<p>Only one side of the <strong>Moon</strong> is visible from Earth because the Moon rotates about its spin axis at the same rate that the Moon orbits the Earth, a situation known as <strong>synchronous rotation</strong> or <strong>tidal locking</strong>.</p>

Why does the Earth only see one side of the moon?

<div>From Wikipedia, the free encyclopedia</div><div role="note" dir="ltr">"Nearside" redirects here. For the usage in road vehicles, see <a href="https://en.wikipedia.org/wiki/Right-_and_left-hand_traffic#Terminology" title="Right- and left-hand traffic" dir="ltr">Right- and left-hand traffic §&nbsp;Terminology</a>.</div><img alt="" src="https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Moon_names.svg/300px-Moon_names.svg.png" width="300" height="225" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Moon_names.svg/450px-Moon_names.svg.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/6/61/Moon_names.svg/600px-Moon_names.svg.png 2x"><div class="caption" dir="ltr">The names of the major <a href="https://en.wikipedia.org/wiki/Lunar_mare" title="Lunar mare" dir="ltr">maria</a> and some <a href="https://en.wikipedia.org/wiki/Lunar_craters" title="Lunar craters" dir="ltr">craters</a> on the near side of the Moon</div><p dir="ltr">The <b dir="ltr">near side of the Moon</b> is the lunar hemisphere that always faces towards <a href="https://en.wikipedia.org/wiki/Earth" title="Earth" dir="ltr">Earth</a>, opposite to the <a href="https://en.wikipedia.org/wiki/Far_side_of_the_Moon" title="Far side of the Moon" dir="ltr">far side</a>. Only one side of the <a href="https://en.wikipedia.org/wiki/Moon" title="Moon" dir="ltr">Moon</a> is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth—a situation known as <a href="https://en.wikipedia.org/wiki/Synchronous_rotation" title="Synchronous rotation" dir="ltr">synchronous rotation</a>, or <a href="https://en.wikipedia.org/wiki/Tidal_locking" title="Tidal locking" dir="ltr">tidal locking</a>.
</p><p dir="ltr">The Moon is directly illuminated by the <a href="https://en.wikipedia.org/wiki/Sun" title="Sun" dir="ltr">Sun</a>, and the cyclically varying viewing conditions cause the <a href="https://en.wikipedia.org/wiki/Lunar_phase" title="Lunar phase" dir="ltr">lunar phases</a>. Sometimes the dark portion of the Moon is faintly visible due to <a href="https://en.wikipedia.org/wiki/Earthlight_(astronomy)" title="Earthlight (astronomy)" dir="ltr">earthshine</a>, which is indirect <a href="https://en.wikipedia.org/wiki/Sunlight" title="Sunlight" dir="ltr">sunlight</a> reflected from the surface of Earth and onto the Moon.
</p><p dir="ltr">Since the <a href="https://en.wikipedia.org/wiki/Orbit_of_the_Moon" title="Orbit of the Moon" dir="ltr">Moon's orbit</a> is both somewhat <a href="https://en.wikipedia.org/wiki/Elliptic_orbit" title="Elliptic orbit" dir="ltr">elliptical</a> and <a href="https://en.wikipedia.org/wiki/Orbital_inclination" title="Orbital inclination" dir="ltr">inclined</a> to its <a href="https://en.wikipedia.org/wiki/Equator" title="Equator" dir="ltr">equatorial plane</a>, <a href="https://en.wikipedia.org/wiki/Libration" title="Libration" dir="ltr">libration</a> allows up to 59% of the Moon's surface to be viewed from Earth (though only half at any moment from any point).
</p><img alt="Over one lunar month more than half of the Moon's surface can be seen from the surface of the Earth." src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Lunar_libration_with_phase_Oct_2007_%28continuous_loop%29.gif/220px-Lunar_libration_with_phase_Oct_2007_%28continuous_loop%29.gif" width="220" height="221" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Lunar_libration_with_phase_Oct_2007_%28continuous_loop%29.gif/330px-Lunar_libration_with_phase_Oct_2007_%28continuous_loop%29.gif 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Lunar_libration_with_phase_Oct_2007_%28continuous_loop%29.gif/440px-Lunar_libration_with_phase_Oct_2007_%28continuous_loop%29.gif 2x"><div class="caption" dir="ltr">The near side as observed (from Earth's <a href="https://en.wikipedia.org/wiki/Northern_Hemisphere" title="Northern Hemisphere" dir="ltr">Northern Hemisphere</a>) over the course of one <a href="https://en.wikipedia.org/wiki/Lunar_month" title="Lunar month" dir="ltr">month</a>, showing the <a href="https://en.wikipedia.org/wiki/Libration" title="Libration" dir="ltr">libration</a> effects</div><h2>Contents</h2><h2><span>Orientation</span></h2><img alt="" src="https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Moon_nearside_LRO.jpg/220px-Moon_nearside_LRO.jpg" width="220" height="220" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Moon_nearside_LRO.jpg/330px-Moon_nearside_LRO.jpg 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Moon_nearside_LRO.jpg/440px-Moon_nearside_LRO.jpg 2x"><div class="caption" dir="ltr">Detailed view by NASA's <a href="https://en.wikipedia.org/wiki/Lunar_Reconnaissance_Orbiter" title="Lunar Reconnaissance Orbiter" dir="ltr">LRO</a></div><p>The image of the Moon here is drawn as is normally shown on maps, that is with north on top and west to the left. Astronomers traditionally turn the map to have south on top to correspond with the northern-hemisphere view in astronomical telescopes, which typically show the image upside down.
