  Morphology is a powerful indicator of a galaxy's dynamical and merger
history. It is strongly correlated with many physical parameters, including
mass, star formation history and the distribution of mass. The Galaxy Zoo
project collected simple morphological classifications of nearly 900,000
galaxies drawn from the Sloan Digital Sky Survey, contributed by hundreds of
thousands of volunteers. This large number of classifications allows us to
exclude classifier error, and measure the influence of subtle biases inherent
in morphological classification. This paper presents the data collected by the
project, alongside measures of classification accuracy and bias. The data are
now publicly available and full catalogues can be downloaded in electronic
format from http://data.galaxyzoo.org.
