SOUTHERN ASTRONOMICAL DELIGHTS J U P I T E R Part 1 : SUMMARY, MYTHOLOGY &
NATURE
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J U P I T E R is the fifth planet out from the Sun, and
easily justifies its main accolade as ‘King of Planets’, being the largest planetary body in the
Solar System and only second in volume to our Sun. It differs
markedly from the four inner terrestrial planets, being a gas
giant with no tangible surface. By mass, Jupiter contains some
2½ times the entire weight of all the other planets combined.
Compared to the Earth, it is about 317 times heavier and 1,320 times
(1.431×1015 km3) by volume.
Lying much further from the Sun than Earth, Jupiter is placed
among the so-called superior planets — beyond the orbit
of the Earth, and whose solar distance averages some 5.20 A.U.
(Astronomical Units) or 778 million kilometres. It takes 11.86 years
(11 years 10 months) to complete one single orbit, averaging the
orbital velocity of 13.07±0.65 km.s-1 —
about 45% that of the Earth.
JUPITER DATA
Discoverer : Prehistoric Satellites : 17 (2000) 67 (2012) 69 (2018) DIAMETER Equatorial : 142,984 km. Polar : 133,708 km. Oblateness Ratio (i) : 13/14 Period (P) : 11.8626 years Synodic Period : 398.88 days Orbital Velocity : 13.07±0.65 km.s-1 Eccentricity (e) : 0.04877 Inclination (i) : 1.3046° Mass : 1.899×1027 kg. Escape Velocity : 59.5 km.s-1 Mean Density : 1.326 g.cm-3 Mean Distance : 778.57±38.05 ×106 km. Sidereal Rotation : 09h 55m 30s (III) Day Length : 09h 55m 33s Max. Diameter (Equator) : 50.1″ (arcsec) Min. Diameter (Equator) : 29.8″ (arcsec) Albedo : 0.52 Maximum Magnitude : −2.9 Minimum Magnitude : −1.5
Jupiter to the naked-eye appears as a very bright pale yellow
coloured ‘star’, being a slightly lighter yellow than the
sixth planet, Saturn. The planet appears as the second brightest
planet visible in the nighttime sky, placed behind only Venus and
being only exceeded by the Moon and the Sun. Successive yearly
oppositions average once each time within the twelve zodiacal
constellations, before moving onto the next one. Sidereal and
synodic periods differ by about 33.62 days, so that, successive
oppositions recurs once every 4 weeks and 5⅓ days.
Jupiter is an attractive target for amateur observers, whose
colourful telescopic appearance, shows the multitudes of reds, pinks
and yellow shadings. It differs radically in appearance than the
other four inner planets of Mercury, Venus, Earth and Mars, as the
visible surface is not solid but is covered by thick dense clouds
that descend to an unknown depths. Telescopically, the Jovian
atmosphere shows various colourful belts, spots, swirls, etc., which
are in constant and rapid change. Obviously the Jovian weather is
far more active than the various clouds and meteorological
atmospheric phenomena we see on Earth.
Through even modest telescopes, the disk appears distinctly oval,
being flattened in the ratio of 13:14. In true size, Jupiter is
decidedly huge compared to the Earth. His gigantic girth is 142,984
kilometres across, but is 133,708 km. at the poles — making
the disk oblate by some 6.49%. This gross distortion is generally
caused by the very rapid rotation of just under 9 hours and 51
minutes — the planetary rotation found in the Solar System.
This is a rotational velocity of 12.7 km.s-1 or about
45,600 kilometres per hour! Such fast rotation also has the likely
consequence of explaining the rapid dynamical evolving atmosphere,
lightning, and possibly the magnetic field.
Table 2. Orbit Extremes of Jupiter
(2000-2050)
Periapsis
Apapsis
07th May 1999
11th Apr 2005
16th Mar 2011
18th Feb 2017
23rd Jan 2023
29th Dec 2028
03rd Dec 2034
08th Nov 2040
From Earth, the axial rotation is only slightly tilted at 3°
07′ (3.12°) to the ecliptic. This is the smallest tilt
among all the planets. This suggests little seasonal changes are
seen at the poles. Also, unlike Saturn, the obvious oval shape
telescopically appears to remain constant and any differences are
not readily seen. Evidence for these changes in general appearance
can be found during the transits and eclipses of the four inner
moons, which can disappear or reappear well away from the observed
disk. Biggest differences occur during quadrature (90°
angle perpendicular to the Sun-Earth), but this effect is
insignificant during any observed opposition.
