An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 4 Search : measurement
absolute measurement
  اندازه‌گیری ِ اوست   
andâzegiri-ye avast

Fr.: mesure absolue   

A measurement in which the comparison is directly with quantities whose units are basic units of the system. For example, the measurement of speed by measurements of distance and time is an absolute measurement, but the measurement of speed by a speedometer is not an absolute measurement. Note that the word absolute measurement implies nothing about → precision or → accuracy (IEEE Standard Dictionary of Electrical and Electronics Terms).

absolute; → measurement.

measurement
  اندازه‌گیری   
andâzegiri (#)

Fr.: mesure   

1) The act of measuring; a measured quantity.
2) The determination of the magnitude or amount of a quantity by comparison (direct or indirect) with the prototype standards of the system of units employed (IEEE Standard Dictionary of Electrical and Electronics Terms). → absolute measurement, → measurement uncertainty, → Roemer's measurement.

Verbal noun of → measure.

measurement uncertainty
  ناتاشتیگی ِ اندازه‌گیری   
nâtâštigi-ye andâzegiri

Fr.: incertitude de mesure   

The interval within which lies the actually measured value of a physical quantity and the true value of the same physical quantity.

measurement; uncertainty, from negation prefix un- + → certainty.

Roemer's measurement
  اندازه‌گیری ِ رؤمر   
andâzegiri-ye Rømer

Fr.: mesure de Rømer   

The first successful measurement of the → speed of light carried out by the Danish astronomer Ole Rømer in 1675 at Paris Observatory. Astronomers knew that the mean period of revolution for Jupiter's innermost satellite → Io (Jupiter I) was 42.5 hours. During this period Io was sometimes eclipsed by Jupiter. Astronomers expected that if Io was visible at some time it must be visible 42.5 hours later. But Ole Rømer discovered that there were many irregularities in Io's orbital period. Sometimes Io appeared too early and other times too late in relation to the expected times. The irregularities repeated themselves precisely at a one-year interval, which meant that they must be connected to the Earth's rotation around the Sun. Rømer attributed this difference in time to the additional distance the light from Io had to travel at different times, and used this information to calculate the speed of light. He found that it takes light 22 minutes to traverse the Earth's orbital diameter; the correct figure was later determined to be 16 minutes and 40 seconds. Rømer was able to measure the speed of light to be 230,000 km s-1. Although this figure was very close to the currently accepted value of 300,000 km s-1, it was rejected by the scientific community of the time, who assumed it to be much too high a figure.

Ole Rømer (1664-1710); → measurement.