Lunar Maria

António Cidadão, of Oeiras, Portugal, many years ago produced a wonderful set of images showing the location of each mare on the Moon. His website has not been updated since 1999 and the contact email address provided there is no longer valid, and even after a thorough Google search I can find no way to contact him to ask permission to link images here to his site. Even worse, because his hosting site is not secure (http: instead of https:), WordPress does not allow me to link directly to his images so I had to put copies into my media library. Please know that the images shown below are all copyrighted by António Cidadão.

Each image shows north is up and west is to the left. This is direction of increasing longitude and therefore west on the Moon, but in our sky, east is to the left. In other words, these annotated images of the Moon are correctly oriented as they would appear to the unaided eye in the sky in the northern hemisphere. In the rest of this article, we will use the moon-centric east-west convention that Cidadão indicates in his image diagrams.

Let’s take a look at each of the lunar maria from moon-west to moon-east. Their fanciful names were mostly given (and codified in 1651) by the Italian astronomer Giovanni Battista Riccioli (1598-1671). Riccioli chose names related to weather, as it was then believed that the Moon, the closest celestial body to the Earth, exerted an influence on the Earth’s weather. This is perhaps not at all surprising given that the phenomenon of tides had been known since antiquity.

Most of the nearside west portion of the Moon is covered by a mare that is so large that it is given a unique designation: Oceanus for “ocean”.

Oceanus Procellarum, the “Ocean of Storms”

Oceanus Procellarum contains the famously bright crater Aristarchus and the associated Aristarchus Plateau. In the image above you will notice what appears to be a tiny mare close to the limb of the Moon west of the southern part of Oceanus Procellarum. This is the lava-flooded crater Grimaldi.

Mare Orientale, the “Eastern Sea”

South of Grimaldi and straddling the lunar limb is Mare Orientale. It is difficult to see because most of it is on the lunar farside, though libration can sometimes bring its oblique visage into view. The name Orientale, meaning “eastern”, describes its location on the eastward-facing limb of the Moon as seen from Earth, rather than its westward direction as seen from the surface of the Moon.

Mare Humorum, the “Sea of Moisture”

Mare Humorum is located just south of Oceanus Procellarum. It is round and inviting, though no spacecraft has ever landed there.

Mare Nubium, the “Sea of Clouds”

Mare Nubium is east of Mare Humorum. The large crater Bullialdus flanks the western edge of Mare Nubium, and Rupes Recta (the “Straight Wall”) flanks its eastern edge.

Mare Cognitum, the “Sea That Has Become Known”

Mare Cognitum lies between Mare Nubium and Oceanus Procellarum. It was named in 1964 after the Ranger 7 probe took the first U.S. close-up pictures of the Moon’s surface prior to crashing there.

Mare Insularum, the “Sea of Islands”

Mare Insularum is north of Mare Cognitum. Its current name was bestowed upon it in 1976 by lunar geologist Don Wilhelms (1930-). The crater Kepler on its western edge separates Mare Insularum from Oceanus Procellarum. The crater Copernicus is on the northeast side of its western lobe.

Mare Vaporum, the “Sea of Vapors”

Mare Vaporum is the mare closest to the center of the Moon’s nearside. The bright crater Manilius lies towards its northeastern edge and the volcanic crater Hyginus and its associated rille (Rima Hyginus) are immediately to its south.

Mare Imbrium, the “Sea of Rains”

Mare Imbrium was created 3.9 billion years ago when an asteroid some 150 miles across crashed into the Moon. This ancient feature is so large that it forms the right eye of the “Man in the Moon” we see when looking at a full or nearly full moon with our unaided eyes.

Mare Frigoris, the “Sea of Cold”

Mare Frigoris lies north and northeast of Mare Imbrium. The dark crater between them is Plato. It is the mare closest to the north pole of the Moon.

