In today's news about Artemis II, after having passed the far side of the moon, on the radio and a news site it was claimed (translation mine):
Due to light conditions, they [the crew] could see things on the far side of the moon nobody has seen before.
I wonder, how could they see things that people on the Apollo missions haven't seen? Is the inclination of Artemis II's trajectory very different than the ones from the Apollo missions?
The Apollo missions were planned for
good visibility during the landing approach, meaning the Sun would be between 7 and 20 degrees behind the LM
A landing just after dawn was chosen to limit the temperature extremes the astronauts would experience.
The Apollo missions landed on the near side of the moon, therefore it was lunar night on the far side of the moon.
But for Artemis II sunlight on the far side of the moon was required.
So all Apollo astronauts looked on the far side of the moon during a lunar night, but the Artemis astronauts during a lunar day.
Its farthest distance from Earth was expected to be 252,756 miles (406,771 km; 219,639 nmi) at 23:02 UTC, and it surpassed Apollo 13's 248,655 miles (400,171 km; 216,075 nmi) record
So the distance record to Earth was only 6600 km or 1.65% more.
But the closest approach of about 4,067 miles (6,545 km; 3,534 nmi)
Aposelene altitude 122.4 km (66.1 nmi; 76.1 mi) Apollo 12
The distance to the surface of the Moon was much greater.
I have heard many television commentators make similar statements this past week, and it bothers me. If carefully worded, the statement can be technically true, but it is misleading.
On Earth, we see only one hemisphere of the moon at any given time: the "near side". However, because of several factors called libration, the exact hemisphere facing the Earth wobbles a little. Over time, the amount of the moon that can be seen from Earth is a little more than one hemisphere. Some parts of the far side (near its border with the near side) have therefore been already seen by humans on Earth. These are not the features being discussed by commentators.
The Apollo landings needed to be on the near side of the moon, so they could stay in radio contact with Earth ground stations. (Relay satellites were not invented yet.) They also wanted full sunlight to give the astronauts maximum illumination. Thus, the missions happened during "full moon" phase on Earth, with the near side towards the Sun. However, this meant that the far side was away from the Sun, too dark for the astronauts to see features on the far side.
The Artemis II flyby happened during a waning gibbous phase, meaning most of the near side was lit. This also meant that a slight crescent of the far side was also lit. The features on this crescent of the far side had not been previously seen by astronauts, and that's what the commentators are talking about.
IMO it would have been more spectacular to perform the Artemis II mission during a new moon, which would have made the entire far side illuminated and visible. NASA has made a big deal about the oblique sunlight of the actual mission creating shadows that can help reveal textures. Meh.
It's important to note that since Apollo, multiple uncrewed spacecraft have imaged the moon, most notably the Lunar Reconnaissance Orbiter, which launched in 2009 and is still being used. It has imaged the entire surface, both near and far side, in direct and oblique sunlight, and at higher resolutions than any images from Artemis II. Indeed, its images led to the discovery of water ice at the south pole that is the motive to use the Artemis program to put a moon base there. So the "features never seen before" already have been imaged.
The carefully worded claim "features never seen before by human eyes" is technically true. Apollo missions didn't see these features, and the LRO and other satellites aren't human eyes. But I do feel the claim misleads people into thinking that we didn't know these features existed; we already had the pictures.
