In classical astrology there are seven planets: the Moon, Mercury, Venus, the Sun, Mars, Saturn and Jupiter. In Astrology the Moon and the Sun are planets and Earth is not. Originally, the planets were defined as visible objects in the sky whose position would change relative to the background of fixed stars.

The outer planets which cannot be seen with the naked eye and were discovered in the past three centuries have since been incorporated into astrology; however, because their years are so long there is still debate about the forces they represent.

Names of the Planets in other languages:

An Domhan

Also: Moon - Gealach; Sun - Grian


Also: Sun - Sonne; Moon - Mond


Also: Sun - Sole; Moon - Luna


Also: Moon - Lune; Sun - Soleil


Also: Moon - Luna; Sun - Sol


Also: Sun - Sol; Moon - Lluna


Also:> Sun - Taiyang; Moon - Yuequi

Planet was an old arcade game released by Alca way back in 1979.

The story

Asteroids marked a whole new era in space games. It was unlike any previous title. It was Atari's second vector game, and it was such an instant hit that they were forced to halt Lunar Lander production simply to try and keep up with the demand for Asteroids. As a matter of fact, the demand for Asteroids was so high that Alca was able to make their own PCB that would run a copy of Atari's revision A Asteroids program, and distribute the sucker all over Europe.

The game

The game is rather simple. You pilot a small wedge shaped ship, and you begin play in the middle of an asteroid field. Large slow moving asteroids surround you, when shot they break into two medium sized asteroids, which will each break into three small, fast moving asteroids. Shooting the small asteroids makes them disappear. Your goal is simply to eliminate all the asteroids from the playing field, while avoiding anything that would cause you to lose a life (touching an asteroid, or getting shot by a flying saucer).

The playfield consists of a single screen (which wraps around in each direction). Your controls consist of five buttons which are "rotate right", "rotate left", "thrust", "fire", and "hyperspace", although some table versions of this game have been reported to contain joysticks. The ship moves rather realistically for a zero gravity craft, which means that it keeps moving even after you stop thrusting. This takes a little practice to get used to, but it really enhances gameplay, as it allows you to do fly-bys of asteroids and enemy ships.

There are two types of flying saucers that you might encounter. The first type is large, slow moving, and stupid. These are quite easy to shoot down. While the second type is small, moves quickly, and is more intelligent in its actions. These are the highest point value objects in the game, but are dangerous to approach.

There are three basic strategies that you might use while playing this game. The first is the newbie method. The idea behind the newbie method is that you do not use the thrust button at all, simply rotate in place, and use the hyperspace button if things get too thick. This method actually works for the first few levels, but is useless later on. The normal method is just to simply play the game, you won't rack up the highest score, but this is the most fun way to play. The final method is known as "lurking". While lurking you should shoot out all the asteroids except for one (or two), and position your ship in a corner. Soon small flying saucers will start appearing regularly, simply shoot these down for points (the best way to hit them is to wrap your shots around to the other side of the screen). This method assures an outrageous score (after some practice), but can get boring fairly quickly. It is also noteworthy to mention that all "Planet" machines contain the earliest revision of the Asteroids software, while almost all actual "Asteroids" machines contain a later revision designed to discourage lurking.

The Machine

Most bootleg games were just shoddy circuit boards purchased from mail order houses located overseas, but not "Planet". Alca actually shipped entire machines. The Planet cabinet was a fairly generic wood grain jobber, with some mirror effects on the front.

The cocktail version was a little uncommon, it was rather unremarkable in appearance, and it was a Japanese style cocktail and not an American style one. Japanese style cocktails have metal legs, American style ones do not.

This game uses a black and white Hantarex X/Y monitor (a vector style monitor). This is unusual because it is a monitor that doesn't exist according to Hantarex. It appears they produced the monitor under the table, as they didn't want to officially custom produce a monitor for a bootleg game. Bootleg Star Castle units have been encountered with the same monitor.

Where to play

This game is Asteroids, so anywhere you can play Planet anywhere you can play Asteroids. Which could include the Mame emulator, your Atari 2600, or any one of the many clones out there.

