Apollo 8 entered lunar orbit on the morning of December 24, 1968. For the next 20 hours, the astronauts circled the Moon, which appeared out their windows as a gray, desolate landscape. They took photographs, scouted future landing sites and on Christmas Eve read from the Book of Genesis to television viewers back on Earth. They also photographed the first Earthrise as seen from the Moon. Apollo 8 proved the ability to navigate to and from the Moon and gave a tremendous boost to the entire Apollo program.
The Apollo 8 mission, like the mission before it, involved little scientific experimentation during flight. However, before and after flight, researchers studied several physiological systems. Investigators evaluated the crewmembers' cardiovascular response to exercise pre- and post flight, using a bicycle ergometer and other exercise equipment, and studied the response of the cardiovascular system to weightlessness using lower body negative pressure and passive stand tests.
The clinical aspects of crew health and safety were investigated by performing medical examinations and conducting inflight medical monitoring as evaluation methods. Investigators also studied musculoskeletal changes, clinical disorders in space due to imbalance between bone formation and resorption, inflight weight loss and inflight caloric intake. Another important aspect of crew health and safety is the protection against radiation, so one experiment focused on analyzing natural and man-made radiation encountered in space, with the goal of finding ways of limiting the astronauts' exposure to radiation. Vestibular system experiments not only aided researchers in gaining a better understanding of the mechanisms that provide balance and coordination, but also contributed to alleviating the symptoms of space adaptation syndrome.
The endocrinology experiments sought to understand biochemical changes in crewmembers by studying the balance of fluids and electrolytes, regulation of calcium metabolism and the adaptation of metabolic processes to the space environment.
Scientists also utilized specific laboratory data to assess the health status of the astronauts prior to their commitment to space flight. This allowed them to detect and identify any alterations in the normal functions of the immunological and hematological systems which could be attributed to space flight exposure and to evaluate the significance of these changes relative to a person's continuing participation in space flight missions. Biochemistry data, when integrated with the data obtained from a complete history and physical examination of each crewmember, permitted an objective assessment of crew physical status.
The detection of potentially pathogenic microorganisms was attempted, so that associated medical problems could be identified early and preventive measures could be established. These objectives included the identification of medically important microorganisms recovered from ill crew members to aid in diagnosis and treatment.