Robert Trumpler 
If you ever get a good look at the glowing band of the Milky Way, you’ll notice that some dark rifts run through it. For a long time, those rifts were the subject of a scientific debate. One side thought they were simply regions with fewer stars, while the other thought they were regions where something was blocking the light of the stars. The debate was settled by a man who was born 125 years ago today.
Robert Trumpler was born into a well-to-do family in Switzerland. Although his father wanted him to take up business, Trumpler instead picked a career in astronomy. In 1915, he was released from the Swiss army so he could take a job with an observatory in the United States.
Over the next 15 years, Trumpler observed about a hundred “open” star clusters — clusters where the stars are only loosely bound together, and that don’t have any particular shape.
He used two techniques to estimate the distances to the clusters. He also compared the colors of the stars in different clusters. From those observations, Trumpler concluded that something in interstellar space must be absorbing some of the light of distant stars — most likely grains of dust.
Trumpler was correct all the way around. Something is blocking the light, and most of it is dust. It’s concentrated in the galaxy’s disk, just as the stars are. So as we look into the Milky Way in the night sky, we also see thick lanes of dust, which absorb the light of the stars beyond.
Script by Damond Benningfield, Copyright 2011