Altitude is the elevation of an object from a known level or datum.

Common datums are mean sea level and the surface of the WGS-84 geoid, used by GPS.

In the United States and the UK aviation altitude is usually measured in feet.

Everywhere else in the world the altitude is measured in metres. Atmospheric pressure decreases as altitude increases.

This principle is the basis of operation of the pressure altimeter, which is an aneroid barometer calibrated to indicate altitude instead of pressure.

It is the fall in pressure that leads to a shortage of oxygen (hypoxia) in humans on ascent to high altitude..

For more information about the topic Altitude, read the full article at Wikipedia.org, or see the following related articles:

Altimeter — An altimeter is an active instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, ...  > read more

Sea level — Mean sea level (MSL) is the average (mean) height of the sea, with reference to a suitable reference surface. Defining the reference level, however, ...  > read more

Boiling — Boiling is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to a temperature such that its vapor pressure is above ...  > read more

Military aviation — Military aviation is used to attack or defend a country through the sky. There are many types of military aircraft, but the basic types of military ...  > read more

Related Stories

High Altitude Soccer Teams Have Significant Advantage Over Lowland Teams (January 4, 2008) — Soccer teams from high altitude countries have a significant advantage when playing at both low and high altitudes, finds a new study. In contrast, lowland teams are unable to acclimatise to high ...  > read more

54 Per Cent Of Air Passengers Experience Significant Reduction In Oxygen Levels (April 27, 2005) — Air passengers experience a significant reduction in oxygen levels according to research in the May isssue of Anaesthesia. 54% of those studied in the air by qualified anaesthetists displayed levels ...  > read more

Exploring How The Body Adapts To Exercise At Altitude: Hypoxia Affects Muscle And Nerve Responses (July 12, 2009) — Exercise requires the integrated activity of every organ and tissue in the body, and understanding how these respond to the decreased oxygen levels present at moderate to high altitude is the focus ...  > read more

Historical Look At Physiology And WWII Air War (April 11, 2008) — World War II-era physiologists helped solve physiological problems related to flight, research that helped pave the way for an Allied victory in the air. Physiologists trained a 145-pound St. Bernard ...  > read more

Engineering Students Launch Record-breaking Balloon (June 18, 2008) — Early-career engineers at Lockheed Martin who are also earning engineering degrees at Cornell broke the world amateur high-altitude balloon record in a recent near-space flight that exceeded 125,000 ...  > read more

Search ScienceDaily

Flying and Radiation Risk