Matter that is produced whenever a fundamental particle is created, to comply with the laws of conservation of matter and energy. Every time fundamental particles are created, antiparticles must also be created. Antiparticles have exactly the same characteristics as their particles, except that they have the opposite charge as their particles.

If antimatter exists in the Universe, it must be well separated from matter or the two would annihialte. Current theories mostly assume that there was a slight excess of matter over antimatter in the very early Universe. The mutual annihilation of particles and antiparticles caused the Universe to become dominated by the surviving residue of matter.

Also known as peculiar A stars, a group of stars with magnetic fields thousands of times stronger than the Sun’s. The strong magnetic fields cause elements such as europium, chromium and silicon to concentrate on their surfaces, causing the stars’ spectral features to vary as the stars rotate.

The point in the orbit of a celestial body, such as a planet or comet, that is furthest from the Sun.

Asteroid 1862, diameter 1.4 km, discovered by K. Reinmuth in 1932. It is the prototype of the Apollo group of asteroids, whose orbits cross that of the Earth.

The first manned Moon Landing. Neil Armstrong touched down on the Moon on July 20, 1969 at 20:17 UT. Over six hours later, Armstrong placed his left foot on the Moon’s surface and declared to a television audience of a billion, “That’s one small step for a man, one giant leap for mankind.” Buzz Aldrin followed him 15 minutes later. Armstrong and Aldrin then collected lunar samples, took pictures and set up seismic, solar wind and laser-ranging experiments. They spoke with President Nixon via telephone and unveiled a plaque celebrating Apollo’s achievements “for all mankind.” They returned to their craft after two hours and 31 minutes on the surface, joining Michael Collins who had remained in the command module. After returning to the Earth’s atmosphere, they splashed down in the South Pacific on July 24.

The third intended Apollo moon-landing mission. Fred Haise, James Lovell and Jack Swigert embarked on April 11, 1970. Almost 56 hours into the flight, an explosion shut down two fuel cells and began to leak oxygen into space. The astronauts used the Lunar Module LM engines to fire them around the Moon and back toward the Earth, shut down the damaged command module and retreated into the LM. They then survived the next 86 hours by switching everything off except the environmental control and communication systems. Ice formed inside the spacecraft as temperatures dropped to freezing. Mission control helped improvise a carbon dioxide scrubber when exhaled gases threatened to poison them. They returned to the command module after reaching Earth and splashed down after almost six days in space.

An American space programme, which in 1969 successfully achieved its objective: a manned landing on the Moon. The programme consisted of 17 missions in all. Numbers 1 to 6 were unmanned test flights and Apollo 13 was aborted following an explosion on board, though the astronauts were returned safely to Earth. Six Moon landings took place between 20 July 1969 and 11 December 1972. The astronauts collected samples of lunar rocks and soils weighing a total of nearly 400 kilograms, and took many photographs both on the surface and from lunar orbit. A variety of scientific experiments were carried out on the surface of the Moon, including ones to detect cosmic rays and the solar wind. The Apollo craft consisted of three modules: the Command Module CM, the Service Module SM and the Lunar Module LM. The Command and Service Modules CSM remained in lunar orbit with one astronaut on board while the other two astronauts made the descent to the Moon’s surface in the Lunar Module. The descent stage was left on the Moon when the astronauts returned to lunar orbit by means of the ascent stage, and rejoined the Command and Service Modules. The Service Module was jettisoned shortly before re-entry into the Earth’s atmosphere.

Apollo	Astronauts	Landing date	Landing site
11	Armstrong, Aldrin, Collins	20 July 1969	Mare Tranquillitatis
12	Conrad, Bean, Gordon	19 November 1969	Oceanus Procellarum
14	Shepard, Mitchell, Roosa	5 February 1971	Fra Mauro
15	Scott, Irwin, Worden	30 July 1971	Hadley Rille
16	Young, Duke, Mattingly	21 April 1972	Cayley-Descartes highland region
17	Cernan, Schmitt, Evans	11 December 1972	Taurus-Littrow region

The United States space program which brought the first human beings to the Moon.

On January 27, 1967, the primary crew for Apollo 1 were simulating a countdown on internal power when a spark from the wires set fire to the interior of their capsule. The fire spread rapidly, and the inward-opening door made it impossible for the crew to escape. They died within minutes. To prevent a tragedy like that from happening again, pure oxygen was replaced with a mixture of nitrogen and oxygen, the command module was equipped with more fire-resistant materials, and the escape hatch was redesigned so it could be opened from the inside.

