[image: 4884c1a9d13ad474af87fd216acdb0eda166032dr1-500-638v2_hq.jpg]
*Graeae*:  The Grey Ladies
Every quest involves far more than the quest's ultimate aim.   Be it
Jason's search for the golden fleece or, in this case, Perseus' mission to
slay Medusa, a quest's fulfillment occurs only after the hero survives many
other adventures that test his strength, courage and intellect.   When
Athena commanded the young Perseus to kill Medusa, one of the three
gorgons, she did not tell him where he would actually find them.  In order
to find the gorgons, Perseus first had to locate their strange sisters, the
Graeae, the only ones who knew where the gorgons resided.   The daughters
of the minor ocean deities Phorcys and Ceto, the three Graeae were Deino
("dread"), Enyo ("waster of cities") and Pemphredo ("saffron attired.")
Unlike any other children before or since, the triplets emerged from the
womb as old women, hence the name "Graeae," or "Grey ladies."    Such was
their advanced state of decay that they collectively had only one eye and
one tooth.  The sisters had to share each among themselves. Having been of
divine origin, the Graeae were entitled to preside over some region of the
world.   By virtue of their decrepitude and hideous appearance, the Graeae
became demi goddesses of swamps and the stygian gloom:  dreadful and
miasmic places through which even the most intrepid explorers are reluctant
to travel.   Perseus, however, did venture into their lair and found them
crouching together around the hollow of a rotting ash tree.   Perseus
concealed himself while they chatted and cackled over a meal of cold fish
and toadstools.   He noticed that the sisters would constantly pass the
tooth and eye around while they ate and kept a watch out for prey that
might come within reach.  At the moment when one sister was passing the eye
to another, Perseus ran forward and grabbed it. He stood back while the
Graeae sisters shrieked with rage and fear.    Since Perseus held their
eye, none of them could see.    "Return the eye!" they all wailed, reaching
blindly out around them.  Perseus replied, "Before I return your eye, you
must tell me where I can find Medusa."    The sisters then all fell
silent.   Enyo then asked faintly, "Who's Medusa?"   You see, Medusa was
not always a gorgon. Athena transformed her into one as a punishment for
her having had sexual relations with Poseidon in her temple.    Before the
transformation, there were only two gorgons:  Stheno and Euryale.
Thinking he was being mocked, Perseus angrily shouted, "You will tell me
the location of the gorgon Medusa at once!"   The sisters trembled
uncontrollably at the sound of the young man's wrath and started whispering
among themselves.   Finally, Deino said, "You seek the gorgons?"      "I
do," Perseus answered, his tone even more severe.   "They live on an island
at world's end: the last place the Helios chariot shines down upon before
it settles into the sea."  Pemphredo told him,tears streaming out of her
empty eye sockets.    "If you're lying," Perseus warned them, "I shall
return with sword in hand and will take all of your heads."      Now, in
one version, Perseus courteously placed the eye back into Enyo's hand while
commanding her not to use it for an hour so he would have ample time to
leave without being seen.     In another version, Perseus discourteously
tossed the eye into a nearby lake and invited the sisters to retrieve it
themselves.     The first version appeals to those who want to regard
Perseus as a noble paladin who behaved honourably in all occasions.  The
second appeals to those who saw Perseus as hot blooded, angry and
reckless.    Well, had he been a cad or a Chevalier, Perseus at least
managed to locate the gorgons with the assistance of the Graeae: the matron
goddesses of the world's eerie and eldritch enclaves.


THE SOUTHWORTH PLANETARIUM
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Founded January 1970
Julian Date: 2458990.16
2019-2020:  CLI

THE DAILY ASTRONOMER
Wednesday, May 20, 2020
Remote Planetarium 38: Telescopes II - Orbiting Telescopes
_____________________________________
Helpful term:
*Air*
       beneficial to the lungs, detrimental to astronomy.
______________________________________

Astronomers have learned what they've learned about the cosmos  by studying
the light that celestial objects either emit or absorb.   Each light beam
is akin to a long tapestry on which information pertaining to the
associated celestial body is contained.    For instance, we can know a
star's chemical composition through its spectrum and its luminosity by its
apparent brightness and distance.    The particular challenge confronting
astronomers is the thin gaseous layer enshrouding this planet.       When
light leaves its origin, the beam travels at light speed through the outer
space vacuum for most of its journey, be it less than 4.5 years (Alpha
Centauri) or 2.2 million years (Andromeda Galaxy).  Yet, during the last
millionth of a second of its trip, the beam penetrates our atmosphere where
it can be scattered, absorbed and distorted.  Just think of the elite ultra
marathoner who maintains a steady 4 minute mile over a 72 mile stretch only
to falter clumsily and disastrously a quarter stride shy of the finish
line.       Air is the astronomer's bane.  Yes, it sustains their lives,
but often hampers sky watching.      Unfortunately (ok, most fortunately)
the astronomical community can do nothing to eradicate the atmosphere.
However, the advent of rocketry has given them a means by which they can
circumvent most of it.

