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, being 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, 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.


Discoverer : Prehistoric
Satellites : 17 (2000) 67 (2012)
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
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 star, being 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
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′ (6.12°) to the ecliptic, being the smallest 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.


In 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, overseeing 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. The 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 ever more. 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.

Jupiter worshippers 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.


Jupiter is also prominently noted for its four large moons each 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, but at last count, this discovered total number has reached sixty-seven (2012).

Presently, the sixth planet of Saturn now has the second most number of moons with the total of sixty-two (2009) Over the last few decades the total moon counts orbiting around Jupiter and Saturn are more like a discovery race. 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.


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 degrees 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 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, an dedicated atmospheric probe had been launched and then plunged into the 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 will be the Juno mission, that is already well underway, whose arrival is planned for July 2016.

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.


Last Update : 28th December 2012

Southern Astronomical Delights © (2012)

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