</p><p dir="ltr">West and east on the Moon are where you would expect them, when standing on the Moon. But when we, on Earth, see the Moon in the sky, then the east–west direction is just reversed. When specifying coordinates on the Moon it should therefore always be mentioned whether <a href="https://en.wikipedia.org/wiki/Geographic" title="Geographic" dir="ltr">geographic</a> (or rather <a href="https://en.wikipedia.org/wiki/Selenographic_coordinates" title="Selenographic coordinates" dir="ltr">selenographic</a>) coordinates are used or <a href="https://en.wikipedia.org/wiki/Astronomical" title="Astronomical" dir="ltr">astronomical</a> coordinates.
</p><p dir="ltr">The actual orientation you see the Moon in the sky or on the horizon depends on your geographic <a href="https://en.wikipedia.org/wiki/Latitude" title="Latitude" dir="ltr">latitude</a> on Earth. In the following description a few typical cases will be considered.
</p><UL><LI>On the north pole, if the Moon is visible, it stands low above the horizon with <a href="https://en.wikipedia.org/wiki/Lunar_north_pole" title="Lunar north pole" dir="ltr">its north pole</a> up.</LI><LI>In mid northern latitudes (North America, Europe, Asia) the Moon rises in the east with its northeastern limb up (Mare Crisium), it reaches its highest point in the south with its north on top, and sets in the west with its northwestern limb (Mare Imbrium) on top.</LI><LI>On the equator, when the Moon rises in the east, its N — S axis appears horizontal and Mare Foecunditatis is on top. When it sets in the west, about 12.5 hours later, the axis is still horizontal, and Oceanus Procellarum is the last area to dip below the horizon. In between these events, the Moon reached its highest point in the <a href="https://en.wikipedia.org/wiki/Zenith" title="Zenith" dir="ltr">zenith</a> and then its selenographic directions are lined up with those on Earth.</LI><LI>In mid southern latitudes (South America, South Pacific, Australia, South Africa) the Moon rises in the east with its southeastern limb up (Mare Nectaris), it reaches its highest point in the north with its south on top, and sets in the west with its southwestern limb (Mare Humorum) on top.</LI><LI>On the south pole the Moon behaves as on the north pole, but there it appears with <a href="https://en.wikipedia.org/wiki/Lunar_south_pole" title="Lunar south pole" dir="ltr">its south pole</a> up.</LI></UL><img alt="" src="https://upload.wikimedia.org/wikipedia/commons/thumb/5/59/Diurnal_motion_by_latitude.svg/752px-Diurnal_motion_by_latitude.svg.png" width="752" height="179" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/5/59/Diurnal_motion_by_latitude.svg/1128px-Diurnal_motion_by_latitude.svg.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/5/59/Diurnal_motion_by_latitude.svg/1504px-Diurnal_motion_by_latitude.svg.png 2x"><div class="caption">Schematics of moonrise on different Earth latitudes</div><p dir="ltr">The two hemispheres have distinctly different appearances, with the near side covered in multiple, large <a href="https://en.wikipedia.org/wiki/Lunar_mare" title="Lunar mare" dir="ltr"><i dir="ltr">maria</i></a> (Latin for 'seas'). These lowlands were believed to be seas of <a href="https://en.wikipedia.org/wiki/Lunar_water" title="Lunar water" dir="ltr">lunar water</a> by the astronomers who first mapped them, in the 17th century (notably, <a href="https://en.wikipedia.org/wiki/Giovanni_Battista_Riccioli" title="Giovanni Battista Riccioli" dir="ltr">Giovanni Battista Riccioli</a> and <a href="https://en.wikipedia.org/wiki/Francesco_Maria_Grimaldi" title="Francesco Maria Grimaldi" dir="ltr">Francesco Maria Grimaldi</a>). Although no bodies of <a href="https://en.wikipedia.org/wiki/Liquid" title="Liquid" dir="ltr">liquid</a> exist on the Moon, the term "<i dir="ltr">mare</i>" (plural: <i dir="ltr">maria</i>) is still used. <a href="https://en.wikipedia.org/wiki/Far_side_of_the_Moon" title="Far side of the Moon" dir="ltr">The far side</a> has a battered, densely cratered appearance with few maria. Only 1% of the surface of the far side is covered by maria,<sup dir="ltr"><a href="https://en.wikipedia.org/wiki/Near_side_of_the_Moon#cite_note-1" dir="ltr">[1]</a></sup> compared to 31.2% on the near side. According to research analyzed by NASA's <a href="https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_Laboratory" title="Gravity Recovery and Interior Laboratory" dir="ltr">Gravity Recovery and Interior Laboratory</a> (GRAIL) mission, the reason for the difference is because the Moon's <a href="https://en.wikipedia.org/wiki/Crust_(geology)" title="Crust (geology)" dir="ltr">crust</a> is thinner on the near side compared to the far side.<sup dir="ltr"><a href="https://en.wikipedia.org/wiki/Near_side_of_the_Moon#cite_note-2" dir="ltr">[2]</a></sup> The dark splotches that make up the large lunar maria are <a href="https://en.wikipedia.org/wiki/Lava" title="Lava" dir="ltr">lava</a>-filled <a href="https://en.wikipedia.org/wiki/Impact_basin" title="Impact basin" dir="ltr">impact basins</a> that were created by asteroid impacts about four billion years ago. Though both sides of the Moon were bombarded by similarly large impactors, the near side hemisphere crust and upper mantle was hotter than that of the far side, resulting in the larger impact craters.<sup dir="ltr"><a href="https://en.wikipedia.org/wiki/Near_side_of_the_Moon#cite_note-3" dir="ltr">[3]</a></sup> These larger impact craters make up the <a href="https://en.wikipedia.org/wiki/Man_in_the_Moon" title="Man in the Moon" dir="ltr">Man in the Moon</a> references from popular mythology.
</p>

