Navigation and Measurements in Space
Especially important for science fiction worlds, knowing the correct terms and concepts used in space is crucial for generating a sense of realism. The list of words and definitions below should help get you started as well as potentially providing you with ideas.
- Ablation: when the atmosphere melts away the surface of an incoming meteorite.
- Accretion: the accumulation of gas and dust into stars and planets
- Albedo: the reflective index of an object. The higher the albedo of an object, the more it reflects light from nearby sources such as a sun, and the easier it is to see in space.
- Altitude: The angular distance of an object above the horizon
- Antipodal point: a point on the direct opposite side of a planet
- Apastron: the point of greatest separation between two stars in a binary system
- Aphelion: The point in the orbit of a planet or other celestial body where it is farthest from the sun.
- Apogee: The point in the orbit of a moon or satellite where it is farthest from earth.
- Axis: a theoretical line straight through the center of rotation of an object.
- Azimuth: the angular distance of an object around or parallel to the horizon from a zero point.
- Bar: a unit of measurement for atmospheric pressure. One bar equals 0.987 atmospheres, 1.02 kg/cm2, 100 kilopascal, and 14.5 lbs/square inch.
- Blueshift: a shift in an objects spectrum toward the blue end of the light spectrum. Blueshift indicates an object is moving towards an observer. The larger the blueshift the faster the movement.
- Celestial equator: a hypothetical line dividing the celestial sphere into a northern and southern hemisphere.
- Celestial poles: the north and south poles of the celestial sphere.
- Celestial sphere: a hypothetical sphere surrounding the earth.
- Cepheid variable: a variable star whose light pulses at regular intervals.
- Declination: the angular distance of an object from the celestial equator.
- Density: the amount of matter within a given volume.
- Doppler effect: the apparent change in wavelength of either sound or light emitted by an object in relation to an observer’s position when those relative positions are changing. The Doppler effect can be used to calculate an object’s speed and direction. An approaching object will have a shorter wavelength (blue) while a receding object will have a longer wavelength (red).
- Eccentricity: a measure of how much an orbit differs from a perfect circle.
- Ecliptic: a hypothetical line traced by the sun as it moves through the earth’s sky during the year.
- Equinox: the two points the Sun crosses the celestial equator during its’ yearly path. The equinoxes mark the start of the Spring and Autumn seasons.
- Escape velocity: the required speed necessary for an object to escape the gravitational pull of a planet or other body.
- Extragalactic: anything outside the galaxy
- Geosynchronous orbit: An orbit where the orbital velocity matches the rotational velocity of the orbited body or planet. An object in geosynchronous orbit will remain above the same location on the planet or body below.
- Inclination: a measure of the tilt of a planet’s orbital plane in relation to Earth.
- Kelvin: a temperature measure often used in sciences. Absolute zero, the temperature where all molecules stop their motion, is reached at 0 degrees Kelvin. Water freezes at 273 degrees Kelvin.
- Light year: the distance light can travel in a year, approximately 5.8 trillion miles.
- Luminosity: the amount of light emitted by a star.
- Meridian: a hypothetical circle through the North and South poles of the celestial equator.
- Nadir: the point directly beneath an object.
- Obliquity: the angle between a body’s equatorial and orbital plane.
- Orbit: the path of a celestial body as it moves through space.
- Parsec: a unit of distance equal to 3.26 light years.
- Perigee: the point in an orbit at which an object is closest to the Earth.
- Perihelion: the point in an orbit at which an object is closest to the Sun.
- Radial velocity: the movement of an object towards or away from a stationary observer.
- Redshift: a shift in an object’s spectrum toward the red end of the light spectrum. Redshift indicates an object is moving away from an observer. The larger the redshift the faster the movement.
- Retrograde orbit: an orbit of a satellite that is opposite to the direction of planet’s rotation.
- Universal time: the standard measure of time used in space which corresponds to Greenwich Mean Time.
- Zenith: a point directly overhead from an observer.
