By Darryl Baynes

Special to the Salisbury Post

SALISBURY — It is Eclipsemania here in the U.S. The eclipse of 2017 is coming Aug. 21, and it has been in the news and all over television. It is such a big deal that Lowe’s in Salisbury is selling solar viewing glasses.

Let’s look at why this is such a big deal and talk about what an eclipse is in the first place.

Most people understand that the moon orbits the Earth and the Earth orbits the sun. The moon is 238,900 miles away from Earth, and its orbital period around the Earth is 29.5 days. Throughout that period, you can see the moon mostly at night, and there are times when you can see the moon during the day. In order to see the moon, the light from the sun must be shining on it. The moon itself does not give off any light; it only reflects light from the sun.

Depending on when you look at the moon on its 29.5-day trip around Earth, you will see more or less of it. When the moon is directly opposite the sun, it is a full moon. When the moon is between the sun and Earth, it is a new moon, which is when you can’t see the moon at all because the part of the moon that is reflecting light is away from your field of view.

If the moon’s orbit were the same around the Earth at all times, we would have eclipses every month. It happens that the moon’s orbit or its inclination is off by 5 degrees. This results in every orbit being a little different than the orbit before. The change allows for the variability in the frequency of eclipses.

The word “eclipse” comes from the Latin “eclipsis,” which means “to leave out.” An eclipse is when one celestial body moves into the shadow of another celestial body. Just as there are seasons here in Salisbury, there are also eclipse seasons. The orbit of the moon has two points where it lines up with the Earth’s orbit and the sun. These two points are eclipse seasons, about 38 days long and six months apart.

When one of those points lines up with the orbit of the Earth and the sun, an eclipse can occur. The 5-degree inclination prevents eclipses from happening each month. As a result, there are two eclipse seasons per year. During each eclipse season, there will be at least one lunar and one solar eclipse. Right now, there is a lunar eclipse occurring in Europe and Asia. A solar eclipse occurs approximately every 18 months somewhere in the world.

Here on Earth, we can observe two types of eclipses, lunar and solar. Lunar means of or pertaining to the moon. Solar means of or pertaining to the sun. Total blockage of the sun’s light from your perspective represents a total eclipse; partial blockage of the sun’s light from your perspective represents a partial eclipse. When Earth comes in between the sun and the moon and the angle is such that Earth will block out all the light of the sun from hitting the moon, we will experience a lunar eclipse.

Since the moon’s orbit is 29.5 days, we can expect that about 14 days before or after a solar eclipse, there will be a lunar eclipse. On Aug. 6, there was a full moon in the sky here in Salisbury. Two weeks later on Aug. 21, there will be a new moon that will create the total eclipse of 2017.

The reason the eclipse of 2017 is so important is because the last time there was a total solar eclipse whose path of totality moved across the United States from coast to coast was in 1918. Also, the 2017 eclipse will give the most number of people in history in the United States the opportunity to see a full or partial eclipse from their own homes.

Here in Salisbury, you will see a partial eclipse. According to my friends at the Franklin Institute Science Museum in Philadelphia, the eclipse from Salisbury will begin at 1:12 p.m. The maximum coverage of 95.9 percent will be at 2:41 .m., and the end of the partial eclipse will be at 4:03 p.m. The longest view of a total eclipse from the ground was almost eight minutes.

The longest view of all was 74 minutes from the view of the Concorde, which was tracking the shadow of the sun across North Africa at about 1,000 miles per hour in 1973. The time of the eclipse demonstrates how fast the Earth is spinning in space as it rotates from day to night.

We are all scientists. We wonder, question and test our theories about the world. An understanding of science is nothing more than an understanding of ourselves.          

Dr. Darryl Lee Baynes is president and founder of Interactive Science Programs