All but two of these dim constellations are, at least in part, visible from southern Arizona; Chamaeleon and Mensa require a trip south to see.
The southern constellation Mensa, the Table Mountain (declination -70° to -85°) is a ghost of a constellation, exhibiting no star brighter than magnitude 5.1. That’s 17 times fainter than Polaris! In fact, that’s fainter than all the stars of the Little Dipper asterism! Mensa does have one claim to fame, however. The Large Magellanic Cloud, satellite galaxy of our Milky Way galaxy, straddles most of the border that Mensa shares with Dorado, the Swordfish.
Mensa is far and away the dimmest constellation. But Mensa is a small constellation, bested in size by 74 of the 88 constellations. So perhaps it is not too surprising that a small constellation is less likely to harbor a bright star. Another measure of faint, perhaps, is to determine which of these twelve constellations with no star brighter than 4th magnitude is largest. That might be more remarkable, because one is less likely to find no bright stars in a large area of sky than in a small area of sky. By this measure, Camelopardalis, the Giraffe, wins without a doubt. Camelopardalis is the 18th largest constellation, and yet contains no star brighter than magnitude 4.0. It is that empty region you might have not noticed midway between Capella and Polaris, best viewed at evening twilight’s end during the month of February each year.
Here in southern Arizona, we can theoretically see 92.4% of the celestial sphere. I say “theoretically” because atmospheric extinction, light pollution, local topography, and obstructions limit the amount of the celestial sphere that we can see well. Also, far southern objects (down to δ = -58° at φ = 32° N) spend very little time above our horizon each day.
Practically speaking, then, we see somewhat less than 92% of all that there is to see from spaceship Earth.
Percent of the Celestial Sphere Visible
where |φ| is the absolute value of your latitude in degrees
What are the most prominent objects we are missing, and what objects that we can see are they closest to?
Alpha Centauri
Never visible north of latitude 27° N, the nearest star system beyond our solar system is Alpha Centauri. Alpha Centauri A & B are bright stars, having a visual magnitude of 0.0 and +1.3, respectively, and in 2023 they are separated by just 8 arcseconds, about 1/4 of the angular separation between Albireo A & B. While Alpha Centauri A & B—which orbit each other once every 79.8 years—lie just 4.36 ly away, a faint red dwarf companion, Proxima Centauri (shining at magnitude +11.1), is even closer at 4.24 light years. It is not yet known whether Proxima Centauri, discovered in 1915, is gravitationally bound to Alpha Centauri A & B, or just presently passing through the neighborhood. Proxima is a full 2.2° away (over four moon-widths) from Alpha Centauri A & B.
When Arcturus (α Boo) and Zubenelgenubi (α Lib) are crossing our celestial meridian, so are Alpha & Proxima Centauri below the southern horizon.
Large Magellanic Cloud
The Large Magellanic Cloud (LMC), the largest satellite galaxy of our Milky Way galaxy and easily visible to the unaided eye, lies directly below our southern horizon when Rigel has crossed the meridian and Bellatrix is preparing to do so.
Small Magellanic Cloud
The Small Magellanic Cloud (SMC), the second-largest satellite galaxy of the mighty Milky Way lies underneath our southern horizon when M31, the Great Andromeda Galaxy, crosses the meridian near the zenith.
47 Tucanae
The 2nd brightest globular cluster in the sky (after Omega Centauri) is impressive 47 Tucanae. It is just 2.3° west and a little north of the Small Magellanic Cloud, so crosses the meridian below our horizon just as M31 is nearing the meridian.
Eta Carinae Nebula
Four times larger and brighter than the Orion Nebula, NGC 3372, the Eta Carinae Nebula, is a spectacular star-forming region containing a supermassive (130 – 180 M☉) binary star (Eta Carinae) that may go supernova at any time. When Leo the Lion is straddling the meridian, the Eta Carinae Nebula sneaks across as well.
Any other spectacular objects I should be including that are south of declination -58°? If so, please post a comment here.
The equator of the Moon is defined by its rotational axis. It is the great circle contained by the plane that is perpendicular to the line connecting the north and south poles of the Moon.
Here is a list of named lunar features through which the Moon’s equator passes, from lunar east to lunar west on the part of the Moon visible from the Earth.
Remember, lunar longitude is opposite the direction in the sky. East longitude is the west/right side of the moon, and west longitude is the east/left side of the moon as viewed from the northern hemisphere of the Earth.
The diameter of each feature is included, followed by the depth of the feature, where available.
