September 20, 2017

Event of the Week: 20.07.09: A VERY long solar eclipse!!!



The astronomical event of the year is about to take center stage this Wednesday. A total eclipse of the Sun, the longest possible for a VERY long time! Those lucky enough to have secured a ticket or live along the Pacific/Southeast Asia corridor will see an eclipse of a duration of up to 6 minutes and 39 seconds, near the maximum 7 minutes and 31 seconds possible. This is a consequence of the Earth passing aphelion a few weeks ago (read: a visually small Sun) and the a large New Moon very near perihelion (remember the year’s smallest Full Moon a few weeks back?)

The Moon’s shadow makes planet fall at 00:53 Universal Time (UT) just off the coast of India, then crosses the subcontinent over Nepal and Bhutan into China, then passes over Shanghai as it sweeps off through the Ryukyu Islands just north of Okinawa, for a maximum totality very near Iwo Jima at 2:35:19 UT. No doubt, this spot in the Pacific will be the target of several cruise lines… The path then skirts Kwajalein and the Marshall islands for a grand finale at 4:18 UT. In general, the farther east you are, the better your weather prospects will be. Don’t forget, this is monsoon season in southeast Asia; weather around the Himalayan region is always dicey, at best. As of late last week (the time of writing this!), two tropical systems were churning in the Pacific, including tropical storm Molave near Taiwan. Get your front seat if you can, and don’t forget to properly protect your eyes during those partial phases. This will be the longest possible totality until 2132! If you (like astroguyz) find yourself on the wrong side of the planet, several web casts abound. Just don’t forget that the action starts Tuesday night East coast time! This is one eclipse that will be witnessed by a large swath of humanity! This eclipse is also part of saros series 136, which also produced long duration eclipses all exceeding 7 minutes in 1937, 1955, 1973.

The astro-term for this week is; gravitational lensing. One of the great predictions of Einsteins General Theory of Relativity is that gravity bends light. What does this have to do with this week’s solar eclipse, you might ask? Well, in 1919, a Royal Astronomical Society journeyed to two separate sites in the path of totality; one on the African island of Principe and one to the coast of Brazil. The idea was that the enormous mass of the Sun would deflect the light of nearby background stars observed during totality. Initial findings were that target stars observed in the Hyades star cluster were indeed deflected by 1.75 arc seconds, a tiny but discernible amount. This observation, although recently contested as to whether the team could have measured such a tiny amount in the short duration of an eclipse, still stands as an initial proof. Today, astronomers see evidence of gravitational lensing in much more massive objects; large galaxy clusters lensing distant quasars. And yes, the historic solar eclipse of 1919 was of the same illustrious saros series 136!

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