Clyde Tombaugh was born in Streator, Illinois, on Feb. 4, 1906. He was interested in astronomy since childhood. At age 20, Tombaugh ground his own mirror and built a telescope out of spare farm equipment. His interest in planets motivated him to ask for a job at Lowell Observatory in Flagstaff, Arizona. He was hired in 1929, the year of the Great Depression, to search for an unknown planet.
Astronomers calculated that there must be another planet beyond Neptune because both Uranus and Neptune seemed to be affected by an unknown gravitational attractor in the outer solar system. Not all scientific knowledge comes through careful study because it turned out the calculations were wrong mainly due to an error determining the mass of Neptune. Serendipity took over because the mass error led Tombaugh to scan the area of the sky where he eventually found Pluto. After 10 months of laborious work, Tombaugh discovered Pluto on Feb. 19, 1930.
From the start, this new find was an oddity. First, it was too small to affect the orbits of ice giant planets Uranus and Neptune. Second, Pluto’s orbit was out of the normal plane of all the other planets. It even crosses Neptune’s orbit to temporarily make Neptune the farthest known planet from the Sun.
More recently, Pluto has been demoted to the status of “dwarf planet” for many reasons. Pluto is joined by a number of other “Trans Neptunian Objects” that form a sort of outer asteroid belt, called the Kuiper Belt.
It amazed me how Clyde Tombaugh made a name for himself through his interest in astronomy, along with his determination and perseverance. I decided to pay tribute to him by re-discovering Pluto on my own. Of course, I knew where to look thanks to Clyde, so it didn’t take me 10 months. However, Pluto is smaller than Earth’s moon and is over 3 billion miles away. Add to this that it’s passing through the constellation Sagittarius in a rich field of distant stars that all look alike. The only way I could differentiate Pluto from the stars was to photograph the area of the sky for two nights in a row and look for something that moved.
I took several 200 second photographs through Mount Sangre Observatory’s 17-inch reflector. Clyde only had a 13-inch reflector that took writing paper size black and white glass plate emulsion photos. I then used a tool in PixInsight’s image processing program called “Blink” to compare the images of the same star field on two consecutive nights. This is essentially the same technique that Tombaugh used with his mechanical Blink Comparator. The following image comparison shows how Pluto moved with respect to the much more distant background stars over a 24-hour period. I used the raw grainy images on purpose because so little light reflects off of Pluto that any processing would disrupt and/or remove key photons. If you zoom in on Pluto to where it becomes pixelated, you’ll see what appears to be a bump at the 5 to 6 o'clock position. This, I believe, is Pluto’s largest moon, Charon, which orbits so close to the dwarf planet that the two of them meld together in these incredibly distant images.