Jupiter also has a slightly non-circular orbit with respect to
the Sun, whose orbital eccentricity (e) is 0.04877. In its
orbit, the planet reaches it closest approach or periapsis
(perijove) once every 11.86 years. This repeatably occurs in the
zodiacal constellation of Sagittarius at the ecliptic longitude of
273.87°. Times for recent or upcoming periapsis and apapsis are
listed in Table 1.
MYTHOLOGY of JUPITER
“Estne Dei sedes nisi terra,
et pontus, et aër, et cœlum, et virtus?
Superos quid quærimus ultra?
Iupiter est, quodcunque vides, quodcunque
moveris.”
“Has God a dwelling other
than earth and sea and air and heaven and virtue?
Why do we seek the gods beyond?
Whatsoever you see, wheresoever you go, there is
Jupiter.”
(Cato on consulting the oracle of Ammon at Siwa in
the
Egyptian desert about the divinity of Julius Caesar.}
Marcus Annaeus Lucanus (Lucan) (39-65 AD) Pharsalia (‘De Bello
Civili’ or ‘On Civil War’), ‘The Temple of Ammon’9, 580 (Written 61 AD—c.65
AD?)
Among the ancient Greek pantheon of gods, he is known as
Zeus, whose translated name means ‘sky.’
Likewise in Roman mythology, his name is known as Jupiter,
and is similarly placed as the chief god, who oversees Nature and
all the other gods and Mankind. In classical mythology, Zeus /
Jupiter is one of the sons of the first Titan, Cronus / Saturn and
was mothered by Rhea. He is related to several brothers, include
Neptune and Pluto, with his sister Ceres. Jupiter rose in importance
when he usurped all of the original twelve Titans during their
internal war, in which, he overthrew their rule after much struggle.
These twelve were finally demoted because of their crimes down into
the lowest parts of Tartanus or Hell, placed even underneath
the realm of Pluto and his domain of the Underworld. (See Greek Mythology Discussion : Saturn Pt.
2) Some say this dismal place lies on the edge of the blank
void or emptiness where disorderly rumblings resides with the first
god of all, Chaos. Here these Titans can do no further harm. It was
from the political vacuum after these events that Jupiter supplanted
his supreme rule in kingship over all the world – influencing
both the gods and humankind for evermore. For this singular
achievement of bring order to the world, Jupiter is very importantly
associated and has been assigned as having full governance of law
and order from heaven to and human society. Here he sits atop Mount
Olympus on his golden imperial throne, overseeing all the earthly
affairs under his domain.
Worshippers of Jupiter during ancient times, did firmly believed
that his god-like powers could directly control various aspects of
atmospheric phenomena such as rain, storms, and commonly in anger,
both thunder and lightning. Among the tenants of Roman, religion he
was greatly venerated, and sometimes feared, but was also worshipped
in praise and revered by all. Jupiter in mythology has many
offspring to various wives, goddesses, or human lovers, who all
seemingly took his alluring fancy. Each of these children born to
him were to hold various levels of influence or importance. For Man,
he had rule over the human condition, which included relationships
and of their various fates. Those who impeded his often complex
schemes, or did crimes against others, were to suffer greatly from
his often vengeful and sometimes cruel nature. Jupiter had absolute
power over death or pain, but he could also show exoneration or
kindness over any of his many minions.
The JOVIAN MOONS
Jupiter is also prominently noted for its four large moons. These
are named in order of distance from Jupiter; Io,
Europa, Ganymede and Callisto. They were first
seen by Galileo in 1610, who eventually imagined them like some
mini-solar system. Telescopically, these moons are seen to change in
positions over several minutes. We find both Ganymede and Callisto
are both larger than the planet Mercury, and all of them are larger
than our own Moon. [See Jupiter
Pt.2.]
Surrounding the planet are myriads of other tinier moons. Most
are of little interest to the observer because they are hard to see
even with the largest telescopes, each appearing as only tiny
pinpoints. In 1963, the number of Jovian moons was twelve,
which increased to sixteen (1989), and thirty-two
(2002), sixty-three (2005). This remained until 2009, when
the discovered total number reached sixty-seven (2012) then
sixty-nine (2018).
