Picture of the Week #25
Pluto, July 1997. 30-inch telescope at McDonald Observatory
This is a stack of 4 images taken over a 5 day period. If you look to the bottom of the frame, you will see 4 dots - red, green, blue and yellow, each representing Pluto on a different night. Three look regularly spaced with the red dot is further away. There would have been a spot between the red and green, but that night was cloudy, so no observation was made.
How the composite image was made:
If you look at the upper left and lower right corners, you will see two bright stars, which helped to find the field in each of the images. I took three of the frames and pulled them into Photoshop, each in a different channel. When the star images lined up, they appeared white, but the object that was different on each of the frames (Pluto), appeared as a red, green and blue dot from the object's image in each of the channels.
The fourth image was stacked (as a greyscale) over the combined image from above. The two images were added, and the fourth image of Pluto was hand-colored yellow.