As the incredible year of 2014 draws to a close, we have prepared a small treat for all of the readers of this blog who have followed Rosetta’s progress over the months, in particular those who like to download images and play with them.
ESA started our CometWatch in July, when Rosetta was still a few thousand kilometres away from Comet 67P/Churyumov-Gerasimenko. We saw this curiously-shaped comet grow larger and richer in details as the spacecraft got closer and closer until rendezvous at 100 km on 6 August. The NAVCAM images released over that period provided a good overview of our approach this amazing new world.
In September, as Rosetta drew closer to the comet, we had to switch to taking four-image mosaics in order to ensure that we could cover enough of it for navigation purposes. Since then, ESA have been publishing some of these four-image sets as montages and mosaics, as well as releasing the individual frames so that you could work with them and create your own mosaics. Some have been taken within 8 km of the surface of 67P/C-G, providing amazing views.
But to mark the end of this exciting year, instead of just one new image, montage, or mosaic, the last CometWatch release of the year is … a movie, featuring no less than 24 montages based on NAVCAM images taken between 19 November and 3 December 2014. A reduced version of the movie can be seen inline here, but the full-sized version is available if you click through.
These images were taken while Rosetta was in a 30-km orbit around the comet (see this video showing the trajectory of the spacecraft after 12 November). As usual, each montage comprises four individual images taken over a 20-minute period, at either around 11:00 UT (12:00 CET) or 23:00 UT (0:00 Next Day CET). At 30 km from the comet’s centre, the pixel scale is about 2.56 m/pixel.
As Comet 67P/C-G rotates with a period of 12.4 hours, images taken at 12-hour intervals result in views that are slightly offset with respect to one another, as the comet will have completed slightly less than a full rotation in that time.
In addition, there is also the orbital motion of Rosetta with respect to the comet: over the two weeks over which the images were taken, Rosetta completed almost one full orbit at 30 km from the comet.
Taking these factors into account, we have ordered the images according to the apparent rotation phase in order to make a movie. In fact, we have sorted the images in an almost reverse chronological sequence, starting with a montage taken on 2 December, then working backwards one day at a time to 19 November. The last montage in the sequence, however, is from 3 December.
Given the limited time available to us in the run up to Christmas, this is all we have been able to do: a phase-ordered sequence of montages made into a movie. There has been no processing of the images apart from the removal of the basic instrumental signature.
But we know that you can do better, and as a thank you to everyone who has produced and shared dozens and dozens of excellent NAVCAM mosaics and images over the past few months, we’ve made the full set of 24 montages and of 96 individual 1024 x 1024 pixel frames available for download.
So, if you have the time over the holiday period, we invite you to create your own mosaics and perhaps even your own movies, and to share them on your social networks under the terms of the Creative Commons licence that applies to NAVCAM images (CC BY-SA IGO 3.0). Let us know about them in the New Year.
For those who want to know exactly where the spacecraft was at the moment when each image was taken and perhaps factor that into their movie-making, the so-called ‘SPICE’ files for Rosetta are available here, and the tools to read and process those files can be found here. Few parameters are already included in the filenames of the provided images, such as rotation phase, date and time (rot.phase_ESA_ROSETTA_NAVCAM_yymmddThh).
We hope you have enjoyed following our CometWatch in 2014 and we are looking forward to another exciting year as 67P/C-G gets closer and closer to the Sun. Rosetta will be there to monitor its changes and discover what it really means “to live with a comet”.
Source: Rosetta blog