2009.02.28 00:44:11

Rick Fienberg

That's not a typo in the title. I really meant to write "moonth" rather than "month." After all, where does the word "month" come from? From the Moon! Our satellite takes a "moonth" — actually 29½ days — to go through a complete cycle of phases.

As February wanes, the Moon is a waxing (growing) crescent, getting thicker from night to night. On the 27th it's very close to brilliant, starlike Venus during evening twilight, as shown in the accompanying illustration from Sky & Telescope magazine.

On March 4th the Moon reaches first quarter, which many people call a half Moon because exactly half the Earth-facing side is illuminated. (Do you know which half? If you're in the Northern Hemisphere, it's the right half. But if you're south of the equator, it's the left half!)

Next time the Moon reaches first quarter, in early April, it'll be time for 100 Hours of Astronomy! Indeed, those of us who had a hand in scheduling this global astro-extravaganza chose the dates April 2-5 in part because the Moon will be near first quarter that weekend. At this phase the Moon is highest in the sky around sunset and makes an ideal target for early-evening viewing. Not only that, but at first quarter the Moon's mountains, valleys, and craters stand out especially well along the terminator — the boundary between lunar day and night — because sunlight comes from the side (as seen from Earth) and casts especially strong shadows. No doubt the Moon will be the life of the star party during 100 Hours of Astronomy.

The Moon was the first celestial target that attracted Galileo's telescopic attention in 1609. What he saw there came as quite a shock — maybe not to Galileo himself, but certainly to almost everyone else. Since antiquity scientists had maintained that the Moon, being a heavenly body made of some otherworldly heavenly stuff, was perfectly smooth. (I've never understood how the ancients explained the dark mottling of the lunar surface: the patches we see forming the man in the Moon, or the rabbit in the Moon, or some other fanciful shape. Supposedly these were regions of different densities, but shouldn't a perfectly round heavenly globe be perfectly uniform too?) As you can see for yourself in even the smallest telescope, the Moon isn't smooth at all — its surface is covered with peaks and valleys and cracks and craters. It's a real world, not an idealized sphere.

With his very first telescopic observations of the night sky, Galileo literally united heaven and Earth. Unfortunately, this set him on a collision course with the Roman Catholic Church, which didn't take kindly to an upstart young scientist challenging centuries of orthodoxy.

Here are a few photos of the Moon that I shot through a small refractor; from right to left, they show the Moon in its waxing-crescent, first-quarter, and waxing-gibbous phases. Those last two are what you'll see during 100 Hours of Astronomy.

Here's a little-known fact: Galileo wasn't actually the first person to look at the Moon through a telescope. That honor appears to go to Thomas Harriot, an Englishman who drew some sketches of the magnified Moon several months before Galileo. But Harriot never published his results, whereas Galileo wrote a popular book, Sidereus Nuncius (The Starry Messenger), to share his discoveries with the world. (The above drawing of the Moon is taken from the book.) So Galileo is the one who gets the credit for introducing the telescope to science.

Speaking of British astronomy, a recent survey conducted by U.K. organizers of the International Year of Astronomy 2009 revealed that nearly a third of British citizens are likely to associate Galileo's name with wine (think Gallo), a ship (think galleon), or fashion (I'm not sure about this one) before associating it with astronomy!

And speaking of small telescopes, I'd like to call your attention to another IYA2009 cornerstone project I'm involved in: the Galileoscope. It's a high-quality, low-cost telescope kit developed especially for IYA2009 to make the wonders of telescopic astronomy more accessible to the world's children. Easily assembled without tools in minutes, the Galileoscope is a 50-mm-diameter achromatic refractor of focal length 500 mm that comes with an eyepiece of focal length 20 mm (magnification 25x) and a 2x Barlow lens (yielding 50x when used with the supplied eyepiece). With the Galileoscope anyone can see the celestial wonders that Galileo first glimpsed 400 years ago and that still delight stargazers today: lunar craters and mountains, four moons circling Jupiter, the phases of Venus, and Saturn's rings.

Significantly, the instrument accepts almost any optical accessory that has a standard 1.25-inch (31.75-mm) barrel, and it attaches to a standard photo tripod (not included). Even more significantly, the kit costs just U.S. $15 each plus shipping, or U.S. $12.50 each plus shipping for orders of 100 or more (for example, from astronomy clubs, science museums, and other centers of astronomy education and outreach). Check it out at www.galileoscope.org!