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EARTH AT APHELION:
Earth circles the sun, right? Not exactly.
Earth's orbit is an ellipse, not a circle, which means the sun-Earth
distance varies throughout the year. On July 3rd and 4th, Earth
is at "aphelion," the most distant point in its orbit.
Around this time, the sun looks about 1.7% smaller and sunlight
is 3.4% less intense than the annual average. But don't expect any
relief from the heat: full
story.
VOLCANIC SUNSETS:
The plume of volcanic dust and sulfur dioxide
that has caused so many pretty sunsets over the USA this week has
crossed the Atlantic and reached Europe. "The purple color
of the sky on June 30th was unbelievable," says Rafael Gallego,
who sends this picture from Carrión de los Céspedes, Spain:
Similar reports are pouring in from France, England, Denmark, the
Netherlands, Canada and many US states. Here's what to look for:
When the sun goes down, delicate ripples
of white appear over the western horizon. Then, as the twilight
deepens, the sky turns a lovely shade of "volcanic lavender."
The source of the phenomenon is Russia's Sarychev
Peak volcano. It erupted on June 12th, hurling massive plumes
of sulfur dioxide (SO2) and other debris into the stratosphere.
The white ripples that herald these sunsets are made of volcanic
aerosols--a mixture of ash and sulfur compounds. Blue light scattered
by fine volcanic aerosols combines with ordinary red sunset rays
to produce the telltale lavender.
Earth-orbiting satellites are monitoring Sarychev's sulfur
dioxide plume as it circumnavigates the globe at high latitudes,
spreading the phenomenon from Russia to the USA to Europe and back
again. All northern sky watchers should be alert for volcanic sunsets.
UPDATED: 2009
Sarychev Sunset Gallery
[See also: 2008
Kasatochi Sunset Photo Gallery]
ART OR SCIENCE?
Researchers at the National Center for Atmospheric Research (NCAR)
in Boulder, Colorado, have created an unprecedented 3D supercomputer
model of a sunspot. The result is not only scientificially informative,
but also a thing of beauty:
To create the virtual sunspot, researchers programmed NCAR's IBM
bluefire supercomputer with the laws of magnetohydrodynamics, sprinkled
in some ground-based observations of actual sunspots, and hit "go."
The bluefire is capable of 76 trillion calculations per second;
even so, the program took weeks to complete. The final model contains
1.8 billion points and covers a 3D domain 31,000 miles by 62,000
miles wide and 3,700 miles deep.
Physcists are now studying movies
of the virtual sunspot to develop new insights into the dynamic
behavior of these planet-sized behemoths. More than one onlooker
has gasped in amazement when shown the surprisely lovely subsurface
structure of the 'spot.
Is it art or science? You
decide.
2009
Noctilucent Photo Gallery
[previous years: 2008,
2007, 2006,
2005, 2004,
2003]
Explore
the Sunspot Cycle
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