How the Sun, Earth and Moon aligned to help unblock the Suez Canal

The container ship Ever Green ran aground in the Suez Canal days before a full Moon helped raise tides and lunar perigee raised them a little more.

Posted 6:43 p.m. Mar 31, 2021 — Updated 6:43 p.m. Mar 31, 2021

Tony Rice

, NASA Ambassador

The more than four football field long container ship Ever Given entered the Suez Canal at a bad time. Officials are pointing to a sandstorm as a factor in the grounding of the massive container ship the morning of March 23.

Winds reaching 46 mph "caused the hull to deviate … and accidentally hit the bottom and run aground” according to the ship's operator Evergreen Marine and the Suez Canal Authority.

More than 30,000 cubic meters of sand were removed from the banks and floor of the canal. For comparison this is enough to fill about 12 Olympic swimming pools or nearly half the volume of Spaceship Earth, the geodesic sphere at Walt Disney World's Epcot theme park.

Workers removed more than 30,000 cubic meters of sand from the banks and floor of the Suez Canal in freeing the container ship Ever Given, enough to fill about 12 olympic sized swimming pools or about half the volume of Epcot's Spaceship Earth at the Walt Disney World Resort in Florida. Images: Suez Canal Authority, base Spaceship Earth image by Steven Miller

Fortunately the Earth, Moon and Sun literally aligned a few days later, aiding a tugboats working to free the ship.

How a supermoon helped refloat the Ever Given

Spring tides, unusually high tides, occur twice each month during new and full Moons. The added gravitational effects of the Sun, (new) Moon, Earth or Sun, Earth, (full) Moon lineup, pull just a bit more on the oceans.

When the Moon reaches full or new phase near perigee, the closest point in its orbit to Earth, those perigean spring tides are even higher.

Often between 6-8 times a year, the new or full moon coincides closely in time with the perigee of the moon — the point when the moon is closest to the Earth. These occurrences are often called 'perigean spring tides.' High tides during perigean spring tides can be significantly higher than during other times of the year. (NOAA)

The Moon reached full phase the evening of March 28 and perigee a day and a half later. Tides peaked around 11 am and 11:30 pm local on March 27 and each high tide over the next several days was among the highest of the year.

The difference isn't much, a few inches at most, but it was enough to assist the pair of powerful seagoing tugs along with 11 other tugboats in pushing the ship back into the channel.

By 3pm local on March 29 officials reported the ship was freed and back underway.

Had crews needed more time to free the ship, the job would grow more difficult as the Moon moves to a right angle from the Sun. This postilion cancels some of the Sun's gravitational pull resulting in high tides that are about 16 inches lower.

But isn't the first supermoon of 2021 in April?

There is not an "official" definition of a supermoon. Of the five most often referenced definitions, only the one created by Fred Espenak, a retired NASA astrophysicist who is best known for lunar and solar eclipse predictions, fits.

He describes a supermoon asany "full Moon occurring at a distance 90% or greater of perigee during the current lunation."

Other sources such as Sky and Telescope magazine, the EarthSky astronomy radio series and TimeAndDate.com have chosen varying distances for their supermoon rules.

In the end the Sun, Earth and Moon lined up when the Moon was close, creating the right tidal conditions for recovery crews.

Why do supermoons happen in fours?