Wyld
Center: 98.101˚ E, 1.416˚ S
Range: 96.395˚ - 99.806˚ E, 3.121˚ S - 0.289˚N
Crater; libration zone
58 mi
James Hart Wyld (1913-1953), American rocket engineer
Dorsum Cloos
Center: 90.410˚ E, 1.149˚ N
Range: 90.387˚ - 91.144˚ E, 0.268˚ S - 2.576˚ N
Wrinkle ridge; libration zone
64 mi
Hans Cloos (1885-1951), German geologist
Mare Smythii
Center: 87.049˚ E, 1.709˚ S
Range: 80.941˚ - 92.719˚ E, 7.456˚ S - 4.496˚ N
Mare; libration zone; Smyth's Sea
232 mi, 3.1 mi
William Henry Smyth (1788-1865), English naval officer and astronomer
Schubert J
Center: 78.935˚ E, 0.012˚ S
Range: 78.579˚ - 79.292˚ E, 0.344˚ S - 0.320˚ N
Crater
12 mi
Friedrich Theodor von Schubert (1758-1825), German astronomer & geographer
Jenkins
Center: 78.041˚ E, 0.372˚ N
Range: 77.418˚ - 78.663˚ E, 0.251˚ S - 0.994˚ N
Crater
24 mi, 1.9 mi
Louise Freeland Jenkins (1888-1970), American astronomer
Schubert X
Center: 76.750˚ E, 0.310˚ N
Range: 75.940˚ - 77.561˚ E, 0.501˚ S - 1.121˚ N
Crater
32 mi
Friedrich Theodor von Schubert (1758-1825), German astronomer & geographer
Nobili
Center: 75.949˚ E, 0.166˚ N
Range: 75.260˚ - 76.638˚ E, 0.523˚ S - 0.855˚ N
Crater
26 mi, 2.4 mi
Leopoldo Nobili (1784-1835), Italian physicist
Maclaurin X
Center: 68.708˚ E, 0.091˚ N
Range: 68.403˚ - 69.014˚ E, 0.214˚ S - 0.397˚ N
Crater
15 mi
Colin Maclaurin (1698-1746), Scottish mathematician
Maclaurin O
Center: 67.557˚ E, 0.135˚ S
Range: 66.873˚ - 68.241˚ E, 0.819˚ S - 0.548˚ N
Crater
23 mi
Colin Maclaurin (1698-1746), Scottish mathematician
Mare Spumans
Center: 65.303˚ E, 1.302˚ N
Range: 63.613˚ - 66.733˚ E, 1.062˚ S - 3.722˚ N
Mare
87 mi
The Foaming Sea
Webb C
Center: 63.833˚ E, 0.149˚ N
Range: 63.267˚ - 64.398˚ E, 0.247˚ S - 0.544˚ N
Crater
21 mi
Thomas William Webb (1807-1885), English astronomer
Sinus Successus
Center: 58.520˚ E, 1.124˚ N
Range: 56.519˚ - 60.188˚ E, 0.861˚ S - 2.872˚ N
Bay
82 mi
Bay of Success
Mare Fecunditatis
Center: 53.669˚ E, 7.835˚ S
Range: 40.771˚ - 63.340˚ E, 21.695˚ S - 6.112˚ N
Mare
429 mi, 1.1 mi
Sea of Fertility
Taruntius P
Center: 51.585˚ E, 0.060˚ N
Range: 51.473˚ - 51.696˚ E, 0.051˚ S - 0.172˚ N
Craterlet
5 mi, 0.9 mi
Lucius Tarutius Firmanus (fl. 86 B.C.), Roman philosopher, mathematician, and astrologer
Dorsum Cayeux
Center: 51.220˚ E, 0.763˚ N
Range: 50.922˚ - 52.000˚ E, 0.598˚ S - 2.113˚ N
Wrinkle ridge
59 mi
Lucien Cayeux (1864-1944), French sedimentary petrographer
Dorsa Cato
Center: 47.701˚ E, 0.213˚ N
Range: 46.605˚ - 49.599˚ E, 1.165˚ S - 2.233˚ N
Wrinkle ridges
87 mi
Marcus Porcius Cato (234-149 B.C.), Roman soldier, senator, and historian
Rima Messier
Center: 44.545˚ E, 0.756˚ S
Range: 43.357˚ - 45.581˚ E, 1.561˚ S - 0.015˚ N
Rille
62 mi
Charles Messier (1730-1817), French astronomer
Lubbock R
Center: 40.453˚ E, 0.167˚ S
Range: 40.060˚ - 40.845˚ E, 0.559˚ S - 0.225˚ N
Crater
15 mi
Sir John William Lubbock (1803-1865), English banker, barrister, mathematician, and astronomer
Maskelyne T
Center: 36.593˚ E, 0.040˚ S
Range: 36.507˚ - 36.678˚ E, 0.125˚ S - 0.046˚ N
Craterlet
3 mi
Nevil Maskelyne (1732-1811), English astronomer
Maskelyne A
Center: 34.089˚ E, 0.032˚ N
Range: 33.603˚ - 34.574˚ E, 0.453˚ S - 0.517˚ N
Crater
18 mi
Nevil Maskelyne (1732-1811), English astronomer
Mare Tranquillitatis
Center: 30.835˚ E, 8.349˚ N
Range: 16.924˚ - 45.490˚ E, 4.051˚ S - 19.375˚ N
Mare
544 mi
Sea of Tranquility
Rimae Hypatia
Center: 22.777˚ E, 0.340˚ S
Range: 19.690˚ - 25.975˚ E, 1.406˚ S - 0.672˚ N
Rilles
128 mi
Hypatia (c.370-415), Alexandrian philosopher, mathematician, and astronomer
Lade A
Center: 12.726˚ E, 0.161˚ S
