Tom Tompkins
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The black sand at this exhibit is magnetite, a naturally occurring iron oxide mineral found in almost all igneous and metamorphic rocks.
The black sand we use at this exhibit comes from nearby Ocean Beach—but it originates in the Sierra Nevada Mountains to the east. There, granite containing iron ore breaks down into tiny grains of black sand that then erode, getting carried by rivers to San Francisco Bay and beyond.
Not usually magnetic in and of itself, black sand can and will become magnetized in the presence of another magnet. As each tiny grain of magnetized black sand becomes a (temporary) magnet itself, the magnetic field in that spot gets amplified, and more black sand gets attracted—ultimately creating the porcupine-like spikes that you see here.
When cosmic rays from outer space reach the Earth’s atmosphere, they crash into air molecules and knock free many more particles. These particles go on to crash into more air molecules and create even more particles. Thus a single particle from outer space—called a primary—can create a shower of particles from the Earth’s atmosphere—called secondaries. Primaries (which are actually protons) rarely reach the Earth’s surface; almost all of the tracks in this exhibit are from secondaries (muons and electrons).
Artist’s rendering of showers of particles produced by cosmic rays. (click image to enlarge)
Before he founded the Exploratorium, Frank Oppenheimer used cloud chambers while working as a physicist at the University of Minnesota. In this 1948 photo, Frank and his colleagues loaded various sensors—including a small cloud chamber—into a sphere to be lofted 100,000 feet into the atmosphere by balloon, to document the interactions of cosmic rays. Photo courtesy of Lawrence Berkeley Lab, University of California, Berkeley. (click image to enlarge)
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Related Snacks
The black sand at this exhibit is magnetite, a naturally occurring iron oxide mineral found in almost all igneous and metamorphic rocks.
The black sand we use at this exhibit comes from nearby Ocean Beach—but it originates in the Sierra Nevada Mountains to the east. There, granite containing iron ore breaks down into tiny grains of black sand that then erode, getting carried by rivers to San Francisco Bay and beyond.
Not usually magnetic in and of itself, black sand can and will become magnetized in the presence of another magnet. As each tiny grain of magnetized black sand becomes a (temporary) magnet itself, the magnetic field in that spot gets amplified, and more black sand gets attracted—ultimately creating the porcupine-like spikes that you see here.
When cosmic rays from outer space reach the Earth’s atmosphere, they crash into air molecules and knock free many more particles. These particles go on to crash into more air molecules and create even more particles. Thus a single particle from outer space—called a primary—can create a shower of particles from the Earth’s atmosphere—called secondaries. Primaries (which are actually protons) rarely reach the Earth’s surface; almost all of the tracks in this exhibit are from secondaries (muons and electrons).
Artist’s rendering of showers of particles produced by cosmic rays. (click image to enlarge)
Before he founded the Exploratorium, Frank Oppenheimer used cloud chambers while working as a physicist at the University of Minnesota. In this 1948 photo, Frank and his colleagues loaded various sensors—including a small cloud chamber—into a sphere to be lofted 100,000 feet into the atmosphere by balloon, to document the interactions of cosmic rays. Photo courtesy of Lawrence Berkeley Lab, University of California, Berkeley. (click image to enlarge)
Related Exhibits