The Eastern and Western Hemispheres

The Eastern and Western Hemispheres are the longitude analogue of the Northern and Southern Hemispheres. The /learn/the-northern-and-southern-hemispheres support covers the equator-bisected pair; this article covers the prime-meridian-bisected pair. The key structural contrast is that the Eastern/Western split is chosen, not given. The /learn/the-prime-meridian pillar covers the line itself; the 1884 conference that fixed it is covered in /learn/the-1884-international-meridian-conference. This article covers the geography of the two halves, the population asymmetry, the relationship to time zones and the date line, the distinction between the “Western Hemisphere” and the “Western world”, and the alternative 20°W/160°E convention that some atlases use.

Definition

A hemisphere is half of a sphere. The Eastern and Western Hemispheres are specifically the halves separated by the great circle formed by the prime meridian and the antimeridian:

• Eastern Hemisphere: every point with longitude between 0° and +180° (exclusive at both ends or with conventions for the boundaries).
• Western Hemisphere: every point with longitude between 0° and −180° (or equivalently between 180° and 360° when using the 0°–360° convention).

The prime meridian and the antimeridian together form the dividing great circle. Both are explicitly named meridians: the prime meridian defines 0° longitude per the IERS Conventions, and the antimeridian is its counterpart on the opposite side of Earth. The /learn/the-international-date-line support covers the political line that broadly follows the antimeridian but bends to keep individual countries on a single calendar day.

A chosen convention

The key contrast with the latitude hemispheres is that the longitude hemispheres are set by treaty, not by physics. The latitude axis has a free origin: Earth's rotation fixes the equatorial plane, and the equator is therefore the unique natural latitude origin. The longitude axis has no such anchor; any meridian could serve as 0° with no loss of generality, and the choice has to be made by agreement.

Prior to the 1884 International Meridian Conference in Washington, DC, national prime meridians varied widely: Paris, Cadiz, Pulkovo, Madrid, Amsterdam, Washington, and Ferro (modern El Hierro in the Canary Islands) were all used in different national chart systems. The 1884 conference adopted Greenwich by a 22–1–2 vote, primarily because by that date roughly 72% of the world's shipping tonnage already used Greenwich-referenced charts. The /learn/the-prime-meridian pillar covers this decision in more depth.

The Eastern/Western Hemisphere convention is therefore downstream of the 1884 vote. If the conference had chosen Paris, the “Western” Hemisphere would have been a different set of points. The convention is meaningful and globally used, but it is historical, not necessary.

Geography

Each continent's position relative to the prime meridian:

| Continent | Eastern | Western | Notes | |---|---|---|---| | North America | — | All | Greenland eastern fringe touches the prime meridian; otherwise entirely Western | | South America | — | All | Atlantic coast lies as far east as ~34°W | | Europe | Mostly | Western fringe | The UK, Ireland, France, Spain, Portugal, and small parts of Iceland have territory west of the prime meridian | | Africa | Mostly | Far-western fringe | Western Sahara, Mauritania, Senegal, the Gambia, Cape Verde, Mali, Guinea, Liberia, and Sierra Leone are partly or wholly west of 0° | | Asia | All | — | Easternmost extent at ~169°E in Chukotka | | Australia | All | — | Western Australia at ~113°E to Norfolk Island at ~168°E | | Antarctica | Half | Half | The continent spans all longitudes; the convention assigns it to both | | Pacific Islands | Mostly | Some | Hawaii, French Polynesia, and the eastern Polynesian islands are Western; Fiji, Tonga, Tuvalu, and the western Pacific are Eastern |

Most of the populated landmass — Eurasia and Africa — is in the Eastern Hemisphere. The Western Hemisphere is dominated by the two Americas plus the Pacific islands closer to them.

A handful of countries straddle the prime meridian. The most populated is the United Kingdom: the prime meridian crosses Lincolnshire, East Sussex, and East Yorkshire as well as Greater London. France is crossed near Le Havre and Villers-sur-Mer; Spain through Castellón; Algeria, Mali, Burkina Faso, Togo, and Ghana further south. The prime-meridian-spanning countries are conventionally treated as belonging to whichever hemisphere holds most of their territory and population.

Population

About 85% of the world's 8 billion people live in the Eastern Hemisphere, per UN population data. The Western Hemisphere holds roughly 1.2 billion, distributed as:

• United States: ~340 million
• Brazil: ~215 million
• Mexico: ~130 million
• Colombia: ~52 million
• Argentina: ~47 million
• Canada: ~40 million
• Peru: ~34 million
• Venezuela: ~28 million
• Chile, Ecuador, and Cuba in the 18–22 million range each
• Plus the rest of Central America and the Caribbean

The Eastern Hemisphere's 6.8 billion is dominated by China and India together (~2.85 billion), with the rest distributed across Indonesia (~280 million), Pakistan (~240 million), Nigeria (~230 million), Bangladesh (~175 million), Russia (~145 million), Japan (~125 million), and many other large national populations.

