Apollo 17 in the context of "Apollo program"

Apollonius is a lunar impact crater located near the eastern limb of the Moon. It lies in the region of uplands to the west of Mare Undarum and northeast of the Sinus Successus on the Mare Fecunditatis. It was named after Greek mathematician Apollonius of Perga. It is southwest of the crater Firmicus, and north of Condon.

The outer rim of Apollonius is somewhat worn and is overlain by a pair of small craters (including Apollonius E) across the western wall. The nearly flat interior floor has a low albedo and has been covered by lava. It lacks a central peak or notable small craters across the bottom.

The Blue Marble is a photograph of Earth taken on December 7, 1972, by Harrison Schmitt aboard the Apollo 17 spacecraft on its way to the Moon. Viewed from around 29,400 km (18,300 mi) from Earth's surface, a cropped and rotated version has become one of the most reproduced images in history.

In the original NASA image, named AS17-148-22727 and centered at about 26°19′49″S 37°25′13″E / 26.33028°S 37.42028°E / -26.33028; 37.42028 with the South Pole facing upwards, The Blue Marble shows Earth from the Mediterranean Sea to Antarctica. This was the first time the Apollo trajectory made it possible to photograph the south polar ice cap, despite the Southern Hemisphere being heavily covered in clouds. In addition to the Arabian Peninsula and Madagascar, almost the entire coastline of Africa and most of the Indian Ocean are clearly visible, a cyclone in the Indian Ocean is also visible, the South Asian mainland and Australia is on the eastern limb, and the eastern part of South America lies on the western limb.

The age of Earth is estimated to be 4.54 ± 0.05 billion years. This age represents the final stages of Earth's accretion and planetary differentiation. Age estimates are based on evidence from radiometric age-dating of meteoritic material—consistent with the radiometric ages of the oldest-known terrestrial material and lunar samples—and astrophysical accretion models consistent with observations of planet formation in protoplanetary disks.

Following the development of radiometric dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. The oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old. Calcium–aluminium-rich inclusions—the oldest known solid constituents within meteorites that are formed within the Solar System—are 4.5673 ± 0.00016 billion years old giving a lower limit for the age of the Solar System.

Human spaceflight (also referred to as crewed spaceflight, or more historically manned spaceflight) is spaceflight with a crew or passengers aboard a spacecraft, often with the spacecraft being operated directly by the onboard human crew. Spacecraft can also be remotely operated from ground stations on Earth, or autonomously, without any direct human involvement. People trained for spaceflight are called astronauts (American or other), cosmonauts (Russian), or taikonauts (Chinese); and non-professionals are referred to as spaceflight participants or spacefarers.

The first human in space was Soviet cosmonaut Yuri Gagarin, who launched as part of the Soviet Union's Vostok program on 12 April 1961 at the beginning of the Space Race. On 5 May 1961, Alan Shepard became the first American in space, as part of Project Mercury. Humans traveled to the Moon nine times between 1968 and 1972 as part of the United States' Apollo program, and have had a continuous presence in space for 25 years and 30 days on the International Space Station (ISS). On 15 October 2003, the first Chinese taikonaut, Yang Liwei, went to space as part of Shenzhou 5, the first Chinese human spaceflight. As of December 2025, humans have not traveled beyond low Earth orbit since the Apollo 17 lunar mission in December 1972.

The Artemis program is a Moon exploration program led by the United States' National Aeronautics and Space Administration (NASA), formally established in 2017 via Space Policy Directive 1. The program is intended to reestablish a human presence on the Moon for the first time since the Apollo 17 mission in 1972, with a stated long-term goal of establishing a permanent base on the Moon. This will facilitate human missions to Mars.

Two principal elements of the Artemis program are derived from the now-cancelled Constellation program: the Orion spacecraft (with the ESM instead of a US-built service module) and the Space Launch System's (SLS) solid rocket boosters (originally developed for the Ares V). Other elements of the program, such as the Lunar Gateway space station and the Human Landing System, are in development by government space agencies and private spaceflight companies, collaborations bound by the Artemis Accords and governmental contracts.

The atmosphere of the Moon is a very sparse layer of gases surrounding the Moon, consisting only of an exosphere. For most practical purposes, the Moon is considered to be surrounded by vacuum. The elevated presence of atomic and molecular particles in its vicinity compared to interplanetary medium, referred to as "lunar atmosphere" for scientific objectives, is negligible in comparison with the gaseous envelopes surrounding Earth and most planets of the Solar System, and comparable to their exospheres. The pressure of this small mass is around 3×10 atm (0.3 nPa), varying throughout the day, and has a total mass of less than 10 metric tonnes. Otherwise, the Moon is considered not to have an atmosphere because it cannot absorb measurable quantities of radiation, does not appear layered or self-circulating, and requires constant replenishment due to the high rate at which its gases are lost into space.

Roger Joseph Boscovich was the first modern astronomer to argue for the lack of atmosphere around the Moon in his De lunae atmosphaera (1753).

Lunar regolith is the unconsolidated material found on the surface of the Moon and in the Moon's tenuous atmosphere. Lunar soil typically refers to only the finer fraction of lunar regolith, which is composed of grains 1 cm in diameter or less, but is often used interchangeably. Lunar soil differs substantially in properties from terrestrial soil. Lunar dust is even finer regolith than lunar soil, with grain sizes less than one millimeter.

Lunar regolith is primarily the result of mechanical weathering. Continual meteoric impacts and bombardment by solar and interstellar charged atomic particles of the lunar surface over billions of years ground the basaltic and anorthositic rock, the regolith of the Moon, into progressively finer material. This situation contrasts fundamentally to terrestrial soil formation, mediated by the presence of molecular oxygen (O₂), humidity, atmospheric wind, and a robust array of contributing biological processes.