Mare Serenitatis, the “Sea of Serenity”

Now we begin our tour of the eastern hemisphere of the Moon’s nearside. Mare Serenitatis has the distinction of being the landing site of the last human mission to the Moon, Apollo 17, in 1972. It was also the landing site of the Soviet unmanned spacecraft Luna 21 just one month later.

Mare Tranquillitatis, the “Sea of Tranquility”

Mare Tranquillitatis is perhaps the most famous of the lunar maria, as it was there that humans first set foot on the surface of the Moon in 1969. The Apollo 11 landing site is located near its southwest corner.

Mare Nectaris, the “Sea of Nectar”

Mare Nectaris lies south of Mare Tranquillitatis. This small, isolated, and nearly circular mare sports a prominent crater, Theophilus, at its northwest corner.

Mare Fecunditatis, the “Sea of Fertility”

East of Mare Nectaris lies Mare Fecunditatis. Superposed upon Mare Fecunditatis is the striking crater pair Messier and Messier A with two prominent rays evocative of a comet’s tail. Named after the famous French comet hunter Charles Messier (1730-1817), these craters and their associated rays were formed from a grazing impact from the east.

Mare Crisium, the “Sea of Crises”

Mare Crisium is a round and isolated mare that makes it easy to remember why it is called the “Sea of Crises”. The Soviet Luna 24 unmanned sample return mission landed there in 1976. The six ounces of lunar materials it brought back to Earth are the last lunar samples scientists have received.

Mare Anguis, the “Serpent Sea”

Mare Anguis lies just northeast of Mare Crisium and is called the “Serpent Sea” for its serpentine shape rather than the more fanciful name “Sea of Serpents” referred to by some science fiction authors.

Mare Undarum, the “Sea of Waves”

Mare Undarum lies southeast of Mare Crisium. Its uneven texture and lack of uniform smoothness appears to justify its name as “the sea of waves”.

Mare Spumans, the “Foaming Sea”

Mare Spumans lies south of Mare Undarum and east of Mare Fecunditatis. The bright crater Petit on the western side of this tiny mare evinces a bit of foam on “the foaming sea”.

Mare Australe, the “Southern Sea”

Mare Australe hugs the southeastern limb of the lunar nearside. Though obliquely viewed from Earth and wrapping around to the lunar farside, favorable libration makes it visible in its entirety on occasion.

Mare Smythii, “Smyth’s Sea”

Mare Smythii on the eastern limb of the Moon is one of two lunar maria named after people. The lucky honoree is English hydrographer and astronomer William Henry Smyth (1788-1865). The lunar equator passes through Mare Smythii.

Mare Marginis, the “Sea of the Edge”

Mare Marginis lies east of Mare Crisium, right along the lunar limb. The crater Goddard on the northeast side of Mare Marginis exhibits bright deposits on its northeastern side. This crater and its associated deposits can only be seen from Earth during favorable librations.

Mare Humboldtianum, the “Sea of Alexander von Humboldt”

Mare Humboldtianum lies along the northeastern limb of the Moon and is the other lunar mare named after a person. The German astronomer Johann Heinrich von Mädler (1794-1874) named this feature after German geographer and explorer Alexander von Humboldt (1769-1859).

This completes our tour of the 21 maria on the nearside of the Moon.


António Cidadão’s Home-Page of Lunar and Planetary Observation and CCD Imaging, Moon-“Light” Atlas.  Retrieved 22 April 2020.

Ewen A. Whitaker, Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature (Cambridge University Press, 2003).

