The Astrolabe:Astronomical Computer

Posted on October 1, 2008 by Rashid Faridi

The astrolabe is a very ancient astronomical computer for solving problems relating to time and the position of the Sun and stars in the sky. Several types of astrolabes have been made. By far the most popular type is the planispheric astrolabe, on which the celestial sphere is projected onto the plane of the equator. A typical old astrolabe was made of brass and was about 6 inches (15 cm) in diameter, although much larger and smaller ones were made.

Astrolabes are used to show how the sky looks at a specific place at a given time. This is done by drawing the sky on the face of the astrolabe and marking it so positions in the sky are easy to find. To use an astrolabe, you adjust the moveable components to a specific date and time. Once set, the entire sky, both visible and invisible, is represented on the face of the instrument. This allows a great many astronomical problems to be solved in a very visual way. Typical uses of the astrolabe include finding the time during the day or night, finding the time of a celestial event such as sunrise or sunset and as a handy reference of celestial positions. Astrolabes were also one of the basic astronomy education tools in the late Middle Ages. Old instruments were also used for astrological purposes. The typical astrolabe was not a navigational instrument although an instrument called the mariner’s astrolabe was widely used. The mariner’s astrolabe is simply a ring marked in degrees for measuring celestial altitudes.

The history of the astrolabe begins more than two thousand years ago. The principles of the astrolabe projection were known before 150 B.C., and true astrolabes were made before A.D. 400. The astrolabe was highly developed in the Islamic world by 800 and was introduced to Europe from Islamic Spain (Andalusia) in the early 12th century. It was the most popular astronomical instrument until about 1650, when it was replaced by more specialized and accurate instruments.Astrolabes are still appreciated for their unique capabilites and their value for astronomy education.

Useful links:

History of the astrolabe

Mariner’s Astrolabe

The Electric Astrolabe

The Parts of an Astrolabe

The Stereographic Projection

Astrolabe on Wikipedia

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Coral Reefs are Dying Due to Pollution Caused by Us

Posted on September 30, 2008 by Rashid Faridi

An aerial handout picture of a construction site surrounded by Caribbean seawater at the Yucatan resort of Cancun, May 27, 2008. Local environmental problems like sewage, farm runoff and overfishing could kill off much of the worlds reefs decades before global warming does, according to an expert near Cancun.

An aerial handout picture of a construction site surrounded by Caribbean seawater at the Yucatan resort of Cancun, May 27, 2008. Local environmental problems like sewage, farm runoff and overfishing could kill off much of the world's reefs decades before global warming does, according to an expert near Cancun.

Coral reefs like Chitales, near the northern tip of a Caribbean reef chain stretching from Mexico to Honduras, are dying around the world as people and cities put more stress on the environment.

Climate change alone could trigger a global coral die-off by 2100 because carbon emissions warm oceans and make them more acidic, according to a study published in December.

But local environmental problems like sewage, farm runoff and overfishing could kill off much of the world’s reefs decades before global warming does, said Roberto Iglesias, a biologist from UNAM university’s marine sciences station near Cancun.

“The net effect of pollution is as bad or maybe worse than the effects of global warming,” said Iglesias, a co-author of the study in the journal Science on how climate change affects reefs.

Human waste like that from Cancun’s hotels and night spots aggravates threats to coral worldwide like overzealous fishing which hurts stocks of fish that eat reef-damaging algae.

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World’s Biggest Atlas

Posted on September 30, 2008 by Rashid Faridi

Copies of the largest world atlas ever produced have gone on sale at an earth-shattering price of £2,000 each. Dubbed “the ultimate book about our world”, the luxurious, limited edition Earth is hand-bound in leather with gilded edges and silver-plated corners.The atlas and its case together weigh 30kg – more than the maximum many airlines set passengers for their baggage allowance.

The 576 pages contain 154 maps and 800 photographs backed with detailed descriptions of every country’s geography, history and culture. Lying closed, the atlas takes up a third of a square metre with four gatefolds opening out to two square metres each. Ten cartographic experts at the British map company Global Mapping spent eight months compiling Earth with more than 100 overseas colleagues including fellow map makers, geographers and oceanographers. They worked with detail from a continuously updated world database of digital mapping.

Global Mapping’s Alan Smith said: “We all had to keep to the same, consistent specification to make sure everything tied in universally from the way we shaded hills to the presentation of political geography. The sheer physical size of the atlas is amazing. The overall content, including the maps, text and photographs, is very much more detailed than any other atlas ever produced.”

Only 3,000 hand-numbered copies of Earth have been made – one for every 3.3 million people in the world. The atlas is expected to appeal to specialist collectors, libraries, rich individuals with a penchant for mapping and companies seeking lavish, once-in-a-lifetime corporate gifts. Taking the exclusive level even higher, one thousand copies from the print run have had their covers redone in gold leather with gold plated corners at the request of distributors in the Middle East.

Earth is the brainchild of Australian map publisher Gordon Cheers who has already received several hundred orders for copies. He described it as “a time capsule of where we are in the world today”.

The atlas may be impressive but its 30kg weight still pales into insignificance when compared to the mass of the planet itself – estimated at an unpronounceable 6,000,000,000,000,000,000,000,000 kg.

Earth can be ordered at http://www.mapstop.co.uk/product251_Earth-Atlas.aspx
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Global Warming:Europe is warming faster, Mediterranean is drier, North ever wetter

Posted on September 29, 2008 by Rashid Faridi

Dry land emerges from the shallow waters of the Ticino river under the Old Bridge in Pavia, northern Italy, in this file photo from July 1, 2005.

Dry land emerges from the shallow waters of the Ticino river under the "Old Bridge" in Pavia, northern Italy, in this file photo from July 1, 2005.

Europe is warming faster than the world average and governments need to invest to adapt to a changing climate set to turn the Mediterranean region arid and the north ever wetter, a study showed on Monday.

Europe’s mountains, coasts, the Mediterranean and the Arctic were most at risk from global warming, according to the report by the European Environment Agency and branches of the World Health Organization and the European Commission.

“Global average temperature has increased almost 0.8 C (1.4 F) above pre-industrial levels, with even higher temperature increases in Europe and northern latitudes,” it said.

Europe had warmed by 1.0 C.

Northern Europe would get wetter this century while more of Europe’s Mediterranean region might turn to desert, based on trends already under way, it said. European heatwaves like in 2003, during which 70,000 people died, could be more frequent.

“Annual precipitation changes are worsening differences between a wet northern part of Europe and a dry south,” it said.

That meant a need to review everything from irrigation to the ability of southern rivers to help cool nuclear power plants.

Among other impacts, seas were rising in a threat to coasts, some fish stocks had moved 1,000 km north in the past 40 years — pushing cod not caught by trawlers away from the North Sea — and two-thirds of Alpine glaciers had vanished since 1850.
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