Eclipses occur when the full moon is opposite the sun in the sky with the Earth directly between them, preventing sunlight from shining on the moon. This causes Earth’s dark umbral shadow to fall on the moon creating a red-orange glow.
It doesn’t happen very often since the moon orbits Earth at a 5-degree tilt to the ecliptic of Earth’s orbital plane as it revolves around the sun. So, most of the time the full moon swings either north or south of Earth’s shadow. But twice in its 29.5-day orbit, the moon crosses the ecliptic. So, a lunar eclipse happens when the full moon coincides with either of these two passings.
An actual eclipse lasts about 3 ½ hours. The first and last parts are known as the penumbra, which means the pale outer fringe of the Earth’s shadow. This is faint and may not even be noticeable. After the moon passes through the penumbra, the next phase is the partial eclipse when the moon enters or exits the full umbra of Earth’s shadow. During this time, you can begin to see a partial shadow on the moon which gradually grows until it reaches the full eclipse or umbra.
The umbra of this eclipse will last one hour and 18 minutes. During this time the moon develops a reddish glow which can vary from bright orange to a dark red orange. This red light comes from all the sunrises and sunsets on Earth occurring during this time period. Our atmosphere scatters and reflects the sunlight shining on Earth and diverts some of it into Earth’s umbral shadow. This is the spectacular part of the eclipse to see. This is also the only time air pollution does any good as it intensifies the color.
We will get two lunar eclipses this year. The first one will occur on the evening of May 15, and the second one will occur on Nov. 8. On the East Coast, the lunar eclipse occurs from 10:29 p.m. on May 15 until 12:56 a.m. on May 16. Since we’re two hours earlier here, the Lunar eclipse here starts at 8:30 p.m. on May 15 and ends at 10:39 p.m. Unfortunately, it won’t be dark here when the lunar eclipse begins. But we should still be able to see it.
It starts with a partial eclipse and then changes to a full eclipse. After a while it changes back to a partial eclipse. So, hopefully, the sky will be clear that night. Then we can go out and start looking at the moon. In the beginning, we’ll just see a partial eclipse. But eventually, it will change to a full eclipse. That’s when the moon looks very dark.