- by John Hlynialuk

Jupiter is the one planet that is rightfully called "The King of Planets". Modern observations reveal Jupiter to be a planet of stupendous size: 11 times Earth's diameter and 1300 times the volume, - imagine a ping pong ball beside a basketball. Spectacular cloud patterns in its atmosphere are as large as Earth but are prosaically referred to as "little spots" coloured red, brown or white by various gases. The familiar one, the Great Red Spot, is a gigantic swirling mass of sulphurous gases, -a 400-year-old hurricane which could easily swallow two Earths with room to spare. Only sunspots are larger than this giant atmospheric structure. Everything on Jupiter is truly king-sized.

I have often wondered why the early astronomers with no telescopes to see Jupiter close up managed to attach their chief mythological figure to this planet. Zeus and Jupiter are the Greek and Roman names for the same god king, but this planet is one of five naked eye wanderers and there would be no reason based on visual appearance to put it on the royal pedestal. Still, the ancient stargazers got it right and I have a theory that it was more than just a coincidence.

What makes the five planetary stars ("planetes" in Greek) stand out is that they wander. None are fixed on the celestial sphere like ordinary stars; furthermore they wax and wane in brightness, once again, unlike normal stars. For example, Mars, is sometimes a bright beacon in the sky (as it will be this summer), and at other times an average "star" not much brighter than those in the Big Dipper. Top brightness marks go to the planet Venus which often becomes the most brilliant planet in the sky, much brighter than Mars and the others, and shining bright enough to be seen in broad daylight.

Another distinguishing feature of three of the five naked eye planets, Mars, Jupiter and Saturn, is that at times, they are visible near the Sun and at other times, appear in a dark sky all night long with the Sun totally absent. The other two, Venus and Mercury never stray far from good old Sol, and rise in the morning sky just ahead of the Sun or set just after the Sun in the evening sky. In addition, Venus and Mercury move much more quickly across the sky than the other three. Mercury is fastest and covers more celestial territory per night than any other planet. Mars takes two years and Jupiter takes just shy of 12 years to travel around the entire sky. The slowpoke Saturn takes close to 30 years to circle the zodiac once.

So, what were the probable rationales for the planet names? Mercury, the fleet-footed messenger of the gods (Hermes to the Greeks) was an obvious choice for the fastest moving planet. Similarly, Venus the Roman goddess of beauty (Aphrodite to the Greeks) was an easy association with the most brilliant, beautiful light in the sky at night apart from the Moon. As for the Roman god Mars (Ares to the Greeks), there was a planet in the sky with a distinct reddish colour, not blood-red, of course, but different enough to connect it to the god of war.

As for Jupiter (the Greek god Zeus), the name would be appropriate given a modern knowledge of this giant planet. For the ancients, assigning the name of the most important god of mythology to one specific point of light out of five, could have been a coincidence, but I think there may be some rhyme behind the reason. Zeus/Jupiter takes just under 12 years to travel entirely around the sky, passing through each constellation of the zodiacal in turn. And Jupiter spends very close to one year in each "house", like a monarch surveying his domain, honouring each occupant with a year-long stay that repeats every 12th year.

This suggestion is just that, my theory of why a specific name was chosen. You need not buy it, and I admit I am not an historical astronomer but an observational one, so I may have this all wrong with the chicken before the egg, so to speak. I welcome comments from anyone with knowledge of Greek history who can elaborate or refute this story.

Our next two viewing events involve, you guessed it, more Jupiter-watching at the Fox Observatory June 9 and yes, the Great Red Spot will be visible, by Jove! Later in June, we celebrate the start of summer at Keppel Henge in Big Bay at solar noon on the summer solstice, June 21. See our website www.bluewaterastronomy.com for more details.

Clear skies and happy Jupiter-watching!