Tonight’s the Full Hunter’s Moon, so be sure to spend a bit of time polishing up your moon tan with a stroll outdoors. A full moon is always directly opposite the sun in the sky and rises around sunset. For Duluth, Minn., moonrise is at 5:57 p.m. or 32 minutes before sunset. To find moonrise time for your location, click HERE and key in your city, state or country. Be sure to add one hour to the times shown to convert to Daylight Saving Time.
During other lunar phases, we only see a part of the moon because of the varying angles between Earth, sun and moon. At full phase, all three orbs are lined up. The sun shines over the Earth’s “shoulder” hitting the moon’s face square on and lighting up one whole side of the lunar globe. Just as a light shining directly in your face hides the shadows cast by your nose, cheekbones and yes, your wrinkles, so the sun shining in the moon’s face hides all shadow detail. The result: a flat, pasty, two-dimensional-looking moon.
Without shadows to reveal lunar contours and the craggy details of crater walls and mountain peaks, most amateur astronomers don’t bother looking at the full moon. Besides, it’s about the only time we can get some rest, right? But I’m here to tell you that I’ve been smitten the past few years by the spectacle of all the rayed craters that come into their own when the moon hits your eye like a big pizza pie.
Rayed craters are craters surrounded by halos of impact debris that were excavated when meteorites and asteroids struck the moon long ago. Pulverized rocks from those impacts shot out like fountains miles above the moon’s surface before falling back and blanketing the vicinity of the newly-formed craters. Some of the falling rocks were large enough to create secondary impact craters which in turn exposed more fresh crustal materials. That’s why the rays are bright compared to much of the lunar surface – the impacts that made them happened relatively recently.
Recent in astronomy is always a dubious term. In the case of rayed craters, the impacts occurred in the past billion years compared to 3-4 billion for the majority of the craters we see. Over time, exposed material on the moon’s surface darkens due to a constant pounding by subatomic particles streaming from the sun called the solar wind.
The youngest and most magnificent rayed crater is Tycho located near the “bottom” or south end of the moon. It’s only 109 million years and its rays stretch across many hundreds of miles. Tycho and the trio of Copernicus, Kepler and Aristarchus comprise the best and the biggest of the rayed craters. All can be seen with the naked eye though any pair of binoculars will make the task much easier. While shadow detail may be compromised at full moon, rays shine their brightest then.
If you own a telescope, I’m going to ask you to take the next step and examine the moon at low to medium magnification tonight. Yes, you’ll feel like you’re going blind in one eye but rest assured, it’ll be worth it. Splayed across the disk – especially the central area – are many dozens of additional rayed craters. There’s nothing like the sight of them. Centered on their respective, freshly-punched craters, I’m reminded of brilliant beacons, tiny explosions, stars and flares. What will you see? May your sky be clear tonight.