Anomalous cosmic rays (ACRs):

Cosmic rays that originate from the interstellar space beyond the heliopause and differ from other types of cosmic rays in that they are singly charged, contain more helium than protons, and contain more oxygen than carbon.


A unit of angle corresponding to 1/3600th of a degree; 1/60th of an arcminute. An arcsecond is approximately the size of a dime viewed from a distance of 1 mile.


Advanced Radio Interferometry between Space and Earth.


Aeronautics and Space Engineering Board.


Study of the origin, evolution, and distribution of life in the universe.

Astronomical unit (AU):

A basic unit of distance equal to the separation between Earth and the Sun, about 150 million km.


A glow in a planet’s ionosphere caused by the interaction between the planet’s magnetic field and charged particles from the Sun.


The separation between telescopes in an interferometer. The largest baseline determines the finest detail that can be discerned with an interferometer.

Bow shock:

Also, “bow wave,” where the interstellar flow is slowed, heated, and deflected by the solar wind. In a planetary magnetosphere, the bow shock is the boundary at which the speed of the solar wind abruptly drops as a result of its approach to the magnetopause.

Brayton power conversion:

An open-cycle power-conversion system that uses a thermodynamic cycle featuring heat addition and rejection at constant pressure. This cycle represents the idealized behavior of the working fluid in a gas turbine engine.


Electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus.


The energy per unit mass of a spacecraft once it gets away from Earth’s gravitational field. If C3 > 0, the launch vehicle sends the spacecraft directly to its destination—outside Earth’s sphere of influence. If C3 < 0, the launch vehicle sends the spacecraft into Earth orbit, and the spacecraft then has to use its own propulsion to leave Earth’s sphere of influence. The units of C3 are km2s−2.

Celestial mechanics:

A term for the application of physics, historically Newtonian mechanics, to astronomical objects such as stars and planets.

centiSievert (cSV):

One-hundredth of a Sievert, the SI unit of radiation dose equivalent, which indicates what dose of x-rays or gamma rays produce the equivalent damage.


The right- or left-handedness of an asymmetric molecule. Absence of symmetry on reflection.


Cosmic infrared background radiation.


The Cosmic Background Explorer, a NASA mission launched in 1989 to study the cosmic background radiation from the Big Bang.

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