Hinode SOT Plate Scale Reinvestigated by G-Band Images on the 2012 Transit of Venus.

The Hinode Solar Optical Telescope (SOT) successfully observed the transit of Venus with an unprecedented high spatial resolution on 5 - 6 June 2012, providing images of the aureole refracted by the atmosphere of Venus and the dark Venus disk against the bright solar surface. The transit of Venus provided a unique opportunity for calibrating the plate scale of SOT images. With the examination of the radius of the dark Venus disk, we determined the plate scale of G-band 430.5 nm images with high accuracy: 0.05369±0.00005 arcsec pixel. The radius was defined at the intensity level of the 0.5 transmittance and compared with the angular radius of Venus including the thickness of the atmosphere determined with the measurements of SPICAV onboard Venus Express. Thanks to the high spatial resolution, SOT images show that the dark Venus can be well represented by an ellipse. We observed 7.6 km difference in altitude between the equator and the polar regions. [ABSTRACT FROM AUTHOR]