These seem to be almost as common as actual Asteroids machines in Europe, although they are best avoided as the monitor is a real wild card, and there are not really any repair parts made for it.

The IAU hath decreed1:

A planet is a celestial body that

  • is in orbit around the Sun,
  • has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
  • has cleared the neighbourhood around its orbit.

Fiat. Fiat. Fiat.

Looking up at the lights in the night sky probably predates humanity, but it most likely took a peculiar human compulsion to deduce order from the Universe before anyone wondered what those lights were. Most lights rise in the east, circle about a single point in the sky, and set in the west. Throughout most of human history, these could not be observed to change position with respect to one another and were designated "fixed stars".

Some lights, however, weren't quite so constant. Two big ones, the Sun and the Moon, circled but at different speeds from the stars. Many grew long tails, passed once, and were never seen again, presaging some momentous events on earth. Some fell to the ground. A few wandered drunkenly across the sky, rising and setting at odd times, their paths appearing to shoot forward and double back relative to the fixed stars.

These last were constant enough to always appear, but erratic enough to provide information that had to be explained. The earliest explanations invariably came from religious mythologies created by cultures doing the explaining. The ancient Sumerians named them Enki, Inanna, Zib, Nanna, Utu, Gugulana, Enlil, and Ninurta after major deities. The Egyptians called the same lights Sabgu, Ba'ah, Aten, Aah, Seba-djai, Heru-deshret, Her-wepes-tawy, Her-ka-pet.

The ancient Greeks2 realized that two of the wanderers, Eosphoros ("the morning star") and Hesperos ("the evening star") were really the same body. Sometimes associated with Hera, it became confused with Aphrodite because of a myth where Eosphoros vies with Aphrodite for beauty. Thus, they knew of five such wanderers (planeta): Hermes, Aphrodite, Helios, Selene, Ares, Zeus, and Cronos. When the Romans covered their culture with a Greek veneer these became Mercury, Venus, Sol, Diana Lucifera (or just "Luna"), Mars, Jupiter, and Saturn.

The planets' wanderings were carefully charted by astrologers for casting horoscopes, but no-one attempted to explain their motions until Claudius Ptolemy. In his Almagest, which appeared around 150 AD, the seven planets went around the Earth, but the planets themselves followed curious circles (or "epicycles") imposed upon the major circles.

As more and more observations were made that did not fit Ptolemy's epicycles, new theoretical factors were added into the system, which became more and more complicated. In 1514 a Polish canon and physician, Micolaj Kopernik, gave a hand-written pamphlet to his friends in which he asserts that the Sun us at the center of the Universe, not the Earth. This and the underlying mathematical work developed into De revolutionibus orbium coelestium, published at his death in 1543.

Being the time of the Reformation, a monk named Giordano Bruno interpreted Copernicus' heliocentric theory as a refutation of Papal authority over the Universe. This did not please the Vatican, and they burned him at the stake for it in 1600, incidentally investing the Ptolemaic system as Church dogma and marking the Copernican system as heretical.

But real science was breaking out. In 1575, King Frederik II of (Lutheran) Denmark gave Danish astronomer Tycho Brahe his own little fiefdom on the island of Ven in which to carry out his obsession with astronomical observations. Brahe collected so much data that his student Johannes Kepler was able to realize that planetary orbits (including Earth's, but not the Moon's) were ellipses around the Sun.

Galileo's use of a telescope to discover four moons circling Jupiter expanded the list of planets (yes, they were considered planets at the time), but this also forced Galileo to accept the Copernican view of the Solar System. Galileo was within the Vatican's reach, so he got in Big Trouble.

The real star *cough* of the show is Newton, whose theories of physics resulted in precise mathematical formulae which could calculate planets' orbits and masses. The first big success was the 1758 return of a comet predicted by Edmond Halley. An empirical rule proposed in 1766 by Johann Titius predicted the solar distances of the known planets rather well, except for a gap between Mars and Jupiter. This (and Saturn's deviations from its expected orbit) allowed William Herschel to discover a whole new planet (now named Uranus to extend the Roman mythological system) in 1781.

