Scorpius:  The Declawed Scorpion
Quietly creeping and silently seething, there in the hollow of southwestern early evening sky sets the arched frame and beating heart of the loathsome scorpion Scorpius.  Redundant of name, but formidable in nature.  A dark, brooding, spectre of peril sliding with gentle menace along our southern summer sky.  Each year, when Orion descends into retreating late spring twilight, it emerges onto the dark stage.  There in the underbrush this dreaded denizen of the Arachnid clan casts lurid eye upon the elongated frame of the unsuspecting virgin Virgo. Also redundant of name, but recumbent in posture,  Virgo has already set, wholly unaware that down on the haze-obscured horizon lurks the designing Scorpius in the grip of untoward intention, snapping his claws together in a frenzy of unconstrained excitement.

         Scorpius:  I'm  gonna get me some of that!

       But wait, Kahuna!

        Scorpius the scorpion has no claws.   One can't snap claws together in any type of frenzy if one doesn't have any claws to begin with.   Certainly, he has a stinger, a curved body, and a massive beating heart.    Yet, little good will those organs do him if he is sans claws down there in the sultry bayou of the southwestern sky.     So, he can cast a lurid eye, even furtively if he desires, but no other move can he make for, as they say in the land of the combustible Jambalaya, "that body ain't made for snatching!"

           DA:  Ah, too bad.  Here, have a pop tart.

          Scorpius: Jerk...

          DA:  Oops, you dropped it

            You understand, Scorpius is an ancient constellation of various associations. Perhaps the most famous of these is the story involving Orion.   When the boastful hunter Orion bragged that he could slay any beast in the world, Artemis fashioned the scorpion out of spare parts to destroy Orion.   This feat Scorpius accomplished in short order, nipping the hunter on the ankle almost as soon as he landed on Earth.  Orion died and, along with his killer, was placed in the sky.    Orion and Scorpius were arranged so that they would never be in the sky simultaneously, thereby precluding them from engaging in combat ever again.

           Scorpius is low in the southeastern evening sky in the summer, whereas Orion is high in the southern sky in the winter.  When Orion sets, Scorpius appears.    At this latitude the two antagonists cannot be in the sky together.   (They can be in the sky together around the Antarctic circle: a region known to the ancients as the underside of Terra Incognita.)

            Years ago, Scorpius the Scorpion was much larger than he is today.  Apart from the j-shaped body, stinger, and head, it also had a set of super claws at the west,  perfect for Orion nipping and maiden snatching.   Unfortunately, Roman Dictator Julius Caesar (100 - 44 BCE), in an effort to cast his own personal imprint on everything he saw (the sky, the calendar, the recumbent Cleopatra) detached the claws from the Scorpion's body.     These claws were transformed into another constellation known as "Libra the Scales."    This "set of scales" is one of the few inanimate objects on the firmament. (Sagitta the arrow; Scutum the shield are other examples.)
             The purpose of this detachment might have been to make the zodiac, as it was then called, conform in proportion to the Julian calendar.   The calendar had twelve moon-ths (months) and each month would have its own zodiac symbol. Before the Scorpion's truncation, the zodiac had eleven constellations.   
With the addition of Libra, the zodiac consisted of twelve constellations aligned along the sun's apparent annual path through the sky.
                   Today, this construct is known as the "ecliptic."
               The Sun passes through Libra during early November.   It passes through Scorpius during the last part of November.    Some refer to Scorpius as the "Thanksgiving constellation" because the Sun is generally in Scorpius during the range of dates on which Thanksgiving can occur. (November 22 - 28)
            Libra's two brightest stars, Zubenelgenubi and Zubenelschmali, are the Northern and Southern claws, respectively. These star names represent the last remnant of what used to be the strong and dangerous claws of the now declawed Scorpion.

THE SOUTHWORTH PLANETARIUM

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Julian Date: 24591129.16

2020-2021:  XXVI

              "Eddie Van Halen was born the year Albert Einstein died.   Who doesn't believe in reincarnation now?"

THE DAILY ASTRONOMER

Wednesday, October 7, 2020

Remote Planetarium 104:  General Relativity I:  A description of gravity

Once again, let's review Isaac Newton's "Universal Law of Gravitation."

Every massive particle in the Universe attracts every other massive particle. The magnitude of the gravitational force exerted between any two objects is directly proportional to the masses of both and inversely proportional to the square of their separation distance.

Imagine, for instance, two asteroids in deep space.   The masses of each are 500,000 kilograms and they are one million miles apart.       Despite this considerable separation distance, the asteroids still exert a gravitational pull on each other.    If their masses increased or if they were brought closer together, this gravitational pull would increase.  However, if the masses decreased, the force between them would be reduced in proportion to the mass loss.      If the separation distance doubled, the force would be reduced to one quarter of its original value.       Treble the separation distance and the force would be reduced to one ninth its original value.    Continue to increase the separation distance and the force diminishes rapidly.   However, it doesn't reduce to zero no matter how far apart the bodies become.  

          Although Newton provided a detailed description of gravity, he was troubled by the very notion of "action at a distance."    In fact, he conceded that any rational thinking person would find the concept of action mediated over a vast distance to be unacceptable.     Despite these metaphysical misgivings, however, Newton's quantified model of gravity became a cornerstone of physics for more than two centuries.

The Physics World was upended in 1905 when Albert Einstein (1879-1955), published his Special Theory of Relativity in which space and time, regarded classically as disparate, were fused into one single continuum called "space-time."      Special Relativity was founded on the principle that light speed is a constant in all inertial reference frames.   So, for instance, if an observer is traveling at 80% light speed while another remains stationary, they would both measure a light beam's velocity as being equal to light speed, or approximately 186,290 miles per second.      The implication of this light speed consistency is that time dilates and length contracts for the moving observer.      

In 1915,  Einstein published his General Theory of Relativity, which revolutionized gravitation by describing it not as a force mediated between two massive particles, but instead as a distortion of the space-time continuum caused by the presence of a massive object.             Every massive object induces an "indentation" in the space-time fabric.  The more massive (and more dense) the object, the "deeper' this indentation becomes.     According to the General Theory of Relativity, gravity is not a mysterious force connecting objects at a distance.  Instead, it is a massive object's reaction to another massive object's space-time distortion.   

This image shows a simplified view of space-time distortion.     Both the Earth and its moon distort their local space time geometries.   Consequently, smaller objects within the vicinity of either will be "trapped" within the gravity well.  

The  best known analogy is that of a taut rubber sheet on which a dense metal ball has been placed.     Imagine tossing smaller balls along the sheet both toward and away from the larger one.   Those balls that stray close to the large ball will either follow bent paths around it or will be drawn into its dent.   Conversely, the paths of the more distant balls are unaffected by the large ball.

Earth isn't pulling you down.  Instead, you are trapped within the planet's gravity well.      So, too, is the moon.     Earth is ensnared within the Sun's space-time distortion.      

Tomorrow, we'll focus on how gravity affects time as well as space.  They are, after all, aspects of the same continuum.  

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