On this last day of 2009, it is important to realize that, beyond our home planet, a year, the cherished span by which we measure our history and our lives, is merely a segment of time. And while the duration of a year correlates with the period of Earth's orbit around the sun, the specific timing of man's calendar year is not tied to any natural cycle; rather, it is a product of human culture, influenced by politics and religion.
It might be argued that our year should begin at the winter solstice (the beginning of the solar cycle as perceived from Earth) but that would produce a 6 month variance of the calendar between the Northern and Southern Hemispheres. Of course, were it not for the tilt of our planet's axis, the seasons would not exist and we would not have solstices. If that were the case, the period of sunlight (for any given location) would not vary through the year and humans would likely be fixated on the moon, measuring our lives and our history in lunar cycles.
Beyond Earth, a year has no more significance than, say, 23 seconds, 51 hours or 813 days; it is just our measure of time based on our planet's orbit and on our experience of seasonal change. If we lived on Mercury, our year would be 88 Earth-days long while, on Neptune, an Earth-year would take us only 1/165 of the way around the sun. When viewed from the perspective of our galaxy, a year becomes even less significant as a period of time; it takes somewhere in the neighborhood of 230-250 million years for our solar system to orbit the center of the Milky Way. As in all aspects of natural science, it is important to acknowledge that our perspective, as observers from planet Earth, can temper our understanding of the Universe. Happy New Year!
