Footprints on the moon: use your telescope to explore the apollo landing sites.
THE APOLLO MISSIONS to the Moon were the most audacious trips ever taken. Nine crews of three men each left the gravitational bond of Earth and traversed the 384,000-kilometer (240,000-mile) gulf that separates our planet from its nearest neighbor. Apollo will be remembered for all time as the moment when humans first left the comfort and safety of Earth to set foot upon another world. The photographs that the astronauts made and the samples that they collected from the lunar surface are still incredibly valuable today.
Our current understanding of the Moon seems so complete that it is perhaps difficult to imagine a time when even the origin of lunar craters was still the subject of hot scientific debate. In 1968, a year before Apollo 11 touched down on the lunar surface, there was considerable evidence that craters formed as the result of impacting asteroids or comets, but some scientists still argued that craters were vast volcanoes. Even the ages of the biggest features, the lunar "seas," called maria, were highly uncertain. In the months leading up to the launch of Apollo 11, two of the most senior lunar scientists published papers suggesting that the mare lavas were only 600 million years old, in disagreement with other estimates that pegged them as 3 to 4 billion years old.
Apollo would ultimately provide the necessary evidence to settle these issues for good.
APOLLO 11 at Tranquillity Base On July 20, 1969, Neil Armstrong and Buzz Aldrin approached the lunar surface in their landing module, Eagle. Although a Ranger spacecraft, a Lunar Orbiter, and a Surveyor lander had already mapped the area in detail, Armstrong was greeted with the unexpected sight of a boulder-strewn landing site complete with a small impact crater. If Eagle landed as planned, it would have crashed. But with his spacecraft's fuel nearly exhausted, Armstrong steered the lunar module to a smooth area downrange and set down safely.
Armstrong had trouble finding a landing spot, and you will have a hard time finding it too. The reason for your difficulty is the reason that the area was picked in the first place--it looks bland and smooth. That said, the general region of Tranquillity Base, as the landing site was dubbed, is easy to find.
The Apollo 11 rock samples collected by Armstrong and Aldrin were eagerly studied when they were brought to Earth. Scientists discovered that Mare Tranquillitatis was made of 3.6-billion-year-old basaltic lava and the Moon rocks contained no evidence of water or air. Nor did they contain any of the much feared "moon bugs." Indeed, the samples confirmed that the Moon is a dry, lifeless world.
APOLLO 12 South of Copernicus
A mere four months after Armstrong, Aldrin, and Collins returned to Earth, Apollo 12 was on its way back to the Moon. Pete Conrad achieved a precise landing 163 meters (535 feet) from Surveyor 3, a robotic spacecraft that had bounced to a stop there 31 months earlier. Again the target site was a relatively bland stretch of mare, but this time situated about 400 km south of the magnificent ray-crater Copernicus. The lavas here turned out to be similar to those at Tranquillity Base, but approximately a half billion years younger.
On one of their two moonwalks, the crew collected bright ray material that had been ejected during the formation of Copernicus. Dating this sample showed that Copernicus formed about 810 million years ago--old, but not ancient like the surrounding mare. The crew also brought back to Earth pieces of Surveyor 3 for study. Scientists found that these parts had changed very little, demonstrating that erosion on the Moon is an extremely slow process and, as such, the lunar surface hardly changes even throughout millions of years.
APOLLO 14 at Fra Mauro
Following the failure and dramatic safe return of Apollo 13, Apollo 14 touched down on the northern edge of the crater Fra Mauro, roughly 135 km east of the Apollo 12 landing site. But this was not a smooth mare surface--mission commander Alan Shepard had to pilot Antares over a gently rolling, rough target area, which he did to perfection.
