Now that exams are over, you may have some time to stay up late and enjoy an amazing astronomical event.
At about 10:30 p.m. May 15, step outside and take a look at the moon. You might notice that the moon is a bit darker than it was earlier in the evening. Over the next several hours you will have the opportunity to witness a total lunar eclipse.
This year we are treated to a total eclipse, and you will be able to see the famous blood moon. From about 11:30 p.m. May 15 until about 12:55 a.m. May 16, the moon will take on a deep red color. The name makes it sound scary, but it is just simply a natural phenomenon having to do with our atmosphere.
A lunar eclipse occurs when the Earth is between the sun and the moon. Our planet casts a shadow across the moon. In a total eclipse, the moon can mover deep into Earth’s shadow or umbra. If you watch the eclipse progress, you can see the moon gradually darken as it enters the penumbral phase of the eclipse. By about 9:40 p.m., you will notice the moon starting to grow darker as shown below.
By about 10:40 p.m., the moon will be into the umbral phase of the eclipse and appear noticeably darker. Sometimes it is interesting to think about what an eclipse will look like from space. The next frame in the image shows a simulation of what you would see at a position 300 km from the moon, looking in the direction of the sun. That black dot partially obscuring the sun is us. If you were on the surface of the moon, you would experience a solar eclipse as the Earth blocks your view of the sun.
As the moon moves deeper into Earth’s shadow, we see the color start to redden. Our atmosphere acts as a giant lens refracting the longer reddish wavelengths of sunlight and bending them just enough, so they strike the moon. Blue light is more highly scattered by the atmosphere than light at the red end of the spectrum. In fact, that is part of the reason the sky looks blue. During the eclipse, the moon is illuminated by the long reddish wavelengths, which are reflected back to us. If you are still out watching the eclipse after 1 a.m. May 16, you will see the moon start to brighten up.
Get some rest; graduation starts early May 16. No need to watch the moon return to normal by around 2:30 a.m. If you happen to miss it this time, you can always set your alarm for about 1:20 a.m. March 14, 2025, and see a replay.
A lunar eclipse like this one, always occurs when the moon is full. That is because the moon is opposite of the sun in our sky, and we can be in between them. You might think we should have an eclipse every month, and we should not have to wait so long for the next one. Few people realize that the plane of the moon’s orbit is slightly tilted compared to our orbital plane. You can see this from a point in space looking back at the moon and Earth as shown below.
Sometimes, on a full moon, the Earth casts a shadow out into space, and there is no eclipse. Only when the moon is in just the right part of its orbit, does it fall into the shadow region, and we see an eclipse. Have fun observing the eclipse, and don’t be late for graduation.