Totality Eclipse of the Heart-Land: Some Information on Today’s Solar Eclipse

BRIDGEPORT, Pa. — On Monday, August 21, 2017, all of North America will be treated to an eclipse of the sun. Anyone within the path of totality can see one of nature’s most awe inspiring sights – a total solar eclipse. This path, where the moon will completely cover the sun and the sun’s tenuous atmosphere – the corona – can be seen, will stretch from Salem, Oregon to Charleston, South Carolina. Observers outside this path will still see a partial solar eclipse where the moon covers part of the sun’s disk.

All of the U.S. will be treated to at least a partial eclipse, but viewers in the aptly named “path of totality,” a 60- to 70-mile-wide strip of land cutting across the country, will experience a total eclipse, resulting in two minutes of darkness in the middle of the day. The eclipse will enter Oregon at 10:15 a.m. PT and exit South Carolina at 2:50 p.m. ET, touching on 14 states along the way.

This year’s eclipse will be the first one to cross the entire continental U.S. since 1918.  The last total solar eclipse viewed from contiguous United States was on February 26, 1979 whose path passed through the northwestern U.S. states of Washington, Oregon, Idaho, Montana, North Dakota and Canadian provinces of Saskatchewan, Manitoba, Ontario and Quebec. After the August 2017 total solar eclipse, the next annular solar eclipse that can be seen in the continental United States will be on October 14, 2023 which will be visible from Northern California to Florida. Following this, we will have a total solar eclipse on April 8, 2024 visible from Texas to Maine.

Since 1503, there have been 15 total solar eclipse paths that have crossed the path of the August 2017 eclipse.  Calculations show that it will take about 1000 years for every geographic location in the Lower-48 to be able to view a total solar eclipse.

Some things to remember from the National Aeronautics and Space Administration (NASA):

1.) Do not stare at the Sun: The rods and cones in the human retina are very sensitive to light. Even a thin sliver of the sun’s disk covers thousands of these light-sensitive cells. Normally during daylight conditions, the iris contracts so that only a small amount of light passes through the lens and then reaches the retina. This level of indirect sunlight is perfectly OK and the eye has evolved over millions of years to safely see the daylight world under most circumstances. The problem is that the sun’s surface is so bright that if you stare at any portion of it, no matter how small, it produces enough light to damage individual retinal cells.  It takes a few seconds for this to happen, but afterwards you will see a spot as big as the solar surface you glimpsed when you look away from the sun at some other scenery. Depending on how long you gazed at the sun and how badly the retinal cells were damaged,  this spot will either fade away in time or remain permanent.  You should never assume that you can look away quickly enough to avoid eye damage because every person is different in terms of their retinal sensitivity, and you do not want to risk being the one who damages their eyes just to try to look at the sun.  If you want to see what the sun looks like, use a properly-equipped telescope.

2) When was the first Solar Eclipse?: Historians and astronomers believe that the legendary eclipse that two Chinese astrologers  Hsi and Ho failed to forecast occurred on October 22, 2134 B.C.E, making it the oldest solar eclipse ever recorded in human history. The Babylonian eclipse on May 3, 1375 BCE is the oldest successfully predicted and recorded in the western world, and there is evidence that the Babylonians knew about the Saros Cycle (18 years 11 days) and could use it to predict the approximate years of eclipses.

3) Can you see Solar Eclipses off Earth?: The only requirement for a total solar eclipse is that the angular size of the sun has to match the angular size of some other object that passes in front of it. When the disk of the object is smaller than the sun, this is called a transit. It is also called an eclipse when the disk of the object is much larger than the sun, but in general this would not allow the corona to be viewed, which is how we define total solar eclipses viewed from Earth. When humans were rooted to the surface of Earth, this was only the case for the moon as the eclipsing object. But there are many known moons and asteroids across our solar system, and from a suitable vantage point near any of them, we can find a distance where again the angular size of the object matches that of the sun to form a total solar eclipse. There are so many different vantage points  to choose from that each case has to be specified. For example, eclipses need not be observed from the surfaces of a planet. In fact, Venus and the outer planets have inaccessible surfaces. Instead, we might consider standing on the surface of a planetary moon and waiting for another moon to pass in front of the sun. Given the myriad of planetary moon orbits, finding those instances where the angular sizes match is a significant computational challenge.  Jupiter frequently passes across the sun as viewed from its moons, but its diameter is huge compared to the sun.  There are 5 satellites capable of completely occulting the Sun: Amalthea, Io, Europa, Ganymede and Callisto.  All of the others are too small or too distant to be able to completely occult the Sun, so can only transit the Sun. 

4) Can I photograph the eclipse with my smartphone? The short answer is a definite ‘yes!’, but of course you have to be careful that you minimize glimpsing the bright sun with your  eyes without the benefit of a proper filter. As for your camera, there is no valid reason why you would want to point your smartphone camera at the brilliant, un-eclipsed sun without putting a filter over the lens. During totality, you do not need the filter, of course! Unless you have a telephoto lens for your smartphone, you will only be able to take unmagnified images of the eclipse in your sky. These photos can be very exciting because the field-of-view is large enough that you can compose the shot with your friends and local scenery in the shot, at the same time a recognizable, eclipsed sun during totality hangs dramatically in the darkened sky. You will easily be able to capture with most smartphone cameras the darkened disk of the moon surrounded by a clearly recognizable bright solar corona. Many examples of these kinds of wide-angle shots can be found on the Internet. Of course, if you use the camera’s digital zoom, you will see a pixelized, enlarged image that will not show much actual detail in the corona. To get around this, you need a telephoto lens for your smartphone. There are many styles of telephoto lenses for smartphones. Avoid the ‘clip on’ lenses because they constantly slip and have to be precisely lined up on the camera lens to work. They are often of low optical quality. The best lenses are rated as 12x and above, and come with their own smartphone mounting bracket. At these magnifications, a tripod is essential because of camera jitter. A decent 12x lens and tripod adapter will cost you about $30.00, but you can also use this system for great ‘close up’ shots in sport and nature settings too!  The telephoto  lens will give you enough magnification that you will clearly see some of the details in the bright corona. You should test your system by taking night-time photos of the moon so you understand how large and detailed the moon will appear in your shot. The sun/mon during eclipse are equal-sized so this is a good way to compose your eclipse shots too.  Also experiment with the settings on your camera using a downloadable app like Camera+ or NightCap Pro, which allow you more flexibility in setting up the exposure, f/stop and other factors.

5) Why do eclipse tracks move eastward even though the Earth rotates from West to East? Because the Moon moves to the east in its orbit at about 3,400 km/hour. Earth rotates to the east at 1,670 km/hr at the equator, so the lunar shadow moves to the east at 3,400 – 1,670 = 1,730 km/hr near the equator. You cannot keep up with the shadow of the eclipse unless you traveled at Mach 1.5.