<p>The <b>near side of the Moon </b>is the lunar hemisphere that always faces towards <a href="https://en.wikipedia.org/wiki/Earth">Earth </a>, opposite to the <a href="https://en.wikipedia.org/wiki/Far_side_of_the_Moon">far side </a>. Only one side of the <a href="https://en.wikipedia.org/wiki/Moon">Moon </a>is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth—a situation known as <a href="https://en.wikipedia.org/wiki/Synchronous_rotation">synchronous rotation </a>, or <a href="https://en.wikipedia.org/wiki/Tidal_locking">tidal locking </a>. </p>

<p>The Moon is directly illuminated by the <a href="https://en.wikipedia.org/wiki/Sun">Sun </a>, and the cyclically varying viewing conditions cause the <a href="https://en.wikipedia.org/wiki/Lunar_phase">lunar phases </a>. Sometimes the dark portion of the Moon is faintly visible due to <a href="https://en.wikipedia.org/wiki/Earthlight_(astronomy)">earthshine </a>, which is indirect <a href="https://en.wikipedia.org/wiki/Sunlight">sunlight </a>reflected from the surface of Earth and onto the Moon. </p>

<p>Since the <a href="https://en.wikipedia.org/wiki/Orbit_of_the_Moon">Moon's orbit </a>is both somewhat <a href="https://en.wikipedia.org/wiki/Elliptic_orbit">elliptical </a>and <a href="https://en.wikipedia.org/wiki/Orbital_inclination">inclined </a>to its <a href="https://en.wikipedia.org/wiki/Equator">equatorial plane </a>, <a href="https://en.wikipedia.org/wiki/Libration">libration </a>allows up to 59% of the Moon's surface to be viewed from Earth (though only half at any moment from any point). </p>

<p>The image of the Moon here is drawn as is normally shown on maps, that is with north on top and west to the left. Astronomers traditionally turn the map to have south on top to correspond with the northern-hemisphere view in astronomical telescopes, which typically show the image upside down. </p>

