The 2012 transit of Venus across the face of the Sun was viewed not only by millions of people and hundreds of telescopes on Earth, but also by a handful of telescopes in space which are dedicated to observations of the Sun.

A new paper published yesterday describes observations from two of these observatories: Japan's Hinode and NASA's Solar Dynamics Observatory. Between them, these two spacecraft observed the transit in wavelengths ranging from visible to UV to X-ray.

At each of the observed wavelengths, the effective radius of the planet was measured. The effective radius at visible wavelengths matched well with cloud-top altitudes as measured from Venus Express; the effective radius at shorter wavelengths is much higher, due to the increased opacity of the atmospheric gases at these wavelengths.

This comparison of planetary radius measured during transits at different wavelengths is exactly how exoplanetary atmosphere characterization is performed; therefore the present work serves as an important validation tool for exoplnaetary study. It also paves the way to study of exoplanetary transits using high-energy telescopes such as ESA's ATHENA mission, due to launch in 2028.

The research was led by Fabio Reale of the University of Palermo, and is published in Nature Communications, which is an open access publication so can be viewed free of charge at the following link: rdcu.be