Doing the Local Motion

Last month, we discussed how the appearance and behavior of the Sun, the Moon, and Venus can be explained through the combined effects of various forms of “local” motion: the Earth and Moon rotating about their axes; the Moon revolving around the Earth; and Venus revolving around the Sun.  As you know, our own planet is in constant motion too.  Every year, the Earth completes a 600 million-mile journey around the circumference of an enormous circle with the Sun at the center (to get some idea of how truly colossal 600 million miles is, if you were to drive that distance, you would be on the road for almost a thousand years).  This translates into a constant speed of 19 miles per second, which is far faster than any supersonic jetliner, or even the shuttle.  

With the exception of the Earth’s axial rotation, which is responsible for our day/night cycle, the orbital motion of the Earth is woven more deeply into the fabric of our lives than any other form of local motion.  Consider: Virtually every one of our major sporting events, every one of our major holidays, every one of our major religious observances, and even Halloween, occurs at virtually the same time every year.  The adherence to that rigid schedule means that these shared cultural events occupy a particular point in space as well as in time.  They each have a reserved location on the Earth’s orbital path. 

The connection between these all-too-familiar activities and this underlying astronomical truth is not widely appreciated.  In part, this is due to the nature of the events themselves.  Let’s face it, folks: Tennis tournaments, football games, horse races, and Fourth of July celebrations do little to promote astronomical awareness; to the contrary, they tend to focus our attention firmly on a small piece of terra firma.  Even if we turn our attention to the objects in the sky, the impact of our orbital motion remains subtle.  There is very little hint of that motion in the behavior of the Sun, the Moon, or Venus, for instance.  Indeed, you would be hard-pressed to notice changes of any sort on a day-to-day basis (contrast that with the Moon’s orbital motion, which places it in a noticeably different location in the sky every night).  However, if we observe the night sky over a longer period of time, such as the three or so months that make up each of our seasons, the changes wrought by the motion of “Spaceship Earth” finally become apparent; so apparent, in fact, that they blow the observable effects of the other local motions completely out of the water. For, given enough time, the Earth’s journey around the Sun completely alters the thousands of stars that are visible across the night sky.

Tomorrow night, suppose you were to go out about an hour and a half after sunset and assumed the standard viewing position for our visualization exercises, which is facing due south.   Your mission, should you decide to accept it, will be to note and memorize a select few of the star patterns that you see when you look up.  Then, once a month for the next twelve months, you go out and observe again, constantly comparing the star patterns you see then with the patterns you saw the month before.

With myriads of stars to choose from, which patterns should you to focus on?  Good question.  On the one hand, I’d like you to bite off enough patterns to appreciate the breathtaking scope of the changes that the Earth’s rotation brings to the night sky.  On the other hand, I don’t want to overload your powers of observation and memorization with too many patterns.   To help me out of this dilemma, let’s restrict the objects of interest to just those star patterns that figure in that most unscientific of astronomically related disciplines: Astrology!

Astrology?  Why would a hard-nosed scientist like me want to have anything to do with astrology? As you know, I love to push back the barriers of ignorance, and going with astrology allows me to kill two “birds of astronomical ignorance” with one stone.   For the vast majority of us, astrology has something in common with the highlights of our calendar year: Although astrological concepts are embedded quite deeply into our culture and our consciousness, the connection between astrology and the Earth’s orbital motion is not widely understood.  By illustrating the effects of the Earth’s orbital movement with reference to astrological star patterns, I can make explicit the common underlying connections between astrology, the Earth’s motion around the Sun, and the changing view of the stars in the night sky throughout the year.

Am I being too ambitious here?  Perhaps, so lets create some suspense, and save the nitty gritty until the next blog.  In the meantime, feel free to share your present understanding of these connections in the comments section!