More than 7,000 satellites, both active and inactive, orbit the Earth. All are human-made except for one — the moon. It's the sole orb circling our planet that nature intended. While you can marvel at the moon anytime, full moons make especially good occasions. The one coming up on Wednesday, October 20th is named the Hunter's Moon, while the indigenous Anishinaabe of the Great Lakes region call it the Falling Leaves Moon. Both names are fitting.

Sometimes, passing clouds will refract the moon's light and create temporary halos (large rings) or smaller, colorful coronas. If you regularly check the sky on full-moon nights you may see these and other compelling naked-eye phenomena. Contributed / Bob King
Sometimes, passing clouds will refract the moon's light and create temporary halos (large rings) or smaller, colorful coronas. If you regularly check the sky on full-moon nights you may see these and other compelling naked-eye phenomena. Contributed / Bob King

Because the moment of full moon occurs around 10 a.m. Central Time Wednesday, the moon will appear nearly as full on Tuesday night the 19th as it will on the 20th. Like getting two full moons for one.

Do you remember last month's Harvest Moon? Successive moonrises then were just 15-20 minutes apart instead of the usual hour because of the moon's shallow angle to the horizon at rising. In the olden days, these quick ascents provided farmers with extended light through the evening for bringing in the harvest. We'll experience nearly the same effect this month during the Hunter's Moon, with moonrises about 20 minutes apart for the next few nights.

During the September full moon I tried a little experiment. I wanted to see if I could read a book by moonlight. First, I took a 20-minute walk to dark-adapt my eyes as much as possible. Then I cracked open my Superior Hiking Trail guide to a random page and angled the book toward the moon for the fullest illumination. As long as my eyes were within a several inches of the page I found that indeed I could read (slowly) by moonlight.

WDAY logo
listen live
watch live
Newsletter signup for email alerts

I tried the experiment again last night with the 2-days-before-full moon. I even upped the ante and used the local newspaper, which is printed in smaller type. THAT was a challenge! But I was able to stumble along even if I couldn't read every word. I think I'll try again in December and January, when the full moon stands highest and the snowy landscape reflects and amplifies its light. I could use the help.

The pupil (center) is where light enters the eye. Our pupils dilate (open up) in darkness to let in more light and contract in bright light. Contributed / Alexageev, CC BY-SA 3.0
The pupil (center) is where light enters the eye. Our pupils dilate (open up) in darkness to let in more light and contract in bright light. Contributed / Alexageev, CC BY-SA 3.0

As we age, the size of our pupil shrinks. The pupil is the round, black circle in the center of the iris through which light passes to the retina. In children it can dilate to about 8 mm (0.3-inch), but in older adults it may only open to 4-5 mm (0.2-inch). A narrower pupil allows in less light, the reason older folks can't see as well in the dark compared to kids. It also makes book-reading by moonlight more challenging. I'm certain a 10-year-old would have had better success at reading that newspaper!

The full moon always lies opposite the sun in the sky, rising when the sun is setting. Contributed / Stellarium
The full moon always lies opposite the sun in the sky, rising when the sun is setting. Contributed / Stellarium

A full moon by definition lies 180° opposite the sun in the sky, so it rises right around the time the sun sets. To make sure you don't miss the moment the Hunter's Moon peeps over the horizon, check your moonrise time here.

At the same time the full moon comes up, you'll also also notice a long, gray band fringed in orange rising all along the eastern horizon. This is the Earth's shadow cast on the atmosphere. Both moon and shadow lie opposite the sun, so you'll see our natural satellite shining from squarely within this gray specter. The orange fringe is reddened sunlight scattered back to our eyes by the upper atmosphere and called the Belt of Venus.

As seen in this photo taken in 2009, this week's full Hunter's Moon will rise with Earth's shadow (gray band) and the orange-pink Belt of Venus. Contributed / Bob King
As seen in this photo taken in 2009, this week's full Hunter's Moon will rise with Earth's shadow (gray band) and the orange-pink Belt of Venus. Contributed / Bob King

Once the moon rises and rounds out, you'll notice how much higher it climbs during the night compared to a summer full moon. Once again, that goes back to the full moon lying opposite the sun. In October, the sun is rapidly sinking southward and getting lower in the sky, while the full moon is doing the opposite: moving north and quickly climbing. When the sun reaches its lowest point on the winter solstice, the full moon will shine triumphantly in the same place the sun stood on the first day of summer. I love the rhythm of this seesaw relationship between the two brightest objects in the sky.

A fun and easy project at full moon is to try and identify as many lunar seas (maria) as you can. This map-diagram will help. Contributed / NASA, GSFC, Arizona State University
A fun and easy project at full moon is to try and identify as many lunar seas (maria) as you can. This map-diagram will help. Contributed / NASA, GSFC, Arizona State University

At full moon, the sun illuminates the entire nearside of the moon. Without shadows, the lunar landscape looks flat and pasty compared to other phases, when the sun shines off to the side of the moon (rather than directly over it). Side-lighting makes craters and peaks cast long, luscious shadows.

One thing you can see well at full moon are the vast lava plains called lunar seas or maria. These big, gray patches were once enormous craters punched out by larger asteroids. They later filled with lava from the lunar mantle, which gives them a relatively smooth, dark appearance, the reason long-ago skywatchers likened them to seas.

The lunar farside — the approximately 50 percent we can't see from Earth — also has phases. They're complementary to what we see on the nearside. When the moon is full, it's new moon on the farside. The moon is no different from the Earth in that regard — half in daylight and half in the shadow of night.

I hope you have clear skies tonight (Oct. 19), tomorrow or the following night, so you can relish the moonlight. Maybe you'll even borrow a bit of that light to read by.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.