ASTRONOMY holds one’s heart and mind — and breadth — in a firm grip, and continues to open newer vistas until it sends the mind reeling into the unknown; into an altogether new world of discoveries.

Now the moons — an integral part of the solar family, they come in all sizes and shapes, colours and forms. Other than the ominous moon of the Earth, the first few were discovered by Galileo Galilee (1564-1642) in 1610AD (named: Io, Europa, Ganymede, and Callisto in that order). The moons continued to be discovered right up to the time of Clyde Tombaugh (1906-1997), who is credited with locating the last planet Pluto and its moon, Charon in 1930.

Clyde was a self-trained astronomer with no education of any kind in astronomy or allied sciences, save deep enthusiasm. He asked questions which astronomers working at the thin desert air of Flagstaff, Arizona, USA’s observatory would answer out of sympathy, and concern.

It would not be out of place to mention that your servant here is like our friend Tombaugh, not formally educated in astronomy except at the graduation level (97 per cent), but it is also my part to tell you that, like him, I trained myself — working day and night over the secrets of the universe until the day when I could stand up and say that yes, now I understand a part of its basics. Maybe not anymore than just the basics.

Many young people approach me wondering whether they will ever be able to make it in astronomy and I tell them not to lose heart, for astronomy needs them just as much as they need astronomy. Keep the interest alive. You will make it one day, soon enough! Seek help wherever available; books, museums, people, whatever else. But also use the bare, open sky to make observations night and day.

Back to the moons! In all there are well over 100 of them; perhaps as many as 150 or so. Any chunk of rock will qualify as one. Saturn alone has some 63 moons, or satellites. While it is popularly known to have 23, others are embedded in the ominous ring system. These have been found to encircle the daddy planet just the same.

Another important thing before we proceed: Charon was not the last moon discovered in 1930. Numerous moons have been found and photographed in great detail by the many satellites between 1960s and now, and currently, many such satellites are in hot pursuit. In fact, the moonlets of Saturn are one significant outcome of their ramblings.

Most moons are rather irregular and ungainly looking chunks or large mountains, pock marked with frequent smash-ups of smaller rocks and boulders that happen to collide with the larger bodies every now and then, leaving a footprint, in the shape of a crater, every time that happens. The collisions may take place every 25,000-30,000 years, which is a very small period on geological, or celestial time scale.

In determining the distance between planets, let us examine how it is worked out. While distances undergo a rather small change in the case of planets and the Sun, those between the planets change every now and then, and decrease or increase by far. The planets move at different speeds, as you know, and also know why. In their respective orbits their distances and position in the sky changes too. That makes their distances highly variable from one another. Hence, one cannot say for sure as to how far one planet is from the other. Therefore, it is best to give their distances from the Sun. As these are expressed in AUs (astronomical unit, which is the average distance between the Earth and the Sun, or, 93 million miles, i.e. 150 million km). The average distance of planets from one another, therefore, is worked out on as-is-where-is basis or the maximum a planet veers away from the other in the course of its orbit. Keep in mind the detail of the planets we encountered so far. It is as follows:

Planet Days Years Dist. From the Sun in AUs

Mercury 88.0 0.241 0.88 Venus 224.7 0.615 0.723 Earth 365.25 1.000 1.000 Mars 687.00 1.881 1.524 Jupiter 4332.5 11.862 5.203 Saturn 10,759.3 29.458 9.539

Keep a printout handy for use while you pursue astronomy earnestly.

You know it for sure that planet Mercury is the closest to the Sun. Then, moving outward we find Venus, Earth, Mars, Jupiter and Saturn. Now think how our ancestors found which planet came first, in order of their sequence. Remember that they had no recourse to telescopes. They had to rely on observation alone. They did so by marking out the background stars of a planet in question. Then the time it took for that planet to come back to that (or those) stars after having roamed the sky, and completing one full circuit of the skies. That time is the planet’s year! Since the more distant planets had not been discovered as yet, the job was easily accomplished within a lifetime.

Another stunning fact about skies. The two moons/satellites of planet Mars, called Phobos and Deimos (Fear and Panic) were discovered in the year 1877 by an American, Asaph Hall. Strangely, these moons had been predicted first by Jonathan Swift in his world famous classic, Gulliver’s Travels (1720), and then by the great Frenchman, Voltaire, in his book, Micromegas, in 1750, some 150 years before these were actually discovered! How, that we shall probably never find out!

In the course of their travels, which are not synchronised but random, the Earth and Saturn may come as close as 1,200,000,000 km (745,000,000 miles) from each other. Next they may drift apart to a whopping distance of 1,658,000,000 km (1,030,000,000 miles). These are unearthly distances, not meant to remember or keep a record of, but to know and understand thoroughly. That will be our last discourse on moons of Saturn. We shall take up some of the salient ones to serve as example.

More about Saturn and its moons, and some other features in the next issue!

The writer is a professional astronomer and a former head of PIA Planetarium. He can be reached at astronomerpreone@hotmail.com