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Unit Of Luminous Intensity (candela)

Originally, each country had its own, and rather poorly reproducible, unit of luminous intensity; it was necessary to wait until 1909 to see a beginning of unification on the international level, when the national laboratories of the United States of America, France, and Great Britain decided to adopt the international candle represented by carbon ...

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Candela
Engineering

Infrared Headphones

Infrared headphones use infrared light to carry an information signal from a transmitter to a receiver. Sounds simple enough, but the actual process is very complicated. The human ear gathers sound as ... Continue reading

InfraredHeadphones
Biology

Eukaryotic Organisms

Eukaryotes include fungi, animals, and plants as well as some unicellular organisms. Eukaryotic cells are about 10 times the size of a prokaryote and can be as much as 1000 times greater in volume. ... Continue reading

EukaryoticOrganisms
Biology

St. John's Wort

St. John's wort is an herb that has been used for centuries for medicinal purposes, including to treat depression. The composition of St. John's wort and how it might work are not well understood. ... Continue reading

StJohnsWort
Astronomy

Crab Nebula

For millions of years a star shone in the far off constellation of Taurus. So far away, and so faint that even if our eyes were ten thousand times more sensitive, the star would still not be visible ... Continue reading

CrabNebula

Voyager Phone Home

VoyagerAfter historic visits to Jupiter and Saturn, Voyager 1 is now on course to be the first human-made object to leave our solar system. In space for more than 25 years, it has already traveled farther than any other spacecraft. It is not clear when Voyager 1 will reach the heliopause boundary, where the influence of our Sun ends. The boundary is thought to exist somewhere from 8 to 22.5 billion kilometers (5 to 14 billion miles) from the Sun. When Voyager 1 does cross over, scientists will be able to measure the interstellar environment without the influence of the Sun for the first time.

Voyager 1 is speeding along at about 57,600 kph (35,790 mph) - fast enough to travel from the Earth to the Sun three and a half times in one year. As of March 2002, Voyager 1 was at a distance of 12.4 billion kilometers (84 Astronomical Units) from the Sun. But it could still take more than 20 years to escape our solar system. Its sister spacecraft, Voyager 2, will be the next object out of our solar system. Pioneer 10 and Pioneer 11 also are on courses that will eventually take them into interstellar space.

All four spacecraft are carrying messages from humanity. Both Voyagers carry a gold record 'greeting to the universe' containing sounds and images selected to portray the diversity of life and culture on Earth.