astronomy

Ablation

process in which the atmosphere melts away and removes the surface material of an incoming meteorite

Absolute Magnitude

scale for measuring the actual brightness of a celestial object without accounting for the distance of the object; measures how bright an object would appear if it were exactly 10 parsecs (about 33 light-years) away from Earth

Absolute Zero

temperature at which the motion of all atoms and molecules stops and no heat is given off; 0 degrees Kelvin

Accretion

process by which dust and gas accumulates into larger bodies such as stars and planets

Accretion Disk

disk of gas that accumulates around a center of gravitational attraction

Achondrite

stone meteorite that contains no chondrules

Albedo

The reflective property of a non-luminous object

Albedo Feature

dark or light marking on the surface of an object that may or may not be a geological or topographical feature

Angular Size and Distance

apparent size of an object in the sky, or the distance between two objects, measured as an angle

Antimatter

matter consisting of particles with charges opposite that of ordinary matter; protons have a negative charge while electrons have a positive charge

Antipodal Point

point that is on the direct opposite side of a planet.

Apastron

point of greatest separation of two stars

Aperture

size of the opening through which light passes in an optical instrument such as a camera or telescope

Aphelion

point in the orbit of a planet or other celestial body where it is farthest from the Sun

Apogee

point in the orbit of the Moon or other satellite where it is farthest from the Earth

Apparent Magnitude

apparent brightness of an object in the sky as it appears to an observer on Earth

Asterism

prominent star pattern that isn't a whole constellation, such as the Northern Cross or the Big Dipper

Asteroid

small planetary body in orbit around the Sun, larger than a meteoroid but smaller than a planet

Astrochemistry

branch of science that explores the chemical interactions between dust and gas interspersed between the stars

Astronomical Unit (AU)

unit of measure equal to the average distance between the Earth and the Sun, approximately 93 million miles

Atmosphere

layer of gasses surrounding a planet, moon, or star

Aurora

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

Aurora Australis

the southern lights; this is an atmospheric phenomenon that displays a diffuse glow in the sky in the southern hemisphere

Aurora Borealis

the northern lights, this is an atmospheric phenomenon that displays a diffuse glow in the sky in the northern hemisphere

Averted Vision

viewing an object by looking slightly to its side

Axis

the poles, this is an imaginary line through the center of rotation of an object

Azimuth

angular distance of an object around or parallel to the horizon from a predefined zero point

Baily's Beads

few "beads" of sunlight; shining between mountain peaks and through the valleys along the Moon's edge in the moment before totality in an eclipse

Bar

unit of measure of atmospheric pressure

Barlow Lens

lens that's placed into the focusing tube to effectively double or triple a telescope's focal length and, in turn, the magnification of any eyepiece used with it

Big Bang

theory that suggests that the universe was formed from a single point in space during a cataclysmic explosion about 13.7 billion years ago

Binary

system of two stars that revolve around a common center of gravity

Black Hole

collapsed core of a massive star

Black Moon

an extra new moon that occurs in a season

Blue Moon

a second full moon in a single month

Blueshift

shift in the lines of an object's spectrum toward the blue end; object is moving towards the observer

Bolide

used to describe an exceptionally bright meteor; produce a sonic boom

Caldera

volcanic crater that is extremely large, usually formed by the collapse of a volcanic cone or by a violent volcanic explosion

Catena

series or chain of craters

Cavus

hollow, irregular depression

Celestial Coordinates

grid system for locating things in the sky; anchored to the celestial poles and the celestial equator; declination and right ascension are the celestial equivalents of latitude and longitude

Celestial Equator

line that divides the celestial sphere into a northern and southern hemisphere

Celestial Poles

North and South poles of the celestial sphere

Celestial Sphere

imaginary sphere around the Earth on which the stars and planets appear to be positioned

Cepheid Variable

variable star whose light pulsates in a regular cycle; period of fluctuation is linked to the brightness of the star

Chaos

distinctive area of broken terrain

Chasma

name used to describe a canyon

Chondrite

meteorite that contains chondrules

Chondrule

small, glassy spheres commonly found in meteorites

Chromosphere

part of the Sun's atmosphere just above the surface

Circumpolar

denotes an object near a celestial pole that never dips below the horizon as Earth rotates and thus does not rise or set

