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(Continued from Part I)

While the names associated with the planets in Western Culture can mostly be traced back to gods of ancient Rome, other cultures seem to have seen their gods in the heavens as well.  Today, the planets and other celestial bodies (and the features of them) are named by the International Astronomical Union (IAU), which is a world-wide association of astronomers.  The IAU has, in many cases, continued the naming conventions started by the Greeks (who originally named the planets after their gods, perhaps on the belief that the planets were the gods going about their business in the cosmos) and maintaining the same naming themes.  Either way, taking a look at the gods associated with the planets of our solar system is a great introduction to the Greek and Roman pantheons and to how cultures related their gods to the world around them.  I’ve also included some basic facts on the planets themselves, as an introduction to our solar system and to compare the features of the planets.

The Inner Planets


The planet Mercury probably moves as swiftly though the heavens as its winged shoe-wearing namesake was believed to have traveled.  The god Mercury is associated with a number of things, from travel to thievery in Roman mythology, and was grafted to the Roman pantheon from Hermes of Greek mythology.  One of Hermes/Mercury’s first acts as a child was inventing the lyre and stealing the cattle of Apollo (to whom he gifted the lyre as restitution), and he often acted as the messenger of the gods (hence the winged sandals, which he once lent to Perseus in his quest to kill Medusa).    In Babylonian mythology, the planet Mercury was associated with Nabu, son of Marduk, and god of wisdom and writing.

The planet Mercury is currently being visited by a NASA mission, aptly named MESSENGER, which has been orbiting the planet and collecting data since last Spring.  Mercury takes 88 Earth days to orbit the sun, and during two Mercury-years, rotates on its axis about three times (so Mercury has about 1.5 “days” each “year”).  The planet is thought to be composed of a large, dense iron core (which may be at least partially molten) with a thin, crater covered silicate crust and a very thin atmosphere (caused by solar winds blasting atoms off the surface of the planet, which quickly escape into space due to the extreme heat).  Mercury is both very hot and very cold, with a highly variable temperature ranging from -300 to 800 degrees Farenheit.  Much about Mercury is still a mystery, due to its proximity to the sun, some forms of observation aren’t an option, and the last mission to Mercury, in the 1970’s only mapped 45% of its surface.  In fact, the orbit of Mercury so erratic that was thought to be influenced by another (hypothetical) planet (sometimes called Vulcan), until the development of Einsten’s Theory of Relativity.


The Roman goddess of love and beauty is the only female deity to have a planet as her direct namesake.  This may have something to do with the planet being the brightest object in the sky after the Sun and Moon.  Venus is often called the Evening Star or Morning Star because it is visible in the evening after sunset and in the morning before sunrise.  Though the Romans named the planet after Venus (who corresponds with the Greek Aphrodite), the Greeks themselves personified the planet of Venus as two brother deities–Hesperus (in the evening) and Phosphorus/Eosphorus  (in the morning).  Several geographical features are named after goddesses of other pantheons–a large plateau is named for Lakshmi, mountains named for Danu, a volcano named after Sif, while its northern “continent” is named after the Babylonian goddess Ishtar (Ishtar Terra) and its southern “continent” is named after Aphrodite (Aphrodite Terra).

image from nasaLike Mercury,the planet of Venus  is what is known as an inferior planet (because its closer to the Sun than Earth, not because Earth is better!) and when viewed from a telescope, it has phases (much like our Moon–Mercury does as well, but they can be harder to see).  These planetary phases are actually part of the evidence that allowed early scientists to support heliocentric theory–the idea that the planets revolve around the sun.  Some other interesting characteristics of Venus–a Venus-day takes about 225 Earth-days to complete, and rotation around the sun is completed in about 2 Venus-days.  Venus also rotates the opposite direction of Earth and most of the other planets.

In some ways, Venus is much like our planet of Earth–like Earth, it is terrestrial, it has an atmosphere and it is similar in size (and therefore similar in gravity).  But it is also quite different, and because of some of those differences, the planet was not well-explored until the early 1990’s, and there is still much about the planet that is being determined.  The atmospheric pressure of Venus is like being half a mile underwater on Earth, and it is mostly made up of carbon dioxide (96.5%) with thick layers sulphuric acid clouds.  Due to the greenhouse effect, Venus actually gets hotter than Mercury!  Because of this heat, landing probes on Venus and getting information before the conditions destroy them has been difficult, while viewing the features of the planet is tricky because of the dense cloud cover.


Earth is the only planet whose name does not derive from Greek/Roman mythology, but rather from Old English and Germanic…and while it is technically not even a deity name, etymologically the word earth might be ultimately derived from references to the Norse goddess Jörð, the mother of Thor.

As far as we know, our planet is the only one with life. It is also the only one with liquid water. Both of these traits have contributed to the composition of our atmosphere, which is a mixture of 78% nitrogen, 21% oxygen and 1% other gases.  The outer atmosphere acts as a sort of shield that protects the planet underneath from many harmful rays from the sun and a number of small meteors.  The cycles of water, nitrogen and carbon, some of which takes place in our atmosphere, are essential to life’s continuance (and when they are messed with, can cause lots of problems).

The surface of the earth is made up of giant puzzle piece-like rock sheets that float on top on molten rock of the earth’s mantle (the inner layer).  Deep inside of the earth is the core–the outer core which is molten hot magnetic metal and the inner core which is solid metal.  The movement of Earth around its elliptical orbit takes about 365 days and the rotation on its axis takes roughly 24 hours.


The planet Mars is named for the Roman god of  war. The planet might have gotten this association due to its red color, a designation that is echoed in Hindu mythology, where the planet of Mars is called Mangala and ” is identified with the war god Karttikeya” as well as in Babylonian mythology, where Mars is known as the war-like god of death and destruction, Nergal (interestingly, ancient Mayans may have associated Venus with warfare).  Mars, while associated with the Greek god Ares, is viewed differently in the Roman Religion.  Rather than being a god of destructive power, Mars is associated with military might as a means of keeping peace, as a father of Rome (and in one myth of Romulus and Remus), and even as a god of agriculture.

The planet itself is of considerable interest due to its similarity and proximity to Earth.  From spacecraft we have sent to Mars, we know that while much of its geological features are quite old (craters and such similar to the moon are found predominately in the southern hemisphere), there are some significantly younger features as well (relatively younger plains, ridges and rift valleys are predominantly found in the northern hemisphere).  The cause of this is unknown.  Our explorations have also determined that Mars once had plate tectonics like Earth, but the plates are now stationary and the crust of Mars is thought to be much thicker than that of Earth.  Mars has quite a bit of evidence of erosion from water and, though water is not an active force shaping Mars today, there is a frozen sea on the planet.  It is thought that Mars used to be quite earth-like, but the lack of plate tectonics meant that there was no recycling of certain elements, such as carbon dioxide.

Asteroid Belt:

The asteroid belt is an area of the solar system between the orbits of Mars and Jupiter that contains somewhere around 40,000 asteroids (which are basically space rocks), most of which as .5 miles in diameter.  The largest of these asteroids include Vesta, Pallas, Hygeia and Ceres–Ceres is large enough that (like Pluto) it is actually considered a dwarf planet.  The asteroid belt is thought to have originated during planet formation in our solar system, as a sort of failed planet.  Over the millennial, countless collisions have created the asteroid belt we have today.

More Solar System Activities Projects:

Solar System Model
Figure out your age in space!
Make (and use) your own astrolabe!
Exploring the Earth’s Magnetic Field (from NASA)
Magnetometer from a Soda Bottle
Free Printable Space Themed Activities