Introducing the first entirely new globe of the Moon's surface in more than 40 years.
I've always been fascinated with cartography, and I've got a particular soft spot for globes. I love 'em all: Earths with raised relief or now-obsolete borders, celestial spheres old and new, globes of Mars and Venus. When I was very young I had a glow-in-the-dark Moon globe that doubled as a coin bank. I've even made myself a crude set of four spheres portraying Jupiter's Galilean satellites.
So you can imagine my joy when, last week, the first samples of the new Sky & Telescope Moon globe arrived. With a diameter of 12 inches (30 cm), it's the standard size for most others these days. In fact, Replogle Globes has been making and marketing a lunar likeness for more than 40 years. Then why, you might ask, was another one needed?
For one thing, the Replogle version doesn't show the real Moon. Instead, it's an airbrushed map derived from the U.S. Air Force's Lunar Astronautical Charts. Chances are you've never heard of these — that's because they were created during the 1960s in support of NASA's nascent lunar-exploration program.
Make no mistake: the LAC series was meticulously compiled and executed. But Replogle's adaptation doesn't look anything like what you'd see in the eyepiece — there's little distinction between the dark lunar maria and the brighter highlands, for example.
That old globe, while serviceable, just wasn't satisfying. So for years I've been prowling around for a suitable database of lunar photos to make a new one. The Clementine orbiter, launched in 1994, got pole-to-pole coverage, but its images lacked enough resolution and snap. Then came Japan's highly successful Kaguya spacecraft, which orbited from 2007 to 2009, but its images had issues with coverage and lighting angles.
Eventually, the Lunar Reconnaissance Orbiter Camera, launched aboard a NASA spacecraft in 2009, made this new Moon globe possible. You're probably familiar with LROC's high-resolution views of the Apollo landing sites. But it's the camera's wide-angle channel that really caught my attention, as evidenced by this half-gigabyte portrayal of the lunar near-side.
The pieces finally started coming together about a year ago. Mark Robinson, leader of the LROC team, told me the instrument was just completing a global mapping effort with 100-m resolution. The final mosaic consisted of more than 15,000 images acquired between November 2009 and February 2011, with the Sun shining on the surface at incidence angles between 55° and 70° at the equator, lighting favorable for identifying surface features. Several months of back-and-forth ensued to deal with small gaps and imaging artifacts.
Cartographic specialist Trent Hare of the U.S. Geological Survey helped get the LROC data into the right projection — a daisy-shaped image — that would be used to make each hemisphere.
Meanwhile, imaging editor Sean Walker had been perusing the LROC images and likewise came to the conclusion that the time was right for a next-gen lunar globe — one with exquisite, magnifying-glass detail. Joel Toner, Sky & Telescope's publisher, gave the green light for the project to proceed. From the get-go, we wanted something that looked like the Moon (which, in reality, is quite dark) and yet could be labeled clearly with feature labels. So, once we had the two "daisies," it fell to Walker's imaging wizardry to tweak the balance and contrast for both realism and usefulness.
Aarrgh — those #&@$%# labels! How were we going to decide what would be identified and what wouldn't? I started with the USGS's master list of lunar features and selected all the craters with a diameter of at least 75 km (on the near side) and 85 km (on the far side). Then I grabbed the names of every dark feature — all the lunar real estate called mare, lacus, sinus, or palus — along with lots of well-known smaller craters, rilles, peaks, valleys, and spacecraft landing sites. Walker, along with editors Alan MacRobert, Tony Flanders, and Robert Naeye, added even more "must have" features — a collection that kept getting longer and longer.
By the time we were done, the list had grown to 850 names! The task of adding those to the daisies fell to Gregg Dinderman. Placing them accurately on maps that would eventually be sliced, diced, and glued onto a round ball was a tedious, frustrating Adobe Illustrator marathon. Thank you, Gregg! And we fussed a lot with those labels, checking and rechecking every one. ("Is the correct spelling Tsander or Zander?" "Bel’kovich or Belkovich?" "Fitzgerald or FitzGerald?")
I'm thrilled with (and very proud of) the final result — the first entirely new globe of the lunar surface in more than 40 years. It's emblematic of Sky & Telescope continuing efforts to produce astronomical products that are accurate, timely, and useful. I hope you get a chance to see one soon, and I'd welcome your feedback.
By the way, this might not be the only lunar globe that gets produced from LRO data. For example, the LROC original is so detailed that making a globe 32 inches across — the largest in Replogle's repertoire — isn't completely wacky. But I'll save that story for a future posting.