<p>West and east on the Moon are where you would expect them, when standing on the Moon. But when we, on Earth, see the Moon in the sky, then the east–west direction is just reversed. When specifying coordinates on the Moon it should therefore always be mentioned whether <a href="https://en.wikipedia.org/wiki/Geographic">geographic </a>(or rather <a href="https://en.wikipedia.org/wiki/Selenographic_coordinates">selenographic </a>) coordinates are used or <a href="https://en.wikipedia.org/wiki/Astronomical">astronomical </a>coordinates. </p>

<p>The actual orientation you see the Moon in the sky or on the horizon depends on your geographic <a href="https://en.wikipedia.org/wiki/Latitude">latitude </a>on Earth. In the following description a few typical cases will be considered. </p>

<ul><li>On the north pole, if the Moon is visible, it stands low above the horizon with <a href="https://en.wikipedia.org/wiki/Lunar_north_pole">its north pole </a>up. </li><li>In mid northern latitudes (North America, Europe, Asia) the Moon rises in the east with its northeastern limb up (Mare Crisium), it reaches its highest point in the south with its north on top, and sets in the west with its northwestern limb (Mare Imbrium) on top. </li><li>On the equator, when the Moon rises in the east, its N — S axis appears horizontal and Mare Foecunditatis is on top. When it sets in the west, about 12.5 hours later, the axis is still horizontal, and Oceanus Procellarum is the last area to dip below the horizon. In between these events, the Moon reached its highest point in the <a href="https://en.wikipedia.org/wiki/Zenith">zenith </a>and then its selenographic directions are lined up with those on Earth. </li><li>In mid southern latitudes (South America, South Pacific, Australia, South Africa) the Moon rises in the east with its southeastern limb up (Mare Nectaris), it reaches its highest point in the north with its south on top, and sets in the west with its southwestern limb (Mare Humorum) on top. </li><li>On the south pole the Moon behaves as on the north pole, but there it appears with <a href="https://en.wikipedia.org/wiki/Lunar_south_pole">its south pole </a>up. </li> </ul>

<p>The two hemispheres have distinctly different appearances, with the near side covered in multiple, large <a href="https://en.wikipedia.org/wiki/Lunar_mare"><i>maria </i> </a>(Latin for 'seas'). These lowlands were believed to be seas of <a href="https://en.wikipedia.org/wiki/Lunar_water">lunar water </a>by the astronomers who first mapped them, in the 17th century (notably, <a href="https://en.wikipedia.org/wiki/Giovanni_Battista_Riccioli">Giovanni Battista Riccioli </a>and <a href="https://en.wikipedia.org/wiki/Francesco_Maria_Grimaldi">Francesco Maria Grimaldi </a>). Although no bodies of <a href="https://en.wikipedia.org/wiki/Liquid">liquid </a>exist on the Moon, the term "<i>mare </i>" (plural: <i>maria </i>) is still used. <a href="https://en.wikipedia.org/wiki/Far_side_of_the_Moon">The far side </a>has a battered, densely cratered appearance with few maria. Only 1% of the surface of the far side is covered by maria,<sup><a href="https://en.wikipedia.org/wiki/Near_side_of_the_Moon#cite_note-1">[1] </a> </sup>compared to 31.2% on the near side. According to research analyzed by NASA's <a href="https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_Laboratory">Gravity Recovery and Interior Laboratory </a>(GRAIL) mission, the reason for the difference is because the Moon's <a href="https://en.wikipedia.org/wiki/Crust_(geology)">crust </a>is thinner on the near side compared to the far side.<sup><a href="https://en.wikipedia.org/wiki/Near_side_of_the_Moon#cite_note-2">[2] </a> </sup>The dark splotches that make up the large lunar maria are <a href="https://en.wikipedia.org/wiki/Lava">lava </a>-filled <a href="https://en.wikipedia.org/wiki/Impact_basin">impact basins </a>that were created by asteroid impacts about four billion years ago. Though both sides of the Moon were bombarded by similarly large impactors, the near side hemisphere crust and upper mantle was hotter than that of the far side, resulting in the larger impact craters.<sup><a href="https://en.wikipedia.org/wiki/Near_side_of_the_Moon#cite_note-3">[3] </a> </sup>These larger impact craters make up the <a href="https://en.wikipedia.org/wiki/Man_in_the_Moon">Man in the Moon </a>references from popular mythology. </p>

Near side of the Moon

Why does the Earth only see one side of the moon?

Other curated ideas on this topic: