NASA Releases New Photos of Saturn's Rings and Clouds 34
skade88 writes "Launched in 1997, Cassini has taken over 300,000 pictures of Saturn since it started orbiting the planet and the mission is due to run through 2017. NASA has released some new photos including: Saturn's rings, clouds, Saturn's moon Janus, and the shadow of another one of Saturn's moons Mimas."
Go to the source... (Score:5, Informative)
http://saturn.jpl.nasa.gov/
Has all the images, none of the space.com ads
Re:Black-and-white? (Score:5, Informative)
From NASA's FAQ page [nasa.gov]:
Why are so few of the Cassini pictures in color?
Creating color images is a complex task requiring much more labor and computer time than black and white images. This is because all Cassini images are recorded in black and white. The camera records the amount of light (not the color of the light) coming through a filter in front of the sensor. It is the filters that come in color.
To create color images scientists take three black and white images of the same target with the red, green, and blue (RGB) filters. In other words, one image records the amount of red light (using a red filter), another records the amount of green and one the amount of blue light (using green and blue filters respectively). Color renditions of the scene are then constructed on the ground by combining images taken with the different filters.
Unfortunately, these three images are not taken simultaneously. Consequently, intricate fitting and geometric transformations are needed to construct the color image because the spacecraft, planet, rings and moons have all moved a little during the time it takes to record the images using the different filters.
What controls when a picture is taken?
The scientists determine this when they do the observation designs. The path of Cassini is known, as are the paths of the Saturn's moons, so it's a matter of looking at the varying geometry with time and selecting the camera pointing directions and shuttering times that will gather the most scientifically interesting images. These commands are then built into sequences that are sent to the spacecraft from days to weeks in advance of the observations.
Re:Black-and-white? (Score:5, Informative)
Also, most color photos from NASA are gong to be in fake color and exaggerated contrast, made to highlight certain features (or impress congressmen), not to look accurate.
Actually, they don't really have a real color view they can show us. Sensors on spacecraft see multi-band (read color) images as single bands representing intensity for each band. These black and white views are actually the view of a particular band filtered on the wavelength of the light it is looking for.
The false-color images derived by NASA generally use 3 bands to create a RGB style image with a single particular band standing in for Red, Green, and Blue. The reason these images are false-color is that often the Red band is all or in part filtering to find infrared light, and the blue is sometimes filtered more toward violet and UV.
They really often times can't make a true color image. Because there is more science value derived from being able to see values in bands that are tuned slightly away from the visible (especially wrt infrared).