Comet 46P/Wirtanen from South-East France
The comet nucleus is at the core of the brightest spot in the lower right part of the image, and the green diffuse cloud around it is its coma. The green colour is caused by molecules – mainly CN (cyanogen) and C2 (diatomic carbon) – that are ionised by sunlight as the comet approaches the Sun. The coma's asymmetry is visible in the image. The diagonal stripes across the image are star trails.
The comet reached perihelion, the closest point to the Sun along its orbit, on Wednesday 12 December, and is on the way to its closest approach to Earth this weekend, when it might become visible to the naked eye from dark locations
This image is a composite of 4×33 short, 15 second exposures taken using LRGB filters on the ROTAT telescope, a coma-corrected Newtonian (60cm f/3.2 equipped with an SBIG STL11000 full-frame CCD). It was taken within the framework of a research project by two 11th grade students from Mannheim, Germany, at the Hector Seminar, an organization that fosters gifted high-school students in STEM subjects; the students are being supervised by Carolin Liefke from Haus der Astronomie in Heidelberg, Germany.
ROTAT, the Remote Observatory Theoretical Astrophysics Tuebingen, is operated by the German foundation Interactive Astronomy and Astrophysics (Stiftung Interaktive Astronomie und Astrophysik), which aims to inspire young adults with hands-on science.
A three-filter version of this image is available here.