Northern Hemisphere

Lore & Background

Due to Earth's axial tilt of 23.439281°, there is a seasonal variation in the lengths of the day and night, and a seasonal variation in temperatures that lags the variation in day and night. Conventionally, winter in the Northern Hemisphere is taken as the period from the December solstice (typically December 21 UTC) to the March equinox (typically March 20 UTC), while summer is taken as the period from the June solstice through to the September equinox (typically on 23 September UTC). The dates vary each year due to the difference between the calendar year and the astronomical year. Within the Northern Hemisphere, oceanic currents can change the weather patterns that affect many factors within the north coast. Such events include El Niño–Southern Oscillation. Trade winds blow from east to west just above the equator. The winds pull surface water with them, creating currents, which flow westward due to the Coriolis effect. The currents then bend to the right, heading north. At about 30 degrees north latitude, a different set of winds, the westerlies, push the currents back to the east, producing a closed clockwise loop. In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the Coriolis effect. As a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres, best seen in ocean circulation patterns in the North Atlantic and North Pacific oceans. Clockwise air circulation is characteristic of high pressure weather cells, while hurricanes and tropical storms spin counterclockwise in the Northern Hemisphere. During the 2.5 million years of the Pleistocene, numerous cold phases, called glacials, or significant advances of continental ice sheets, in Europe and North America, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of the last glacial period ended about 10,000 years ago. Earth is currently in an interglacial period of the Quaternary, called the Holocene. The Arctic is a region around the North Pole (90° latitude) with cold winters and cool summers. Areas inside the Arctic Circle (66°34′ latitude) experience some days in summer when the Sun never sets, and some days during the winter when it never rises.

Reader's Guide

The Northern Hemisphere is defined as the half of Earth that is north of the equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the Solar System as Earth's North Pole. The shadow of a sundial moves clockwise on latitudes north of the subsolar point. During the day at these latitudes, the Sun tends to rise to its maximum at a southerly position. Between the Tropic of Cancer and the Equator, the Sun can be seen to the north, directly overhead, or to the south at noon, depending on the time of year. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from the Southern Hemisphere. The North Pole faces away from the Galactic Center of the Milky Way, resulting in the Milky Way being sparser and dimmer in the Northern Hemisphere compared to the Southern Hemisphere, making the Northern Hemisphere more suitable for deep-space observation, as it is not 'blinded' by the Milky Way. Tropical regions (between the Tropic of Cancer and the Equator) are generally hot all year round and tend to experience a rainy season during the summer months, and a dry season during the winter months. Between the Arctic Circle and the Tropic of Cancer lies the Northern temperate zone, where changes between summer and winter are generally mild, rather than extreme hot or cold, though a temperate climate can have very unpredictable weather. The Northern Hemisphere contains the continents of North America and mainland Eurasia, about two-thirds of Africa, and a small part of South America. Its oceans include the Arctic Ocean, Atlantic Ocean, Indian Ocean, and Pacific Ocean.

Did You Know?

• The Northern Hemisphere contains 67.3% of Earth's land, compared to the Southern Hemisphere's 80.9% water coverage.
• As of 2015, approximately 87.0% of the global population—about 6.4 billion people—lives in the Northern Hemisphere.
• Hurricanes and tropical storms spin counterclockwise in the Northern Hemisphere due to the Coriolis effect.
• The North Pole faces away from the Galactic Center of the Milky Way, making the Northern Hemisphere more suitable for deep-space observation.
• The last glacial period ended about 10,000 years ago, and Earth is currently in the Holocene interglacial.