For solace, look to the heavens.
While one terrible thing after another was happening on Earth in 2017, the news from outer space was chock-full of amazingness to a degree rivaled in my lifetime only by the Apollo moon missions. Those of us fortunate to live in the relative calm and prosperity of the First World have the opportunity, in rare moments of serenity, to bask in a new era of cosmic discovery made possible by extraordinary technology in the service of science’s ceaseless voyage toward truth.
The moon landings were amazing, all right, and especially heartening for Americans at a time when the country was in a state of turmoil and division unique to the 20th Century. It prompted me to buy my first TV, a small black and white device, not that color mattered for a moon landing. But for sheer scale, the exploits of puny humans on our nearest heavenly body 50 years ago can be compared with the significance of 2017’s Year in Space as a Home Depot compared with the One World Trade Center.
Do I exaggerate? Let’s go down a list, in order of least amazing to the most spectacularly profoundly spine-tinglingly amazing:
(1) total solar eclipse viewed by millions across America;
(2) a nearby solar system was found to have several earth-sized planets at a distance from their sun compatible with life as we know it;
(3) the ultra-sensitive LIGO detectors traced gravity waves to the collision of two distant neutron stars (neutron stars, by the way, are some of the most extreme products of stellar evolution in the Universe; wait for mind-boggling factoids yet to come);
(4) the earliest known spiral galaxy was discovered using gravitational lensing with earthbound telescopes;*
(5) Voyager One sailed into interstellar space, still sending data back from more than nine light-hours away (one light-hour = 669,600,000 miles).
We might disagree over the ranking of these events, but taken together they have, in one year, hugely expanded our cosmic horizons, and connected us to the history of the Universe with unprecedented breadth of knowledge.
[WARNING: the following text is replete with details that could exhaust less receptive minds. You might want to take it in stages. Put your Nerd Cap on!]
In this post, I write of the first (and IMHO least) amazing event, the Total Solar Eclipse witnessed by millions in the U.S. on August 21. This post covers the lunar aspect of the eclipse. The next post covers the role of the Sun and Earth, and the take-away.
Eclipse fever breaks out in the USA
Americans lucked out when a total solar eclipse traversed the width of the country west to east on August 21st, a disk of shadow racing at approximately 1,740 miles per hour on the ground (absolute speed of the shadow is a little faster, but the Earth’s west to east rotation slows its speed relative to ground observers). At least five million people (some estimates as high as 20 million) flocked from every corner of the country (and plenty of corners of other countries) to assemble in the 68-mile-wide path of totality. Another 200 million watched it on screens; while some of us contrived makeshift partial-eclipse viewers with paper, or pans of water or oil.
Total solar eclipses are fairly common, occurring about twice every three years. However, their paths are narrow and usually occur over the 70% of the Earth’s surface that is water. What made this eclipse happily unique was a combination of two things: (1) as it traveled over so much populated land, the audience was plentiful, enthusiastic, and sometimes rapt; (2) there was observed a phenomenon predicted by theory but never captured by instruments prior to 2017. The phenomenon consists of “bow waves” in the path of the eclipse. For a description and an account of its significance, see https://news.nationalgeographic.com/2017/12/solar-eclipses-earth-bow-waves-atmosphere-space-science/
(It’s worth watching the informative little video that comes up at this site, that may include a factoid or two you don’t already know, such as the possibility of a “hybrid eclipse.” Wow!)
There’s a totally cool image of the Moon’s shadow from a NASA satellite in this next piece, which also poses a brain-stretching challenge in geometry: https://eclipse2017.nasa.gov/challenge-10-%E2%80%93-shadow-speed-and-earth%E2%80%99s-rotation
The speed of the Moon’s shadow across the Earth’s surface—more than twice the speed of sound—is one small hint of the phenomenal scales that 2017 brought to our attention, not least the dimensions of the eclipse’s major players all within eight light-minutes of us: Sun, Moon, Earth.
SCALE will be a principal theme of these year-in-outer-space posts. If the scale of the Universe doesn’t send prickles up the back of your neck, maybe you’ve been watching too many reruns of The Simpsons.
Moon’s starring role overshadows the stellar reputation of the Sun
In the Eclipse segments of The Most Amazing Year in Space Ever, we’ll examine the three chief players in the celestial drama: Moon, Sun, and Earth. In this post, the Moon.