Presently, the sixth planet, Saturn, now has the second most
number of moons with the total of sixty-two (2018). Over the
last few decades the totals of moons orbiting around Jupiter and
Saturn are now more like a race of discovery. The leading planet
with the largest number of moons has exchanged places several times,
and may do so again in the future as more investigations and new
exploration continues.
The PLANET JUPITER
As previously mentioned, the visible surface of Jupiter is not
solid but is gaseous, whose clouds descend into unknown depths. Most
obvious of the seen features are the main belts and equatorial
zones, all displaying obvious day to day various rapidly changing
shades and colours. Overall composition of the atmosphere consists
of around 89.8% Hydrogen and 10.2% Helium, and this is mixed with
much smaller proportions of several common gaseous compounds such as
methane (0.3%), ammonia (0.026%), water
(0.004%) and carbon monoxide. In much smaller proportions
there are also an intermix of many more complex organic molecules.
These visible rich colours we see are really formed by variety of
ammonia-related compounds such as ammonium hydrosulfide
(NH4SH.)
Two of the most prominent areas are the so-called North and
South Equatorial Zones each placed 9° to 10° either side
of the Jovian equator. These main belts are produced by complicated
atmospheric dynamics that are quite different from what is observed
by Earth-bound meteorologists. The planet comprises an outer
atmosphere whose cloud tops are −125°C. This is
surrounded by a thicker lower gas layers hovering around room
temperatures, and some five times the atmospheric pressure here on
Earth. Into the lower depths, this layer continues to get more dense
until it reaches the probable solid crystalline metallic hydrogen
core or even existing possibly as some large liquid hydrogen and
helium sea. Such material is principally created by the crushing
weight of Jupiter itself that reaches about 70 million
atmospheres, whose central regions may also be very hot. While this
can never be directly observed, either theory of the core may
account for the very powerful magnetic field surrounding Jupiter
itself. Some have also speculate that there could also exist a
smaller Earth-sized rock body at the core, being surrounded by these
exotic states of Hydrogen and Helium.
Jupiter also radiates more energy than it receives from the Sun,
which was first discovered by radio astronomers in B. Burke and K.
Franklin in late 1954 from Seneca in Florida. Energy emissions are
thought to be due to the sizeable magnetic field of Jupiter and the
electrical currents by non-thermal methods by way of synchrotron
radiation. The Jovian magnetic field slowly wobbles by about
11° from the rotational axis, effecting the real nature of
radio emissions. Other radiation suggest some additional causes
might derive from very large atmospheric turbulence from either the
Great Red Spot or perhaps some internal convection zones. Others
think that thunderstorms could significantly contribute to the radio
emissions.
Jupiter has been briefly visited by several spacecraft over
recent years, including Pioneer 10 and 11 (December 1973 &
December 1974), then Voyager 1 and 2 (Closest approaches on 5th
March 1979 & 9th July 1979, respectively.) Both gathered vast
amounts of new data by these earlier brief encounters using various
instruments onboard. More recent was the orbital spacecraft mission
named Galileo, viewing Jupiter in much more detail, and quickly
accumulated more data than all the other missions combined. Galileo
arrived in Jupiter space on 7th December 1995, whose planned fifteen
orbits of the craft more close encounters with the planet, where the
outgoing orbital paths then explored in detail the four main moons
of Jupiter. Discoveries included a wide range of things, such as the
nature of the intense magnetic field, killing any human to a
distance of several millions of kilometres. Galileo ended its
encounters on 20th September 2003 when it was deliberately was
crashed into Jupiter at 48.2 km.sec-1. Earlier on 12th
July 1995, a dedicated atmospheric probe was launched and plunged
into Jupiter to examine winds and the atmospheric composition.
Intense aurorae has also been seen during each mission, included
huge lightning discharges, faint rings, and verification of the very
complicated atmosphere dynamics. Numerous photographs have also
revealed much complexity. A new spacecraft named Juno arrived in
orbit of the planet in July 2016, observing the planetary magnetic
field and atmospheric dynamics especially near the poles.
Disclaimer : The user applying this
data for any purpose forgoes any liability against the author. None
of the information should be used for either legal or medical
purposes. Although the data is accurate as possible some errors
might be present. Onus of its use is placed solely with the
user.