Everyone was talking about the total lunar eclipse that happened this morning! Except they were calling it a Super Blue Blood Moon. Forget all the hype — How does a lunar eclipse work, and why was this one special?
“Super” moon
A supermoon is a little closer to Earth than a normal moon, so it looks a little bit bigger and brighter. 14% bigger and 30% brighter. Here’s a comparison that shows the moon at its apparent largest and smallest.
Source: https://apod.nasa.gov/apod/ap161113.html
This happens because the moon’s orbit isn’t exactly a circle. Sometimes it’s a little closer to Earth (perigee, supermoon), and sometimes it’s a little farther away (apogee, micromoon). The moon orbits the Earth every month, so here’s a perigee *every month,* but it doesn’t always happen during the full moon. Sometimes it’s a super-crescent.
“Blue” Moon
This doesn’t have anything to do with astronomy, but rather with the calendar that we use. A “Blue Moon” is simply the second full moon in a month. No special effects or different colors. (Confusingly, a “Blue Moon” can also be the 4th full moon in a season. That happened back in 2017. Still no special effects or different colors. Sorry.) If you see an image of a Blue Moon, it’s photoshopped or might possibly have been taken near an active volcano. Sorry.
Source: https://www.livescience.com/34143-blue-moon-phrase.html
“Blood” Moon
A “blood moon” is a sensational name for a total lunar eclipse. A lunar eclipse happens when the moon goes into the Earth’s shadow. When the moon is entirely in the Earth’s shadow, it looks dark red. It looks red because red light is shining on it, not because the moon’s surface has turned red. This happens during lunar eclipses because sunlight is shining around the edges of Earth toward the moon. The air in Earth’s atmosphere scatters sunlight and separates the colors, so red light bends around Earth a little bit and goes into the shadow. (By the way, this is exactly the same reason our sky is blue and sunsets are red. It’s called Rayleigh Scattering.)
Source: https://apod.nasa.gov/apod/ap150929.html
Fun Facts
- Lunar eclipses can only occur during the full moon phase.
- Lunar eclipses can only be seen at night.
- The sun-earth-moon alignment that leads to eclipses is called SYGYZY.
- Lunar eclipses can be observed by half of the earth, all at once. (Compare this to Solar Eclipses, which have a narrow path of visibility).
- Lunar eclipses are not uncommon. There are at least a couple every year, visible from somewhere on Earth.
- A lunar eclipse will appear more red if there is a lot of dust in Earth’s atmosphere, like after a volcanic eruption.
- Bonus Fun Fiction: Be careful what you read about the rarity of events like this. Here’s a sciencey-sounding article about a Supermoon Eclipse in 2015 that says the next one won’t be until 2033! When it doubt, check NASA.
Video Simulations
I’m experimenting with how to make videos, so here are three quick lessons on today’s lunar eclipse. You’ll see the eclipse from two places in the United States (east and west), from the surface of the moon, and from the surface of the sun!
The next lunar eclipse visible from North America will occur on Jan. 21, 2019!