Geologists back on Earth regarded Fra Mauro as one of the most important places on the Moon to collect lunar samples. The Fra Mauro material is actually ejecta from the formation of the gigantic (1,200-km-wide) Imbrium impact basin--one of the most significant events in the Moon's history. The samples returned by Apollo 14 showed that Imbrium formed about 3.85 billion years ago. Because Imbrium ejecta are widespread on the nearside of the Moon, they serve as a crucial time marker. Many lunar formations can be dated as being pre- or post-Imbrium, thus dividing the Moon's history into two epochs.
APOLLO 15 at Hadley Rille
With three successful landings on relatively open ground, mission planners allowed Apollo 15 to land at a risky but geologically complex and visually dramatic site. Swooping in over the Apennine Mountains, Dave Scott and Jim Irwin plunked their lunar module, Falcon, down onto a narrow plain between soaring mountains and an ancient lava channel known as Hadley Rille. Compared to the earlier missions, Apollo 15 carried more scientific instruments and a lunar rover--a small, lightweight electric car that allowed the astronauts to roam five times farther afield than previous crews.
The Apennine Mountains towering over the landing site are part of the curved rim of the giant Imbrium impact basin. Apollo 15 astronauts drove up to the base of the mountains to sample rocks suspected to have originated deep within the lunar crust before being deposited on the surface as impact ejecta. On another outing they drove to the 1.5-km-wide, relatively steep-sided Hadley Rille. The rille was formed by rapidly moving lava flows that built up levees along its 80-km length. Dating the rocks that the astronauts collected showed that the rille's lavas erupted 3.3 billion years ago, and the rocks from the uplifted Apennines are 4.5 billion years old--the oldest Moon rocks ever collected.
APOLLO 16 Visits Descartes
The Moon has two basic types of terrain: smooth, relatively young lava plains and ancient, heavily cratered highlands. Apollo 16 was the only mission to land deep within the highlands. The scientific goals were clear: find out what the highlands are made of, and whether the highlands had different volcanism than the maria. The target site was a region of peculiar topography near the crater Descartes, about 250 km west of the large crater Theophilus.
Descartes is an old formation with an unusual deposit of hilly material extending 40 to 50 km to the north. Before Apollo 16 returned samples, lunar experts thought that this hummocky terrain was of volcanic origin. But as soon as Apollo 16 landed, astronaut John Young looked out his lunar-module window and saw that the scientists back home had been wrong.
A 6-inch telescope will reveal the knobby material that seems to spill northward out of Descartes. It really does look like a massive lava flow, but as Young observed, it's not. The Apollo 16 samples weren't volcanic rocks, but rather breccia, conglomerations of rock fragments resulting from the tremendous energy of an impact. We can find breccia on Earth too in places like Meteor Crater in Arizona. There is still some uncertainty as to where the Descartes breccia came from, but many scientists believe the source was either the Nectaris impact basin or the much more distant Imbrium basin.
APOLLO 17 in the Taurus-Littrow Valley
Apollo 17 landed in a scenic valley nestled among the towering Taurus Mountains, near the southeastern shore of Mare Serenitatis. The valley floor consists of mare basalt lava, but the region also has some darker material that had been interpreted as possibly younger volcanic ash. While Apollo 15 had provided evidence of the oldest stages of lunar history, scientists hoped that astronauts at Taurus-Littrow would document relatively recent volcanism. But the researchers were surprised again. Astronaut Jack Schmitt discovered some unusual orange volcanic glassy rocks, formed by explosive eruptions, but the glass beads that gave the soil its color turned out to be 3.7 billion years old! Indeed, all of the Moon rocks collected are vastly more ancient than most of Earth's surface, which, on average, is only a half billion years old.
Apollo 17 landed on a patch of mare immediately north of South Massif. If you have good observing conditions you may notice a dusting of light material extending from South Massif onto the mare floor. Amazingly, this is material that avalanched down the slope of South Massif when ejecta from the formation of the crater Tycho struck the mountain. By dating Apollo 17's rock samples, scientists determined that Tycho formed only 109 million years ago.