Project Gutenberg

Over 56,000 historical books and other documents, most published prior to 1923, are available online for downloading or browsing at Project Gutenberg (, with more being added all the time. A quick search of the term “astronomy” yields the following:

The Discovery of a World in the Moone: Or, A Discovrse Tending To Prove That ‘Tis Probable There May Be Another Habitable World In That Planet (1638)
John Wilkins (1614-1672)

The Study of Astronomy, Adapted to the capacities of youth (1796)
John Gabriel Stedman (1744-1797)

The Martyrs of Science, or, The lives of Galileo, Tycho Brahe, and Kepler (1841)
David Brewster (1781-1868)

Lectures on Astronomy (1854)
The Wit and Humor of America, Volume V. (1911)
George Horatio Derby (1823-1861), writing under the name of John Phoenix
Marshall Pinckney Wilder (1859-1915), editor

Letters on Astronomy: In which the Elements of the Science are Familiarly Explained in Connection with Biographical Sketches of the Most Eminent Astronomers (1855)
Denison Olmsted (1791-1859)

The Uses of Astronomy: An Oration Delivered at Albany on the 28th of July, 1856 (1856)
Edward Everett (1794-1865)

Cosmos: A Sketch of the Physical Description of the Universe, Vol. 1 (1858)
Alexander von Humboldt (1769-1859)

Curiosities of Science, Past and Present: A Book for Old and Young (1858)
John Timbs (1801-1875)

Astronomy for Young Australians (1866)
James Bonwick (1817-1906)

Meteoric astronomy: A treatise on shooting-stars, fire-balls, and aerolites (1867)
Daniel Kirkwood (1814-1895)

Popular Books on Natural Science: For Practical Use in Every Household, for Readers of All Classes (1869)
Aaron David Bernstein (1812-1884)

Half-hours with the Telescope: Being a Popular Guide to the Use of the Telescope as a Means of Amusement and Instruction (1873)
Richard Anthony Proctor (1837-1888)

Astronomical Myths: Based on Flammarions’s “History of the Heavens” (1877)
John Frederick Blake (1839-1906)
Camille Flammarion (1842-1925)

New and Original Theories of the Great Physical Forces (1878)
Henry Raymond Rogers (1822-1901)

Recreations in Astronomy: With Directions for Practical Experiments and Telescopic Work (1879)
Henry White Warren (1831-1912)

The Sidereal Messenger of Galileo Galilei and a Part of the Preface to Kepler’s Dioptrics Containing the Original Account of Galileo’s Astronomical Discoveries (1880)
Galileo Galilei (1564-1642)
Johannes Kepler (1571-1630)
Edward Stafford Carlos ((1842–1927), translator

Sir William Herschel: His Life and Works (1880)
Edward Singleton Holden (1846-1914)

Popular Scientific Recreations in Natural Philosophy, Astronomy, Geology, Chemistry, etc., etc., etc. (1881)
Gaston Tissandier (1843-1899)

Publications of the Astronomical Society of the Pacific, Volume 1 (1889)
Astronomical Society of the Pacific (1889-)

A Textbook of General Astronomy for Colleges and Scientific Schools (1889)
Charles Augustus Young (1834-1908)

Time and Tide: A Romance of the Moon (1889)
Robert Stawell Ball (1840-1913)

Astronomy with an Opera-glass: A Popular Introduction to the Study of the Starry Heavens with the Simplest of Optical Instruments (1890)
Garrett Putman Serviss (1851-1929)

Pioneers of Science (1893)
Sir Oliver Joseph Lodge (1851-1940)

Great Astronomers (1895)
Robert Stawell Ball (1840-1913)

The Astronomy of Milton’s ‘Paradise Lost’ (1896)
Thomas Nathaniel Orchard, M.D.

Myths and Marvels of Astronomy (1896)
Richard Anthony Proctor (1837-1888)

The Story of Eclipses (1899)
George Frederick Chambers (1841-1915)

The Tides and Kindred Phenomena in the Solar System: The Substance of Lectures Delivered in 1897 at the Lowell Institute, Boston, Massachusetts (1899)
Sir George Howard Darwin (1845-1912)

The Royal Observatory, Greenwich: A Glance at Its History and Work (1900)
Edward Walter Maunder (1851-1928)

The Story of the Heavens (1900)
Robert Stawell Ball (1840-1913)

