Solar eclipse

Posted on July 21, 2009 by Rashid Faridi

A solar eclipse occurs when the moon passes between the Sun and the Earth so that the Sun is fully or partially covered. This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from the Earth.

A total solar eclipse is a spectacular natural phenomenon and many people travel to remote locations to observe one. The 1999 total eclipse in Europe helped to increase public awareness of the phenomenon, as illustrated by the number of journeys made specifically to witness the 2005 annular eclipse and the 2006 total eclipse. The most recent solar eclipse occurred on January 26, 2009, and was an annular eclipse. On July 22 2009, the next total solar eclipse will occur.

In ancient times, and in some cultures today, solar eclipses have been attributed to supernatural causes. Total solar eclipses can be frightening for people who are unaware of their astronomical explanation, as the Sun seems to disappear in the middle of the day and the sky darkens in a matter of minutes.

There are four types of solar eclipses:

  • A total eclipse occurs when the Sun is completely obscured by the Moon. The intensely bright disk of the Sun is replaced by the dark silhouette of the Moon, and the much fainter corona is visible. During any one eclipse, totality is visible only from at most a narrow track on the surface of the Earth.
  • An annular eclipse occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon.
  • A hybrid eclipse (also called annular/total eclipse) transitions between a total and annular eclipse. At some points on the surface of the Earth it is visible as a total eclipse, whereas at others it is annular. Hybrid eclipses are comparatively rare
  • A partial eclipse occurs when the Sun and Moon are not exactly in line and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as a partial eclipse, because the umbra never intersects the Earth’s surface.

The Moon’s Two Shadows

An eclipse of the Sun (or solar eclipse) can only occur at New Moon when the Moon passes between Earth and Sun. If the Moon’s shadow happens to fall upon Earth’s surface at that time, we see some portion of the Sun’s disk covered or ‘eclipsed’ by the Moon. Since New Moon occurs every 29 1/2 days, you might think that we should have a solar eclipse about once a month. Unfortunately, this doesn’t happen because the Moon’s orbit around Earth is tilted 5 degrees to Earth’s orbit around the Sun. As a result, the Moon’s shadow usually misses Earth as it passes above or below our planet at New Moon. At least twice a year, the geometry lines up just right so that some part of the Moon’s shadow falls on Earth’s surface and an eclipse of the Sun is seen from that region.

The Moon’s shadow actually has two parts:

1. Penumbra
The Moon’s faint outer shadow.
Partial solar eclipses are visible from within the penumbral shadow.
2. Umbra
The Moon’s dark inner shadow.
Total solar eclipses are visible from within the umbral shadow.

When the Moon’s penumbral shadow strikes Earth, we see a partial eclipse of the Sun from that region. Partial eclipses are dangerous to look at because the un-eclipsed part of the Sun is still very bright. You must use special filters or a home-made pinhole projector to safely watch a partial eclipse of the Sun

LINKS:

Read More on Wikipedia

picture link

http://www.mreclipse.com

Observing Solar Eclipses Safely

Posted in Solar System, Space | 3 Comments

Topographic maps of Indian coalfields to be prepared

Posted on July 20, 2009 by Rashid Faridi

The Central Mine Planning and Design Institute (CMPDI), an arm of the Coal India Limited, signed an MoU with the Survey of India for preparation of the large scale updated topographical maps of 28 major coalfields of the country, based on remote sensing technique. The project, for which the Coal India Limited has funded Rs 117 crore, will be jointly implemented by CMPDI & Survey of India and will complete in five years. This is said to be a major task for the CMPDI to expedite coal exploration, mine planning, environmental management and infrastructure development in the coalfields area to match the coal-based energy demand of the country. CMPDI CMD A.K. Singh said topographical maps will be prepared for about 26,000 sq km area on 1:5000 scale with 2 m contour interval in digital GIS formats. Large scale digital topographical maps will be useful for detail coal exploration, mine planning, infrastructure planning, railway siding for coal transportation, rehabilitation and resettlement and environmental management planning as well as integrated master planning of the coalfields.

Source : http://economictimes.indiatimes.com

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Should we deliberately move species?

Posted on July 20, 2009 by Rashid Faridi

On naked patches of land in western Canada and United States, scientists are planting trees that don’t belong there. It’s a bold experiment to move trees threatened by global warming into places where they may thrive amid a changing climate.

Take the Western larch with its thick grooved bark and green needles. It grows in the valleys and lower mountain slopes in British Columbia’s southern interior. Canadian foresters are testing how its seeds will fare when planted farther north — just below the Arctic Circle.

Something similar will be tried in the Lower 48. Researchers will uproot moisture-loving Sitka spruce and Western redcedar that grace British Columbia’s coastal rainforests and drop their seedlings in the dry ponderosa pine forests of Idaho.

Deliberating moving a species has long been opposed by some, who believe we should not play God with nature and worry that introducing an exotic species — intentionally or not — could upset the natural balance and cause unforeseen ripple effects. It has happened before with dire results. Two decades ago, zebra mussels were accidentally introduced into the Great Lakes and millions are now spent every year removing the pest from water pipes.

The notion of relocating species as a pre-emptive strike against climate change has been largely theoretical. In recent years, some groups have tried assisted migration on a limited basis, most notably the effort by volunteers who last year planted seedlings of the endangered Torreya tree found in Florida to the cooler southern Appalachians.

The Canadian experiment currently under way will cover a broad swath, with tree plantings dotting the Yukon near Alaska to southern Oregon.

Past warmings have forced species to migrate to survive without human help. While some have learned to adapt to new surroundings, other have gone extinct. Faced with the possibility of much more rapid climate change, scientists say, some species may not be able to move fast enough to their new destinations and may need a little power boost to preserve biodiversity.

In North America, some critters have already started their march north. The Edith’s checkerspot butterfly, which vanished from its southern range, is now fluttering 75 miles higher in elevation. Red foxes have encroached farther into northern Canada and evicted the arctic foxes.

Last year, the British Columbia government took the first steps toward ensuring that trees in the province are adapted to future climates by relaxing its seed rules for timber companies when they replant on logged land. Seeds of most tree species can now be planted up to 1,600 feet higher than their current location.

The government’s latest experiment will study how humans can help trees move to more northerly spots where they do not currently grow, but may find themselves existing there years from now. It will not deal with introducing foreign tree species, O’Neill said.

This spring, crews fanned across rugged mountains and began the first dozen plantings on cleared forest land in British Columbia’s southern interior and on a private plot near Mount St. Helens in Washington state.

The project will eventually include 48 plots around British Columbia, Washington state, Oregon, Montana and Idaho. It will test the ability of 15 tree species to survive in environments colder and hotter than they’re used to.

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Solar Cycle Affects Global Climate

Posted on July 19, 2009 by Rashid Faridi

Establishing a key link between the solar cycle and global climate, research led by scientists at the National Science Foundation (NSF)-funded National Center for Atmospheric Research (NCAR) in Boulder, Colo., shows that maximum solar activity and its aftermath have impacts on Earth that resemble La Niña and El Niño events in the tropical Pacific Ocean.

The research may pave the way toward predictions of temperature and precipitation patterns at certain times during the approximately 11-year solar cycle.

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