As Apollo 11 started across the near side of the Moon, essentially in the equatorial plane and going east to west, Armstrong called, ‘‘Apollo 11 is getting its first view of the landing approach. We’re going over the Taruntius crater.’’ This crater, some 30 nautical miles in diameter, was in the northwestern part of the Sea of Fertility. It had a flat floor and a complex of several low peaks at its centre. ‘‘The pictures and maps brought back by Apollos 8 and 10 have given us a very good preview of what to look at here – it looks very much like the pictures, but like the difference between watching a real football game and watching it on television.’’ The clarity of viewing by eye-ball far exceeded that of the pictures. ‘‘There’s no substitute for actually being here.’’
‘‘We’re going over the Messier series of craters now, looking vertically down on them,’’ announced Aldrin, ‘‘and we can see good-sized blocks in the bottom of
Messier-A.” This was a pair of craters, each about 6 nautical miles across. They had originally been known as Messier and Pickering, after French and American astronomers, but Pickering had been renamed Messier-A. The craters were notable for having produced a pair of divergent bright streaks that ran westward across the dark plain of the Sea of Fertility for a distance of about 60 nautical miles.
“And there’s Secchi,” added Armstrong. Named after an Italian astronomer, it was 14 nautical miles in diameter.
Having crossed the Sea of Fertility, they started across the Sea of Tranquility, where they were to land. “We’re going over Mount Marilyn at the present time,’’ said Aldrin. “That’s the ignition point.’’
“Jim’s smiling,’’ pointed out McCandless. Jim Lovell had named the peak after his wife.
Tom Stafford, who had reconnoitred this route on Apollo 10, explained to Jan Armstrong how the astronauts had assigned names they would readily remember to various features that they intended to use as landmarks. However, such names were unofficial. In 1961 the International Astronomical Union had specified how features were to be named: the flat plains would be named in Latin after states of mind, using the traditional (if inaccurate) terms oceanus (ocean), mare (sea), sinus (bay), lacus (lake) and palus (marsh); mountain ranges were to be named after their terrestrial counterparts; and craters were to be named after deceased scientists. In 1967 the IAU had met to discuss the assignment of specific names, but decided to defer naming until the next meeting in 1970. Meanwhile, of course, the crews of Apollo 8 and Apollo 10 had named some features. As the Moon was progressively transformed from an object studied by astronomers using telescopes into a world that was being explored by astronauts, it was inevitable the astronomers would lose ‘ownership’ over it.
As soon as the spacecraft appeared around the limb, the Manned Space Flight Network had begun to track it, to determine its orbit independently of the onboard navigation. ‘‘Our preliminary tracking data for the first few minutes shows you in a 61.6 by 169.5 orbit,’’ McCandless announced. At this time, the spacecraft was at an altitude of 127 nautical miles, and climbing towards apolune. The period of the elliptical orbit was 2 hours 8 minutes 37 seconds.
Armstrong called out landmarks on the line of approach. ‘‘We’re going over Maskelyne, Boot Hill, Duke Island, Maskelyne-W – our yaw-around checkpoint – and Sidewinder.’’ Boot Hill, Duke Island and Sidewinder were unofficial names. The crater Maskelyne, named after an Astronomer Royal, was 13 nautical miles in diameter. Maskelyne-W followed the IAU convention that small craters close to a ‘named’ crater were identified by a letter postfix. The astronauts had dubbed it the Wash Basin. ‘‘Now we’re coming up to the terminator. The landing site is well into the dark.’’ By design, they had arrived prior to sunrise at the landing site. The landing was 26 hours away, and with the Sun rising at 12 degrees per day, it would be some 10 degrees elevation at the time of landing. On the question of the colour of the surface, Armstrong noted that it had appeared tan in the vicinity of the subsolar point, where the Sun shone straight down, and had then faded to grey until, at the terminator, it was ashen.
While the spacecraft had been behind the Moon, its telemetry was taped and, on AOS, was downloaded to Earth. The flight controller responsible for the CSM promptly studied the performance of the SPS during the burn, and noticed that the tank pressure for the nitrogen used to drive the propellant feed valves of Bank-B was anomalously low, although it was holding steady now. Bank-A appeared nominal. McCandless sought clarification. “When you have a free moment, could you give us an onboard readout of nitrogen tank Bravo.”
“We’re showing the pressure in tank Bravo to be 1,960 psi, something like that,” replied Aldrin, “and Alfa is about 2,250 psi.’’ These matched the telemetry, which showed corresponding values of 1,946 and 2,249. Now able to eliminate a telemetry problem, the flight controller delved deeper into the record to further characterise the problem, with a sense of urgency because the SPS engine would soon be called upon to perform the second burn of the lunar orbit insertion sequence.
