By Mark Laurin
David Chandler has been an avid sky watcher for decades, and an active member of the Denver Astronomical Society. He’s also famous for inventing the Night Sky Planisphere, a ubiquitous star-finding tool that astronomers around the world use to spot stars and constellations in the night sky.
To find out how he first got interested in and become passionate about astronomy, I first asked David, “What inspired you to take up astronomy, and when did it happen?”
When I was probably in about fifth or sixth grade I was given an Edmund Star and Satellite Pathfinder planisphere. It’s a terrible star map, but because of the fact that it rotated and indicated what was up at a particular day and time it got me going finding most of the major constellations. I went out in the front yard each night, reviewed the constellations I had learned, and tried to add something new. I started in the summer and remember waiting with anticipation for Orion to become visible in the evening sky as the months went by.
I was in Boy Scouts, so this early experience led me to work on the Astronomy Merit Badge, which is actually an excellent introduction to observational astronomy. One of the requirements, besides identifying at least ten constellations, was to identify eight first magnitude stars. That was a great requirement to include because in practice, finding the patterns of first magnitude stars (like the Summer Triangle and Winter Hexagon and the “arc to Arcturus and Spike to Spica” patterns) are the easiest things to recognize, even in the city. All in all, my crummy little planisphere was a virtual planetarium.
Fast forward to the summer of 1971. I was out of college with a physics degree and working at a summer job on the Blue Ridge Parkway in North Carolina giving my first telescope (a 4.25-inch Tasco Newtonian) a workout. Somehow that summer I found a copy of the Star and Satellite Pathfinder, still in print, and bought it for old time’s sake. I was intrigued by the oval horizon curve on the chart. It looked like an ellipse. The chart said it was designed for 40 degrees north. I figured if that was the case, I should be able to figure out what parameters of the ellipse would generate the correct horizon curve for 34 degrees for Los Angeles. What I discovered quickly was that it should not be an ellipse at all. It was a curve that at the North Pole would be a circle, but it would gradually morph into a half circle at the equator. After about three days playing with the geometry I was able to derive the correct equation for the curve (a small equation with three trig functions, it turns out). So now I had the tool I needed to create a planisphere for any latitude.
The more I worked with the chart the more I realized how distorted it was because of the map projection. I wondered if it was possible to preserve the advantages of a rotating star map and avoid the severe distortion. After several months of pondering this problem I realized that if I used a north polar projection on one side and a south polar projection on the other side, and masked both off for use in the user’s latitude, I could eliminate over 90 percent of the distortion!
I went through several prototypes, plotting the stars by different methods, and eventually wrote a program in BASIC (later Pascal) that plotted the star maps. I published the first version of this planisphere, called The Night Sky, in 1976, printed up 1,000 copies, and went around in person to junior college astronomy departments, up and down California, looking for schools that would adopt it for their astronomy classes. Several did! The astronomy professor at Mt. San Antonio College in Covina, CA said there was going to be a meeting of the International Planetarium Society at CU Boulder in a few weeks, so I signed up and came to Boulder and set up a display table. One big guy came by my table to check out my chart in great detail. A number of other people were hovering around him looking over his shoulder. After a few minutes he said, “This is good!” That was the turning point. This “guy,” it turned out, was George Lovi, who did the monthly star chart centerfolds in Sky and Telescope. Later that day I got a call from the editor of Sky and Telescope and we worked out an arrangement for publishing them on a larger scale.
While I was interviewing David, it took me a few moments to fully digest his experience. The words “just simply amazing” ran through my head a number of times. Then it hit me that I was talking to THE David Chandler, the creator of the Night Sky Planisphere, a fact I hadn’t been aware of when I set up our interview! In a flash, this amazing astronomical aid that I’ve been using for decades became personal. A living, breathing tool with a face, a history, a family, and a legacy.
All of us astronomers have amazing stargazing moments, which leave indelible imprints on us. David shared his with me:
My absolute best star gazing moment came at the intersection of my interest in astronomical computing, my fascination with observing comets, and my habit of challenging myself to see the most subtle visual phenomena possible. On the morning of September 8, 1996 at the Nightfall star party in Borrego Springs, CA while I was looking for a tail on the recently discovered Comet Tabur I observed a very subtle glow that extended several fields of view from the comet.
I had my telescope connected with my computer using software I had written myself, Deep Space, which was a DOS era star mapping program that grew out of my planisphere project. I could track where my scope was pointing with a cursor on the screen. I had the current position for Comet Tabur plotted, with the direction of the tail indicated. It turned out that the direction I was moving the scope was off by about 120 degrees from where the tail should be. I had seen an article in Sky and Telescope that showed a comet’s debris trail along its orbital path, as seen by IRAS, a space based infrared telescope. I wondered if I was seeing the trail. I had a feature I had built into my software called Comet Recovery Mode, which showed the orbital path of the comet projected onto the sky so someone could find returning comets that returned ahead of or behind schedule. On a hunch I turned on Comet Recovery Mode. It turned out that night I was actually looking at the glow of reflected sunlight from debris scattered along the orbital path: potential shower meteors if the earth ever passed through the orbit.
There’s always one person or a few who get us excited about astronomy. And it’s even better when it is a friend. Or, in David’s case, it was because he was the one who had the keys to the car, and his friend Tony Cook had the knowledge of the night sky.
When I was just out of college, I started hanging out with the son of one of my professors and a friend of his, Tony Cook, who were both high school students. We took our small telescopes from the extended Los Angeles light basin out to the desert near Victorville, which was still dark in those days. I was valuable to the group because I had a car. Tony was valuable because he knew how to find things. Tony had a 2.5-inch refractor with which he had, from the light polluted hills above Claremont CA, found about three quarters of the Messier catalog! That would be an incredible achievement with that size telescope even with dark skies. On those desert trips we had Tony’s 2.5-inch refractor, my 4.25-inch Tasco, and a borrowed 6-inch RFT. The high point of the Victorville trips was getting to know the Virgo galaxy cluster. Tony and I developed a long friendly relationship, and we became the quasi-founders of the Pomona Valley Amateur Astronomers. (I say quasi-founders, because it emerged as a public organization as a transformation of Tony’s high school astronomy club.) By the time I left the area, the PVAA had become one of the major astronomy clubs in Southern California. Tony went on to work for the Griffith Park Planetarium in Los Angeles.
David moved to Denver about three years ago and soon thereafter joined DAS. If you haven’t met him, I strongly encourage you to seek him out and introduce yourself at an open house, a monthly meeting, or a special event. As he told me “I’m the tall guy with the beard.”
More than being affable and kind, he has a wealth of knowledge, and from my experience, he’s more than willing to share it. I encourage you to seek him out when you have the chance. Or, if you want to communicate with him before then, shoot him an email at: davidschandler48@gmail.com