Although the Sun is literally the “star” of the show, I’m giving top billing to the Moon. The Moon brought the hustle that made the whole thing come together.
The Moon, raw numbers: our Moon, 6,783 miles in circumference, with a mass about 1/81st that of the Earth, is unique in our solar system in its large size relative to its host planet. Overall, it’s the fifth biggest moon in our solar system, even though the “gas giants” Jupiter and Saturn have scads of hefty candidates. (Those big distant moons, despite their absolute size, appear like pinheads against the immense breadth of Jupiter in a telescope.) It’s bigger than Pluto (4,494 miles in circumference), which is one reason why the formerly over-rated Pluto got booted to the status of dwarf planet. Ganymede, orbiting Jupiter, with a circumference of 16,500 miles, is the Solar System’s biggest satellite, a tad larger than Saturn’s Titan. The sad thing about our Moon is its barren surface, naked rock riddled with thousands of impact craters. Most of the satellites of the gas giants are wrapped in layers of all kinds of interesting stuff. Whatever created our moon was pitiless as well as powerful.
The disproportionate size of the Moon in relation to Earth begs for an explanation. Other satellites (excepting the two little ones of Mars) can be assumed to have been created in two interrelated ways: (1) to have grown out of a disk of matter along with their host planets, accumulating pieces out of the disk by collisions and gravitational capture among themselves, and (2) by the giant planets snagging unsuspecting asteroids as they came in range.
So what’s with our oversized Moon? If it went zipping by at the heady pace of your typical heavenly body, its mass and momentum would have made it difficult for the puny Earth to grab hold of it (although some astronomers suggest Earth stole it from Venus; which, oddly, at about the same size as Earth, has no natural satellites at all). If it formed along with the Earth out of an accretion disk, as happened with the giant planets, then its size compared with other satellites is more than surprising, it’s uncanny.
Currently, the prevailing explanation for the Moon’s origin is the “Giant Impact Hypothesis,” whereby another large celestial body (NASA’s term: “a rogue body”) smashed into Earth and blew a moon-sized chunk into space. There is some controversy over this hypothesis—this is the sort of thing that makes science so fascinating. So here was a bizarre event (creation of an incongruously large satellite by one means or another) that happened right in our celestial back yard, and we haven’t figured out how it happened. For an informed discussion, see: https://www.space.com/19275-moon-formation.html
Despite Earth’s gravitational clutch on our Moon, our beloved companion is gradually receding from us, at a rate of 3.8 centimeters per year. That rate is slowing, so that it’s doubtful it could ever escape Earth’s grasp. Nevertheless, eclipses will become less “total” over the course of millennia, as the receding Moon’s disc shrinks.
If you were worrying that the Moon might eventually break free of Earth and go hunting for a more manly suitor elsewhere in the Solar System—Jupiter and Saturn come to mind—at least be assured there would be no humans around to be disappointed. That’s because well before that event, the Sun will have swollen into a red giant (some 5 billion years hence) with its surface approaching Earth’s orbit—if it doesn’t actually swallow the Earth and Moon, it will bake the pair of them into utter celestial toast.
Due to its large size, the Moon has the property, key to making total eclipses work, of having an actual diameter one 1/400th that of the Sun’s, while being 400 times closer. If you ever got the peculiar feeling that the sun and moon seemed to be the same size in the sky—despite being totally incommensurate in absolute size—seeing an eclipse will confirm there’s not a hair’s breadth of difference in their apparent size. This lunar trick of geometry was widely broadcast on various media prior to the big event, along with myriad warnings about looking at a non-eclipsed Sun with the naked eye. More on this when we get to Earth’s role in the eclipse in a later post.
What you might not have heard is an explanation of why there aren’t more eclipses, since the Moon passes between the Earth and Sun every 28 days. If you viewed the video linked to above (in the paragraph beginning “Total solar eclipses are fairly common”), you have received most of the answer. I will elaborate on this in a post soon to come.
Next post: the Sun’s and Earth’s roles in the eclipse.
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* Later amendment to the oldest galaxy thing – I was reminded that the discovery of the oldest galaxy was made in 2016. It was the discovery of the oldest spiral galaxy that happened in 2017. I deal with the spiral discovery in Part 4 of THE GREATEST YEAR IN SPACE, EVER.