asterism: An easily discernible pattern of stars not officially recognized as a constellation.
astral body: The outer aspect of the body that operates as a vehicle of consciousness and allows us to function on the astral plane.
astral plane: A realm or level of consciousness where magical energies are marshaled for manifestation on the physical plane.
astronomical twilight: The third stage of evening twilight that occurs when the horizon is no longer visible.
aura: A subtle energy field that surrounds all living things.
averted vision: A method for seeing a dim sky object without looking directly at it.
Bayer designation: A naming convention for stars in a constellation that uses Greek letters to rank their brightness. It was created by German astronomer Johann Bayer, who was the first to map the entire sky.
Behenian fixed stars: Fifteen stars defined by Agrippa as particularly powerful for magic.
binary star: A star that actually consists of two stars orbiting each other.
celestial equator: Earth’s equator projected out to the sky, dividing it into north and south.
celestial pole: Points on the celestial sphere above Earth’s North and South Poles.
celestial sphere: The imaginary sphere or dome around Earth that is useful in understanding the movements of celestial objects.
chakra: A center or point of energy within or near the physical body.
circumpolar: A constellation or star that appears to circle one of the celestial poles.
civil twilight: The first stage of evening twilight, when only the brightest stars can be seen.
cones and rods: The two types of light-detecting cells in our eyes. Cones are highly concentrated at the center of the eyes while rods are off to the sides.
constellation: One of eighty-eight official, defined areas of the sky that includes a recognized star pattern. These were created by the International Astronomical Union in 1922.
declination: The north/south position of an object on the celestial sphere.
double star: A star that is actually two when viewed with binoculars or a telescope. Unlike a binary star, these do not orbit each other.
eclipsing binary: A type of binary star where one component eclipses the other, producing a change in overall brightness.
ecliptic: The band or path of the sun around the celestial sphere.
equinox: One of two days of the year when the sun crosses the equator. It is the point at which the ecliptic and equator intersect on the celestial sphere. The spring or vernal equinox occurs around March 20 and the autumn equinox around September 22. These are celebrated as Ostara and Mabon, respectively.
Flamsteed numbers: A system in use today that numbers stars from west to east in each constellation without regard to their brightness. This system was created by English astronomer John Flamsteed.
full darkness: This occurs after the three stages of evening twilight, when faint stars can be seen.
horizon: A boundary where the sky meets the earth or ocean.
light pollution: The illumination of the night sky by artificial light that inhibits observation of celestial objects.
lucid star: A star that can be seen with the naked eye.
magnitude system: A method employed by astronomers to measure the brightness of stars.
meridian: An imaginary line that runs from north to south and passes through your zenith, dividing the sky into east and west.
Messier objects: Nebulae, clusters, and galaxies catalogued by French astronomer Charles Messier. Messier objects are designated by the letter M followed by a number.
meteor shower: Bright streaks of light that appear when meteors burn up while traveling through Earth’s atmosphere.
Milky Way: The great spiral galaxy that contains our solar system, which is located on one of the smaller spurs called the Orion Arm.
multiple star: A star system consisting of three or more stars that may not be distinguishable without binoculars or a telescope.
nautical twilight: The second stage of evening twilight, when the horizon is still visible and the bright stars used for navigation appear.
nebula: An area of interstellar gas and/or dust. The word is Latin and means “cloud.”
open cluster: A group of stars consisting of a few dozen or several thousand stars. Also called galactic star clusters, these have more distance between stars than other types of clusters.
planisphere: A star map with a rotating disk that can be set to show the constellations at any given day or time during the year.
precession: The scientific name for Earth’s wobble, which is caused by gravitational pull of the sun and moon. This movement causes Earth’s rotational axis to change, thus shifting the celestial poles and the equinoxes. It is also called the precession of the equinoxes.
right ascension: The east/west position of a celestial body.
royal stars: Four stars used as calendar markers by the Babylonians that they designated as the guardians of the cardinal directions.
Sabianism: Star worship that was part of the pre-Islamic religion of the Harranians of Mesopotamia.
solstice: One of two days in the year when the sun reaches its maximum northern or southern point. The summer solstice occurs around June 21 and the winter solstice around December 21. These are celebrated as Litha and Yule, respectively.
spectroscopic binary star: Two stars orbiting each other that are too close to be distinguished as separate without a high-powered telescope.
Tropic of Cancer: The northern latitude where the sun is directly overhead at noon on the summer solstice.
Tropic of Capricorn: The southern latitude where the sun is directly overhead at noon on the winter solstice.
twilight: The time between sunset and full darkness that occurs in three stages: civil, nautical, and astronomical. These three stages occur in reverse order at sunrise.
variable star: A star that repeatedly changes brightness.
zenith: The point directly overhead on the celestial sphere.
zodiac: Constellations that provide a backdrop to the sun along the circle of the ecliptic. Traditionally there are twelve; however, in the two thousand years since its inception, Ophiuchus now falls on the ecliptic, making it the thirteenth constellation of the zodiac.