Live Fast, Blow Hard, and Die Young

Massive stars lead short, yet spectacular lives. And, they usually do not go quietly, instead often blowing themselves apart in supernova explosions. Astronomers are curious about the details of the final steps before these violent endings. A new image gives astronomers a look at this critical period of one massive star's life and imminent death. ...

Continue reading...


The Journey of the Monarchs

The life of Monarch butterflies is an amazing one. They develop as caterpillars from the roughly 400 eggs each mother lays on the underside of milkweed plant leaves. Then they spend their brief lives ... Continue reading


When Chlorine Met Sodium...

Sodium is a required element in human physiology. The eleventh element in the periodic table, sodium is a soft, silvery white metal that can be easily cut through with a paring knife. It is highly ... Continue reading


A New Twist on Fiber Optics

By twisting fiber optic strands into helical shapes, researchers have created unique structures that can precisely filter, polarize or scatter light. Compatible with standard fiber optic lines, these ... Continue reading


Earth's Magnetism

Most ancient civilizations were aware of the magnetic phenomenon. Sailors in the late thirteenth century used magnetized needles floating in water as primitive compasses to find their way on the sea. ... Continue reading


Sundials, Ancient Clocks

SundialsAncientClocksThe earliest and simplest form of sundial is the shadow stick. The time of day is judged by the length and position of the stick's shadow. Some nomadic peoples still use this method for timekeeping. The technical name for a shadow stick is a gnomon. As the sun moves through the sky from sunrise to sunset, the shadow of the gnomon rotates 'clockwise.' The shadow is shortest when the sun is directly in the south, defining local noon.

As early as 3500 B.C. the Egyptians began building slender, tapering, four-sided obelisks which served as timepieces. The moving shadow of the obelisk formed a type of sundial, and markers arranged about the base separated the day into divisions as well as indicating the longest and shortest days of the year. However, because of the earth's tilt, the sun's path through the sky changes slightly from day to day, so the shadow cast by the gnomon is not the same every day. Many sundials overcome this problem by angling the gnomon and aiming it north. This type of gnomon is called a style. Because its alignment compensates for the Earth's tilt, the hour marks remain the same all year round.

In the quest for accuracy, many types of sundials evolved, including some very complex portable sundials. In about 30 B.C. Marcus Vitruvius, a Roman architect, described 13 different sundial designs used in Greece, Asia Minor, and Itay. The invention of more accurate mechanical clocks and the standardization of time using time zones made sundials obsolete. Now sundials are used mostly for ornamental purposes.