Gravity Probe A (GP-A) was a satellite-based experiment to test Einstein's theory of general relativity performed by the Smithsonian Astrophysical Observatory. It used a MASER to measure the rate change of a clock in lower gravity with high precision. Albert Einstein, photographed by Yousuf Karsh in 1948. ... For a non-technical introduction to the topic, please see Introduction to General relativity. ... The Smithsonian castle, as seen through the garden gate. ... Spiral Galaxy ESO 269-57 // Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... MolÄ—tai Astronomical Observatory An observatory is a location used for observing terrestrial and/or celestial events. ... A Hydrogen RF discharge, the first element inside an Hydrogen Maser (see description below), courtesy NASA/JPL-Caltech. ... A wall clock A clock (from the Latin cloca, bell) is an instrument for measuring time. ... Gravity is a force of attraction that acts between bodies that have mass. ...

It was launched on June 18, 1976 on top of a Scout launcher and remained in space for 1 hour and 55 minutes, as intended. It then crashed into the Atlantic Ocean. June 18 is the 169th day of the year in the Gregorian Calendar (170th in leap years), with 196 days remaining. ... 1976 (MCMLXXVI) was a leap year starting on Thursday (the link is to a full 1976 calendar). ... The hour (symbol: h) is a unit of time. ... A minute is a unit of time equal to 1/60th of an hour and to 60 seconds. ...

Experimental setup

Gravity Probe A consisted of a MASER system that ran throughout the mission. It represented a "clock" with very high accuracy. The satellite containing the MASER was launched into a highly elliptical orbit, which caused a large change in the "local" gravity seen by the MASER. (Maximum height of the orbit was 6200 miles (10000 km)). At this height, a clock should run 4.5 parts in 10¹⁰ faster than one on the Earth. The clock rate was measured from the ground and compared to the theoretical predictions. Thus, the experiment was able to test the "equivalence principle" with an accuracy of about 150 parts per million. A Hydrogen RF discharge, the first element inside an Hydrogen Maser (see description below), courtesy NASA/JPL-Caltech. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... A mile is any of a number of units of distance, each in the magnitude of 1–10 km. ... A kilometre (American spelling: kilometer), symbol: km is a unit of length in the metric system equal to 1000 metres (from the Greek words χίλια (khilia) = thousand and μέτρο (metro) = count/measure). ... THERE IS NO SUCH THING< MWAHAHAHAHAHAHAHA> In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ...

Results

Gravity Probe A confirmed the prediction that gravity slows the flow of time. Gravity is a force of attraction that acts between bodies that have mass. ... A pocket watch. ...

See also

• Timeline of gravitational physics
• Gravity Probe B