PLUTO

11 - 12 June 2004

These are my first attempt at imaging Pluto. I have limitated myself to find it and to image it during two following nights in order to catch its movement against the sky background. It's mandatory to have some precise charts to find it or to have very recent images showing the faint point unmistakably. I had to make a careful comparison to be sure it was present on my images (I had even thought is was not).

Images taken at prime focus of the 7" newtonian and the ATK-1HS and a IR-blocking filter. A few seconds are enough to see the planet that shines faintly at a magnitude of 13,8.

 15 June 2004

During this observation I had planned to evaluate Pluto's albedo in different wavelenghts, and from this it color. During two hours, four AVI files have been obtained in near infrared, red, green, and blue light. Pluto was located with an excellent precision thanks to "Cartes du ciel" a free software from Patrick Chevalley, that allowed me to download an extremely precise maps from the ESO website. Exposures where 7 seconds in IR, R, G, and 10 seconds in blue light (more than one hundreds of frames added for each band).

The images show that Pluto's albedo decreases as the wavelenght increases. It's dim in IR, but brighter in blue light. Thus, the color composites show it as blue planet. The images have not been well calibrated because of the lack of an objective reference. Nonetheless, the red color of one of the star that is noticeably brighter in long wavelenghts proves that the color is globally correct. This hue may be due to the frozen methane on Pluto's surface ?

As Pluto moved during the two hours, two kinds of registration where mandatory, on for the planet, and another for the stars.

19-20 June 2004

A new experience of multispectral imaging on Pluto, this time with my club's 14" SCT. The more additionnal light power allows to verify the june 15th observation. Moreover, this time some reference images of a white star at same altitude have been taken to correctly equilibrate the color balance, Nu Ophiuchus, currently located 1° north of Pluto. The result is confirmed, Pluto is a blue planet.