Other Worlds: Their Nature, Possibilities and Habitability in the Light of the Latest Discoveries (1901)
Garrett Putman Serviss (1851-1929)

Pleasures of the telescope: An Illustrated Guide for Amateur Astronomers and a Popular Description of the Chief Wonders of the Heavens for General Readers (1901)
Garrett Putman Serviss (1851-1929)

A Text-Book of Astronomy (1903)
George Cary Comstock (1855-1934)

Astronomical Discovery (1904)
Herbert Hall Turner (1861-1930)

A New Astronomy (1906)
David Peck Todd (1855-1939)

New Theories in Astronomy (1906)
William Stirling (1822-1900)

Side-Lights on Astronomy and Kindred Fields of Popular Science (1906)
Simon Newcomb (1835-1909)

The Children’s Book of Stars (1907)
Geraldine Edith Mitton (1868-1955)

Mathematical Geography (1907)
Willis Ernest Johnson (1869-1951)

Astronomical Instruments and Accessories (1908)
William Gaertner and Company (1896-)
now Gaertner Scientific Corporation

The Astronomy of the Bible: An Elementary Commentary on the Astronomical References of Holy Scripture (1908)
Edward Walter Maunder (1851-1928)

A Popular History of Astronomy During the Nineteenth Century, Fourth Edition (1908)
Agnes Mary Clerke (1842-1907)

Astronomical Curiosities: Facts and Fallacies (1909)
John Ellard Gore (1845-1910)

The Future of Astronomy (1909)
Edward Charles Pickering (1846-1919)

History of Astronomy (1909)
George Forbes (1849-1936)

Astronomy for Amateurs (1910)
Camille Flammarion (1842-1925)

Astronomy of To-day: A Popular Introduction in Non-Technical Language (1910)
Cecil Goodrich Julius Dolmage (1870-1908)

The World’s Greatest Books — Volume 15 — Science (1910)
Arthur Mee (1875-1943), editor
Sir John Alexander Hammerton (1871-1949), editor

The Science of the Stars (1912)
Edward Walter Maunder (1851-1928)

Are the Planets Inhabited? (1913)
Edward Walter Maunder (1851-1928)

Woman in Science: With an Introductory Chapter on Woman’s Long Struggle for Things of the Mind (1913)
John Augustine Zahm (1851-1921), writing under the name H. J. Mozans

A Field Book of the Stars (1914)
William Tyler Olcott (1873-1936)

An Introduction to Astronomy (1916)
Forest Ray Moulton (1872-1952)

Scientific Papers by Sir George Howard Darwin. Volume V. Supplementary Volume (1916)
Sir George Howard Darwin (1845-1912)
Ernest William Brown (1866-1938), contributor
Sir Francis Darwin (1848-1925), contributor

The gradual acceptance of the Copernican theory of the universe (1917)
Dorothy Stimson (1890-1988)

Astronomical Lore in Chaucer (1919)
Florence Marie Grimm

Lectures on Stellar Statistics (1921)
Carl Vilhelm Ludwig Charlier (1862-1934)

The Star People (1921)
Gaylord Johnson

Terrestrial and Celestial Globes Volume 1: Their History and Construction Including a Consideration of their Value as Aids in the Study of Geography and Astronomy (1921)
Edward Luther Stevenson (1858-1944)

Terrestrial and Celestial Globes Volume 2: Their History and Construction Including a Consideration of their Value as Aids in the Study of Geography and Astronomy (1921)
Edward Luther Stevenson (1858-1944)

Astronomy for Young Folks (1922)
Isabel Martin Lewis (1881-1966)

Astronomy: The Science of the Heavenly Bodies (1922)
David Peck Todd (1855-1939)

The New Heavens (1922)
George Ellery Hale (1868-1938)

Watchers of the Sky (1922)
Alfred Noyes (1880-1958)

Biography of Percival Lowell (1935)
Abbott Lawrence Lowell (1856-1943)