Mon · Monocerotis
Monoceros Constellation
IAU constellation mapMonMonoceros (Mon) is one of the 88 constellations recognised by the International Astronomical Union. It covers 482 square degrees of the northern sky in quadrant NQ2. Its brightest star is Beta Monocerotis. The Latin genitive of the name is Monocerotis, used to form star names within the constellation. The IAU standardised all constellation boundaries in 1930.
Quick facts
- IAU name
- Monoceros
- Abbreviation
- Mon
- Latin genitive
- Monocerotis
- Hemisphere
- northern
- Area
- 482 sq deg
- Brightest star
- Beta Monocerotis
- Quadrant
- NQ2
- Family
- Orion
- Discovery era
- Petrus Plancius, 1612
Overview
Monoceros is one of the 88 constellations formally recognised by the International Astronomical Union (IAU). It occupies 482 square degrees of sky in the northern hemisphere sky, best visible at latitudes between +90 and -60 degrees in March. The constellation belongs to the Orion family of constellations. Its Latin genitive is Monocerotis, the form used when naming stars within the constellation — for example, the brightest star Beta Monocerotis may appear in catalogues as Alpha Monocerotis or similar. The IAU standardised the boundaries of all 88 constellations in 1930 under the direction of Eugène Delporte, using straight lines of right ascension and declination to eliminate the ambiguities of earlier variable-boundary systems.
Notable stars
The brightest star in Monoceros is Beta Monocerotis. Individual stars within Monoceros are conventionally named using Bayer designation — Greek letters followed by the Latin genitive of the constellation name (Monocerotis) — introduced by Johann Bayer in his 1603 star atlas Uranometria. Flamsteed numbers (numeric designators followed by Monoceros) were added by John Flamsteed in his 1712 catalogue. Variable stars, double stars, and deep-sky objects within the Monoceros boundary are catalogued by the IAU with the abbreviation Mon.
History and catalogue
Monoceros was introduced or documented by Petrus Plancius, 1612. The modern IAU constellation boundaries were formally established in 1930. The designation Mon is the official three-letter IAU abbreviation used in star catalogues, variable star designations, and positional references. The family classification 'Orion' groups this constellation with others sharing a region of sky or a common historical source in astronomical literature.
Sources & further reading (2)
- official-iau — accessed 2026-05-06
- encyclopedia — accessed 2026-05-06
Frequently asked questions
What does the name Monoceros mean?
Monoceros is the Latin name used by the IAU to designate this constellation. The name comes from classical Latin and Greek astronomical tradition. In star catalogues, stars within Monoceros are designated using the genitive form of the name (e.g. Alpha Monoceros or similar Latin genitive forms) — a naming convention introduced by Johann Bayer in his 1603 atlas Uranometria and still in use today.
How large is Monoceros compared to other constellations?
Monoceros covers 482 square degrees of sky. The full sphere of the sky contains 41,253 square degrees, so Monoceros occupies about 1.2% of the total sky. For comparison, the largest constellation is Hydra at 1303 square degrees; the smallest is Crux at 68 square degrees.
When and where is Monoceros visible?
Monoceros is primarily a northern hemisphere constellation, best seen from mid-northern latitudes. Southern hemisphere observers may see it low on the horizon depending on their latitude. The brightest star, Beta Monocerotis, serves as the main visual anchor for locating the constellation. As with all constellations, the best viewing conditions are a dark sky away from artificial light pollution, with the constellation high enough above the horizon to minimise atmospheric absorption.
