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EghtesadOnline: The first full day of summer in the Northern Hemisphere brought with it one of nature's spectacular sky shows: an annular solar eclipse.

On Sunday, the new moon orbited between the sun and Earth, and passed squarely across the face of the sun for viewers along a very narrow path that ran through Iran, Pakistan, India, China and the African continent, IRNA reported. 

But instead of completely blocking the sun, it left a "ring of fire" from the sun when it peaked. This was the last ring of fire solar eclipse of 14th century of Solar Hijri calendar.

The event could be watched live online on the Instagram page of Science & Astronomy Center of Tehran. The eclipse began at 9:05 local time (0345 GMT). For observing the eclipse in person, one must wear proper eye protection like eclipse glasses.

During a total eclipse of the sun, the entire disk of the sun is covered by the moon. The end result is a beautiful spectacle in which a beautiful halo of pearly white light—the solar corona—suddenly flashes into view. Semi-darkness settles over the landscape and a few of the brighter stars and planets may appear. Then after a few seconds or minutes, totality ends and the great show is over.

But an annular eclipse, such as the one that took place on Sunday, falls just short of providing such a celestial pageant, because the moon will be just a little too far from the Earth to completely cover the disk of the sun. The dark conical shadow of the moon (called the umbra), from where we can see a total eclipse, extends for 235,600 miles (379,100 kilometers) out into space.  

But unfortunately, on Sunday, the moon's distance from Earth was 381,500 km from Earth. So the moon's dark umbral shadow will fall 2,400 km short of reaching the Earth’s surface. In such a case, an annular eclipse results. writes, we can imagine a "negative shadow" or anti-umbra, as the mirror image of the umbra, beginning at the tip of the umbral shadow and extending out to infinity. The ground track of the anti-umbra traces out a "path of annularity" and observers who are within this narrow shadow track, which averaged about 53 km in width, saw the dark silhouette of the moon, surrounded by a ring of bright sunlight.

That ring was exceedingly narrow and the moon's apparent diameter was 99.4% as large as that of the sun, so the width of that ring of sunlight at its thinnest measured no more than six-tenths of 1% of the sun.  

Thus, a bright ring of the sun's disk remained uneclipsed, unfortunately bright enough to prevent a view of the solar corona and keeping the sky just bright enough to squelch any view of the stars and most of the planets. 

The term annular is derived from the Latin word annulus, meaning "ring shaped", and in recent years, the mainstream media have branded such events as "ring of fire" eclipses.



Beautiful Celestial Event

While admittedly an annular solar eclipse cannot compare to a total one, it is still a most interesting and exciting celestial event. 

By the time the sun was 80% eclipsed, it had the shape of an elongated crescent. Sunlight was coming only from the sun's redder limb regions; overall illumination on the ground was dusky and yellow, becoming progressively redder until the moment of annularity.

On-site observers probably alluded to how much cooler the air was getting; temperatures may drop 6 degrees Celsius or more. Cumulus clouds—clouds that resemble big balls of fluffy cotton—tend to dissipate, but ground fog might form in lowlands. Shadows became distinctly sharper as the sun became more and more misshapen, narrowing to a thin arc or filament of light. 

Because the geometry of this event is almost like that of a total eclipse, there is every reason to check a few minutes before and after annular eclipse, for faint, mysterious rippling waves of dark and light moving across the ground or along the sides of buildings. 

Called "shadow bands," these waves apparently result from irregularities in the Earth's atmosphere. 

As the ring phase approaches, events accelerated: a weird “counterfeit twilight” fell across the landscape. The eerie dimming at midday, while admittedly not so dramatic as during a total eclipse, may bring about unusual behavior by birds, livestock and insects.

No stars were likely to be seen, but it was easy to spot Venus, shining at a brilliant magnitude of -4.5, 25 degrees west of the sun.

Probably the most readily observable phenomenon at Sunday's eclipse was undoubtedly the formation of Baily’s beads. These are the lingering glints of sunlight appearing through valleys on the eastern limb of the advancing moon, just as a total eclipse begins, and then at the western limb when it ends. 

The nearly identical sizes of the disks should also cause beads to appear at the northern and southern limbs of the moon as well, depending on an observer’s location within the central path. 


Iranians Solar full day Northern Hemisphere