Who Was William Henry Pickering?

William Henry Pickering (1858–1938) was an American astronomer celebrated for his careful studies of the Moon, planets, and comets. He earned his early training at Harvard and later became a professor of astronomy at MIT, where he taught and conducted research for many years. Pickering also played a role in the early development of what would become the Jet Propulsion Laboratory (JPL), applying his knowledge of celestial mechanics to space exploration projects. Among his many discoveries, he found Saturn’s moon Phoebe and several comets, and he was an early adopter of photography for astronomical research. Beyond his discoveries, Pickering had a creative streak—he developed the famous 12-feature visual acuity test for the Moon, turning lunar observation into a fun challenge for amateur astronomers. His work earned international recognition and inspired generations to look more closely at the night sky.

The Pickering Test: From Easiest to Hardest

Pickering’s visual test was simple: the more lunar features you could spot—first with the naked eye, then with binoculars or a telescope—the sharper your eyesight and observing skills. Think of it as a game: how far up the ladder of difficulty can you climb?

For your convenience, you can download these features in a SkySafari skylist format, that you can import directly into the app, by simply downloading it to your device and opening it.

Level 1: Easy Targets

1. Copernicus – A prominent, bright impact crater with a complex system of rays.
2. Nectaris (D) – The dark mare, or basaltic plain, of Mare Nectaris.
3. Humorum (D) – The dark Mare Humorum.
4. Kepler – A bright, small crater with a noticeable ray system.

If you can see these four features, you’ve passed the “easy round.”

Level 2: Intermediate Challenges

5. Gassendi region – The region centered around the Gassendi impact crater
6. Plinius region – A specific region near the crater Plinius.
7. Vaporum (D) – The dark Mare Vaporum.
8. Lubiniezky region – A region near the crater Lubiniezky.

At this level, you’ll likely need binoculars or a telescope to pick out the central peaks clearly.

Level 3: The Real Test

9. Medii (D) – A narrow, dark line near the crater Medii.
10. Sacrobosco region (D) – A dimly shaded area near the crater Sacrobosco.
11. Huygens region (D) – A small, dark spot north-east of the Apennine Mountains.
12. Riphaen Mountains – A very difficult feature to see with the naked eye, even for observers with excellent vision.

These four make up the “expert round”—few observers see them all, even with good telescopes.

When to Look
(Hunter’s Moon: September – October 2025)

The following dates highlight the current moon cycle, but you can take Pickering’s test during any cycle throughout the year. The Moon’s phases simply affect which features are easiest to see:

• September 21 — New Moon
  Invisible tonight—your observing challenge starts in a week.

• September 28 — First Quarter Moon
  Great for Level 1 features: Copernicus, Nectaris, Humorum, Kepler.

• October 2–4 — Waxing Gibbous
  Ideal for Level 2 and 3 features: Gassendi, Plinius region, Vaporum, Lubiniezky region, Medii, Sacrobosco, Huygens region, and Riphaen Mountains.

• October 6 — Full Moon
  Shadows are short, but brighter features like Copernicus and Kepler still stand out.

• After Full (Waning Moon)
  The features reappear in reverse order, lit from the opposite direction. Sometimes the change in lighting makes them even easier to see.

How to Take the Test

• Step 1: Try with your naked eyes. This is how Pickering intended the test to begin.

• Step 2: Use binoculars or a telescope. Optical aids let you climb higher on the difficulty ladder.

• Step 3: Record your results. Keep a log of which features you’ve seen and under what conditions. Those notes will help if you later decide to complete the Astronomical League program.

Beyond Pickering: Earn a Pin for Your Observations

If you enjoy Pickering’s lunar challenge, you can take it a step further with the Astronomical League’s Lunar Observing Program. This program encourages observers to log and sketch 100 features of the Moon, from major seas and craters down to fine details. Many of Pickering’s 12 test features are also on the Lunar Observing Program list. That means by working through his challenge, you’ll already be on your way to earning the Astronomical League’s Lunar Observing certificate and pin. Think of Pickering’s test as both a fun eyesight challenge and a stepping stone toward an official recognition of your lunar observing skills.

Keep Looking Up

Pickering’s 12 lunar features turn the Moon into more than just a pretty sight—they transform it into a challenge, a test, and a way to sharpen your observing skills. And if you want to take things further, you’ll already be on the path toward the Astronomical League’s Lunar Observing Program.

Clear skies and happy moon-gazing!