Illustration of the difference between high and low tide at Hopewell Rocks. Well, I guess you cannot live in Albert County without knowing or at least wondering how the tides work. The ebb and flow of the tides can have a profound effect on the rural people of our fair county. So I thought I would give a rather simple short course on the anatomy of tidal action.
Let us begin with what causes tides and that is, of course, the gravitational pull of celestial bodies, specifically the sun and the moon. The moon is close to us (about 384,400 km away) and is about 75% responsible for the tide. The sun, although far larger than the moon, is 160 million km away and is responsible for about 25% of our tidal action.
Let us begin with what causes tides and that is, of course, the gravitational pull of celestial bodies, specifically the sun and the moon. The moon is close to us (about 384,400 km away) and is about 75% responsible for the tide. The sun, although far larger than the moon, is 160 million km away and is responsible for about 25% of our tidal action.
When the sun, moon and earth are in a straight line in that order (which is called “in conjunction”), we experience a “new moon.” Light from the sun is shining down on the moon on one side and we on earth do not see the moon (although it is, of course, there). We call this “the dark side of the moon.” The moon and sun’s gravity pull together and causing a bulge of water to rise on the side of the earth facing the moon.
On the other side of the earth, there is another bulge. On the side of the earth facing the moon, the water is pulled away from the earth; on the other side, the earth is being pulled ahead of the water. It is during this phase that the tides are higher and are called “spring tides,” which have nothing to do with the season, but rather from a Germanic word “springan” meaning jump up or rise up.
Now when the configuration of the three orbs is the sun then the moon at right angles with the earth, this is the “first quarter.” The sun and moon are pulling somewhat against one another; this diffuses the gravitational pull and causes the tides to be less high. These are called “neap tides.”
When the moon comes around so the configuration is sun, earth and moon in a straight line (which is called “in opposition”), we have a full moon. Although the moon and sun are on opposite sides of the earth, they still work together and the tides are again spring tides. When the three amigos are lined up (i.e., new or full moons) then they are in said to be in “syzygy” (now there is a word for you).
The moon then goes around to a right angle with the earth again to the third quarter and we are back to neap tides.
Finally, the cycle is complete with a new moon once again. This lunar month is roughly 29 days.
To review, the tides are highest at the full and new moons. Not all full and new moons however are equal, there is one very important variable in all of this and that is the position of the moon in its orbit around earth. When the moon is closest to earth (perigee), the gravitational pull is stronger. When perigee occurs at a new or full moon, we have the huge tides – almost 14 metres (46 feet) at Hopewell Rocks and up to 16 metres (52 feet) at certain places in the Bay of Fundy. When the moon is farthest away from earth in its orbit (apogee), the gravitational pull is weaker. Even if this occurs at a new or full moon, the tides may be only average or perhaps slightly above average.
There you have it in the simplest way I know how to explain it; no doubt this raises many questions in your mind, but alas this is all (and perhaps more than) the space that I have been allotted.
About the Author: Paul Gaudet is the Interpretive Services Manager at the Hopewell Rocks. Images were provided by the Hopewell Rocks. TheHopewellRocks.ca
The moon then goes around to a right angle with the earth again to the third quarter and we are back to neap tides.
Finally, the cycle is complete with a new moon once again. This lunar month is roughly 29 days.
To review, the tides are highest at the full and new moons. Not all full and new moons however are equal, there is one very important variable in all of this and that is the position of the moon in its orbit around earth. When the moon is closest to earth (perigee), the gravitational pull is stronger. When perigee occurs at a new or full moon, we have the huge tides – almost 14 metres (46 feet) at Hopewell Rocks and up to 16 metres (52 feet) at certain places in the Bay of Fundy. When the moon is farthest away from earth in its orbit (apogee), the gravitational pull is weaker. Even if this occurs at a new or full moon, the tides may be only average or perhaps slightly above average.
There you have it in the simplest way I know how to explain it; no doubt this raises many questions in your mind, but alas this is all (and perhaps more than) the space that I have been allotted.
About the Author: Paul Gaudet is the Interpretive Services Manager at the Hopewell Rocks. Images were provided by the Hopewell Rocks. TheHopewellRocks.ca
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