The Extra-Terrestrial Equinox!

I hope everyone is ready to celebrate the beginning of Fall tomorrow with the arrival of the Autumnal Equinox.  Did you know that Earth is not the only planet to enjoy equinoxes and solstices?  

Tomorrow the earth marks the point in its journey around the sun at which day and night are equal. The word equinox comes from Medieval Latin equinoxium meaning equality of night (and day) from the Latin word aequinoctium meaning the equinoxes from aequus meaning equal andnox (genetive singular form noctis) meaning night. Many European languages that share common Proto-Indo European roots share this form-the word to express the equality of night and day but only refers to night. A few (the Russian равноденствие for example) express it asequal-day.  

Any planet or moon that has tilt to its axis will have two days in its year in which the tilt reaches maximum and mimimum points as well as two days in its year in which the day and night are equal.  For a planet like Saturn, with an orbital period that lasts 29 years, an equinox occurs every 15 years.  When Saturn had its last equinox, the Cassini Imaging Team was there and compiled this composite of Saturn’s rings as they were pointed directly at the Sun and thus thrown largely in shadow.  It was a mystery for many years why Saturn’s rings waxed and waned, but modern telescopes and technology give us a very clear image of what exactly is happening.  Thanks to NASA and the Cassini Imaging Team we can now see Saturn’s rings up close and in shadow.  

Saturn’s moon Titan also has a pronounced tilt, and Cassini’s on board camera’s caught before and after the Equinox, along with the weather caused by the tilt.  Here on Earth we look forward to cooler days (in the Norther Hemisphere) but on Titan, the storms are positively inspiring!

Images courtesy NASA and Cassini Imaging Team, images in the Public Domain.