Medusa:   The Unseen 

We loathed you for your malignity, shunned you for your ugliness; detested you for the slain multitude you have left in casts of stone; and we celebrated your beheading at the hands of the heroic Perseus.       What we did not do is understand you.    We did not understand that your malignity was grief; your ugliness a punishment, your powers a curse and your slaughter a wanton murder authored by the very goddess who made you the monstrosity that, lamentably, now defines you.   Since we're encountering you during our astronomical excursion, we should strive to see you. 
Not the gorgon Medusa writhing in anguish upon the remote, barren island, but the woman Medusa who traipsed into Athena's temple at the summons of Poseidon, the one she was audacious enough to call her "lover."   The same Poseidon who governed the dark, tide torn sea and stood steadfast against the myriad creatures seeking to undermine his reign.   Unlike the morose Hades who merely collected the shades in Asphodel or the grand Zeus of the boundless skies, Poseidon remained in perpetual conflict with the very domain of his sovereignty.   It was due to the relentlessness of his duties that he devoted precious little time to the young woman who was deeply devoted to him.  Such has it been since their 'love affair" began when she, as a young girl, spied the ocean god in the company of his sea nymphs and became instantly enamored.  As she was so young and beautiful, Poseidon consented to visit her upon occasion.  The naive Medusa regarded these infrequent visitations as evidence of requited love.  She retained this delusion on that beautiful night when Poseidon looked upon Medusa despairing in Athena's temple.    She went there and waited, despite being afraid, for she felt that her presence was an unpardonable intrusion.   She had set her fears aside because she was compelled by the one force that has always made a forfeit of our reason and driven us to actions that are usually irrational and frequently unforgivable:  love.    Mind you, this was not just any love.  This was the love for an Olympian God and therefore destined to rapid dissolution.    Yet, that frail, but resolute,  beautiful, but star-crossed, mortal woman could not have known the consequence of this folly.     In that Athenian temple on that beautiful night Poseidon came upon her in the magnificent human form he assumed on Earth.     For you see, Poseidon was not human.   When in his natural state, he was the greenish gloom of ocean water; just as Zeus, in his undisguised state, was a thunder cloud.     Poseidon sensed Medusa's sorrow when he approached her.     It was to his consternation that she could not at first look at him.     She avoided his eyes even as he stood before her.  When he spoke, in the strangely dulcet yet commanding tone particular to Olympians, and inquired as to her sadness, she initially only shook her head and looked away.   Yet he persisted so that she finally did regard him tearfully. declaring that her anguish was in her youthfulness and beauty.   For, it was these that Poseidon adored and not Medusa herself.     He loved her comeliness and vitality; a loveliness that he had described as beyond that of any mortal rival.     Yet, these would, in time, diminish in his eyee.    She was mortal and would not always possess the physical aspects that Poseidon cherished.     
            "You love me for who I am, and cannot love me for what I will become."
           Poseidon laughed.    "As you love me, dearest Medusa, for who I am in your presence:  mortal man made perfect.  You say my love for you  is for a beauty you cannot retain, but your love for me is for an image that I have merely conjured."
          Medusa's tone became suddenly severe.  Though compared to him she was slight, Medusa reached up and cradled his face in her hands.  The stern  girl stared into Poseidon eyes and said,  "Then come to me aged;  come to me old, unsightly and enfeebled; cast away by a world made hateful by  its aversions and I shall nurture you in my lap and you shall never know another cold, lonely moment."
