You might want to clear some time in your schedule this weekend to look up at the night sky. Those in the western hemisphere will be treated to a rare celestial alignment known colloquially as the “super blood moon.” It sounds pretty cool, but it’s just science — cool science.
The super blood moon will be upon us on Sunday night, January 20-21st. Contrary to the very metal name, this is not your chance to carry out ritual sacrifices. It’s a lunar eclipse that comes at a particular time in the satellite’s orbit. Let’s break that name down and make some sense of it.
The “blood” part of the nomenclature refers to the color of the moon during a full eclipse. As you’re probably aware, eclipses happen when the moon, Earth, and sun are all aligned. Usually, the slightly tilted path means the full moon still gets some light from the sun. During a total eclipse, Earth blocks most light from reaching the moon, but a little bit passes through our atmosphere before falling on the moon. Higher frequencies at the blue end of the spectrum get absorbed completely in the atmosphere, but red light can pass through and reach the moon. The reddish light that reflects back toward us gives the moon a blood-red tone.
Sunday’s eclipse is a “super” blood moon because of the specific time in its orbit when it’s closer to Earth. The moon’s orbit is, of course, not perfectly balanced. At apogee (the most distant part), the moon is 252,000 miles (405,500 kilometers) away. The closest approach (perigee) is just 225,000 miles (363,300 kilometers) distant. A supermoon is a full moon that occurs during that time. So, a super blood moon is an eclipse coinciding with a supermoon. The red color is deeper because of the moon’s position, and it will appear larger than usual.
You’ll be able to see the first hints of the eclipse at about 9:30 PM Eastern Time on Sunday as the moon slides into the penumbra (the Earth’s shadow). That will be subtle, but the shadow should be more visible moving across the surface by 10:30 ET. At 11:41 PM Eastern Time, the eclipse will reach totality. If you’re going to look up at any point that evening, this is the time. It will remain “blood red” for about an hour before the shadow recedes. And if you want to shoot it with your DSLR, read our sister site PCMag’s guide to How to Photograph a Total Lunar Eclipse.
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