☿ Mercury

Named for the Roman god Mercury (Greek: Hermes)

Trade Travel Messages Eloquence Luck

Which sign is Mercury in now?

Mercury by Hendrick Goltzius
Mercury Hendrick Goltzius, 1611 Mauritshuis, The Hague Commons titles it Mercury as personification of painting. He holds a palette, brushes and a caduceus, wears a winged helmet, and a rooster stands at his feet. Public domain, via Wikimedia Commons

The swiftest of the Roman gods: messenger, and patron of merchants, travelers and eloquence.

The god

Mercury was the Roman god of trade, travelers, messages and eloquence, and a guide of souls to the underworld. His name is possibly related to the Latin merx, “merchandise,” and mercari, “to trade.” His temple, dedicated on May 15, 495 BCE in the Circus Maximus between the Aventine and Palatine hills, was thought a fitting place to worship a swift god of trade and travel. His festival, the Mercuralia, fell on May 15, when merchants sprinkled water from his sacred well near the Porta Capena on their heads. From the start he looked like the Greek Hermes, with winged shoes, a winged hat and the caduceus, and he took on Hermes’s stories, like the baby who climbed out of his crib, stole Apollo’s cattle and made the first lyre from a tortoise shell.

How the planet got its name

NASA calls the innermost planet “appropriately named for the swiftest of the ancient Roman gods”: it is the fastest planet, circling the Sun in just 88 days. The Greeks also called it Stilbon, “the shining, glittering one,” and in Babylonian astrology it belonged to Nabu, the god of scribes and wisdom.

Symbols

Winged hat Winged sandals Caduceus Rooster Tortoise

The planet

The smallest planet in the solar system and the nearest to the Sun. Mercury has a large metallic core whose radius is about 85% of the planet’s. Days can reach 430 °C, and with no atmosphere to hold in the heat, nights drop as low as −180 °C. One solar day, from sunrise to sunrise, lasts 176 Earth days, just over two Mercury years.

Diameter
4,879 km 0.38 × Earth
Mass
0.33 × 10²⁴ kg 0.055 × Earth
Gravity
3.7 m/s² 0.38 × Earth's
Length of day
175.9 Earth days sunrise to sunrise
Length of year
88 Earth days one trip around the Sun
Distance from the Sun
57.9 million km 0.39 AU (Earth = 1)
Average temperature
167 °C 333 °F
Moons
None
Rings
No

Figures from NASA’s Planetary Fact Sheet; the temperature is its “mean temperature.” Comparisons with Earth are worked out from the same sheet.

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