Thursday, November 10, 2016

A Reason to Look Up

Life is busy and complicated, but can I request one small favor? Make a note to at least glance at the moon on Sunday or Monday night.

I spend most of my time looking at the screen, the kids, the mess, the road, and the to-do list. I look down to avoid stepping on Legos and cheerios, but the truth is I rarely look up anymore. It’s easy to start thinking life consists of the world as it appears to me at 5’ 7” off the ground.

That feeling evaporates when I look up. Even faster if it’s dark outside. Some of the defining moments of my life include witnessing the wonder of the Milky Way from the roof of a dark observatory, being surrounded by stars in the desert of Big Bend National Park, and losing my sense of direction as thousands of stars gradually appeared in a darkening Utah sky.

Milky Way from Big Bend.
Image Credit: Vincent Lock (CC BY 2.0)
But even here, from my well-lit neighborhood, I regain perspective when I look up. The sight of the bright, predictable moon and the pricks of starlight cutting through the darkness give me a sense of unity and vastness. Here we are, people, planets, stars, galaxies, and even black holes, all in this universe thing together.

Early Monday morning, the full moon will be closer and brighter than it has been in nearly 70 years. The moon follows an elliptical path around the Earth, just like the planets do around the sun. Not only are we not the center of the universe, we’re not even the center of the Earth-moon system. In its 27-day orbit, the moon gets as far as 252,898 miles from us and as close as 221,208 miles. In other words, the moon will be about 13% closer to us early next week than when it is at its farthest.

When a new or full moon is within 90% of its closest approach, it’s called a supermoon. Next week’s supermoon will be the closest one until 2034. The moon will be as close as it ever gets to the Earth within two hours of becoming a full moon. If conditions are clear, the moon could appear up to 14% larger and 30% brighter.

With the excitement of possible visits to Mars and other exotic locations in space, it’s easy to let go of the wonder the moon instilled in previous generations. The moon is our constant companion, predictably disappearing and reappearing according to its position relative to us and the sun. We can describe the moon pretty well and have even walked on its surface, but mysteries remain. We don’t even know for certain how the moon formed or why its orbit looks the way it does. Digging into these mysteries can help us better understand our collective past.

In a recent paper in Nature, a team of astronomers suggest that the moon-Earth history was much more dramatic than current leading theories predict. Evidence suggests that the moon was formed when a giant object hit the early Earth, creating a disc of debris around a spinning Earth. Over time much of the debris accreted, or coalesced, and created the moon. The current models of this process explain a lot, but not everything. For example, there is a curious 5° tilt to the moon’s orbit.
In this recent work, the astronomers modeled possible scenarios for the moon’s formation to see what best matches reality. While not definitive, their research points to an explosive collision that sent the Earth spinning much faster than previous models predict and that knocked the Earth’s axis into a major tilt, somewhere between 60 and 80 degrees. Today the tilt is just 23.5°.

Their best model shows the debris forming a moon very close to the Earth that eventually drifts away, maybe as far as 15 times farther away than where it started. Despite a chaotic early relationship, the gravity of the moon, Earth, and the sun eventually settle the system into the geometry and rhythm we see today. The researchers point out that this revised model doesn’t address all of the unanswered questions about the moon’s orbit, but it seems to be a better match than previous models.

There is something about our shared sky and shared history, whether we understand it completely or not, that has the potential to bring people together. Come Sunday evening, I’ll be looking up at the same supermoon as people of all ages and backgrounds living all around the world. I hope you’ll be looking up with us!

Kendra Redmond

No comments:

Post a Comment