This got the planet-hunting game going in earnest. Astronomers went looking for new planets in the gap between Mars and Jupiter, and on January 1, 1801, Giuseppe Piazzi found one: Ceres. Heinrich Wilhelm Olbers found another, Pallas, on March 28, 1802. Karl L. Harding found a third, Juno, on Septemer 1, 1804. Olbers found the fourth, Vesta, on March 29, 1807. Ceres, Pallas, Juno, and Vesta were much smaller than the other planets, but no-one worried about it for awhile.

John Couch Adams and Urbain Jean Joseph Le Verrier both used pertubations of Uranus' orbit to posit the existence of a new planet. Using Le Verrier's calculations, Johann Gottfried Galle and Heinrich Louis d'Arrest observed a new planet on September 23, 1846, which was eventually named Neptune after an international dispute over whether Couch or Le Verrier should get credit for predicting its existence. Regardless of that, it was the decisive victory for Newtonian physics.

Karl Ludwig Hencke found Astraea in the gap in 1846, and someone found at least one more every year after that. Starting in 1866, the new terms asteroid and minor planet began to be used for the objects in the gap. It was a good system and reduced the number of planets to something considered manageable.

And then in 1930, a 24-year-old astronomer, Clyde W. Tombaugh, found a dot that moved when comparing two photographic negatives of the sky. The dot was named Pluto as a veiled tribute to Percival Lowell.

About the same time, Frederick C. Leonard (1930) and Kenneth E. Edgeworth (1943) proposed the existence of a cloud of icy objects out beyond Neptune, debris left over from the formation of the Solar System. This was named the Kuiper Belt after Gerard Kuiper, who proposed that this was the source of certain comets in 1951.

There have been plenty of attempts to find more planets. In 1973, Rawlins and Hammerton thought they had discovered a Planet X based upon cometary orbit data, but this was never accepted. The acceptance of the impact theory for the K-T Extinction event, and a rough 26 million year cycle observed for mass extinctions on Earth caused several scientists in 1984 to propose the existence of a red or brown dwarf star named Nemesis which perturbs comets into the inner Solar System. This Nemesis Theory has also failed to gain traction.

For seventy years, schoolchildren were taught about the nine planets of the Solar System. But people began to have problems with Pluto. Pluto was always thought of as odd, with its highly eccentric orbit, and was sometimes considered an "escaped moon of Neptune". Estimates of its size kept shrinking, from the size of Mercury down to about the size of the Moon. Then, Pluto was discovered to have its own moon, Charon, so large and so close that the system's center of gravity is out in space. But things really fell apart when A Kuiper Belt object larger than Pluto was found: 2003 UB313, affectionately named "Xena" by its discoverers.

It is no secret that the definition at the beginning of this article, adopted in August 2006 at the IAU's 26th General Assembly in Prague, was specifically tailored to exclude Pluto and similar- or larger-sized Kuiper Belt Objects such as 2003 UB313 (now officially named Eris), of which there are likely to be dozens, if not hundreds. Eris and Pluto are thrown into a new category of dwarf planet, along with the much smaller bodies Ceres and Charon.

The last criterion of the definition makes a lot of people scratch their heads. Could the Earth clear the Kupier Belt if it were moved there? Has it even cleared its own orbit of pesky things like the Moon, not to mention hundreds of Earth-crossing asteroids?

At any rate, the IAU is the governing body for such categorizations, and we will have to live with this definition, and the eight planets that fall into the category.

1IAU resolution 5,

2Often credited to Pythagoras with other such things, but some texts credit it to Ibycus of Rhegium.

Glossary of Ancient Egyptian terms and names

Names of the Planets

Biographies of Nicolaus Copernicus and Tycho Brahe, MacTutor History of Mathematics archive

Wikipedia, for a few of the dates

Stephen Soter, "What Is a Planet?" Scientific American, January 2007, pp 34-41.