            Poseidon was perplexed into an uneasy silence.     What a silly, besotted thing she must have seemed to him.  What effect could that sentiment have had on a god?  A being who could no more know the nature of passionate love than he could know fear of mortal death.  Since he knew not how to respond with words, he responded with an embrace.   
            You know and I know what happened next.  Words stopped and passions were otherwise expressed.      There, in the temple of Athena, they engaged in what was once known as "bodily commerce."     It would be inaccurate to call it lovemaking, for such a term would be paying that deceitful, manipulative, designing Poseidon more credit that he deserves.   It seemed to be lovemaking for the kind and earnest Medusa, a woman who showed herself to be both strong and courageous, as opposed to frivolous and pitiable.  The weak and  cowardly do not love as fully and face despair as determinedly as Medusa did.
            She never asked why Poseidon chose the temple for the sight of their latest liaison.     Even if she had, he likely wouldn't have told her the truth.   The truth being that he wanted their "commerce" to happen in the very sight of Athena, the goddess of war and wisdom.   He wanted Athena to behold in full, clear splendor the body of a mortal woman whose beauty was comparable to that of Athena herself.   Thus, Athena saw Medusa and Poseidon in the one place where neither belonged.     But, of course, that was part of the game which those vain and vicious Olympians played with each other.      Poseidon detested Athena and offered her a particularly stinging insult. Athena would get her own back.  Later, when Poseidon returned to the turbulent seas, Medusa remained sleeping under the shadow of Athena's statue, whose expression, once indifferent, soon became menacing.
                        Medusa arose with her sleep with a start, aroused by a searing pain in her stomach.   She called out for Poseidon, but was answered by silence.  She stood, still nursing her stomach, and under the silvered moon shone herself fully to Athena, whose fury took full form as Medusa was at once transformed.    Skin to scales; teeth to tusks; hands to claws, tresses to serpents;  woman to monster.    Medusa gazed down at her transfigured body and wailed to Poseidon to intervene, to restore her beauty.    Yet, she could not speak.   Her pleads were guttural moans.
                        "Let us behold your beauty now..." the goddess seethed while she watched the wretched Medusa stumble through the darkness away from the temple and out into the sea beyond.     She sank into the waters, hopeful that perhaps Poseidon would be moved to pity and would wash away this horrid curse.        He didn't.     He was then as he had been before: indifferent.   Now that she was deprived of beauty, he would see her no longer.  She swam to the island where the other two gorgons, Stheno and Euryale, resided.  A barren, atoll of rock far removed from the society of men.  There she spent day after day in the company of the only two creatures in this "world made hateful by its aversions" that weren't repulsed by her appearance.  Though they were sisters, she was truly alone.
                  One might have thought that when the young and bold Perseus, with the assistance and to the delight of Athena, herself, traveled to the atoll and beheaded Medusa, she must have welcomed death as a liberation. 
It was only after her death  that Poseidon, in a pointless spasm of contrition, was curiously moved to pity:  he took some of her blood, spilling out of the satchel in which Perseus carried her head, and mixed it with seafoam.    From these two elements he fashioned Pegasus: the beautiful, strong winged horse that became the embodiment of Medusa's true nature: beautiful and free of the world. When Perseus ascended into the ethereal heights and left his stellar imprint upon the celestial sphere, he took with him Medusa's severed head: the grotesque trophy earned in his youth.   It has remained here over the centuries: a despised creature amongst the retinue of heroes and ageless Olympians. When we first hear the stories of Medusa, we are advised to never look at her directly.   For this reason, of course, we have never seen her clearly. 

