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I'm in love with Copernicus . Not the Polish astronomer, although he sure had the right idea about the layout of the solar system with the sun in place of the Earth at center. No, I'm talking about the lunar crater named for him.
Located just northwest of the center of lunar near side, it's a big bulls-eye 58 miles (93 kilometers) across. If someone built a bridge across this giant hole, it would take about an hour to make the crossing.
On Thursday night, July 7, Copernicus will appear astride the lunar terminator, the line that divides the sunlit part of the moon from the part that's still in darkness. As the moon orbits the Earth, the terminator sweeps across the surface at 9.6 miles an hour (15.4 kilometers per hour). That's about the same speed as a beginner averages during a one-hour bicycle ride. In the same amount of time, observers can see changes in the illumination of craters and mountains with their own eyes.
Depending on your time zone, the lighting on Copernicus will vary somewhat Thursday evening. Observers on the East Coast will see it more of it submerged in darkness than those living on the opposite coast. My absolute favorite Copernican moment is catching the crater completely engulfed in shadow with only its circular rim etched by the rising sun. Maybe that will happen tonight. I know it will for someone.
As the sun climbs higher over the lunar landscape and the terminator draws back, sunlight spills down the crater's walls until it illuminates the floor and central mountain peaks, the highest of which soars to 3,900 feet (1.2 kilometers). Many times I've imagined standing on top of that mountain, the sun glaring off to the east in a star-filled sky with the crater below me still shrouded in darkness.
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Copernicus formed during the impact of a small asteroid about 800 million years ago. The collision dug out a capacious hollow and flung fragments of lunar crust far and wide. Upon landing, the shards excavated their own craters, exposing fresh rock and dust from beneath the surface to create a spectacular spider web of bright rays with Copernicus at its center. The rays are subtle in low light, but really jump out closer to full moon. Consider a return visit to the crater at that time, when the rays will be obvious through binoculars.
Telescope viewers will also see additional detail like the upraised, hummocky terrain surrounding Copernicus that resemble wrinkles around the eyes — a testament to the incredible forces unleashed when one massive body strikes another at high velocity.
Battered, airless and to our knowledge, lifeless, the moon is truly an alien world. Yet we can see it in rich detail right from our own backyards.
"Astro" Bob King is a freelance writer for the Duluth News Tribune.
