On Sept. 27, we'll be treated to a supermoon eclipse. Why not brush up on your lunar eclipse knowledge beforehand? There's much to know about these often-spectacular night sky events.
1. Lunar eclipses only occur during a full moon.
When the moon is opposite the sun, with the Earth in between casting its shadow on the moon, a lunar eclipse occurs. We don't have a lunar eclipse at the full moon each month because the moon's orbit is tilted 5 degrees more than the Earth's orbit.
2. 'Syzygy' is the term for when the Earth, sun and moon align.
Jupiter (top), Venus (lower left) and Mercury (lower right) are roughly aligned in the evening sky of May 26, 2013. The photograph of this syzygy was taken near the La Silla Observatory in northern Chile (Photo: Y. Beletsky/ESO/Wikimedia Commons)
In fact, it's the term for when any three bodies line up in space. It comes from the Greek word syzgia, which means "yoked together," and it's pronounced like "sizigee."
3. There are three types of lunar eclipse.
The partial lunar eclipse of Dec. 31, 2009. A partial lunar eclipse is marked by the Earth's shadow only covering a small portion of the moon. (Photo: Stephen Hanafin/flickr)
A lunar eclipse can be total, partial or penumbral. A total eclipse happens when the shadow of the Earth fully covers the moon. A partial eclipse (pictured above) is when the Earth’s shadow covers just a portion of the moon. A penumbral eclipse involves the Earth’s lighter outer shadow (penumbra) covers the moon. Penumbral shadows often go unnoticed by casual sky watchers.
During a total lunar eclipse, the moon will go through partial eclipses on either side of totality.
4. 'Totality' is the term for when the moon is completely darkened.
This can only happen during a total lunar eclipse.
5. You could see a lunar eclipse from the moon.
However, if you were standing on the moon, it's the Earth that would be dark because the sun would be behind it.
6. Refraction causes the moon to look red during an eclipse.
The moon often turns a rusty shade of red during lunar eclipses due to how the Earth's light is refracting. (Photo: Guian Bolisay/flickr)
The moon looks reddish, often called a blood moon, during an eclipse because of the way light is refracted in the Earth's atmosphere. This is called Rayleigh scattering, which is the same reason why sunsets and sunrises are reddish in color.
The exact color of the moon is also influenced by the particles in the Earth’s atmosphere at the time of the event.
7. Lunar eclipses have time limits.
Of course, lunar eclipses don't last forever, but more specifically, lunar eclipses cannot last longer than 3 hours and 40 minutes, according to the National Maritime Museum in London. Also, totality can only last for up to 1 hour and 40 minutes. Some can be much shorter. This is due to the shape of the Earth's shadow. It's cone-shaped, so depending on where the moon is traveling within the shadow, the time it takes to get out of the shadow varies.
8. Eclipses will be different in a several million to a few billion years.
According to SPACE.com, the moon moves away from the Earth at a rate of 1.6 inches each year. This will eventually cause a change in the way the Earth’s shadow appears on the face of the moon.
9. Christopher Columbus once used his knowledge of lunar eclipses to get out of a jam.
Christopher Columbus used a lunar eclipse to trick Arawaks of Jamaica into thinking that his god had become angry with the tribe. (Photo: Camille Flammarion/Wikimedia Commons)
After being marooned in Jamaica, Columbus used a lunar eclipse to get back into the good graces with the native Arawak people. Columbus and his crew had been in Jamaica for several months, and the Arawaks were getting tired of feeding them. To gain back their favor, he used his knowledge of the moon and of lunar eclipses, not to mention a handy almanac that predicted the eclipse of Feb. 29, 1504. He took this information to the chief. Instead of presenting the science, though, Columbus claimed that his god was angry with the travelers' mistreatment. Sure enough, the total eclipse occurred, and out of fear of Columbus and his angry god, the Arawak people went back to taking care of the stranded visitors.