Al Stahler: The shape of our neighborhood
Having sailed around the world, having seen Earth from space, we can be fairly sure that Earth is not flat.
The solar system, on the other hand, is flat … flatter’n a pancake.
The middle “star” in The Hunter’s dagger is not a star at all. Binoculars, held steady (elbows braced on a railing, table, truck door), reveal the middle “star” as a glowing cloud of gas and dust: The Orion Nebula (“nebula” from the Latin for “cloud”). A small telescope reveals more: some parts of the nebula glow brighter than others; and, within one of the brighter regions, a cluster of baby stars.
Our sun was born, four-and-a-half billion years ago, from just such a dusty, gaseous nebula. That cloudy ball of gas and dust collapsed in on itself to form the sun; from wisps of dust and gas remaining, Earth and the other planets formed. Despite that no one was around to see it (at least, no Earthlings), we can be quite sure that this ball of gas and dust was spinning … spinning counter-clockwise, as seen from above the nebula’s north pole (defined as more-or-less the same direction in the sky as Earth’s north pole).
All the sun’s planets circle our star counter-clockwise. The sun, itself, spins counter-clockwise (taking roughly a month to go around). We know which way the ancient nebula spun, because its motion has been “baked-into” our present-day reality.
Looking out in all directions, we see dozens of constellations. Unlike the stars, the planets don’t remain in any one constellation. Instead, they wander from one constellation to another (the word “planet” comes from the Greek “wanderer”). But the planets don’t wander through all eighty-plus constellations. Rather, they circle through just a dozen of them – the constellations of the zodiac (the “circular zoo”).
It’s as if all the planets were rolling around on a gigantic – and very flat – table-top. The solar system – sun and planets – is flat.
But the solar nebula, from which sun and planets formed, was round. How did the solar system come to be so flat?
The yeasty lump from which a pizza-chef prepares the pie starts out as a round ball of dough. But, spun overhead, the centrifugal effect presses the dough outward, along the ball’s equator … even as the poles of the dough draw inward.
As the solar nebula collapsed, four-and-a-half billion years ago, the centrifugal effect kept the nebula’s equator stretched outward … even as gravity pulled the nebula’s poles inward … resulting in a very flat solar system.
Since all the planets – along with the sun and moon – remain always within the zodiac, they sometimes cross paths (the scientific name for this starry circle is the “ecliptic” … when sun and moon cross paths, we get an eclipse).
This Saturday, in the western sky, right after sunset, Venus and the crescent moon will be conjunct – they will be right next to each other. Do not miss seeing this!
The conjunction of Venus and moon this Saturday will be easy-to-see, naked-eye, but if you’d like to see more, come join local astronomers as we set up scopes, 6 p.m., at the junction of state route 49 and the old Downieville Highway. It’s free – bring the kids. Notice the early start time, and dress warm.
Al Stahler enjoys sharing nature with friends and neighbors. His science and nature programs can be heard on KVMR (89.5 FM), and he may be reached firstname.lastname@example.org.
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