As the spacecraft passed over the Ocean of Storms on the darkened part of the near side, McCandless made an unscheduled request. “We’ve got an observation you might make – if you’ve time. There’s been a lunar ‘transient event’ reported in the vicinity of Aristarchus.” An astronomer had suggested that the astronauts take a look at the 22-nautical-mile-wide crater Aristarchus which, although far to the north of the ground track, should be on the near side of the horizon at their current altitude of 167 nautical miles. For many years, astronomers had been actively watching for transient lunar phenomena such as glows in the night. Of course, the sightings were disputed. The best evidence was by the Russian astronomer Nikolai A. Kozyrev of the Crimean Astrophysical Observatory on 3 November 1958, when he secured a spectrogram of a ‘red glow’ that persisted for almost an hour near the central peak of the large crater Alphonsus, but even this was disputed. The Ranger 9 probe was sent diving into this crater in 1965 to investigate the possibility that the peak was a volcano. In fact, the origin of lunar craters was disputed: the traditional theory was they were volcanic calderas, but there was mounting evidence that they were made by large impacts.
‘‘With Earthshine, the visibility is pretty fair,’’ Aldrin pointed out.
‘‘Take a look, and see if you see anything worth noting up there,’’ McCandless said.
‘‘You might give us the time that we’ll cross 45°W,’’ called Aldrin, ‘‘and then we’ll know when to start searching for Aristarchus.”
McCandless had the times at hand, ‘‘Aristarchus should become visible over your horizon at 077:04, and the point of closest approach will be at 077:12.’’
As they passed due south of the crater, Collins reported, ‘‘I’m looking north up toward Aristarchus now, and there’s an area that is considerably more illuminated than the surrounding area.’’
‘‘It does seem to be reflecting some of the Earthshine,’’ Aldrin said. In fact, as Aristarchus has a high albedo (it is one of the brightest features on the near side) it was visible to telescopic observers. ‘‘There is one wall of the crater that seems to be more illuminated and – if we are lining up with Earth correctly – that does seem to place it near to the ‘zero phase’.’’ He suspected that the ‘bright patch’ was merely selective reflection of Earthshine.
“Is that the inner or the outer wall?” McCandless asked. “And can you discern any difference in colour of the illumination.”
“That’s an inner wall of the crater,” Aldrin confirmed. “There doesn’t appear to be any colour.’’
“Have you used the monocular on this?’’ McCandless persisted.
“We’ll give it a try if we have the opportunity next time around,’’ Armstrong promised. “We’re in the middle of lunch.’’
“We’ve about 6 minutes remaining until LOS,’’ McCandless called 15 minutes later, “and to enable us to configure our ground lines, we’d like to know if you’re still planning to have the television up at the start of the next pass.’’
“It never was our plan to do so,’’ noted Armstrong, recalling a debate during mission planning, “but it’s in the flight plan and so I guess we’ll do it.’’ A telecast was to begin as soon as communication was re-established following the far-side passage.
Passing behind the Moon for the second time, the astronauts connected up the television camera. “Which window are we going to use,’’ Aldrin asked, “so that I can figure out how to put the monitor on?’’
“I suppose the best one would be the centre window,’’ Armstrong said. “Don’t you think?’’
“Probably,’’ Aldrin said.
Armstrong, being practical, decided, “Let’s get into attitude, and see what we think.’’
“We’re not going to have much of a television show unless we get high-gain,’’ pointed out Aldrin. Once they were in attitude, he steered the antenna to point at where Earth should rise over the lunar horizon.
“We’ve had AOS by Goldstone,’’ announced Riley publicly. “Television is now on.’’
“We have a good clear television picture,’’ reported McCandless. “We can see the horizon against the blackness of space, and without getting into the question of greys and browns, it looks, at least on our monitor, sort of a brownish-grey.’’
“That’s a good, reasonable way of describing it,’’ agreed Aldrin. “I’d say we’re about 95°E, coming up on Smyth’s Sea.’’
“For your information, your altitude is about 92 nautical miles,’’ McCandless advised.
“We’ll try and pick up some of the landmarks that we’ll be seeing during our approach to the powered descent,’’ Aldrin explained.
“Smyth’s Sea doesn’t look much like a sea,’’ observed Collins. “The area that is devoid of craters, of which there’s not very much, is sort of hilly looking.’’
“We’re now at about 83°E, which is equivalent to 13 minutes before ignition,’’ said Armstrong.
“Of course, you’ll be considerably lower at the initiation of powered descent,’’ McCandless pointed out.
“We’re coming up on the Foaming Sea,’’ said Collins.
The main wall display in the Mission Operations Control Room showed a map of the spacecraft’s ground track across the Moon, with a moving symbol showing its progress. “We show you coming up on landmark Alfa 1 shortly,’’ McCandless noted.
