb0d848-7d94-4ce9-83fd-be6b00e5f697.jpg]
Aurora as seen from the International Space Station.

These charged particles "excite" atoms and molecules within the upper
atmosphere (90- 150 km above Earth's surface.)  Excitation occurs when the
atoms absorb a specific amount of energy that elevates them into higher
energy levels.    When an excited atom settles back to its original state,
it will emit a visible light photon with an energy equal to the energy it
originally absorbed.  These emitted photons comprise the aurora light we
see.    Different gases produce different colors.


   - Excited *oxygen* atoms generally produce a greenish-yellow or red
   light,
   - *Nitrogen* emits a bluish light.

[image: unnamed.jpg]
As the magnetic pole is at such a high latitude, the aurora are generally
restricted to regions surrounding it. At times, a powerful coronal mass
ejection can produce aurora along areas quite distant from the magnetic
poles.


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