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2019-2020:  CLXXI

THE DAILY ASTRONOMER
Monday, July 6, 2020

Remote Planetarium 59:   Intrinsic Variables II - Long Period Variables

Let's begin the week by discussing a star called "wonderful."   Known by the actual name "Mira," this star marks the long throat connecting the faint head and larger body of Cetus, the seamonster.  One can observe Cetus in the early morning eastern sky this time of year.    While seeing Cetus, an observer might or might not find Mira because for much of the year it won't be visible to the unaided eye.     Its brightness varies from a magnitude of 10.1 (minimum) to a magnitude of 2.0 (maximum.)   When a star's magnitude is 6.0 or higher, it generally isn't visible to the unaided eye.   

Mira is the archetype of the "Mira Variables," defined as those stars that are passing through the latter stages of their life cycles.   Their masses are  generally less than two solar masses.   Mira variables are fusing helium in their cores and will soon expel their outer layers as planetary nebulae before leaving white dwarf remnants behind.       Unlike Cepheid variables that pulsate in response to helium ionization in specific layers, Mira variables pulsate because the entire star is expanding and contracting due to turbulent changes within the inner layers.  This turbulence relates in part to the motions of the hydrogen-burning shell enveloping the helium burning core.      Another difference relates to the substantial brightness changes.      Whereas a Cepheid variable's brightness diminishes and increases as the size and temperature increase and decrease, the brightness of a Mira variable will change as energy shifts from the visual to the infra-red part of the electromagnetic spectrum.       As Mira variables are solar mass stars toward the end of their lives,  they will actually be red giants: much larger than the Sun, but also significantly cooler.        Also, recent observations have revealed that Mira variables tend to be enshrouded in diffuse shells containing carbon dioxide, water vapor and other molecules that will affect the star's apparent brightness.  

Mira variables are distinguished by the following characteristics:

• periods between 80 - 1000 days
• masses comparable to that of the Sun. 
• toward the end of their life cycles (Red Giant stage)
• the range of brightness variations can extend many magnitudes

Mira's variability period is 332 days.  So, one can expect it to reach its maximum brightness once a year.   The following list includes the upcoming dates of Mira maxima.    Fortunately, the next Mira maximum occurs around mid to late September, the time of year when its host constellation Cetus is well placed for evening viewing.

Mira Maxima:

• September 20, 2020
• August 18, 2021
• July 16, 2022
• June 13, 2023

The "Mira Light Curve."    We see the variations in Mira's brightness over time in the above light curve.      Notice that the minima and maxima are not consistent, but instead can vary by as much as a magnitude. 

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Rapid astronomer profile:   Johannes Hevelius (1611-1687).    Yes, we've encountered him before.  We saw Hevelius when we were discussing constellations of relatively recent coinage.  (He crafted a few of them, himself.)  Hevelius named the star "Mira," meaning "wonderful," because of its tendency to appear and then reappear.   He first included the name in his 1662 publication "Historiola Mirae Stellae ," (A Short History of the Wonderful Star.)

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When at maximum brightness (magnitude 2.0) Mira is the brightest of the Mira variables.    The next brightest of Chi Cygni, a star within Cygnus the Swan:

Chi Cygni is marked by the black dot to the right of the vertical axis of the "Northern Cross" which is just under Eta Cygni.   Chi Cygni's mean variability period lasts 408 days.   At brightest, Chi Cygni's magnitude equals 3.3.  At its dimmest, the magnitude is approximately 14.1, almost 1600 times dimmer than the faintest naked eye stars.   Because the variability period can itself vary by as much as forty days, we will not post the same maxima calendar we produced for Mira.   Besides, Chi Cygni at maximum is three times dimmer than Mira at maximum.

The Mira-type is the main type of long period variable star.    The only other type is the "semi regular variable," those whose variability itself varies considerably due to interior turbulence.  Astronomers divide semi-regular (SR) variables into four categories (a - d).   

Perhaps the most famous example of a semi-regular variable is Betelgeuse, the star marking Orion's eastern shoulder.  (Orion isn't currently visible due to its close proximity to the Sun.)  Betelgeuse is also toward the end of its life cycle and exhibits irregular variability due to a variety of complex factors, including alterations in its magnetic field and the conveyance of energy through its dynamic outer layers.  In fact, just within the last year we observed Betelgeuse's brightness diminish considerably. Many of us wondered if that red supergiant star was about to explode as a Type II supernova.   It turned out that the dimming was merely part of the irregular variability cycle and not a precursor to an imminent explosion.      

All long period variables, be they Mira-type or semi-regular, are stars nearing the conclusion of their life cycles.       It seems likely that most stars will become variable at some point in these cycles: the type of which depends, of course, on the star's mass.  After all, a star's entire life cycle depends on its mass.

Tomorrow, part three of our Intrinsic Variable lesson with Cataclysmic Stars.

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Skywatching tip: Moon and Saturn

Look for the moon near Saturn this evening!  The moon still will appear full tonight.   The moderately  bright "star" near the moon is Saturn, the most distant planet visible to the unaided eye.

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