Why was the definition of the $ ext{AU}$ changed from a measurement-based value to a fixed number in 2012?
Answer
The previous definition depended on the heliocentric gravitational constant, which changes as the Sun radiates energy.
The previous physics-based definition relied on the Sun's mass via the heliocentric gravitational constant ($G M_{\odot}$). Since the Sun constantly radiates energy and decreases in mass, adhering to this definition would make the AU a time-varying unit, complicating long-term calculations.
Related Questions
What is the exact, fixed value of the Astronomical Unit ($ ext{AU}$) established by the IAU in 2012?Why was the definition of the $ ext{AU}$ changed from a measurement-based value to a fixed number in 2012?Approximately how long does it take light to cross a distance equivalent to one Astronomical Unit?Which unit is primarily used by professional astronomers for mapping distances within interstellar space?What is the meaning behind the name 'parsec'?How does the distance to Proxima Centauri, approximately $267,000 ext{ AU}$, translate into the unit preferred for interstellar mapping?What unit is used to describe the immense distances between galaxy clusters?What method is used for determining distance when even megaparsecs become too cumbersome, such as for the very furthest observable objects?Which of these conversions accurately reflects the relationship between a parsec and the light-year?What was the historical basis for defining the Astronomical Unit before the 2012 standardization?