[image: image.jpeg]
*Aesculapius: Healer and serpent charmer*
A sage word of advice: if your lover is the god of prophecy, don't be
unfaithful. Coronis, the daughter of Lapithian king Phlegyas and
granddaughter of war god Ares, was an excruciatingly beautiful woman whom
Apollo, god of prophecy, lustily pursued. Like Daphne, Coronis wasn't
particularly enamored of Apollo. Unlike Daphne, though, Coronis didn't
flee. She yielded at once to Apollo and agreed to become his lover, even
though she was already passionately in love with Ischys, son of Elatus, a
powerful Lapithian chieftain. She perhaps realized that the consequences
of rejecting a god were generally dire. Coronis was truly unusual in
that she far preferred the mortal lover to the Olympian one. Despite
having become pregnant by Apollo, Coronis continued an illicit affair with
Ischys. Naturally, she took great pains to conceal herself and Ischys
during their clandestine trysts. Of course, she might just as well have
met him at the center stage of the Theatre of Dionysus. Apollo learned
of her infidelity either because, well, he was the god of prophecy and knew
she'd stray or because a raven had informed him that it had witnessed
Coronis and Ischys together. (Apollo was said to have been so incensed he
turned all ravens pitch black. Previously they had been snow white.)
Apollo then pleaded with his sister, Artemis, to dispatch Coronis and
Ischys. Artemis swiftly slew them both with a barrage of her unerring
arrows. When Coronis' distraught father was placing her on a funeral
pyre, Apollo suddenly felt such remorse for having put her to death that he
descended to Earth and withdrew the baby she was carrying. Just as Zeus
had inserted the fetal Dionysus in his thigh before his mother Semele was
consumed in flames, Apollo placed the infant in his chest for the remainder
of the gestational cycle, which lasted less than one moon cycle. When
the child was born, Apollo gave him the strange name "Aesculapius" meaning
"mole-hill builder." Apollo then gave him to the centaur Chiron to raise
and teach. Chiron was unique among the Centaurs for being wise, kindly and
peace-loving. (We'll likely encounter him again later.) Whereas
Chiron's other young male pupils were constantly outside seeking adventure,
the quiet Aesculapius wanted nothing more than to learn every facet of the
healing arts. The profoundly knowledgeable Chiron literally taught
Chiron everything he knew about healing: from herbal elixirs to cold
potions to the laying on of hands. Eventually, Aesculapius' healing
skills equaled and then surpassed that of his teacher. Apart from envying
his student's prodigious skill, Chiron delighted in his progress and told
him that he would eventually mature to become the world's best doctor.
Indeed, he did. Even though just a young man, Aesculapius earned a
reputation for being a divinely gifted healer. Everyone who suffered
sought him out: from warriors bearing grievous wounds to the old seeking
relief from infirmity. He was able to either heal each patient or at
least greatly reduce their pain and distress. Moreover, Aesculapius was
known for being uncommonly kind and compassionate to all, unlike his
ill-tempered, lover-slaying, raven-blackening father. Ironically, these
laudable traits would prove Aesculapius' downfall. Soon after Scorpius
the Scorpion slew Orion the Hunter, Aesculapius gathered Orion in his arms,
murmured an incantation of his own crafting and resurrected him. Orion,
who had been preparing to step into Charon's ferry, withdrew from it and
returned cheerfully to Earth. Charon informed Hades, the Underworld's
presiding god, about Orion's rejuvenation. Hades complained bitterly to
Zeus, the god notorious for punishing mortals who rose above their proper
station. Zeus recognized that Aesculapius' actions were a form of
hubris and promptly struck him down with a thunderbolt. Zeus then
snuffed out Orion's life to "settle accounts." However, he regretted the
necessity of both deaths, for he admired both Orion's hunting prowess and
Aesculapius' deep compassion. He placed both of them in the stars.
Orion as the constellation of the same name and Aesculapius became the
constellation Ophiuchus the Serpent Charmer, for Aesculapius had often
used venom from a sacred serpent in many of his concoctions. Ophiuchus
stands proudly above Scorpius, Orion's killer. The constellation Serpens
the Serpent is draped over his body. It was said that for centuries
after his death, Aesculapius continued to minister to the sick and weak.
