Wednesday, June 19, 2013

Get Ready for the Strawberry Moon at Perigee

If you head to the beach this weekend, you might just get a little bit more space for your blanket in the middle of the day. If you go at night, however, you should be ready for a very high tide. Every month during the full moon, the moon, earth and sun are aligned with the earth in between. The high tide that results from this line-up is called a spring tide. Spring tides also occur on the new moon when the earth, moon and sun are aligned with the moon in the middle. At the half moon, we have what is called a neap tide. These tides are the smallest of the month because the gravitational pull of the sun and moon are in opposition.

We also need to keep in mind that the moon’s 28 day orbit around the earth is not round, but is elliptical. The distance between the moon and earth varies throughout the month and this cycle does not correspond with the spring –neap cycle. When the moon is closest to the earth, it is said to be at perigee, and when it is farthest away, it is at apogee. Perigee often coincides with spring tides on the equinox, but not always. This year, a spring perigee full moon falls on the summer solstice. This is the moon’s closest approach to the earth for all of 2013, and it coincides with what is already a time of very high tides. Saturday's high tide will be at 7:45 PM.

This photograph from the parking lot at the Watch Hill Yacht Club shows what many Rhode Islanders who live in low-lying coastal areas are already noticing. High tides are impacting their neighborhoods more and more each year. Save The Bay has had a team of volunteer photographers out documenting these changes for a few years, and we continually see roads, parking lots, lawns and parks under water at spring high tides. These photographs are a good way to show what a future with sea level rise will look like, and where we need to concentrate our efforts at adapting to more water. Sea level rise is here to stay, and is becoming  more noticeable every year. We will have photographers out this weekend too, to catch the 2013's highest predicted tides. You can see some our high tide photos on our Flickr page.