Before Apollo 17 reached the Moon the American government had already canceled Apollos 18, 19, and 20, and the most glorious episode of exploration in human history was heading toward a quiet end. Perhaps in another dozen years or so, new landing sites will be selected and astronauts will return to the Moon. This time it won't be just to visit, but to live and work there for extended periods. Perhaps you will be among them. Until then, you can use your telescope to visit the Apollo landing sites and explore the places where "men from the planet Earth first set foot upon the Moon."
Finding the Apollo Landing Sites
APOLLO 12 and 14 Because safety was still the main selection criterion, Apollo 12's landing site is in a somewhat monotonous area with few landmarks that make it easy to pinpoint in a telescope. You can find the unremarkable area where Apollo 12 and Surveyor 3 set down by looking southeast of the 38-kilometer-wide crater Lansberg. Alan Shepard piloted Apollo 14 to a landing 135 km to the east of Apollo 12, on the gently rolling hills north of the old, ruined 101-km-diameter crater Fra Mauro.
APOLLO 16 The only mission to land on the lunar highlands, Apollo 16 came to rest some 90 km north of the battered crater Descartes, which is located northeast of the large, flat-floored crater Abufeda.
APOLLO 15 The Apollo 15 landing site is one of the easiest to find and one of the most interesting to observe in a telescope. Look at the area between the prominent Apennine Mountains and the 82-km-wide crater Archimedes. Very close to the mountain scarp is Hadley Rille. The Apollo crew landed near the north end of the rille, just where it bends toward the west.
APOLLO 17 To find the site of the final Apollo landing, look for the small crater Dawes in the gap where maria Serenitatis and Tranquillitatis meet. Now shift your telescope's field of view up along the shore of Serenitatis and turn east just past the first big peak, Argaeus Mountain. There is a rough circle of bright peaks with a big one in the center. That summit is known as South Massif, and Apollo 17 touched down in the patch of mare material just between South Massif and North Massif, immediately to the north.
APOLLO 11 With your telescope working at 100x to 150x, look along the southern shore of Mare Tranquillitatis for the nearly twin, 30-km-wide craters Sabine and Ritter. Then, move eastward along the Tranquillitatis shore to the small (6-km diameter), bright crater Moltke. The Apollo 11 landing site is just north-northwest of Moltke on the Tranquillitatis lavas. The next step in locating the site requires you to pick out three small craters (2 to 4 km wide) in a line east of Sabine and Ritter and north of Moltke. From west to east these craters are named after the Apollo 11 crew: Aldrin, Collins, and Armstrong. Tranquillity Base lies almost midway between Moltke and Collins. Interestingly, Surveyor 5 set down a little west of Collins, towards Aldrin, and Ranger 8 crashed into the Moon about 30 km due north of Armstrong. This area is a junkyard for old spacecraft.
TELESCOPES FOR MOONGAZING
Unlike just about everything else in the night sky, the Moon is bright and chock full of easy-to-see detail. As a result, almost any telescope will give you an impressive view. That said, observing the Moon often involves fairly high magnifications, so quality optics and a tracking mount are important considerations. An instrument in the 4- to 6-inch aperture range on an equatorial mount equipped with a motor drive (like the Maksutov pictured here) is an excellent choice. A telescope of this size has enough resolution to show craters as small as 1 mile (1.6 km) across, yet is portable enough that one person can easily transport and set it up.
There are several fine Web sites that a dedicated Moon explorer will find helpful.
For highly detailed maps of the Apollo landing sites.
The absolute mother lode of Apollo mission information is found at the Apollo Lunar Surface Journal Web site.
Finally, to enjoy a daily dose of lunar geology, there's Charles Wood's Lunar Photo of the Day Web site.
Each month CHARLES A. WOOD takes Sky & Telescope readers on a guided tour of the lunar surface with his column, Exploring the Moon. A noted lunar scientist, Chuck is the author of The Modern Moon: A Personal View.
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|Title Annotation:||observing the moon|
|Author:||Wood, Charles A.|
|Date:||Jan 1, 2007|
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