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The Supermoon and Monster Tides Coming

March 19 – features the closest full moon of 2011. Look for higher-than-usual tides along the ocean coastlines throughout the world.

Moon, Saturn, and Spica on Saturday evening, March 19
What’s more, the bright point of light in the vicinity of tonight’s moon is the planet Saturn, the 6th planet outward from the sun.

Because the full moon shines opposite the sun in our sky, you’ll see the moon beaming all night tonight from dusk till dawn. This extra-close full moon will usher in large tides along the ocean shorelines for the next several days, especially if these high tides are accompanied by strong onshore winds.

Understanding the full moon

Why is this moon so close? The reason is that the 2011 March full moon falls on the same date as perigee – the moon’s closest approach to Earth for this month. At perigee today, the moon lies only 356,575 kilometers (221,575 miles) away. Earlier this month, the moon swung to apogee – its farthest point for the month – on March 6. At that time, the moon was 406,583 kilometers (252,639 miles) distant.

Very commonly, the year’s closest perigee comes on the day that the full moon and perigee most closely align. That is certainly the case for 2011. In fact, this is the moon’s closest encounter with Earth since December 12, 2008. Moreover, the moon won’t come this close again until November 14, 2016. By the way, in all of these “supermoon” years – in 2008, 2011 and 2016 – the full moon occurs on the same date as lunar perigee.

What’s true – and false – about the March 19 supermoon

Why will the tides be higher than usual? At every full moon, the Earth is more or less between the moon and sun. Each month, on the day of the full moon, the moon and sun line up to create wide-ranging tides, known as spring tides. High spring tides climb up especially high, and on the same day low tides plunge especially low.

March 19th's extra-close full moon accentuates these monthly full moon spring tides all the more.

High Tides.jpg

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