[image: tantalus-punishment.jpg]
*Tantalus:* Madly Behaved
In the mythological Universe, most people who died had little to fear.
Charon conveyed their souls across the River Styx to the plains of
Asphodel where they more or less just loitered for all eternity. While
these departed souls languished morosely amidst the fog enshrouded gloom
and even those who had been the most impoverished mortals would have gladly
embraced their poverty just to live again in the sunlit uplands, at least
most of them weren't tortured. Torment was reserved for the select few
who committed the most vile crimes. One of these tormented souls was
Tantalus, whose atrocious behaviour shocked the gods and even perplexed the
poets who recorded his deeds.
Tantalus was the son of Zeus and Pluto, an oceanid not to be confused with
the Roman counterpart to Hades. Though Zeus fathered many, Tantalus was
one of his favorites, despite his comparatively low status: he merely
became a king and never rose to godhead. Zeus often invited him to dine
on Olympus and partake of the delectable fare generally reserved for the
gods. Once Tantalus secretly brought some of the nectar and ambrosia out
of Olympus and gave it to some mortal friends. While his friends dined on
this divine feast, Tantalus entertained them with sordid tales of the gods'
exploits, some of which were so scandalous his friends could scarcely
believe them. Those acts were petty misdeeds compared to what followed.
Tantalus had invited the gods to dine at his palace one evening as a way of
repaying their hospitality. Prior to their arrival, he killed his son
Pelops by cutting his throat. He then dismembered Pelops' body and
tossed the pieces into a stew. It is a matter of debate whether or not he
committed this vile act to test the gods' omniscience or merely because he
ran out of meat. Soon after the gods arrived, Tantalus cheerfully
placed the stew before them. Only Demeter partook of the gruesome meal
due to her consuming distress over her daughter Persphone's abduction. The
others realized at once the source of the stew meat. Enraged beyond
measure, Zeus destroyed Tantalus' kingdom and crushed him under a crag from
Mount Sipylus. Considering these punishments insufficient, Zeus then
consigned Tantalus to Tartarus, the Underworld's punitive region.
Tantalus was submerged neck high in a cool river. Fruit-laden tree
boughs drooped down just above him. There Tantalus remained, pained by
ravenous hunger and burning thirst. Everytime he stooped down to drink,
the river receded below the sandy sediment. Whenever he desperately
reached for the fruit, a wind would push the bough out of reach. It is
said that high above the fruit tree boughs hung a boulder precariously
suspended by a thread. Denied even the respite of sleep, Tantalus knew
only the extreme agony of hunger and thirst, the frustration of always
attempting in vain for any satiation and the abject terror of knowing he
could be crushed under a rock at any moment. That rock was a punishment
meted out to him for having stolen Zeus' golden dog: one of the many pranks
Tantalus played on the god that had indulged him so generously.
Happily, though, the gods resurrected Pelops and Demeter fashioned an
ivory shoulder to replace the one that she had unknowingly consumed.
THE SOUTHWORTH PLANETARIUM
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Julian Date: 245962.16
2019-2020: CXXXII
THE DAILY ASTRONOMER
Thursday, April 23, 2020
Remote Planetarium 19: Lunar Eclipses Part I
[image: WEB11715-2010_640.jpg]
A lunar eclipse occurs when the full moon passes into Earth's shadow cone.
This cone extends for more than 830,000 miles into space. As the
moon's greatest distance is around 250,000 miles, the moon will sometimes
move through the shadow. As the moon's orbit is inclined by 5.1 degrees
relative to the ecliptic (Earth's orbit around the Sun), the moon will
generally travel north or south of this cone. Only when the moon is at or
near a node, the intersection point connecting the two orbits.
We recognize three times of lunar eclipse:
- *TOTAL LUNAR ECLIPSE*: when the moon moves entirely through the umbra
(the inner part of Earth's shadow)
- *PARTIAL LUNAR ECLIPSE:* when the umbra covers only part of the moon.
- *PENUMBRAL LUNAR ECLIPSE:* when the moon only moves through the
penumbra (the outer part of Earth's shadow.)
Today we'll discuss the next total lunar eclipse visible in the eastern
US: an event on May 15-16, 2022
Our focus will be on reading the chart and lunar eclipse map.
[image: 2022-may-16-total-lunar-eclipse (1).jpg]
The purpose of any chart is to convey as much information as possible in a
concise
manner. The chart above pertains to the May 15 - 16, 2022 total lunar
eclipse. Due to the quantity of information, we thought it would be best
to divide this lesson into two parts: one today and the next one on Monday,
April 27th.
*GREATEST ECLIPSE: 04:12:41.6 UT*
"UT" is the Universal Time mentioned previously. Greatest Eclipse is the
point at
which the Moon is as far into Earth's umbra (inner shadow) as possible. Or,
when
the distance separating the moon's center and the center of Earth's shadow
is at a
minimum. This time translates to 12:12:41 a.m. May 16, 2022
*(P1) PENUMBRAL ECLIPSE BEGINS: 9:32:07 p.m.*
Earth's shadow is divided into two regions: the light, outer part of
Earth's shadow, called the 'penumbra,' and the inner region called the
'umbra.' The penumbral eclipse begins when Earth first touches the
penumbra. The moon passes completely into the penumbra before it reaches
the umbra. Honestly, unless you're one of those mystical poetic types
who can actually tell the difference between a whisper of a breeze and a
caressing zephyr, you won't notice much during the penumbral part of a
lunar eclipse. Perhaps the brilliant moon's pallor is rendered a few
phantoms less vibrant, but even that is a stretch.
