Astro Bob: Watch Election Day total lunar eclipse
That's right! Before you cast your ballot, look up to see the full moon glowing like a vision in the western sky.
You can't forget the date of this eclipse. For U.S. citizens it happens on voting day. No, I won't be sending you colorful fliers or taking out TV ads telling you why the moon will either destroy civilization as we know it or make your life better. We'll leave that to the politicians. Nature makes no promises, which if you think about it, is incredibly refreshing.
November is often a cold and cloudy time of year for much of the U.S., but a big event like a total eclipse makes us hopeful for clear skies and another chance to appreciate the beauty of simple things. And what could be simpler? On the morning of Nov. 8, the Moon will play a little game of peek-a-boo.
Total lunar eclipses are uncommon, with an average of two per year. That's the case this year, with the previous eclipse, also a total, happening May 15. Lunar eclipses only occur at full moon, when the moon is directly in line with the sun and Earth and passes through the planet's shadow.
If the moon circled Earth in the same plane as Earth circles the sun, we'd see a total lunar eclipse at every full moon. We don't because the lunar orbit is tilted 5° to that plane. Most full moons, it passes a couple degrees above or below the shadow and remains in full sunlight. FYI, the shadow width at the moon's distance is just 3.6 times the moon's apparent diameter or 1.8°. That's a pretty small target to hit! Eclipses are so infrequent because the sun, earth and moon (in that order) have to have all their ducks in a row.
During this eclipse, the moon will take almost 6 hours to traverse the entire shadow while speeding along at 2,240 miles an hour (3,600 kilometers per hour). That sounds fast, but at its distance of 241,270 miles (388,285 kilometers) it creeps across the sky at the rate of just one moon-diameter (1/2°) an hour.
That means lots of time to enjoy the sight. And remember, you don't need any special equipment to view a lunar eclipse, though I do recommend binoculars during totality for reasons I'll elaborate in a minute.
Eclipses are divided into phases. First, there's the penumbral phase, when the moon enters and traverses the outer, penumbral shadow. You won't see much change in its appearance until 20-30 minutes before partial eclipse, when a gray cast blunts the moon's upper left (eastern) edge.
As soon as the moon contacts the umbra, partial eclipse begins. That first dark "bite" along the moon's left side will give it away. Through binoculars or a telescope you'll notice that the shadow has a fuzzy border. That's because it's cast by the sun, which has an extended disk. At the umbra's edge a little sunlight spills around the sides to soften the darkness. Next time it's sunny outside, take a look at your own shadow, and you'll see the same soft, gray border. Were the sun a point of light instead of a disk, the shadows would be knife-edged.
Further, the shadow that Earth casts is round. The fact that it looks like this at every eclipse no matter the circumstances or location is proof we live on a spherical planet. Feel free to share this fact with your Flat Earth friends.
It takes a little more than an hour for the moon to fully enter the umbra, at which point the total eclipse gets underway. In the final few minutes before totality, only a sliver of sunlit moon remains — a last hope before the shadow swallows all. This transitional moment is one of my favorite parts of a lunar eclipse.
Totality lasts 86 minutes. During this time, the moon gives the sky back all its stars. With lunar glare quenched by Earth's shadow, darkness returns in a profound and moving way. Take a look around to appreciate this remarkable transformation. Then grab those binoculars and enjoy the sight of stars right up to the moon's edge, a sight you'll never see during a typical full moon.
What color and how dark will the moon appear during this eclipse? Hard to know for sure. Since its southern (bottom) half passes closest to the center of the umbra it should appear darker than the upper half, which will lie closer to the shadow's edge.
Color and brightness are affected by the state of the atmosphere at the time of eclipse. If there's widespread cloudiness around the planet, we'll see a darker moon. Suspended dust, particularly from recent volcanic eruptions, can also affect the moon's brightness. Use the Danjon scale to estimate what you see. I'll share your results in a post-eclipse post.
Totality ends and partial eclipse resumes when the moon slowly slides back out of the umbra. Observers from the East Coast to the near west mountain states will see these latter phases in a twilight sky, which will offer some fine opportunities for photos. I'll share photography tips in a second eclipse blog later this weekend.
For observers in the eastern time zone the moon will set either during or just after totality. To see as much of the event as possible you guys will need an unobstructed view of the northwestern sky. Farther west, skywatchers will catch all or nearly all of the eclipse.
We also have a rare event. By good fortune, the eclipsed moon will be near the planet Uranus. From the Midwest, the two will be about three moon diameters (1.5°) apart. Farther west, in the Anchorage, Alaska region, the partially-eclipsed moon will occult or cover up the planet. Pretty cool. For more details about the "cover-up," including disappearance predictions for other cities, click here . Note that the times are UT (Universal Time). Subtract five hours for EST; six for CST; seven for MST; eight for PST and nine for AKST (Alaska).
I hope you and your family (yes, share with the kids!) have clear skies and a wonderful eclipse. Enjoy — the next total lunar eclipse visible anywhere on Earth won't occur until March 14, 2025 .