Measuring the absolute value of the AU

[Alvin]

How can they be sure that the value for the AU is 149,597,870 km? What methods are used to measure it?

 

[neutrino]

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

 

[sir-pinski]

The absolute value of the AU, or Astronomical Unit, is a crucial measurement in astronomy as it is used to determine the distances between objects in the solar system. It is defined as the average distance between the Earth and the Sun, and is currently accepted to be 149,597,870 km.

To ensure the accuracy of this value, scientists use various methods to measure the AU. One of the most common methods is the radar ranging technique, where radio waves are sent from Earth to a planet or asteroid and the time it takes for the waves to bounce back is measured. By knowing the speed of the waves, the distance between the two objects can be calculated.

Another method is the parallax technique, which involves measuring the apparent shift of an object's position against the background stars as the Earth orbits around the Sun. By using trigonometry, the distance to the object can be calculated and compared to the known distance of the AU.

In addition, spacecrafts such as the Voyager 1 and 2 have also been used to measure the AU through their images and data collected from their journeys through the solar system.

Overall, with the use of advanced technology and precise calculations, scientists are able to confidently determine the value for the AU as 149,597,870 km. This measurement is constantly being refined and updated as new techniques and advancements are made in the field of astronomy.