By Geoff Brumfiel of Nature magazine Without fanfare,
astronomers have redefined one of the most important distances
in the Solar System. The astronomical unit (au) — the rough
distance from the Earth to the Sun — has been transformed from a
confusing calculation into a single number. The new standard,
adopted in August by unanimous vote at the International
Astronomical Union's meeting in Beijing, China, is now
149,597,870,700 meters — no more, no less. The effect on our
planet’s inhabitants will be limited. The Earth will continue to
twirl around the Sun, and in the Northern Hemisphere, autumn
will soon arrive. But for astronomers, the change means more
precise measurements and fewer headaches from explaining the au
to their students. The distance between the Earth and the Sun is
one of the most long-standing values in astronomy. The first
precise measurement was made in 1672 by the famed astronomer
Giovanni Cassini, who observed Mars from Paris, France, while
his colleague Jean Richer observed the planet f