Those who desperately needed healing traveled to Aesculapius' temple.
Once there, they prayed to him, offered a sacrifice and then slept for an
entire night within the temple. Aesculapius was then able visit the
patients in their dreams and advise them how to cure themselves. Such
visitations were possible because the realm of Morpheus, the god of dreams,
was connected to the underworld through a dark and narrow conduit.
Consequently, only in dreams could the departed shades mingle with living
souls. In doing so, they offered comfort to the bereaved and, in the
case of Aesculapius, provided helpful hints about how to remain living for
as long as possible.
THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
<http://www.google.com/url?q=http%3A%2F%2Fwww.usm.maine.edu%2Fplanet&sa=D&sntz=1&usg=AFQjCNHulkHuLP13bOG2PkNrPazsGWFs2A>
70 Falmouth Street Portland, Maine 04103
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Founded January 1970
Julian Date: 2459001.16
2019-2020: CLVIII
THE DAILY ASTRONOMER
Monday, June 1, 2020
Remote Planetarium 45: H-R Diagram Part II
Ever since the H-R Diagram was developed around 1910, it has proven to be
astronomy's most powerful tool for discerning stellar properties. We
introduced the H-R Diagram in Remote Planetarium 43. Named for its two
developers, Henry Norris Russell and Enjar Hertzsprung, this diagram
relates stars' spectral types (or effective temperatures) to their absolute
magnitudes (or luminosities.) Last week we focused on the* main sequence*,
the band extending from the lower right to upper left of the diagram. All
stars begin their life cycles on the main sequence, including the Sun,
which still remains there and will continue to do so until it exhausts its
core hydrogen reserves in approximately five billion years.
The image below shows the basic H-R Diagram we saw last week. Along the
lower row are the spectral types. Along the upper row, are listed the
effective temperatures corresponding to the spectral types. Along the
left is listed the absolute magnitude and to the right the corresponding
luminosities.
[image: image.gif]
Now that we've established the main sequence, we will start using the
diagram to learn how to discern the properties of stars. We'll begin
with two examples: Betelgeuse, Orion's eastern shoulder star and Sirius B,
the companion star to Sirius, the brightest star in Canis Major.
*BETELGEUSE:*
Absolute magnitude: -5.85
Spectral type: M2
First, the absolute magnitude places Betelgeuse high along the H-R Diagram,
while the spectral type places it well to the right. We see that
Betelgeuse occupies a position toward the upper right of our diagram.
What inferences can we now make about Betelgeuse based on the information
provided?
- *Betelgeuse is highly luminous.* [It is more than 90,000 times more
luminous than the Sun. This luminosity changes because Betelgeuse is a
variable star. More on that topic later.]
- *Betelgeuse is quite "cool." * [As an M2 star, its effective
temperature is approximately 3,600 K.]
- *Since Betelgeuse is both cool, but highly luminous, we can also
conclude it is quite large.* Remember that a star's luminosity is
proportional to the square of its surface area and to the fourth power of
its effective temperature. [Betelgeuse's radius is approximately 900
times that of the Sun's.]
- *As it is not on the main sequence, it is no longer fusing hydrogen
into helium. *We know that Betelgeuse is toward the end of its life
cycle, but we cannot know precisely what fusion reactions are occurring in
its core. All we know is that its core hydrogen fusion days are over.
- Betelgeuse is a supergiant star
*SIRIUS B*
Absolute magnitude: +11.18
Spectral type: A2
We can set Sirius B low on the H-R Diagram due to its high absolute
magnitude. However, with a spectral type of A2, Sirius B would also be
placed along the right. What can we conclude about Sirius B based on this
information and its lower right position on the HR Diagram?
- *Sirius B's luminosity is very low! * [It is about 5% as luminous as
the Sun.]
- *Sirius B is quite hot. * [With a spectral type of A2, Sirius B's
effective temperature equals 25,000 K.]