Time zones and UTC

The hemispheric split aligns with the time-zone offset convention. Eastern-Hemisphere time zones generally have positive UTC offsets (UTC+1 through UTC+14), corresponding to the Sun reaching the meridian earlier than at Greenwich. Western-Hemisphere time zones have negative offsets (UTC−1 through UTC−12), corresponding to later solar noon. Per NIST, every civil time zone is now expressed as an offset from UTC, which is itself anchored to the prime meridian.

The convention is not strict, however. Some Eastern-Hemisphere countries adopt UTC−12 or similar western-style offsets for practical reasons (the Kiribati Line Islands at UTC+14 are in the Eastern Hemisphere despite being at about 157°W, geographically Western, because Kiribati shifted the date line east in 1995). The /learn/time-zones-explained pillar covers the political compromises that decouple civil time from solar time.

“Western world” versus “Western Hemisphere”

The strict geographic term “Western Hemisphere” refers to the longitude half: anything with negative longitude. The informal political term “Western world” refers to a cultural and geopolitical grouping that originally meant Western Europe and that now informally includes North America, Australia, New Zealand, Japan (in some usages), and several other countries by virtue of shared political and cultural traditions.

The two terms overlap but are distinct:

• Australia and New Zealand are deeply Eastern Hemisphere but are universally considered part of the “Western world”.
• Most of South America is squarely Western Hemisphere but is usually classified as “Latin” or “Global South” rather than “Western” in geopolitical usage.
• China is entirely Eastern Hemisphere and is not part of the “Western world”.
• Russia is mostly Eastern Hemisphere and is variously classified.

The slippage between the geographic and political terms is a constant source of confusion in news writing. This article uses “hemisphere” to mean the strict geographic half.

The Old World and the New World

A related division long predates the 1884 prime meridian decision: the “Old World” (Africa, Europe, and Asia, known to pre-Columbian Mediterranean and European cultures) and the “New World” (the Americas, named after their European “discovery” from 1492 onward). The Old World is roughly the Eastern Hemisphere minus Australia and the Pacific islands; the New World is roughly the Western Hemisphere.

The terminology is no longer used in formal geography because it reflects a Eurocentric framing — Africa, Asia, and Australia all had deep human histories and well-developed civilisations long before European contact. It survives in specific scientific and culinary contexts. Botanists distinguish Old World monkeys from New World monkeys; oenologists distinguish Old World wines (Europe, broadly the classical wine regions) from New World wines (the Americas, Australia, New Zealand, South Africa); historians of agriculture discuss the Columbian Exchange, the post-1492 transfer of crops, livestock, diseases, and people between the two worlds.

The relevance to the hemispheric split is that the Western Hemisphere broadly equals the New World plus the parts of Eurasia and Africa that fall west of the prime meridian. The political and cultural concept of “the Americas” — North, Central, and South America together as a unit — sits inside the Western Hemisphere and is the most natural political grouping for the region. The Organization of American States (OAS), based in Washington, DC, formally groups all 35 sovereign states in the Americas; its membership is essentially the political analogue of the Western Hemisphere's land population.

Trans-Pacific routes and the antimeridian

Air and shipping routes between the Eastern and Western Hemispheres across the Pacific cross both the antimeridian and the International Date Line, with substantial practical consequences. A Tokyo-to-Los Angeles flight departing Narita at 17:00 local time on a Friday will typically land at LAX around 11:00 local time on the same Friday — earlier in the day than it left, because it has crossed the date line westward to eastward, gaining a calendar day. The reverse direction (LAX to Narita) loses a day: a Saturday-evening departure arrives Monday morning rather than Sunday.

The antimeridian crosses few populated landmasses — eastern Russia at Chukotka, the western Aleutians of Alaska, parts of Fiji, and Antarctica — but the surrounding Pacific is heavily used for trans-hemispheric shipping. The /learn/the-international-date-line support covers the bends in the political date line that prevent these routes from splitting communities across two calendar days at any given moment.

The 20°W / 160°E alternative

Some atlases — including older editions of National Geographic — use 20°W and 160°E as the East–West dividing meridians instead of 0° and 180°. The motivation is to keep all of Europe, Africa, and the eastern edge of Greenland inside the Eastern Hemisphere without splitting any continent. With the 20°W boundary, Iceland sits in the Eastern Hemisphere; with the 0° boundary it sits partly Western, partly Eastern.

The 20°W/160°E convention is geographically tidy but does not align with the longitude coordinate system. It is sometimes useful for political or cultural geography but is not the default; the canonical convention follows the IERS Reference Meridian at 0°. When the article uses “Eastern Hemisphere” or “Western Hemisphere” without qualification, the 0°/180° prime-meridian convention is meant throughout.

Sources

• Proceedings of the International Meridian Conference (October 1884) — the founding treaty document.
• IERS Conventions (TN 36) — IRM definition.
• UN DESA, World Population Prospects — population data.
• NIST glossary — time-zone references.
• BIPM, Coordinated Universal Time — UTC anchor at the prime meridian.

For the latitude analogue, see /learn/the-northern-and-southern-hemispheres; for the line that divides this hemispheric pair, see /learn/the-prime-meridian.