The first portrait of a human being onto another world, showing his face: Neil Armstrong back inside Eagle after the historic moonwalk, 16-24 July 1969

Vintage chromogenic print on fiber-based paper, printed 1969, numbered "NASA AS 11-37-5528" (NASA MSC) in red in top margin, with "A KODAK PAPER" watermark on verso, 20,3 x 25,4 cm

The members of the Apollo 11 crew conducted themselves with a cool-even laconic-professionalism throughout the mission, to the general despair of newspaper headline writers.
Once the more difficult and novel aspects of the flight had been successfully completed however, a change of mood became evident.
The photograph shows a tired and elated Armstrong smiling with satisfaction after regaining the cabin of the LM following his and Aldrin’s exploration of the lunar surface.

From the mission transcript before the liftoff from the Moon:
114:22:23 McCandless (Mission Control): We’d like to say from all of us down here in Houston and really from all of us in all the countries in the entire world, we think that you’ve done a magnificent job up there today. Over.
114:22:46 Armstrong: Thank you very much.
114:22:48 Aldrin: It’s been a long day.

Literature:
LIFE, 11 August 1969; National Geographic, December 1969, pg. 746; Moon: Man’s Greatest Adventure, Thomas, ed., pg. 209; Apollo: The Epic Journey to the Moon, Reynolds, pg. 146.