When the moon is exactly lined up between sun and Earth, people in the narrow band of the moon’s central shadow (umbra) witness a total solar eclipse. Those living in the circle defined by the penumbra or outer shadow see a partial eclipse. Credit: Sagredo
If you’re in China tomorrow, I suggest you take a drive down to Shanghai to see the total eclipse of the sun. The moon will be in new phase tomorrow morning and people from India, China, southern Japan and anyone floating in a boat inside the hundred-plus-mile-wide path of totality as it crosses the Pacific will see a total eclipse of the sun.
This eclipse is special because it’s the longest one of the 21st century. Two factors conspire to make it so: the Earth is near its furthest point from the sun in July so the sun’s disk is just a wee bit smaller than usual and the moon happens to be near its closest point to Earth so it’s just a wee bit larger than usual. A smaller sun stays behind a bigger moon for a longer time creating an exceptional eclipse of more than six minutes.
During a total solar eclipse, it’s safe to look at the sun because the bright disk is completely covered by the moon. With the sun out of the way, its pearly, vibrant outer atmosphere called the corona is revealed, along with a rim of bright pink flame called the chromosphere. Credit: Luc Viatour
I saw a total eclipse in Baja California in 1991, when we basked under a black moon surrounded by the halo of the sun’s spectacular corona for almost seven minutes. As you can see from the diagram, the shadow the moon casts is very narrow. Only those living in the path directly beneath it will see a total eclipse. A much larger section of the eastern hemisphere will witness a partial eclipse, where only part of the moon covers the sun.
The path of totality, however narrow, doesn’t just sit in one spot but cuts a long swath across the planet because both the moon and Earth are in motion. In the animation (right) the black dot is the moon’s inner shadow or umbra while the larger circle shows the zone of partial eclipse. Because much of the path slices right through China, the world’s most populous country, this eclipse may be viewed by more people than ever before in history. Shanghai alone has 20 million people. That’s a lot of eyeballs.
Up until totality, you need a safe solar filter for viewing the sun otherwise your retina will be damaged by both ultraviolet and infrared (heat) radiation. Totality can be enjoyed without any filtration at all. I wish I could be there, but if you had to stay at home, our time is coming. Keep August 21, 2017 open because that’s when U.S. observers will be able to jump in a car and just drive to totality. The moon’s shadow will cut a path that morning from Oregon to South Carolina.
If you’d like to learn more about tomorrow’s eclipse, take a look at these two excellent websites:
(Eclipse animation by A.T. Sinclair)