By Lucia Brimer
It was almost sunset, and the astronomer walked in the field near her house with her grandchildren.
“Something exciting will happen tonight in the sky,” she said. “We are going to have a Lunar Eclipse.”
“Oh yes, my teacher was talking about it in school on Friday,” said Chris. “She said we should all try to see it, at least the beginning of it.”
“An eclipse? Isn’t that dangerous to look at?” asked Tyler, who was a few years younger.
“No, that is a Solar Eclipse. Solar means Sun, and you should never look at the Sun, right?” The kids both nodded. “So, you cannot watch a solar eclipse without special eclipse glasses. But this is a Lunar Eclipse. You can look at the Full Moon, can’t you? So, a Lunar Eclipse is completely safe to look at.”
“What is a Lunar Eclipse, Grandma?” asked Tyler.
“Well, you know that the Moon orbits the Earth, right? And that we see different phases depending on how much of the lit half of the Moon we can see.” They stopped and the astronomer drew a diagram in the dirt with a stick. (See Figure 1.)
“So tonight the Moon will be full, because we can see the whole half that is lit by the Sun, right?” said Chris.
“Right! But tonight, the Earth will be positioned exactly between the Sun and the Moon, so the Earth’s shadow will cover the lit side of the Moon.”
“Why doesn’t that happen every time there is a Full Moon, Grandma?” asked Tyler.
“That’s a good question,” she replied. “The Moon’s orbit is tilted. Let me get something from home to make it clearer for you.”
She went into the house and came back out with a flashlight and a hula-hoop with a whiffle ball attached to it.
“Now, Tyler, hold the hula-hoop around your head. Your head can be the Earth. Chris, hold this flashlight, turn it on, and point it at Tyler. The flashlight is the Sun. Tyler, hold the hoop so the ball is between you and Chris. Now, tilt it up a bit. Can you see the flashlight?” (See Figure 2.)
“Yes!” said Tyler.
“So, that is the New Moon phase, right?” asked Chris.
“Yes, it is. Now, turn around, Tyler. Try to keep the hoop tilted in the same direction. Chris, shine the flashlight so it shines on the Moon ball.”
“This is a Full Moon!” said Tyler.
“Yes! And the Earth does not block the Sunlight because of the tilt of the Moon’s orbit. It is tilted at about 5o. Now, Tyler, walk around Chris part way, again keeping the hoop tilted exactly the same way.” When he had gone one quarter of the way around, the astronomer told him to stop. “Now turn around until you are looking away from Chris and at the Moon ball.”
At this point, there was a straight line between the Moon ball, Tyler’s head, and the flashlight. (See Figure 3.) “Chris, now you can shine the flashlight at the Moon, move it across the back of Tyler’s head, and then shine it on the Moon again.”
“Look! I am making a Lunar Eclipse!” exclaimed Chris.
“So, the Moon will disappear tonight for a while?” asked Tyler.
“Not quite,” said the astronomer, “At the beginning, it will seem to disappear. But when most of the Moon is covered with the Earth’s shadow, the entire shadowed part of the Moon will turn a deep, ruddy red color. The media has been calling it a ‘Blood Moon’.”
“There is the Moon!” said Chris. “But it looks just like a regular Full Moon.”
“We will have to watch it for a while and see what happens,” said the astronomer.
They sat together on the porch swing and watched the Moon. “Grandma, I think the Moon seems to be not as bright as usual, especially along the left side,” said Chris.
“That’s a very good observation, Chris. There are actually 2 shadows of the Earth. The outer, fainter one is called the penumbra. That is the shadow that is crossing the Moon now. Tell me when you can see the inner, dark shadow called the umbra.”
In a little while, Tyler said, “Look! The bottom left side is getting dark! Is that the umbra shadow?”
“Yes! It is,” said the astronomer.
They watched as slowly the darkness crept across the Moon. Tyler yawned. “Let’s get you both ready for bed,” said the astronomer. You have school tomorrow, and this will take a couple of hours.”
Every 15 minutes or so over the next hour, they stopped to look outside and see how the Earth’s shadow was covering more of the Moon. Tyler had to go to bed before the eclipse was full, but Chris was able to stay up to see the Moon turn a dark, ruddy red shortly before the Earth’s shadow fully covered the Moon.
“Why does it turn red like that?” asked Chris.
“The sunlight that is shining on the Moon has filtered through the atmosphere around the sides of the Earth. The shorter, blue wavelengths of light are scattered and don’t go straight through. But the longer, red wavelengths are not as scattered and so the Moon looks red. That is the same reason that sunsets and sunrises look red or orange.”
They sat there just looking at the Moon as it became completely covered: a Total Lunar Eclipse.
“Wow, that is really beautiful!” exclaimed Chris.
“Yes, even though I have seen many of them, I still never get tired of seeing Lunar Eclipses.” said the astronomer. “This is one of the extraordinary sights of the night sky.”
“When will we get to see the next one together?” asked Chris.
“Well, Lunar Eclipses happen about every 6 months, but not all of them are total, and they cannot all be seen from here. Some of them occur during the daytime in the USA, so the Moon won't be visible from here. Actually, the next one will be visible on November 8, but it will be very early in the morning, so you will need to get up at 3 o’clock in the morning! Do you think you want to do that?” she asked with a smile.
“I don’t know, Grandma,” she answered sheepishly. “You know I am not much of a morning person!”
“Then I am glad you enjoyed this one, because you won’t see another Total Lunar Eclipse in the USA for several years.”
The short video that follows is a time lapse of a total lunar eclipse from Nov. 19, 2021 by Mike Lewinski.
Here is a short NASA video explaining the umbra and penumbra shadows, as well as the reddening of the fully eclipsed Moon.
Use the following link at Time and Date .com to see how the eclipse will look from your location, and the time of occurrence for each stage of the eclipse. You can also find out when future Lunar and Solar Eclipses will occur.