Most of us know that our earthly home is a sphere that travels through space. It’s actually a minor planet in our solar system. At this writing our solar system is known to contain eight planets. They include the four “terrestrial” planets- -Mercury, Venus, our own earth, and Mars. Earth and Mars are the only two of these that have moons.
Our moon gives us light at night at certain times. Mars has two little moons. Our own moon gives us another way to measure time, and it is a key influence on our planet’s ocean tides.
Jupiter, Saturn, Uranus and Neptune are large gassy planets with a lot of moons. Thanks to the Hubble Telescope and deep space probes we now know all four of these have ring systems, the most prominent being that of Saturn.
What about Pluto? Sorry, it’s been demoted to a dwarf planet.
We know our earth revolves on a tilted axis—23.5 degrees. It keeps that same tilt all the way around its annual orbit around our sun, and that tilt gives us our seasons. When those of us in the Northern Hemisphere are more exposed to the sun due to the tilt we have longer days and warmer weather.
Each 24-hour day is one revolution of our planet. Months are partly based on the phases of the moon. Each year takes slightly more than 365 days. Last week I touched on leap years and how they help correct that little difference, about one fourth of a day each year.
Humans have always had some way to measure and keep track of time. The calendar we use today has been refined over the centuries but dates back to ancient times.
We measure time for any number of reasons. Farmers know when to plant and when to harvest, and we know when to go to work or school. We have time zones in part because of railroads and their need to keep trains from running into each other. Timekeeping, whether it’s days, months or years, is not only cultural, it’s necessary to a safe, orderly life.
Since the earliest recorded times, humans have wanted to know what time it is. Our clocks and watches, not to mention smart phones, help answer that question for us. Technology has changed. The need to know the time has not.
WARREN DOMKE is a columnist for the Pleasanton Express.