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Blue Flash
| Title |
Blue Flash |
| Explanation |
Difficult to observe, the momentary green flash [ http://www.exo.net/~pauld/physics/atmospheric_optics/ green_flash.html ] above the rising or setting sun has been documented as [ http://mintaka.sdsu.edu/GF/ ] a phenomenon caused by the atmospheric bending or refraction of sunlight. Like a weak prism, the Earth's atmosphere breaks white sunlight [ http://micro.magnet.fsu.edu/primer/java/scienceopticsu/newton/ index.html ] into colors, bending red colors slightly and green and blue colors through increasingly larger angles [ http://micro.magnet.fsu.edu/primer/java/ scienceopticsu/refraction/index.html ]. When the sky is clear, a green flash [ http://www.physics.sfasu.edu/astro/research/ sandiego.html ] just above the sun's edge can sometimes be seen for a second or so, when the sun is close to a distant horizon. A blue flash is even harder to see though, because the atmosphere [ http://antwrp.gsfc.nasa.gov/apod/ap000115.html ] must be extraordinarily clear to avoid scattering and diminishing the refracted blue sunlight. Still, from a site near Roques de los Muchachos (altitude 2,400 meters) on La Palma in the Canary Islands [ http://antwrp.gsfc.nasa.gov/apod/ap990410.html ], astrophotographer Mario Cogo captured this dramatic telescopic image of a blue flash on color film in October of 2001. The image of the setting Sun with large sunspot groups [ http://antwrp.gsfc.nasa.gov/apod/ap010315.html ] on its surface is heavily distorted by atmospheric layers. A lingering green rim is just visible under the tantalizing blue flash. |
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Solar Eclipse: A Composite V
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| Title |
Solar Eclipse: A Composite View |
| Explanation |
Yesterday [ http://www.skypub.com/eclipses/s980226c.html ], the Moon's shadow reached out [ http://pao.gsfc.nasa.gov/gsfc/eclipse/eclipse.htm ] and touched the Earth [ http://umbra.nascom.nasa.gov/eclipse/980226/rp.html ], treating a large portion of the Western Hemisphere to an Eclipse of the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap970827.html ]. This composite image [ ftp://pao.gsfc.nasa.gov/newsmedia/eclipse/COMPOSITE.TXT ] combines pictures of the Sun made from both Earth and space. The central direct image of the solar surface was recorded yesterday by the Extreme Ultraviolet Imaging Telescope [ http://umbra.nascom.nasa.gov/eit/ ] on board the space based SOHO observatory. It is surrounded by a telescopic picture of the Sun as seen from the island of Aruba during the total eclipse. The surrounding view of the eclipsed Sun reveals the gleaming solar corona [ http://sohowww.nascom.nasa.gov/descriptions/mission/english/ wind_and_corona.html ], visible to ground based observers [ http://antwrp.gsfc.nasa.gov/apod/ap951024.html ] during totality. Such combined images can help connect explosive events and features on the Sun's surface with the corona and solar wind. |
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