Advanced Composition Explorer
A NASA spacecraft to study the composition of the solar wind and cosmic rays, launched 1997 August. It is stationed in a halo orbit around the L1*Lagrangian point 1.5 million km sunwards of the ...
atmosphere
A gaseous envelope gravitationally bound to a celestial body; in the case of the Earth, with an average composition, by volume, of 79% nitrogen, 20% oxygen, 0.03% carbon dioxide, and traces of rare ...
aurora
An emission of light from the Earth's high atmosphere, caused principally by oxygen atoms or nitrogen molecules that are excited by electrons accelerated within the magnetosphere. The visible aurora ...
auroral oval
A high-latitude ring of more or less permanent aurora, girdling the geomagnetic pole at a distance of 2000–2500 km under quiet geomagnetic conditions. There are two ovals, one in either hemisphere, ...
bow shock
The shock wave in front of an object moving through a gas or liquid medium. The most familiar solar-system example is the shock-wave front between the magnetic field of a planet and the solar wind. ...
carbon dating
The determination of the age of an organic object from the relative proportions of the carbon isotopes carbon-12 and carbon-14 that it contains. The ratio between them changes as radioactive ...
Cluster
A fleet of four ESA satellites to investigate the interaction between the solar wind and the Earth's magnetic field. The first two, named Salsa and Samba, were launched in 2000 July, followed in ...
comet
A small body, composed of ice and dust, in orbit around the Sun. The name derives from the Greek kometes, meaning ‘long-haired’. Comets are thought to exist in vast numbers in the Oort Cloud and ...
corona
A series of coloured rings in the sky that surround the Sun or Moon, caused by the diffraction of light by small water droplets.
corona
1 An extremely hot (about 2 million K), highly ionized gas surrounding the Sun. Certain other stars also have coronae. The Sun's corona is visible at total eclipses as a white region extending out to ...
coronal hole
A region in the Sun's corona of very low density, about 100 times less than that of coronal active regions. Coronal holes show up as apparent voids in X-ray images or, at the limb, by an absence of ...
corpuscular radiation
1 Any particles (i.e. protons, electrons, neutrons, atomic nuclei, ions, and atoms) emitted at high speed from a star or other object, as for example in the solar wind. Material can also be lost in ...
cosmic radiation
A variety of high‐energy particles (mainly protons (92%) and alpha particles (6%) ) that bombard the Earth from outer space.
CUTLASS
(Co-operative UK Twin Located Auroral Sounding System)A pair of backscatter radar systems for studying the interactions between the solar wind, the magnetosphere, and the ionosphere. The radars are ...
earthshine
A faint illumination of the dark part of the Moon when it is a thin crescent, caused by sunlight reflected from the Earth; also known as earthlight. The effect is popularly termed ‘the old Moon in ...
EISCAT
(European Incoherent Scatter)An international radar system that studies the interaction between the solar wind and the Earth's magnetosphere and ionosphere. The main radar transmitters are located ...
Genesis
A NASA project to collect charged particles from the solar wind and return them to Earth. It was launched in July 2001 and returned in September 2004.
geomagnetic field
The Earth's magnetic field shows variability on all time-scales, ranging from nanoseconds to millions of years. Most transient variations are of external origin, reflecting interactions between the ...
heliosphere
The region of space around the Sun within which the solar wind flows. The heliosphere is thought to be about 100 AU in radius, and is bounded by the heliopause, beyond which interstellar gas exerts ...
Interkosmos
A Russian-based cooperative science space programme. It was established by the USSR in 1967 with members of Eastern European and other communist nations; each state financed its own experiments ...
