Gaia is a cornerstone mission in the science programme of the European Space Agency (ESA). The spacecraft construction was approved in 2006, following a study in which the original interferometric concept was changed to a direct-imaging approach. Both the spacecraft and the payload were built by European industry. The involvement of the scientific community focusses on data processing for which the international Gaia Data Processing and Analysis Consortium (DPAC) was selected in 2007. Gaia was launched on 19 December 2013 and arrived at its operating point, the second Lagrange point of the Sun-Earth-Moon system, a few weeks later. The commissioning of the spacecraft and payload was completed on 19 July 2014. The nominal five-year mission started with four weeks of special, ecliptic-pole scanning and subsequently transferred into full-sky scanning mode. We recall the scientific goals of Gaia and give a description of the as-built spacecraft that is currently (mid-2016) being operated to achieve these goals. We pay special attention to the payload module, the performance of which is closely related to the scientific performance of the mission. We provide a summary of the commissioning activities and findings, followed by a description of the routine operational mode. We summarise scientific performance estimates on the basis of in-orbit operations. Several intermediate Gaia data releases are planned and the data can be retrieved from the Gaia Archive, which is available through the Gaia home page.

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The photodegradation technique was used to record the visible spectra for carotenoids and chlorophylls in virgin olive oil. Principal component analysis of the visible spectra for 81 samples of this type of oil with widely variable composition revealed that only two components contribute more than 99.7% of the spectral information. The Varimax factors and the absorbances of the oil pigments are linearly related. The joint use of these spectra and the absorbances at 455 and 670 nm allows the accurate reproduction of the visible spectrum for any virgin olive oil sample. Therefore, one can question whether a commercially available product is actually virgin olive oil if a comparison of its experimental and simulated absorbance values gives R(2) < 0.995 and RMSD > 0.006. The simulated spectra provide CIE L *a*b* chromatic coordinates that describe the color of the samples with little difference from those provided by the spectra for real samples.

Four polynomial expressions are obtained that provide a good approximation and an easy, rapid calculation of the chromatic coordinates and the chroma-L*, a*, b*, and C-for the illuminant C and the standard observer, for a virgin or extra virgin olive oil; absorbance is measured at only 480 and 670 nm. These are as follows: L*= 0.556458(A 480 ) 2 − 2.. These give acceptable results, making the method a practical alternative to the extremely laborious Commission Internationale d'Eclairage (CIE) L*a*b* system, by which 391 absorbance values must be measured individually, nanometer by nanometer, before applying more complex equations. The validity of the proposed method has been confirmed by comparison, using a set of 20 sample oils different from the set of 25 oils used to generate the order of the equations. The variations between the values provided by the proposed and standard methods, respectively, had a mean of 0.00 for each of the chromatic variables-L*, a*, b*, and C; SD were moderate (0.71, 0.52, 1.22, and 1.22, respectively); the root mean square and the R 2 terms also confirmed the validity of the method.

The CIE 1976 (L*, a*, and b*) color space for virgin olive oil was determined. Such a space encompasses any acceptable sample of this type of oil irrespective of the agronomic treatment that the olives have undergone because its color is due to two types of pigments, a systematic combination of which provides the whole range of theoretically possible colors. Color is quantified from the visible spectra for pure samples. Therefore, the pigment spectra, which were the averages of those for several samples, were determined in a medium highly similar to the source oil following application of a photochemical method. A combination of the pigment spectra provided 651 spectra for virtual samples, the colors of which spanned the entire color space for virgin olive oil. The positions of more than 100 Spanish olive oil samples of diverse origins in the color space were also determined, and the results were examined in relation to oil type and quality. Similar color spaces can be obtained for other foods, which can thus be characterized in terms of an additional physical property.