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There are 8 valence electrons in the noble gases, the family of elements furthest to the right on the Periodic Table.

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What type of tide occurs during the quarter moon phases?

The exceptionally low high tides (and high low tides) that occur during the quarter-moon phase are known as "neap tides." Conversely, the exceptionally high and low tides that occur during full and new moons are known as "spring tides." Strictly speaking, however, although there is a correlation between moon phase and tidal activity, this is not truly due to the moon. Tides are caused by the moon's orbit around the earth; the moon's gravity pulls a swell of water on the the side of the earth facing it, and a corresponding bulge on the opposite side. These vary several times per day, with the moon's once-daily orbit of the earth. So, there are about 12 hours between high tides. Moon phases, on the other hand are purely a visual phenomenon, varying based on the the viewing angle of the moon from our vantage point, here on earth, relative to the sun. When the sun is shining behind the moon, we observe a new moon. On the front side? A full moon. When the earth, moon, and sun are aligned at roughly a 90 degree angle? A half moon. And, of course there's every phase in between. During any given day during the cycle, the tides continue to rise and fall independent of what lunar phase we happen to observe. The spring and neap tides are actually caused by the sun. Like the moon, the sun also exerts a gravitational pull on the side of the earth that faces it, causing high tides every twelve hours -- solar tides; Although this effect is far weaker than the lunar tides (about half the effect), the height of the tide at any given time is a composite of the gravitational vectors of the sun and moon, added together, like constructive or destructive interference. Thus, when the sun and moon are on the same side of the earth (or opposite sides), their collective gravity works together and magnifies the effect, and tides are higher and lower than usual; this is what occurs during new moons and full moons -- the spring tides. Alternately, when the sun and moon are located at 90 degrees with respect to the earth, the sun and moon pull along different axes, and cancel each other out to some degree; this is what occurs during quarter moons, when tides vary far less than at other times of the month... not so high and not so low. There is also a proxigean spring tide, an extremely high tide that occurs very rarely when the moon's orbital eccentricity also magnifies these gravitational tidal effects. This occurs when the moon's lowest point of orbit (proxigee) coincides with a full or new moon (already very high tides). Incidentally, lunar phases are not caused by the earth's shadow falling on the moon. This would be an eclipse, which is quite rare.