Science & history · Astronomy words
The astronomy dictionary
60 words astronomers use, chosen because they are worth knowing and not often explained, each with how to say it, what it means and why it matters. One of them is the Astronomy Word of the Day; Next word keeps going for as long as you like.
Astronomy Word of the Day
A
- Accretion uh-KREE-shun The growth of an astronomical object by collecting surrounding material.
- Albedo al-BEE-doh A measure of how much incoming radiation a surface or body reflects.
- Analemma an-uh-LEM-uh The pattern of the Sun's position when recorded at the same mean solar clock time throughout a year.
- Anorthosite uh-NOR-thuh-syte An igneous rock composed mostly of plagioclase feldspar, a group of minerals common in planetary crusts.
- Aphelion ap-HEE-lee-un The point in a body's orbit where it is farthest from the Sun.
- Asterism ASS-ter-iz-um A recognizable pattern of stars that is not itself an officially defined constellation region.
- Asteroseismology ass-ter-oh-size-MOL-uh-jee The study of stellar oscillations to learn about the interiors of stars.
- Astrometry uh-STROM-uh-tree The precise measurement of the positions and motions of celestial objects.
- Azimuth AZ-ih-muth A direction measured around the horizon, usually in degrees clockwise from north.
B
- Barycenter BAIR-ih-sen-ter The center of mass of a system of bodies.
- Baryogenesis bair-ee-oh-JEN-uh-sis A proposed process that produced an excess of baryonic matter over antimatter in the early universe.
- Bolide BOH-lyde An exceptionally bright meteor, often one that breaks apart or ends in a brilliant flash.
C
- Chondrule KON-drool A small, usually rounded mineral object that crystallized from molten or partly molten material in the early solar system.
- Chromosphere KROH-muh-sfeer A layer of the Sun's atmosphere above the photosphere and below the transition region.
- Circumpolar sur-kum-POH-ler Describing an object that stays above the horizon throughout its daily circuit for a particular observer.
- Collimation kol-ih-MAY-shun The alignment of a telescope's optical components so that they work together as intended.
- Coronal KOR-uh-nul Belonging to the corona, the thin, very hot outer atmosphere of the Sun or another star.
- Cryovolcano kry-oh-vol-KAY-noh A volcanic feature that erupts volatile-rich material such as water or icy mixtures rather than molten silicate rock.
D
- Declination dek-lih-NAY-shun The angle of a celestial object north or south of the celestial equator.
E
- Ecliptic ih-KLIP-tik The Sun's apparent annual path against the background stars, or the plane of Earth's orbit underlying that path.
- Ephemeris ih-FEM-er-iss A table, dataset, or computational representation giving a celestial object's position at specified times.
- Evection ih-VEK-shun A periodic variation in the Moon's orbital motion caused by the Sun's gravitational influence.
G
- Gegenschein GAY-gun-shyne A faint patch of sunlight scattered by interplanetary dust in the direction opposite the Sun.
- Gnomon NOH-mon The part of a sundial or related instrument that casts a shadow used for measurement.
H
- Heliopause HEE-lee-uh-pawz The boundary separating solar-wind plasma from the surrounding interstellar plasma.
- Heliophysics hee-lee-oh-FIZ-iks The science of the Sun and of how its light, particles and magnetic fields shape the space around Earth and the other planets.
- Helioseismology hee-lee-oh-size-MOL-uh-jee The study of the Sun's oscillations to investigate its interior.
I
- Interferometry in-ter-fih-ROM-ih-tree Combining waves from separate light paths or telescopes and using their interference to make measurements.
- Irradiance ih-RAY-dee-unss The power of light or other radiation arriving on a surface, for each square meter of that surface.
K
- Kilonova kil-uh-NOH-vuh A transient glow powered by radioactive decay in matter ejected by a merger involving neutron stars.
L
- Libration ly-BRAY-shun The changing orientation of the Moon as viewed from Earth, which makes it appear to rock.
- Luminosity loo-mih-NOSS-ih-tee The total power a star or other object gives off as light and other radiation, in all directions.
- Lunation loo-NAY-shun One complete cycle of lunar phases, usually measured from one new Moon to the next.
M
- Magnetar MAG-nuh-tar A neutron star whose exceptionally strong magnetic field drives distinctive high-energy activity.
- Magnetohydrodynamics mag-nee-toh-hy-droh-dy-NAM-iks The study of how electrically conducting fluids and magnetic fields affect one another.
- Mascon MASS-kon A concentration of mass associated with a positive gravitational anomaly.
N
- Nucleosynthesis noo-klee-oh-SIN-thuh-sis The production of atomic nuclei through nuclear reactions.
- Nutation noo-TAY-shun An oscillatory change in the orientation of a rotating body's axis.
O
- Occultation ok-ul-TAY-shun The hiding of a celestial object by another body passing in front of it.
- Orrery OR-uh-ree A mechanical model illustrating the arrangement and orbital motions of bodies in the solar system.
P
- Parallax PAIR-uh-laks A change in an object's apparent position caused by a change in the observer's viewpoint.
- Penumbra pih-NUM-bruh The part of a shadow where an extended light source is only partly blocked.
- Periapsis pair-ee-AP-sis The point in an orbit closest to the body being orbited.
- Perihelion pair-ih-HEE-lee-un The point in an orbit around the Sun where the orbiting body comes closest to the Sun.
- Photometry foh-TOM-ih-tree The quantitative measurement of received light from an astronomical source.
- Photosphere FOH-tuh-sfeer The visible surface of the Sun or another star, the layer from which most of its light escapes.
- Planetesimal plan-ih-TESS-ih-mul A solid body formed in a young planetary system that can contribute to the growth of planets.
- Precession pree-SESH-un A gradual change in the direction of a rotation axis or the orientation of an orbit.
R
- Refraction rih-FRAK-shun The bending of light as it passes at a slant from one material into another, such as from space into Earth's air.
- Regolith REG-uh-lith Loose material covering solid bedrock, including dust and broken rock.
- Reionization ree-eye-uh-nye-ZAY-shun The process that ionized much of the universe's intergalactic gas again after an earlier neutral period.
- Rille RIL A long, narrow trough or channel on a planetary surface, especially the Moon.
S
- Saros SAIR-oss An eclipse recurrence interval of about 18 years, 11 days, and 8 hours, corresponding to 223 lunations.
- Scintillation sin-tih-LAY-shun Rapid fluctuations in a received astronomical signal caused by an irregular intervening medium.
- Selenography sel-uh-NOG-ruh-fee The mapping and description of the Moon's surface.
- Spaghettification spuh-get-ih-fih-KAY-shun The stretching and transverse squeezing of an object by extreme tidal forces.
- Spectroscopy spek-TROSS-kuh-pee The study of radiation separated by wavelength or frequency.
- Spicule SPIK-yool A narrow, short-lived jet of plasma in the solar atmosphere.
- Syzygy SIZ-ih-jee An approximately straight-line arrangement of three celestial bodies.
T
- Tektite TEK-tyte Natural glass made from terrestrial material melted and ejected during an impact.
No word matches. Try fewer letters, or clear the filters.
The levels are Skywatcher (no background needed), Observatory (some astronomy helps) and Deep Space (technical). Every word cites where it can be checked; the writing is Cool Moon Facts’ own. Your saved words.