Most of the time, astronomy is practiced from on high: atop mountains, from balloons, or better still, from outer space. The high altitudes overcome the blurring effects of Earth's atmosphere, and provide a look at types of energy that the atmosphere blocks.
For some things, though, astronomy is best practiced down low: under water, under ice, or underground. These "deep" observatories use the barriers of water, ice, and rock to screen out unwanted radiation, allowing scientists to look for particles that are abundant but shy.
One of the first underground laboratories was built almost a mile below ground in the Homestake gold mine in South Dakota. Starting in the 1960s, researchers used a tank filled with dry-cleaning fluid to hunt for neutrinos. These particles are produced in the hearts of stars and rush into space at almost the speed of light. But they seldom interact with normal matter. The underground location helped isolate the rare occasions when they did collide with other particles.
Today, both the gold mine and the neutrino experiment have shut down. But scientists are operating or preparing new experiments for Homestake -- experiments to study both neutrinos and the even more elusive particles of dark matter. In fact, Homestake could even become the first underground national laboratory, giving scientists many new opportunities to study the universe from down low.
More about underground astronomy tomorrow.
Script by Damond Benningfield, Copyright 2011