Measuring the absolute value of the AU

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SUMMARY

The Astronomical Unit (AU) is defined as approximately 149,597,870 kilometers, representing the mean distance between the Earth and the Sun. This value is derived from the radius of an unperturbed circular orbit that a massless body would maintain around the Sun over a period of 365.2568983 days, with the Gaussian constant set at 0.01720209895. While the AU is a standard measure, it is slightly less than the average distance of 150 million kilometers or 93 million miles due to orbital eccentricities.

PREREQUISITES
  • Understanding of orbital mechanics
  • Familiarity with the concept of the Gaussian constant
  • Knowledge of astronomical measurements
  • Basic grasp of circular orbits
NEXT STEPS
  • Research the methods used to measure astronomical distances
  • Explore the implications of orbital eccentricity on distance measurements
  • Learn about the historical evolution of the definition of the Astronomical Unit
  • Investigate the role of the Gaussian constant in celestial mechanics
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Astronomers, astrophysicists, educators in space science, and anyone interested in the measurement of astronomical distances.

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How can they be sure that the value for the AU is 149,597,870 km? What methods are used to measure it?
 
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An Astronomical Unit is approximately the mean distance between the Earth and the Sun. It is a derived constant and used to indicate distances within the solar system. Its formal definition is the radius of an unperturbed circular orbit a massless body would revolve about the sun in 2*(pi)/k days (i.e., 365.2568983... days), where k is defined as the Gaussian constant exactly equal to 0.01720209895. Since an AU is based on radius of a circular orbit, one AU is actually slightly less than the average distance between the Earth and the Sun (approximately 150 million km or 93 million miles).

http://neo.jpl.nasa.gov/glossary/au.html
 

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