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Out of the three quantities that characterize the state of an isolatedgaseous body: pressure, temperature and volume the radius is the only onedirectly measurable for the Sun, what is specially true in the optical windowand for ground base measurements. The Heliometer of Observatorio Nacional, inRio de Janeiro, measures the distance between two opposite limbs of the Sun inthe same field of view, through the reflection on a 10 cm parabolic mirrorsplit on its half and forming an appropriate angle. This configuration is freefrom optical aberrations and focal variations along the measurement direction.The mirrors are made on CCZ vitro-ceramic and the telescope structure is ofcarbon steel, resulting that there is no flexion or temperature deformation.The instrument is compact, and can perform hundreds of measurements per dutyday, around all heliolatitudes. It attains an accuracy on the solar radius of0.01 arcsec, becoming the ideal instrument to monitor from the ground the solardiameter, and to bridge satellites and astrolabes historical series of data. Wediscuss the first years of regular observation, with emphasis on theinstrumental calibrations and on the statistic study of the derived timeseries, attitude series, and solar geometry series. On basis of these series weobtain how well the Heliometer and Solar Astrolabe results are matched.

The Heliometer of Rio de Janeiro in Operation - 2010 to 2013