Circumpolar Star

a star that never sets but always stays above the horizon; always visible depending on which hemisphere the observer is in

Circumstellar Disk

torus or ring-shaped accumulation of gas, dust, or other debris in orbit around a star in different phases of its life cycle

Collimation

aligning the optical elements of a telescope so that they all point in the proper direction

Coma

area of dust or gas surrounding the nucleus of a comet

Comet

gigantic ball of ice and rock that orbit the Sun in a highly eccentric orbit

Compound Telescope

telescope with a mirror in the back and a lens in the front

Conjunction

event that occurs when two or more celestial objects appear close together in the sky

Conjunction

when the Moon or a planet appears especially close either to another planet or to a bright star

Corona

outer part of the Sun's atmosphere; visible from Earth during a total solar eclipse

Cosmic Ray

atomic nuclei (mostly protons) that are observed to strike the Earth's atmosphere with extremely high amounts of energy

Cosmic String

tube-like configuration of energy that is believed to have existed in the early universe

Cosmogony

the study of celestial systems, including the Solar System, stars, galaxies, and galactic clusters.

Cosmology

branch of science that deals with studying the origin, structure, and nature of the universe

Culmination

moment when a celestial object crosses the meridian and is thus at its highest above the horizon

Dark Adaptation

eyes' transition to night vision, in order to see faint objects

Dark Matter

term used to describe matter in the universe that cannot be seen, but can be detected by its gravitational effects on other bodies

Debris Disk

ring-shaped circumstellar disk of dust and debris in orbit around a star; may form planets

Declination

angular distance of an object in the sky from the celestial equator

Declination

celestial equivalent of latitude, denoting how far an object in the sky lies north or south of the celestial equator

Density

amount of matter contained within a given volume

Disk

surface of the Sun or other celestial body projected against the sky

Doppler Effect

apparent change in wavelength of sound or light emitted by an object in relation to an observer's position

Double Asteroid

asteroids that revolve around each other; binary asteroid

Double Star

grouping of two stars; can be apparent, where the stars seem close together, or physical, such as a binary system

Dwarf Planet

celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite

Earthshine

sunlight reflected by Earth that makes the otherwise dark part of the Moon glow faintly

Eccentricity

measure of how an object's orbit differs from a perfect circle

Eclipse

total or partial blocking of one celestial body by another

Eclipsing Binary

binary system where one object passes in front of the other, cutting off some or all of its light

Ecliptic

imaginary line in the sky traced by the Sun as it moves in its yearly path through the sky

Ejecta

material from beneath the surface of a body such as a moon or planet that is ejected by an impact such as a meteor and distributed around the surface

Electromagnetic Radiation

another term for light; created by fluctuations of electric and magnetic fields in space

Electromagnetic Spectrum

full range of frequencies, from radio waves to gamma waves, that characterizes light

Ellipse

an oval shape; Kepler discovered orbits were elliptical

Elliptical Galaxy

galaxy whose structure is shaped like an ellipse and is smooth

Elongation

angular distance of a planetary body from the Sun as seen from Earth

Ephemeris

A table of data arranged by date. Ephemeris tables are typically to list the positions of the Sun, Moon, planets and other solar system objects.

Ephemeris

timetable with celestial coordinates that indicates where a planet, comet, or other body moving in relation to background stars will be in the sky

Equinox

two points at which the Sun crosses the celestial equator in its yearly path in the sky

Escape Velocity

speed required for an object to escape the gravitational pull of a planet or other body

Event Horizon

invisible boundary around a black hole past which nothing can escape the gravitational pull

Evolved Star

star that is near the end of its life cycle where most of its fuel has been used up

Extinction

apparent dimming of star or planet when low on the horizon due to absorption by the Earth's atmosphere

Extragalactic

term that means outside of or beyond our own galaxy

Extraterrestrial

term used to describe anything that does not originate on Earth

Eyepiece

lens at the viewing end of a telescope; responsible for enlarging the image captured by the instrument

Faculae

bright patches that are visible on the Sun's surface, or photosphere

Field of View

circle of sky that you see when you look through a telescope or binoculars

Filament

strand of cool gas suspended over the photosphere by magnetic fields, which appears dark as seen against the disk of the Sun