Glossary

Despite the enormous efforts of the specialists in the various topics included in this issue of UNAM Internacional to inform us clearly and simply about their work, many astronomical concepts and terms remain difficult for most of us to understand. Therefore, we undertook the task of selecting those hard terms that our guest editorial team—Dr. Omaira González Martín, Dr. Yilen Gómez Maqueo Chiu, and Dr. Willian Lee Alardín—has explained to facilitate reading.

Absorption line: Occurs in the spectra of astronomical sources like stars, when a small region of the spectrum (line) has less emission. It is through measuring the absorption lines that we can know what a star is made up of.

Accretion: Process by which celestial objects gain mass through gravity.

Active galaxies: Those that emit a tremendous amount of energy from their nucleus—far more than can be explained by the combined light of their stars. This excess energy is produced by non-stellar processes, typically due to the presence of a supermassive black hole at the galactic center. Non-active galaxies are those without these active nuclei.

Angular resolution: The smallest angle that a telescope or an astronomical instrument can distinguish between two nearby objects.

Arcsecond: Unit of angular measurement equal to 1/3600 of a degree.

Astrophysical jet: An astronomical phenomenon where outflows of matter are emitted as extended beams along the axis of rotation.

Baryonic acoustic oscillations: Time fluctuations in the density of the visible matter. They happened at the universe’s beginning, right after the Big Bang.

Biosignature: A characteristic, element, molecule, substance, or feature that can be used as evidence of past or present life.

Blazar: A type of active nucleus whose relativistic jet is aligned with Earth’s line of sight.

Blueish photons: Light emitted or reflected that displays a predominant hue in the blue range.

Cepheid: A star with periodic variable brightness. Measuring the period can be used to determine the distance to the star, because its period depends on how luminous the star is.

Cosmic Microwave Background (CMB): The microwave emission that fills out all the observable universe. It is a relic of the formation of the universe.

Cosmic rays: Charged particles with extremely high energy that come from space.

Dark energy: A proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe.

Dark matter: Invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation, but it does interact gravitationally due to its mass.

Diffraction grating: An instrumental component that separates light into the different wavelengths of the electromagnetic spectrum.

Electromagnetic spectrum: It is composed of all the radiation of different energy: from the long radio waves, through infrared light, visible light, ultraviolet light, X-rays, and up to the energetic gamma rays.

Electronvolt: Energy unit defined as the kinetic energy acquired by an electron when accelerated through an electric potential difference of 1 volt.

Event horizon: Theoretical boundary surrounding a black hole beyond which gravity becomes so intense that nothing, not even light, can escape.

Exoplanet: Extrasolar planet; refers to a planet that is orbiting a star that is not the Sun.

Extreme universe: The most violent, energetic, and exotic phenomena and environments in the cosmos, where physical conditions (temperature, density, or gravity) far exceed anything we can experience or recreate on Earth.

Galaxy kinematics: Area of astronomy studying the motion of stars, gas, and dark matter within galaxies.

Gamma rays: Electromagnetic waves with a very samll wavelength.

Gamma-ray bursts: Result of explosions of supernovas or of the collision of two neutron stars. They are the most energetic phenomena in the universe.

Hubble constant: Cosmological parameter that quantifies the universe’s current expansion rate.

Infrared: Electromagnetic radiation with wavelengths between 0.75 microns and 300 microns.

Initial mass function: The distribution of stars of different mass that are formed from a molecular cloud through the process of star formation.

Integral field spectrograph: Allows a spectrum at each point of an image.

Interferometry: A technique  that interferes two wave fronts. From the characterization of the interference pattern information on the structure of the observed source can be obtained.

Ionized hydrogen region: An extended astronomical object where a source of radiation, typically a massive star, has ionized the hydrogen in the surrounding material. Hydrogen has lost its only electron and is thus ionized.

Ionizing radiation: A form of electromagnetic energy so high it can remove electrons from atoms or molecules.

Ionosonde: A scientific instrument that studies the ionosphere, a layer of Earth’s atmosphere. It emits radio waves toward the ionosphere and analyzes the reflected signals.

Light polarization: Property of the electromagnetic waves that describes the orientation of their oscillations.

Light year: The distance that light travels in one a year in vacuum: 9.46 trillion kilometers.

Long-slit spectroscopy: A surface with a long slit where the light of the object passes by.

Magnetomter: Instrument that measures the magnetic field.

Martian regolith: The layer of loose and fragmented material that covers the surface of Mars. It is composed of a mixture of dust, sand, and rocks.

Methanol maser: A natural microwave amplifier due to the presence of a methanol molecule that emits an intense beam of radiation.

Microquasar: A stellar system consisting in two objects where one of them is a star and the other is a compact stellar object (black hole or neutron star).

Multi-messenger astronomy: Observation and interpretation of different signals, both in the electromagnetic spectrum and particles, received from the same astronomical event.

Multi-object spectroscopy: Surface with several slits where the light of different objects passes by simultaneously.

Nebula: A large cloud of gas and dust.

Neutron star: It is formed through the collapse of a stellar core with 1 to 3 times the mass of the Sun, such that all the protons and electrons in the core are crushed into neutrons that stop the collapse.

Optical or visible light: Electromagnetic radiation emission or light that the human eye can see, with wavelengths between 380 and 750 nanometers.

Parallax: The apparent difference in position of an object as seen from different points of view, which allows the distance to the object to be measured.

PeV:  1,000,000,000,000,000 electronvolts.

Plasma: The most common state of matter in the universe, found in stars, nebulae, and the interstellar medium.

Pulsar: A highly magnetized neutron star that rotates rapidly and emits radiation in pulses at regular intervals.

Quasar: A galaxy that contains a very bright nucleus, where the feeding process of a supermassive black hole at its center produces its light. They are the brightest persistent objects in the universe. Their name quasars is a phonetical adaptation of QSO (quasi-stellar object) because they look like stars at optical wavelengths.

Radio waves: Electromagnetic waves that with wavelength of less than a millimeter to over 100 thousand meters. They are used in TV and radio broadcasting and in radio astronomical observations.

Redshift: The shift toward longer wavelengths (toward the red end of the visible spectrum) of the light emitted by a celestial object. This effect occurs because the universe is expanding: the farther away a galaxy is, the faster it is moving away from us, stretching the light along its path.

Relativistic jet: An astrophysical jet where the velocity of the outflows of matter reaches a significant fraction of the speed of light.

Relativistic speed: Velocity so high that it reaches a significant fraction of the speed of light.

Signal-to-noise ratio: A quantity that compares a useful signal’s intensity with the observation’s background noise.

Spectrometer/spectrograph: Instrument that separates light into the different wavelengths of a range of the electromagnetic spectrum.

Spectroscopy: An observational technique that studies how light interacts with matter by measuring how the light is absorbed or remitted.

Spectrum: Amount of light of an astronomical object per unit of wavelength.

Supernova: A very energetic explosion of a very massive star when it has consumed via fusion all its fuel.

Transient event: An astronomical event that can last a fraction of a second to weeks or years and that can emit electromagnetic radiation and gravitational waves. Typically it is associated with the destruction of an astrophysical object.

Transiting exoplanet: An exoplanet that eclipses its star when viewed from Earth, causing a transit or dip in brightness of the light coming from the star. This is the most successful exoplanet detection technique.

X rays: Electromagnetic waves with a bigger wavelength than that of gamma rays.

Zodiacal light: A faint, diffuse glow in the form of a band or cone visible in the night sky, caused by the scattering of sunlight off interplanetary dust particles.