sōlāris

Sōlāris comes from sōl, the Latin word for the sun. Sōl was also the name of the Roman sun deity, identified with Greek Helios. The adjective meant 'of or relating to the sun.' Solar eclipses, solar heat, solar time — the word was descriptive and astronomical from the start.

The solar calendar — based on the Earth's orbit around the sun — gradually replaced lunar calendars in the Western world. Julius Caesar introduced the Julian calendar in 46 BCE, fixing the year at 365.25 days with a leap year every four years. Pope Gregory XIII corrected the accumulated drift in 1582 with the Gregorian calendar, which dropped ten days and refined the leap year rule. The solar calendar won because agricultural societies needed to predict seasons, and the sun tracks seasons more reliably than the moon.

Solar energy entered English vocabulary in the nineteenth century. The first solar-powered steam engine was built by Augustin Mouchot in France in 1866. The first silicon solar cell was created at Bell Labs in 1954 by Daryl Chapin, Calvin Fuller, and Gerald Pearson. It converted about 6 percent of sunlight to electricity. Modern solar panels exceed 25 percent efficiency. The word 'solar' shifted from astronomy to energy within a generation.

The solar system — the sun and everything that orbits it — was named in the seventeenth century as the Copernican model became accepted. Before Copernicus, there was no 'solar' system because the sun was not recognized as the center. The word required the science. Once the science arrived, the word was obvious: it is the sun's system. Sōl's system.