If you haven't seen Jupiter and Saturn yet this season it's completely understandable. They don't rise until around 4:30 a.m. local time and are best visible starting an hour before sunrise low in the southeastern sky. Jupiter stands about 10° high in early April, equal to a fist held vertically at arm's length. Saturn's a little higher and shines to the upper right of Jupiter. My favorite place to see them is along the shore of Lake Superior, with its unobstructed view of the eastern sky.
This week the waning crescent moon joins the scene and stops by each planet in back-to-back conjunctions. The moon is ever so helpful when it comes to finding planets. That's because it orbits in nearly the same plane as they do, called the ecliptic. Since the moon circles around the entire sky in about a month, it briefly lines up — lies along the same line of sight — with each of the eight planets in events called conjunctions. Find the moon, and you don't have to look far to see the planet.
Jupiter and Saturn are currently 12.5° apart which is coincidentally equal to the distance the moon moves eastward each day as it orbits the Earth. On Tuesday, April 6 the lunar crescent hangs 4.5° (three fingers) below Saturn at dawn. Then on the following morning, April 7, we'll see it a similar distance below Jupiter. The robins will be up watching. Why not join them and start the day with a beautiful celestial sight set to the soundtrack of the spring bird chorus?
So how did we get so lucky to live in a flat solar system where all these memorable alignments occur? Borrowing from Genesis, the original dense cloud of dust and gas which gave birth the solar system was without form, twisting about in space as it orbited the center of the Milky Way Galaxy. We don't know what initiated its collapse, but a shock wave from a nearby supernova may have been the trigger.
Compression from the explosive event would have compacted fluffy material into denser stuff that further contracted under its own gravity to form a spinning disk with the proto-sun at its center. Whatever the original cloud's shape, it possessed some amount of twist or rotation. As every parent of a 2-year-old knows, nothing sits still in the universe. As the cloud collapsed, it spun faster the same way a skater spins faster when she draws in her arms during a spin.
A skater stays in one piece and maintains her shape because she's solid, but a formless cloud flattens into a whirling disk as its spin increases. At its center, where the most matter is concentrated, the temperature and pressure rose high enough for hydrogen to fuse into helium, releasing the energy that "ignited" the sun. Farther out, leftover clumps of matter in the disk underwent gravitational collapse to form everything else: planets, moons, comets and asteroids.
All the material comprising our solar system was forged in the bellies of earlier generations of stars and released into space during and at the end of their lives. Stellar crumbs left on the table not only made the planets possible but life itself.
In virtually frictionless space the planets continue to whirl around the sun to this day. Every conjunction reminds us again of that remote time when it all began.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.