A transit of Venus across the Sun took place on June 6, 2012.　Since it was night time, the phenomenon was not visible in Chile, but we captured Venus just before passing across the face of the Sun with a Japanese12-m antenna, which is a part of the ALMA telescope. You can see Venus (a tiny, dot-like planet) located to the upper left of the Sun.

At this position, Venus is optically invisible to us because it turns its night side to the Earth. However, we could capture its “back shot” by receiving radio waves (at 230 GHz) emitted from a hot planet Venus with a parabola antenna. This image was created by synthesizing two separately-processed images of Venus and the Sun; the latter emits overwhelmingly stronger radiation than the former.

The light-colored parts on the sun’s surface are active regions that have strong radio intensity. About 30 minutes after this observation (5:14 PM on June 5, Chilean Time), the Sun and Venus went below the horizon, and then an hour later the transit of Venus started.
Credit: ALMA (ESO/NAOJ/NRAO)