The year 1923 marks the true beginning of orbiting telescope history.  in
that year physicist Hermann Oberth (1894-1989) published "Die Rakete zu den
Planetenraumen," or "The Rocket in Planetary Space."  Contained within that
seminal paper was the outline for the deployment of a telescope above most
of Earth's atmosphere.  Recall that while Earth's atmosphere extends
hundreds of miles above the planet's surface, 99.999% of it is located
below 100 kilometers.
American physicist Lyman Spitzer (1914-1997) published a paper in 1946
entitled "Astronomical Advantages of an Extraterrestrial Observatory."   In
that paper he cited two distinct advantages to an orbiting observatory:



   - *angular resolution     *Angular resolution is the smallest separation
   by which two separate objects can be distinguished.      For instance, the
   star Albireo (in Cygnus the Swan) is a *binary star,* meaning it
   consists of two stars gravitationally bound together.  To the unaided eye,
   Albireo looks like a single star.  Through most telescopes, one can see
   both of Albireo's stars.  On the ground atmospheric disturbance and
   *diffraction* are two the two main causes that reduce resolution.
    Diffraction is the process by which a light beam is spread out when
   passing through a narrow aperture.  * In space, only diffraction would
   limit angular resolution.*
   - *Infrared and UV * Earth's atmosphere absorbs radiation along many
   parts of the electromagnetic spectrum.     The image below reveals how far
   into the atmosphere the various radiation types can penetrate:

[image: OSC_Astro_05_02_Radiation2.jpg]
The small band comprising the "visible spectrum" penetrates all the way
down to Earth's surface, which is why we can see each other.    Some UV
(ultraviolet) rays and Infrared radiation also reach the ground. (The
former is responsible for sunburns, the latter for the Sun's heat.)   We
also see a radio "window," a large section of the radio segment of the EM
spectrum.      Higher energy EM waves, such as middle to far UV, X-rays and
Gamma rays do not reach the planet's surface, which is why we're so happily
alive right now.    Notice that the orbiting satellites featured on the
graphic above are positioned at a high enough altitude to receive all the
incoming radiation.

Between 1962 - 1975, NASA launched eight Orbiting Solar Observatories
(OSO)'s intended, naturally, to study the Sun.   The OSO's studied solar
flares, gamma ray bursts and even observed a flare emitted from Scorpius
X-1, a strong x-ray source approximately 9000 light years from Earth.

In 1965 NASA appointed Spitzer to be the head of a committee whose aim was
to develop a list of primary scientific objectives for any such orbiting
telescope.   Over the  next decade, NASA, encouraged by the successes of
the OSOs continued to pursue other orbiting telescope ventures.
 Although they faced widespread spending cuts in 1974 due to economic
pressures, NASA finally obtained the initial funding of $38 million in
1978.  (A much more substantial amount in the 1970s than it is today.)     With
the assistance of the ESA space agency, NASA started construction of an
orbiting telescope that would be named the Hubble Space Telescope in honor
of American astronomer Edwin Hubble (1883-1959) whose observations led to
the discovery of the cosmic expansion.

[image: edwinhubble.jpg]
American astronomer Edwin Hubble

The grinding of the Hubble Space Telescope's primary mirror.

The Hubble Space Telescope was initially scheduled to launch in October
1986.  Unfortunately, the Space Shuttle Challenger exploded in January
1986. This tragedy not only cost the lives of seven astronauts, including
New Hampshire school teacher Christa McAuliffe, but it also suspended all
space shuttle flights for more than two years.  The first Space Shuttle to
be launched following the Challenger Disaster (STS 26  Discovery) lifted
off on September 29, 1988.    On April 24, 1990, STS-31 was launched and
deployed the Hubble Space Telescope into orbit.      After years of
political wrangling, funding cuts, and the other logistical difficulties
that attend all space science missions, the HST was finally going into
orbit.  The HST's launch was hailed as a triumph for NASA, ESA and the
entire astronomical community that would benefit from the first major
observatory to have ever be stationed well above Earth's surface.

The triumph was short lived.    Within weeks of the launch, researchers
received the first Hubble images.  Though slightly superior in image
quality than most ground based telescopes, the images lacked the resolution
the astronomers expected.   The outer perimeter was ground 2200 nano meters
too fine: too large an error in the unforgiving world of optics.   The HST
images were deemed far inferior to what they could have been had the optics
been working perfectly.   If the 1986 Challenger disaster was NASA's worst
tragedy, the 1990 HST deployment proved to be its most embarrassing
debacle.

On December 2, 1993 STS-61 was launched.   The crew's mission was to
install corrective equipment designed to fix Hubble's faulty optics.
After three years, NASA was hoping to finally have a well working space
observatory and, in the process, to redeem itself.      This redemption
effort was an astounding success.

The three images below of the galaxy M100  show us the extent of the
improvement.   The left image was captured before the installation of the
corrective equipment.  The central image was captured soon after the
installation.  The right image is was taken in 2018.

[image: PIA22913-HubbleSpaceTelescope-ComparisonOfCameraImages-20181204.jpg]

Ever since that vital serving mission, the Hubble Space Telescope has
become the most scientifically productive space craft ever launched.   As
we proceed through this course, we will see many of the images the HST has
captured over the last twenty-seven years:  star clusters, nebulae,
galaxies and much more!

[image: James_Webb_Space_Telescope_2009_top.jpg]
In March 2021, NASA plans to launch the James Webb Space Telescope,
Hubble's worthy successor.     Unlike the Hubble Space Telescope that
orbits Earth at an approximate altitude of 250 miles, the Webb Telescope
will be stationed around the Second LaGrange point between the Earth-Sun
orbit

[image: l2.3.jpg]

Who knows what the Webb telescope will reveal?  If the HST is any
indication, the Webb telescope's images and discoveries will be beyond all
imagination.

Tomorrow, we begin our journey through the Universe beyond solar system.


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