By Dr. Robert Thorson

Last week I read the poem “Spring” by Gerald Manley Hopkins to a large audience. Midway through it, I quoted: “What is all this juice and all this joy?” This was not a rhetorical question, for the poet’s reply occurs in the next line: “A strain of the Earth’s sweet being in the beginning / In Eden garden.”

It was then that I began thinking about two recent natural disasters, the typhoon in Myanmar, which washed away more than 100,000 people, and the earthquake in China, which crushed more than 30,000. Both were powerful acts of nature, from which – after the shock and grief – will emerge new beginnings.

That’s the way the Earth works. The beauty of spring is no exception. It’s a completely random phenomenon, arising from the most violent event in all of Earth’s history.

I have no problem worshiping the return of the sun. I do it every morning when I walk outside to greet the new day, sometimes during the first glimmer of dawn. I do it in spring when I am completely taken in by the fragrance of flowers and the music of bird song. Both phenomena are due to an unexpected chance collision between the early Earth and a Mars-sized proto-planet.

The Victorian era Jesuit priest-turned-poet reminds us that “nothing is so beautiful as spring.” What he does not say is that this softest, most polychrome season arises from something harder and darker.

Early Earth spun at a much faster rate, probably with an axis of rotation much closer to vertical relative to the plane of the ecliptic, its path around the sun. Then, zooming in from the recesses of our solar system came . . . “The descending blue; that blue is all in a rush with richness.”

The collision was oblique. It didn’t strike the Earth straight on. Rather, it struck somewhere nearer the top or bottom, rather than at the equator, which gave our planet its weird tilt of 23.5 degrees. It is this strong tilt that sends us into winter when our northern hemisphere begins to tilt away from the sun, and into summer when it begins to tilt toward our source of warmth. Spring is the turning point between these modes.

The collision probably also struck somewhere off-center relative to the prime meridian. This would have either sped the spin or slowed it down, depending on which side it slammed into. The measure of our days is governed by this rate of spin, less that which we’ve lost to the tides by turbulent friction.

The oblique collision did something else important. It created the moon. The kinetic energy of the collision was transformed into heat, which melted or partially melted both Earth and the proto-planet. Were the collision straight on, the two celestial bodies might have simply merged. Were it a glancing blow, the debris might have been carried far away. Instead, the middling angle of the collision splashed the debris into low orbit, forming a lumpy planetary ring that quickly congealed into the moon. Earth and moon are actually a double planet system rotating around a common center of gravity, and revolving together in the ecliptic plane rather than Earth’s equatorial plane.

Since then, the moon has likely played a role in creating what the poet found so exquisite, about spring, the “thrush’s eggs . . . echoing timber . . . glassy pear tree leaves . . . racing lambs.” Astronomers believe that having a massive moon so nearby stabilized the Earth’s orbit, thereby preventing its wobble from careening out of control with disastrous climatic consequences. This stable orbit, when combined with continental drift, gave rise to Earth’s incredible climatic zonation, which, in large measure, accounts for its great biodiversity, and to seasonal rhythms such as the nesting of birds.

I am thankful for the double obliquity of this planetary collision. It gave us our days. It gave us our springs. It gives us hope that beauty will forever rise above disaster.

But to whom or what should we be thankful? Frankly, I don’t think it matters. Being thankful for a spring sunrise is enough.