Astronomical Terms and Definitions Glossary

Our glossary includes definitions of astronomical terms that are commonly used on in the Farmers’ Almanac and on FarmersAlmanac.com.

Aph. – Aphelion: The point at which a body in an elliptical orbit around the Sun is at its greatest distance from the Sun. Earth is in aphelion in early July.

Apo. – Apogee: The point at which a body moving in an elliptical orbit around the Earth is at its greatest distance from the Earth.

Ascending Node: The point of the Moon’s (or planet’s) orbit at which it crosses, from south to north, the plane of the Earth’s orbit extended to meet the celestial body. ☊

Combust: When the Moon, star or planet is not visible due to its proximity to the Sun.

Conjunction: The alignment or close alignment of two or more Astronomical bodies. ☌

CL. – Close: Used in this Almanac to define a conjunction. Example: Saturn/Moon cl. ev., means that Saturn and the Moon are close (or in conjunction) in the evening.

Declination: The angular distance to a specific point on the celestial sphere, measured in degrees either north or south from the celestial equator in a direction perpendicular to the point.

Descending Node: The point at which the Moon’s (or planet’s orbit) crosses, from north to south, the plane of the Earth’s orbit extended to meet the celestial body. ☋

Dionysian Period: Named for the monk Dionysius Exiguous who, in the AD. 500’s, introduced the present custom of reckoning time by counting the years from the birth of Christ. The current Dionysian Period began on January 1, 1672.

Dominical Letter: Used in reckoning civil calendars. It is determined by the date on which the first Sunday of the year falls. If January 1 is a Sunday, the letter is A; and so on to G when the first Sunday is Jan. 7. Should the year in question be a leap year, the letter applies only through the month of February and then takes the letter before.

Eclipse – Annular: Is when a solar eclipse occurs with the apparent size of the New Moon marginally smaller than that of the Sun. As a result, the rim of the Sun’s disc remains visible around the dark disc of the Moon.

Eclipse – Lunar: When the Moon passes into the Earth’s shadow.

Eclipse – Solar: When the New Moon orbits between the Earth and the Sun and casts its shadow upon the Earth’s surface.

Ecliptic: The Sun’s apparent path among the constellations.

El. – Elongation: Apparent angular distance of a member of the Solar System from the Sun as seen from the Earth.

Epact: The Moon’s age in the lunar cycle at the beginning of each solar year, which begins on January 1, at 0h 00m Greenwich Mean Time. The Moon’s age cannot exceed 29 days; however, when it is less than one day old, the Epact is considered to be 30 and not zero.

Evening Star: A term that is applied to any planet when the planet is visible in the evening sky and crosses the meridian before midnight.

Golden Number: After a period of 235 lunar months or 19 years, the phases of the Moon recur in the same order and on the same dates as the preceding cycle. The Golden Number is used in reckoning civil calendars and represents the year’s position in this 19-year cycle.

Gr. El. – Greatest Elongation: When a planet attains its greatest apparent angular distance from the Sun in the sky.

Inf. – Inferior: Inferior conjunction is when an “when an “inferior planet” (Mercury or Venus) passes between the Earth and the Sun.

Jewish lunar Cycle: Similar to the 19-year cycle upon which the Golden Number is based.

Julian Period: Devised in 1582 by Joseph Scaliger as a way to measure lime. Scaliger had Julian Day (JD) #1, named after his father, Julius Scaliger, which began at noon on January 1, 4713 B.C., the most recent time that three major chronological cycles began on the same day – 1.) the 28-year solar cycle; 2.) the 19-year lunar cycle; 3.) the 15-year indication cycle used in ancient Rome to regulate taxes. It will take 7,980 Julian years to complete the period, the product of 28, 19 and 15.

Mer. – Meridian: A great circle on the celestial sphere passing through the north and south celestial poles and the zenith (overhead point) of a given place.

Moon Highest or Lowest: The day of the month that the Moon appears at its highest or lowest point on the meridian.

Moon’s Southing: Also known as the Moon’s “Meridian Passage” or “Upper Culmination.” It’s when the Moon appears exactly above the south point of the observer’s local horizon.

Morning Star: A term that applies to any planet when it is visible in the morning sky and crosses the meridian after midnight.

Occ. – Occultation: An eclipse of a star or planet by the Moon or another planet.

Opposition: The position of an astronomical object when it is opposite the Sun in the sky, and as a consequence, crosses the meridian at midnight. ☍

Per. – Perigee: The point at which a body moving in an elliptical orbit around the Earth is at its closest approach to the Earth.

Peri. – Perihelion: The point at which a body in an elliptical orbit around the Sun is at its closest distance to the Sun. Earth is at perihelion in early January.

Roman Indiction: A 15-year cycle used in reckoning ecclesiastical calendars. It was established in ancient Rome on January 1, 313 A.D. as a fiscal term to regulate taxes. In order to figure out the Roman indictions, add 3 to the number of years in the Christian era and divide by 15. The remainder of the year is Roman indiction – no remainder is 15.

Solar Cycle: A 28-year cycle used in reckoning civil calendars. At. the end of the cycle, it restores the first day of the year to the same day of the week.

Tears of Saint Laurence: During the 19th century, Irish farmers, as well as Catholics in England and Germany, noted an annual shower of shooting stars around the night of the Feast of St. Laurence (August 10 on the Catholic calendar). Today, the display is better known as the Perseid Meteors.

Zodiac: Greek, zÖon, “animal” (all but one of the twelve Zodiacal constellations represent living creatures); the circular zone on the celestial sphere, centered on the ecliptic and extending in width to about 9 degrees on either side. Within this zone the motion of the visible planets, the Sun and the Moon take place. It is divided into twelve zones, each 30 degrees long, called the signs of the Zodiac. It was (and still is) highly regarded in astrology.

See our Weather Glossary here.

See our Hurricane Glossary here.

See our Marine Warnings Glossary here.

See our Gardening Terms Glossary here.

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