Friday, November 5, 2010

East of the Sun and West of the Moon

As autumn begins to slowly give way to the end of another year and the days steadily become depressingly shorter, the one bright spot I can always look forward to is the appearance of a certain cluster of stars in the early morning sky. Starting just before midnight and lasting till dawn, the stars that make up Orion's belt and the winter triangle show up like clockwork every year for their seasonal march across the heavens and are probably the easiest stars for any novice stargazer to identify.  Even with all the city lights they are clearly visible.  Of course, depending on what part of the northern hemisphere a person comes from the names will be different but, regardless of the name they are given, the stars never change their pattern.

Orion's Belt
Orion's belt, also known as the Magi, or the Three kings, with its easily identified three stars in a row, forms the middle of the constellation named after Orion the hunter, and serves as the starting reference point for the other winter stars.  Two others which help define the shape of the constellation are the bright star below the belt named Rigel, and the one above named Betelgeuse (Orion's shoulder). Betelgeuse is also the first vertex of the roughly equilateral winter triangle formed with Procyon, to the left and Sirius, the brightest star in the sky, down below.  These late autumn/winter stars; Rigel, Betelgeuse, Procyon and Sirius, are 4 of the brightest 10 objects, as viewed from earth, outside the solar system.

Winter Triangle
The ancients were fanciful in their imaginings of what the stars represented; lustiness, fairness, warfare, wisdom and who knows what else, never mind how this had something to do with when a person was born. Nonetheless, it continued to occupy a lot of unscientific thinking throughout the ages as various cultures tried to find some sort of correlation between the imagined celestial constellations and the future. Orion tries to remain below the radar of all this nonsense but, if you look a little further above Betelgeuse, you will find the twin stars of Castor and Pollux which form the heads of the Gemini constellation.

Zodiac Constellations

I only mention these distant stars as a way of introducing the role the solar system in general, and the moon in particular, plays in our daily ocean tides; an astronomic phenomenon of which most people are completely unaware. Tides are the rise and fall of sea levels caused by the combined effects of the Earth's rotation and gravitational forces of the sun and moon.  With the moon taking nearly 30 days to orbit the earth this means the tides change approximately 1 hour each day and the rise and fall of these tidal changes depends on where the moon is in relation to the sun.

Tidal Influences

When the Sun and the Moon are aligned, as in the new or full moon phase of each month, the gravitational pull on the earth and its oceans is strongest, producing large tidal bulges (referred to as spring tides) with correspondingly higher and lower tides.  Conversely, when the moon and sun are at right angles to one another in the quarter moon phase, the weaker tidal bulges (called neap tides) produce low tidal change.  In the ocean the tidal range is usually less than 2 feet but, in coastal areas, the tidal range can be anywhere from near zero in the Mediterranean & Caribbean Seas to 53 feet in the Bay of Fundy.  In Vancouver the tidal range is generally around 12 feet. Learning to read and understand local tide charts is indispensable to mariners if they want to avoid accidental grounding or being carried away because they haven't let out enough anchor rode.

Northern Constellations

Of course with the Moon just being something that revolves around the Earth, which in turn revolves around the Sun, a star that revolves around who knows what and fades into insignificance in comparison to most of the others in the Universe, it's hard to put it all into perspective when you are either lying on your back in a field or floating out in the ocean.  But once you can find a star you recognize and determine whether you are either east of the sun or west of the moon you should be okay.

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