“Alfa 1 isn’t large,” Collins pointed out, “but it’s extremely bright.” The small bright-rayed crater designated A-1/11 was one of four craters in a featureless part of the small dark plain known as the Foaming Sea. If provided sextant sightings on landmarks of known positions, program P22 would calculate the parameters of the spacecraft’s orbit and, if so instructed, update the state vector. Alternatively, with knowledge of the orbit, it could process the sightings to calculate the positions and elevations of the terrain. Collins was to track this crater as practice for supporting the subsequent powered descent by Eagle.
“We show you over the Sea of Fertility now,’’ McCandless prompted.
“The crater that’s in the centre of the screen now is Webb,’’ explained Aldrin. “We will be looking straight down into it about 6 minutes before the powered descent.’’ This crater, named after a British astronomer, was 11 nautical miles in diameter and was located on the eastern part of the Sea of Fertility. Aldrin moved the camera to a side window to show an oblique view to the south of their ground track.
“We’re getting a beautiful picture of Langrenus, with its rather conspicuous central peak,’’ noted McCandless.
“The Sea of Fertility doesn’t look very fertile to me,’’ mused Collins. “I don’t know who named it.’’
Armstrong speculated, “It may have been named by the gentleman this crater was named after – Langrenus – who was a cartographer to the King of Spain and made one of the early reasonably accurate maps of the Moon.’’ On Earth, his wife at home exclaimed, “So that’s what he was doing with the World Book in his study!’’ In 1645 Michel Florent Van Langren (Langrenus in Latin) issued the first map of the Moon to include names, although his successors rejected most of his names. The crater later named in his honour was 74 nautical miles across. In fact, the Sea of Fertility was named by the Jesuit priest Giovanni Battista Riccioli, who, working with Francesco Grimaldi in Italy, published a map of the Moon in 1651. They had their own craters near the western limb.
Aldrin changed window again in order to view straight down, and announced, “Crater Secchi.’’
“We’re getting a good view of the track leading into the landing site now,’’ said McCandless.
“This is very close to the ignition point for the powered descent,’’ Aldrin noted. “We’re passing Mount Marilyn, that triangular-shaped mountain in the centre of the screen at the present time, with crater Secchi-Theta on its far northern edge.’’ And then, as another crater came into view, “The bright, sharp-rimmed crater at the right edge of the screen is Censorinus-T. We’re now at the 1-minute point in the powered descent.’’ Continuing west, they passed from the Sea of Fertility onto the Sea of Tranquility.
“For your information, your altitude is 148 nautical miles,’’ said McCandless.
“I’m unable to determine altitude at all by looking out the window,’’ Collins remarked.
“I bet you could tell if you were down at 50,000 feet,’’ quipped McCandless.
“There’s a good picture of Boot Hill,’’ said Aldrin. “That’ll be 3 minutes 15 seconds into the descent.’’ Then, “That’s Duke Island to the left. The biggest of the
craters near the centre of the picture right now is Maskelyne-W. It’ll be a position check in the descent at about 3 minutes 39 seconds; it’ll be our downrange position check and crossrange position check prior to the yaw-around to acquire the landing radar. Past this point, we’ll be unable to see the surface until very near the landing area.’’ Nearing the terminator, the illumination highlighted the shallow undulations on the Sea of Tranquility, in particular a pair of sinuous rilles whose snake-like appearance had prompted their names of Sidewinder and Diamondback. “The landing point is just barely in the darkness.’’ The crater Moltke was named after the nineteenth-century Prussian strategist Count H. K.B. von Moltke, who arranged for the publication in 1874 of a map of the Moon prepared by J. F.J. Schmidt. The crater was 3.5 nautical miles in diameter, and situated about 28 nautical miles southeast of where Apollo 11 hoped to land. The eastern crest of its raised rim was catching the Sun’s rays, but the rest of it was still in darkness.
Collins, who was doing the ‘flying’, had observed that after he set the docked vehicles into a given attitude, the main axis tended to drift (despite counteracting thruster firings) towards vertical with the LM on the bottom, and he thought this instability might be a gravity-gradient effect produced by the mascons. ‘‘It looks like that LM just wants to head down towards the surface.’’
‘‘That’s what the LM was built for!’’ McCandless retorted.
Now in darkness, Aldrin switched off the television, and communication with the spacecraft lapsed as the crew prepared for the second manoeuvre of the lunar orbit insertion sequence, which was to occur on the far side of the Moon at the end of the current revolution.
Meanwhile, at home
It was an excellent telecast, lasting over 30 minutes. Joan Aldrin had returned from the hairdresser in time to watch it. She had been accompanied by Jeannie Bassett who, driving, had tried in vain to evade the photographers. As the lunar landscape passed by, Joan lost interest. When they crossed the terminator into darkness, she said, ‘‘Well, now I just have to get through the next 24 hours.’’ Lurton Scott had taken the Collins children to the cinema while Pat Collins and Clare Schweickart reviewed newspaper coverage of the mission; they broke off to watch the telecast. After watching, Jan Armstrong spread a large-scale map on the floor and reviewed the features on the approach route and in the immediate vicinity of the landing site.