Editing Observational astronomy (section)

=== Measuring results ===
Astronomers have a number of observational tools that they can use to make measurements of the heavens. For objects that are relatively close to the Sun and Earth, direct and very precise [[astrometric|position measurements]] can be made against a more distant (and thereby nearly stationary) background. Early observations of this nature were used to develop very precise orbital models of the various planets, and to determine their respective masses and gravitational [[perturbation (astronomy)|perturbation]]s. Such measurements led to the discovery of the planets [[Uranus]], [[Neptune]], and (indirectly) [[Pluto]]. They also resulted in an erroneous assumption of a fictional planet [[Vulcan (planet)|Vulcan]] within the orbit of [[Mercury (planet)|Mercury]] (but the explanation of the [[precession]] of Mercury's orbit by [[Albert Einstein|Einstein]] is considered one of the triumphs of his [[general relativity]] theory).