The attribution of planets and stars on ancient and medieval coins requires quite a bit of analysis. The star symbol was used to represent a variety of objects, ranging from deities to the sun, comets, and planets, and even sometimes, stars! And in some rare instances, some have interpreted stars to represent geographical territories and divisions of the church, although these more earthly attributions are somewhat questionable. To make the interpretation more confusing, pellets were sometimes used to represent the planets, in addition to their more common use as decorations, pelleted circles, and as a mark of denomination.
The number seven also plays a role here. This number was very special to the ancients, and seven planets were known to ancient man: Mercury, Venus, Mars, Jupiter, and Saturn, along with the sun and the moon. The word planet is derived from the Greek word meaning wanderer, and these seven bodies constantly changed their positions in the heavens.
In addition to the seven planets, the Pleiades star cluster, known as the seven sisters, was very special, as it signaled the time to plant in the spring, and the time to harvest in the fall.
Without any other evidence, a single star depicted on a coin must be attributed to the representation of a deity, but multiple stars can be analysed for other meanings. For example, the reverse of a coin form ancient Uranopolis depicts the solar disk, a crescent moon, and five stars. Certainly, the five stars represent the five visible planets other than the sun and the moon.
Two stars, without other information, usually represent the Dioscuri (Castor and Pollux). These two mythical brothers were placed by Zeus into the constellation of Gemini. In Rome, they were believed to have assisted the Romans against the Latins in the Battle of Lake Regillus (496 BC). Sometimes, they are depicted by their busts; other times by their star crowned, egg-shaped helmets, and sometimes by just two stars.
But two stars are not always the Dioscuri. For example, two stars are found above a bull on the reverse of several bronze coins of the Roman Emperor Julian II (360-363 AD). One star is between the horns, and the other above the shoulder. In the spring of 360, Julian's troops rose in revolt against Constantius, and Julian II was proclaimed as Augustus. The depiction of the bull is well understood. Julian II often slaughtered bulls to Mars, the Roman god of war.
Could one of the stars represent Mars? Certainly! On 4 May 360, Venus joined Mars to form a single star between the horns of Taurus, the Bull, as the constellation set in the western sky. Two weeks earlier, Mars was between the horns, and Venus rested on the shoulder of the bull. There can be little doubt that this planetary conjunction, or grouping, is shown on this coin.
And sometimes, the Pleiades are depicted. In 74 BC, L. Lucretius Trio of the Roman Republic struck a denarius with the god Sol on the obverse, and a crescent moon with seven stars on the reverse. The seven stars cannot be the seven planets, as the moon is depicted as a crescent. But twice the year before, on 11 October and 4 December 75 BC, the moon occulted the Pleiades star cluster. While the passage of the moon in front of the Pleiades is not rare, it happens infrequently enough to be noticeable.
The presence of a crescent moon with stars does not always mean that the moon has joined a stellar group, but sometimes depicts a stunning pairing of the crescent moon with a close multi-planet conjunction. During 109-108 BC, Man. Aquillius struck a denarius with the radiate head of Sol on the obverse, and Luna in a biga on the reverse. Above the biga is a crescent moon and three stars, and below, a fourth star.
Soon after sunset on 17 June 109 BC, a very thin crescent moon was in conjunction with Jupiter, Mars, and Venus. Mercury was just above the horizon, but may have been lost in the twilight. Saturn was not too far away in the southwestern sky. This would have been a spectacular sight to see, as the trio woiuld have remained visible as the sky darkened into night. Either Mercury or Saturn could be represented by the star below the biga.
Pellets were sometimes used as representations of the the planets. In the eastern religions, circles and disks were often hung on military vexilla, or standards, to represent the seven planets. This topic is discussed in detail in "Visions Explained." Many examples of ancient coins exist where seven pellets are found in a grouping, and are most likely a depiction of the seven planets. Two examples from ancient Coritani are shown below.
A medieval example provides the most definite example. During the period 1180-1191, Philip II of France changed the coin design of using three pellets within a crude church to five pellets. In September of 1186, all five of the known planets came together within a 5 degree area of the sky in the constellation of Libra, about half a fist of an outstretched arm. As early as 1184, Arab astrologers in Spain and Sicily proposed prophecies about this great conjunction, including great natural and political disasters, and benefits for the French. And Philip assumed the tiltle of "the God-given."