- *Since Sirius B is both cool, but not very luminous, it must be quite
small.* [Its radius is 0.8% that of the Sun.] In fact, Sirius B is not
an active star at all. It is, instead, a stellar remnant known as a *"white
dwarf." * It is no longer generating energy in its core through
thermonuclear fusion reactions. We will be discussing white dwarf stars
in greater detail later this week.
In these two examples, we were able to infer more information about these
two stars merely by knowing their absolute magnitudes and spectral types.
Before proceeding, we will introduce another stellar category:
*luminosity
class.*
- *O-Ia+ * *Hypergiants*. Extremely rare form of high luminosity
star. Example Cygnus OB2-12: luminosity 2 million times that of the
Sun.
- *Ia Luminous supergiants. * Also quite rare. Luminosity more than
a hundred thousand times that of the Sun. Example: Eta Carinae.
- *Iab Intermediate luminous supergiants. *Luminosity: tens of
thousands of times greater than the Sun. Example: Betelgeuse
- *Ib* *Less luminous Supergiants *Stars that are just luminous
enough to be classified as supergiants. Luminosities more than 10,000
times that of the Sun.
- *II Bright giants *Still highly luminous, but not considered
supergiants due to their spectra. Luminosity thousands of times greater
than the Sun's. Example: Omicron Scorpii
- *III Normal giants *Generally stars between 10 and a couple
thousand times that of the Sun. Example: Arcturus
- *IV Subgiants* Stars that are more luminous than main sequence
stars but not as luminous as giant stars. Example: Bellatrix
- *V Dwarfs * Main sequence stars. The luminosity is directly
related to mass. Example: The Sun
- *VI Subdwarfs* Stars that are still fusing hydrogen into helium in
their cores but are less luminous than main sequence stars. These stars
are believed to be "metal poor," which decreases their outer layer opacity
resulting in reduced radiation pressure. Example: Kapteyn's Star
- *VII White dwarfs*. Stellar remnants. All thermonuclear fusion
reactions have ceased. Example: Sirius B
Below we can see the different luminosity class locations within the H-R
Diagram:
[image: 800px-HR-diag-no-text-2.svg.png]
[Note: The L and T spectral types refer to "brown dwarfs," those gaseous
bodies that did not become sufficiently massive to produce temperatures
necessary for thermonuclear fusion reactions to occur. We will discuss
brown dwarfs in greater detail later.]
Now that we've included these sections, the H-R Diagram will also enable us
to determine a star's luminosity class.
Let's now classify some of the night sky's best known stars: Aldebaran,
Altair, Antares and Deneb.
[Note: The Sun's absolute magnitude is 4.86. Any star with a lower
absolute magnitude will be intrinsically brighter than the Sun. Any star
with a higher absolute magnitude will be intrinsically fainter.]
*Aldebaran (Taurus the Bull)*
Absolute magnitude: -0.641
Spectral type: K5
Cooler than the Sun, but much more luminous.
When we place Aldebaran in its proper HR position, we see that it is a
giant star.
*Luminosity class III*
*Altair (Aquila the Eagle)*
Absolute magnitude: 2.22
Spectral type: A7
Hotter than the Sun
We can fit Altair directly into the main sequence.
* Luminosity class V*
*Antares (Scorpius the Scorpion)*
Absolute magnitude: -5.28
Spectral type: M1
Cooler than the Sun but significantly more luminous
Antares is located in the upper right hand region, the realm of the
supergiants. *Luminosity class: Iab*
*Deneb (Cygnus the Swan)*
Absolute magnitude: -8.38
Spectral type: A2
Much hotter and much more luminous than the Sun. We place Deneb high along
the H-R Diagram, but much farther left than Betelgeuse and Antares. Still
a supergiant.
*Luminosity class: Ia*
One can see those stars and many others on this H-R Diagram sample provided
below.
[image: 089dd7456475e0e829408b3696cd8cab.jpg]
We can now place any star on the H-R Diagram with just two pieces of
information. That placement alone yields more information pertaining
to the star's luminosity class. Tomorrow, we'll learn how to truly know a
star's properties, mass and life spans also by using the "astronomer's
stone."
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