On August 24, 2006, the International Astronomical Union defined the term "planet" in such a way that former planet Pluto and newly discovered SDO Eris would be excluded from the planetary club. While some people take this as a deliberate stab against Pluto, and it may indeed be just that, it is not unprecedented. Many celestial bodies were considered planets at one time, and subsequently downgraded. These include the Sun, the Moon, the asteroids Ceres, Pallas, Juno, and Vesta, the Galilean moons of Jupiter, and some of the largest moons of Saturn. In fact, most newly discovered bodies were termed planets until 1851, when the planet count grew to 23, and astronomers began to term the small objects "asteroids". The difference with Pluto is that it has been considered a planet for over seventy years in contemporary time. Its closest competitor, Ceres, was considered a planet for the first half of the 19th century.

The decision has been controversial, but was long overdue. Recent years have seen the discovery of many celestial oddities. More and more large objects are discovered in the outer reaches of our own solar system. Planet-mass objects have been observed orbiting pulsars. We see Brown Dwarfs, barely more than planets themselves, happily orbiting larger stellar companions. Even rogue planets, appearing to orbit nothing at all, have been found. How, then, do we define a planet?

Under the IAU ruling, a planet is defined as a celestial body that:

  • is in orbit around the sun. The first criterion limits the definition to our own solar system. With the discovery of new extrasolar planets by the day, it should be noted that such objects are covered under a separate agreement signed in 2003.
  • has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape. This is where the guidelines get fuzzy. How round is round enough? The Earth itself is not a perfect sphere (although it varies by only 0.33%). Naturally, all the major planets and Pluto, Eris, Ceres, and several others meet this guideline, but hard numbers should be established for borderline objects.
  • has "cleared the neighborhood" around its orbit. This is arguably the most controversial aspect of the new definition. However, even this can be seen as perfectly logical. While there are many asteroids which occupy the same orbit as Earth (and, indeed, all the other planets, too), their combined mass is tiny when compared with Earth's itself. The ratio µ of Earth's mass to that of all other objects in a similar orbit is about 1.7 million. The planet with the smallest µ is Mars at 5,100. Compare this with Pluto, with a µ of merely 0.077 (sharing an orbital zone with Neptune doesn't help things). Dwarf planets Ceres and Eris weigh in at 0.33 and 0.10, respectively. Likewise with "roundness", a clear distinction should be made for borderline objects, perhaps µ=1,000 (an object thereby accounting for 99.9% of the mass in its orbital zone). However, Pluto and the others are clearly well below any arguable threshold.

Naturally, further discussion and elaboration of the definition is needed. This will likely be a prominent topic at the next IAU General Assembly in 2009. However, for the time being, Pluto and the others remain "dwarf planets".

Please don't misunderstand me. I love Pluto as much as the next guy. I'm eagerly awaiting the New Horizons flyby in 2015. But the more I think about it, the more I agree with the IAU ruling. Pluto has always been an oddity, but no more. Instead of being the tiny one with a crooked orbit, it's now King of the Dwarf Planets. For the naysayers, consider this: if Pluto were discovered today, would we call it a planet?

Plan"et (?), n. [OE. planete, F. planete, L. planeta, fr. Gr. , and a planet; prop. wandering, fr. to wander, fr. a wandering.]

1. Astron.

A celestial body which revolves about the sun in an orbit of a moderate degree of eccentricity. It is distinguished from a comet by the absence of a coma, and by having a less eccentric orbit. See Solar system.

⇒ The term planet was first used to distinguish those stars which have an apparent motion through the constellations from the fixed stars, which retain their relative places unchanged. The inferior planets are Mercury and Venus, which are nearer to the sun than is the earth; the superior planets are Mars, the asteroids, Jupiter, Saturn, Uranus, and Neptune, which are farther from the sun than is the earth. Primary planets are those which revolve about the sun; secondary planets, or moons, are those which revolve around the primary planets as satellites, and at the same time revolve with them about the sun.


A star, as influencing the fate of a men.

There's some ill planet reigns. Shak.

Planet gear. Mach. See Epicyclic train, under Epicyclic. -- Planet wheel, a gear wheel which revolves around the wheel with which it meshes, in an epicyclic train.


© Webster 1913.

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