*PENUMBRAL MAGNITUDE: 2.3726*
This number measures the fraction of the Moon's diameter enclosed by the
penumbra during the moment of greatest eclipse. The penumbra is the outer
part of
Earth's shadow.
*UMBRAL MAGNITUDE: 1.4137*
This value measures the fraction of the Moon's diameter enclosed by the
umbra
during the moment of greatest eclipse. The umbra is the inner part of
Earth's
shadow. If the umbral eclipse were partial, the magnitude would be less
than 1.
*P. RADIUS: 1.2854*
"Penumbral Radius" Measures the size of the penumbra's radius in terms of
Earth's
radius. The Penumbra's radius is about 1.3 times larger than Earth's at
cross section
of Earth's shadow.
*U. RADIUS: 0.7580*
"Umbral Radius." Measures the size of the umbra's radius in terms of Earth's
radius. We should certainly expect this value to be smaller than 1, as
Earth's
shadow cone tapers down as one moves away from Earth.
*GAMMA: -0.2532*
Measures the minimum distance between the center part of the Moon and the
central part of Earth's shadow. This occurs at the moment of greatest
eclipse. The
value is in terms of Earth radii. If the center of the Moon passed directly
through the
center of Earth's shadow, Gamma would be zero. The Gamma value is negative
because the Moon's center is south of the central shadow point.
*(U1) UMBRAL ECLIPSE BEGINS 10:27:53 p.m. *
This is when the 'action' starts. The umbra is the dark interior
shadow. Once the umbral eclipse begins, we'll see Earth's curved shadow
against the moon. We'll watch the shadow migrate across the moon
until the moon is completely immersed in Earth's shadow.
*(U2) TOTALITY BEGINS: 11:29:03 p.m.*
Totality begins when the moon is completed inside Earth's umbra. The
moon will not be wholly lost from sight. Instead it will appear
reddish, because Earth's atmosphere scatters blue light, but directs red
light into its shadow. (We see a blue sky during the sky because of
this effect.) The eclipsed moon will reflect this reddish light back
to us, producing the ominously named 'blood' moon. One effect that we
think is absolutely magnificent is the 'spherical moon' phenomenon. During
totality, the color differential across the moon's facade lends it a
spherical
appearance. The moon actually appears as a crimson sphere in space, as
opposed to the full moon's usual disc-like appearance.
*(U3) TOTALITY ENDS: 12:53:56 a.m. (May 16, 2022)*
At this moment, the moon starts to move out of Earth's inner shadow.
We'll still see Earth's curved shadow on the moon as it retreats
across the face.
*(U4) UMBRAL ECLIPSE ENDS: 1:55:07 a.m. *
At this moment, the moon moves completely out of Earth's umbra. The
eclipse is now just penumbral and, well, most people will have turned in by
then.
*(P4) PENUMBRAL ECLIPSE 2:50:48 a.m. *
If you have some ancient Nordic prophecy to fulfill by watching the
entire eclipse, well, your task ends now. For the last 55 minutes, you
have beheld a moon looming high over an eerie and quiet world but
haven't noticed much, except for the utter lack of humans around you.
*SAROS SERIES: 131*
A Saros cycle is about 6,585.3 days, or 18 years and 11.3 days. Each
eclipse that
occurs within a given Saros will have similar geometry, because it occurs
in just
about the same point in the Moon's orbit relative to that of Earth and the
Sun. Each
Saros begins and ends with a series of penumbral lunar eclipses (when the
moon
passes only through Earth's outermost shadow.) These are followed by a
series of
partial eclipses which are then followed by total lunar eclipses. Each
eclipse within a
given Saros cycle is separated by 18 years and 11.3 days. We can use that
knowledge to predict the next occurrence of an eclipse of that Saros series.
For instance, the next Saros 131 lunar eclipse after the May 15-16, 2022
event will occur on May 26, 2040. The following Saros 131 lunar
eclipse will then happen on June 6, 2058. The Saros 131 cycle started with
a penumbral eclipse on May 10, 1427 and will end with a penumbral eclipse
on July 7, 2707
*WHAT IS THE DANJON SCALE?*
The Danjon Scale, named for French astronomer André-Louis Danjon (1890
–1967), measures the brightness of a lunar eclipse during totality. 1967),
measures the brightness of a lunar eclipse during totality.
Atmospheric conditions are the most important factor determining the
Danjon rating of an eclipse. Danjon rating of an eclipse. In fact, the
lunar eclipses seen in
the year or two following powerful volcanic eruptions have had Danjon
ratings of 1 or even 0. ratings of 1 or even 0.
The scale is as follows:
- *L = 0* Very dark eclipse. Very dark eclipse. The moon is nearly
invisible
- *L = 1 *Dark grey eclipse; perhaps a ruddy red or brown Moon
observable, but its features are vague
- *L = 2* Deep red eclipse. Deep red eclipse.The interior of the moon
appears a dark red, while the outer regions are brighter outer regions are
brighter
- *L = 3 *Brick- red eclipse. Moon rim brighter and a l Moon rim
brighter and a lighter shade of red
- *L = 4* Very bright copper Very bright copper-red or orange eclipse.
red or orange eclipse. The umbra might even assume a bluish tint. The umbra
might even assume a bluish tint. We cannot accurately predict the Danjon
rating for the eclipse.
We cannot accurately predict the Danjon rating for the eclipse. You can
observe the eclipse, yourself, however.
Tomorrow, the next quiz.
Monday, Part II of Lunar Eclipses
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