Editing 4 Vesta (section)

===Early measurements===
{{stack|[[File:New SPHERE view of Vesta.jpg|thumb|[[Spectro-Polarimetric High-Contrast Exoplanet Research|SPHERE]] image is shown on the left, with a synthetic view derived from ''Dawn'' images shown on the right for comparison.<ref>{{cite web |title=New SPHERE view of Vesta |url=https://www.eso.org/public/images/potw1826a/ |website=www.eso.org |access-date=25 June 2018}}</ref>]]}}

Photometric observations of Vesta were made at the [[Harvard College Observatory]] in 1880–1882 and at the [[Observatoire de Toulouse]] in 1909. These and other observations allowed the rotation rate of Vesta to be determined by the 1950s. However, the early estimates of the rotation rate came into question because the [[light curve]] included variations in both shape and [[albedo]].<ref name="McFadden2008"/>

Early estimates of the diameter of Vesta ranged from {{convert|383|km|0}} in 1825, to {{convert|444|km|0|abbr=on}}. [[Edward Charles Pickering|E.C. Pickering]] produced an estimated diameter of {{convert|513|±|17|km|abbr=on}} in 1879, which is close to the modern value for the mean diameter, but the subsequent estimates ranged from a low of {{convert|390|km|0|abbr=on}} up to a high of {{convert|602|km|0|abbr=on}} during the next century. The measured estimates were based on [[photometry (astronomy)|photometry]]. In 1989, [[speckle interferometry]] was used to measure a dimension that varied between {{convert|498|and|548|km|0|abbr=on}} during the rotational period.<ref name="Hughes1994"/> In 1991, an [[occultation]] of the star [[SAO 93228]] by Vesta was observed from multiple locations in the eastern United States and Canada. Based on observations from 14 different sites, the best fit to the data was an elliptical profile with dimensions of about {{convert|550|×|462|km|0|abbr=on}}.<ref name="Povenmire2001"/> ''[[Dawn (spacecraft)|Dawn]]'' confirmed this measurement.{{efn|name=vesta_measurement|The data returned will include, for both asteroids, full surface imagery, full surface spectrometric mapping, elemental abundances, topographic profiles, gravity fields, and mapping of remnant magnetism, if any.<ref name="nssdca 2007_043a"/>}} These measurements will help determine the thermal history, size of the core, role of water in asteroid evolution and what meteorites found on Earth come from these bodies, with the ultimate goal of understanding the conditions and processes present at the solar system's earliest epoch and the role of water content and size in planetary evolution.<ref name="nssdca 2007_043a"/>

Vesta became the first asteroid to have its mass determined. Every 18 years, the asteroid [[197 Arete]] approaches within {{val|0.04|ul=AU}} of Vesta. In 1966, based upon observations of Vesta's [[gravitational perturbation]]s of Arete, Hans G. Hertz estimated the mass of Vesta at {{val|1.20|0.08|e=-10|u=M<sub>☉</sub>}} ([[solar mass]]es).<ref name="science160_3825"/> More refined estimates followed, and in 2001 the perturbations of [[17 Thetis]] were used to calculate the mass of Vesta to be {{val|1.31|0.02|e=-10|u=M<sub>☉</sub>}}.<ref name="aaa430"/> ''Dawn'' determined it to be {{val|1.3029|e=-10|u=M<sub>☉</sub>}}.