Range: 11.773˚ - 13.680˚ E, 1.114˚ S - 0.793˚ N
Crater
35 mi
Heinrich Eduard von Lade (1817-1904), German banker and amateur astronomer
Lade B
Center: 9.796˚ E, 0.016˚ N
Range: 9.412˚ - 10.180˚ E, 0.368˚ S - 0.399˚ N
Crater
15 mi
Heinrich Eduard von Lade (1817-1904), German banker and amateur astronomer
Rhaeticus F
Center: 6.438˚ E, 0.060˚ S
Range: 6.134˚ - 6.742˚ E, 0.364˚ S - 0.244˚ N
Crater
11 mi
Georg Joachim Rheticus (1514-1574), Austria-born astronomer & mathematician
Rhaeticus
Center: 4.924˚ E, 0.032˚ N
Range: 4.192˚ - 5.657˚ E, 0.701˚ S - 0.764˚ N
Crater
30 x 27 mi, 1.0 mi
Georg Joachim Rheticus (1514-1574), Austria-born astronomer & mathematician
Rhaeticus L
Center: 3.484˚ E, 0.205˚ N
Range: 3.257˚ - 3.711˚ E, 0.022˚ S - 0.432˚ N
Crater
9 mi
Georg Joachim Rheticus (1514-1574), Austria-born astronomer & mathematician
Sinus Medii
Center: 1.027˚ E, 1.634˚ N
Range: 3.371˚ W - 5.551˚ E, 2.048˚ S - 4.641˚ N
Bay
178 mi
Bay of the Center
Mösting E
Center: 4.591˚ W, 0.178˚ N
Range: 5.189˚ - 3.992˚ W, 0.421˚ S - 0.777˚ N
Crater
27 mi
Johan Sigismund von Møsting (1759-1843), Danish banker, finance minister, and astronomy enthusiast
Sömmering
Center: 7.526˚ W, 0.193˚ N
Range: 7.987˚ - 7.065˚ W, 0.268˚ S - 0.654˚ N
Crater
17 mi, 0.8 mi
Samuel Thomas von Sömmering (1755–1830),German physician and anatomist
Lansberg
Center: 26.627˚ W, 0.312˚ S
Range: 27.266˚ - 25.988˚ W, 0.951˚ S - 0.327˚ N
Crater
24 mi, 1.9 mi
Philippe van Lansbergen (1561-1632), Dutch astronomer and mathematician
Mare Insularum
Center: 30.640˚ W, 7.792˚ N
Range: 39.195˚ - 22.153˚ W, 0.596˚ S - 16.345˚ N
Mare
318 mi
Sea of Islands
Oceanus Procellarum
Center: 56.677˚ W, 20.671˚ N
Range: 81.084˚ - 26.850˚ W, 16.266˚ S - 57.433˚ N
Mare
1611 x 353 mi
Ocean of Storms
Lohrmann D
Center: 65.273˚ W, 0.141˚ S
Range: 65.442˚ - 65.104˚ W, 0.310˚ S - 0.028˚ N
Crater
7 mi
Wilhelm Gotthelf Lohrmann (1796-1840), German selenographer
Rimae Hevelius
Center: 66.377˚ W, 0.809˚ N
Range: 67.849˚ - 63.582˚ W, 1.284˚ S - 2.956˚ N
Rilles
113 mi
Johannes Hevelius (1611-1687), Polish astronomer
Lohrmann
Center: 67.383˚ W, 0.440˚ S
Range: 67.898˚ - 66.867˚ W, 0.955˚ S - 0.075˚ N
Crater
19 mi, 1.0 mi
Wilhelm Gotthelf Lohrmann (1796-1840), German selenographer
Rimae Riccioli
Center: 73.071˚ W, 1.515˚ S
Range: 76.809˚ - 68.566˚ W, 4.754˚ S - 1.247˚ N
Rilles
249 mi
Giovanni Battista Riccioli (1598-1671), Italian astronomer
Schlüter P
Center: 85.208˚ W, 0.054˚ N
Range: 85.550˚ - 84.865˚ W, 0.289˚ S - 0.397˚ N
Crater; libration zone
12 mi
Heinrich Schlüter (1815-1844), German astronomer
Now that we’ve taken a tour of nearside features along the equator, let us turn to the lunar north and south celestial poles. As you know, the Earth’s north celestial pole (NCP) is currently located quite close to Polaris. However, on the Moon, the NCP is located in Draco near the Cat’s Eye Nebula (NGC 6543), about two-thirds of the way between Polaris and the center of the Head of Draco.
The Moon’s south celestial pole (SCP) is located in the constellation Dorado inside of the Large Magellanic Cloud (LMC). If you were stationed at the south pole of the Moon, you would see the Large Magellanic Cloud directly overhead at all times!
The Moon has many fascinating places, tempting us to explore. Some of them have quite interesting names. One of my favorites is Lacus Perseverantiae, Lake of Persistence. Its location is 62.0˚ E and 8.0˚ N. See if you can find it here. (Hint: under Layers : Overlays select Nomenclature, and under Settings select Show Graticule.) Have fun exploring!