Apollo 4,5 and 6 were unmanned flights in which the equipment for reaching the moon was tested. Apollo 7 was a manned flight in October 1968. A crew of 3 spent 10 days in Earth’s orbit.

Apollo 8 set off on December 21, 1968, with crewmembers William Anders, Frank Borman and James Lovell. They were the first human beings to leave Earth’s orbit and travel to the far side of the Moon. They orbited the Moon 10 times in 20 hours. During that time, they beamed back television pictures of their view from space and read a Bible passage from Genesis over the television. They returned to Earth on December 27, 1968,

Apollo 9, with crewmembers Dave Scott, Rusty Schweickart and Jim McDivitt launched in 1969. On March 3, while in Earth orbit, Scott and Schweickart flew a lunar module LM, and later completed a spacewalk in new spacesuits.

In May 1969, Apollo 10 completed the final dress rehearsal for the lunar landing. Tom Stafford and Eugene Cernan, in the LM Snoopy, descended to only nine miles from the lunar surface while John Young orbited the moon.

Neil Armstrong, Edwin “Buzz” Aldrin, and Michael Collins, the crew of the Apollo 11, blasted off for the Moon on July 16, 1969. Armstrong and Collins moved into the lunar module, Eagle, once they were in orbit. On Sunday, July 20, the Eagle landed in the Sea of Tranquility. Armstrong took his first step onto the Moon over six hours later.

Apollo 12 returned to the Moon in November 1969, landing in the Ocean of Storms. In April 1970, an explosion on Apollo 13 put the crew at risk, but they were able to return safely to Earth. Ten months later, Apollo 14, commanded by Alan Shepard, touched down on the Fra Mauro Highlands.

Budget cutbacks caused Apollo 18, 19 and 20 to be cancelled. This left only three more chances of visiting the Moon. These missions used an improved LM which could carry more equipment and could remain on the surface for up to three days, and a battery-power lunar rover vehicle which allowed crews to travel much further. The last Apollo mission, Apollo 17, blasted off from the Taurus Littrow Valley on December 14, 1972. Eugene Cernan was the last human being to set foot on the Moon.

A joint US-Soviet space mission launched in 1975. Soyuz 19 lifted at 12:08 UT on July 15,1975. Seven hours and 22 minutes later, an Apollo spacecraft followed it. Both spacecraft arrived in the same orbit and established visual contact after more than 50 hours of maneuvers. After docking, astronauts Stafford and Slayton sealed themselves into the docking module. The remaining hatch separating the two crews was then opened and Soyuz commander Leonov stretched out his arm and clasped Slayton’s. The embrace was witnessed by television viewers around the world. The next joint US-Russian docking flight did not occur until 1995.

A joint US/Soviet space project in July 1975 in which an Apollo programme Command and Service Module docked with a Soviet Soyuz space station in Earth orbit at an altitude of 225 kilometres. The two teams of astronauts were able to visit each other’s craft and they performed a number of experiments jointly.

An adjective used in conjunction with astrophysical quantities as in apparent magnitude to mean as perceived by an observer on Earth or at a particular locality. Calculations or corrections may be required to deduce the absolute value.

The luminosity of a star or other astronomical object as it appears to an observer on Earth. The apparent luminosity depends on both the actual energy output of the object and its distance.

Apparent visual magnitude is a star’s brightness to the eye. Ancient astronomers developed a brightness scale ranging from one to six; the brightest stars being first magnitude and the faintest, sixth magnitude. The scale was refined by modern astronomers so that a star of first magnitude is exactly 100 times brighter than a star of sixth magnitude. Objects that are brighter than magnitude one are assigned negative magnitudes. Fainter objects, invisible to the naked eye, have progressively larger magnitudes.

A measure of the relative brightness of a star or other celestial object as perceived by an observer on Earth. Apparent magnitude depends on both the absolute amount of light energy emitted or reflected and the distance to the object. The smallest numbers correspond to the greatest brightness. To encompass very bright objects, the scale is extended to zero and on to negative numbers. For example, the apparent magnitude of the full Moon is -12.6 and that of the planet Venus at its brightest is -4.7. The term apparent magnitude, without further qualification, is usually taken to mean apparent visual magnitude, the relative brightness as seen over the visible part of the spectrum. See also: magnitude, absolute magnitude, photometry.

The position on the celestial sphere an object would be in if it were observed from the centre of the Earth. It is calculated by correcting the observed position for the effects of atmospheric refraction, diurnal aberration and diurnal parallax.