Notable Total Solar Eclipses Throughout History

screen-shot-2017-02-07-at-2-20-53-pmFor centuries, scientists have taken advantage of the special circumstances of total solar eclipses to learn about our solar system. More than 2,100 years ago, the Greek astronomer Hipparchus compared observations of such an eclipse made from different spots on Earth to calculate the distance between the Moon and Earth. His estimate of 268,000 miles is within about 11 percent of the actual distance, which is not bad considering the archaic observing techniques of the time.

In 1868, British astronomer Norman Lockyer and French astronomer Pierre Jules César Janssen independently discovered helium, the second most abundant element in the universe, while observing a total solar eclipse. Helium’s name derives from the circumstances of its discovery—the word helium comes from Helios, the Greek god of the Sun. Twenty-seven years would pass until scientists found helium on Earth.

The 2017 total solar eclipse will stretch across the United States, from the Pacific to Atlantic oceans. The last one to do this occurred on June 8, 1918. As for the 2017 eclipse, Lowell astronomers and other staff left Arizona in 1918 in order to observe the event. Observatory staff used a variety of instruments for this work, including two lenses–each with a diameter of five inches and focal length of 38.7 feet—borrowed from the U.S. Naval Observatory (these were two of the so-called “Transit of Venus objectives”, used to observe the transits of 1874 and 1882).

1918More famously, in 1919 British astronomer Arthur Eddington traveled to an island in the Pacific Ocean to photograph stars around an eclipsed Sun. Albert Einstein had predicted in his general theory of relativity that starlight would not travel in a straight line but instead bend slightly as it passed by an object, whose gravity would tug on the starlight. Eddington saw a perfect opportunity to test this prediction by observing and measuring starlight as it passed by the darkened Sun during a total eclipse. Eddington’s findings seemed to support Einstein’s prediction (later astronomers have debated the accuracy of Eddington’s measurements) and made Einstein an instant global celebrity.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian


The Path of the 2017 Solar Eclipse

The path of totality for the 2017 eclipse reaches a maximum width of 71 miles and stretches in a southeasterly route from the Pacific northwest to the middle of the Atlantic coastal plain, passing over 14 states including Oregon, Montana, Idaho, Wyoming, Nebraska, Iowa, Kansas, Missouri, Illinois, Kentucky, Tennessee, North Carolina, Georgia, South Carolina.


Lowell Observatory astronomers, educators, volunteers, and support staff will host the 2017 Lowell Observatory Solar Experience in Madras, Oregon, which is right in the middle of the path of totality. Lowell chose Madras largely based on past weather patterns; Madras has one of the highest probabilities of good weather on August 21 of any site along the path of totality.


On average, total solar eclipses occur once every 18 months. But the path from which such events are visible is narrow and varies with each eclipse, so total solar eclipses cross the same geographical area on Earth only about once every 375 years. Arizona is in the middle of a 399-year wait; it hasn’t witnessed a total solar eclipse since Thomas Jefferson was president back in 1806 and will have to wait until 2205 to see the next one (for the 2017 event, the Sun will only be partially eclipsed as seen from Arizona).

The last total solar eclipse to cross into United States territory was in 1991, when a July 11 event was visible from Hawaii. The last one seen from the continental United States occurred on February 26, 1979 but the last one to stretch across the entire country—like the 2017 version—happened on June 8, 1918. The next one visible from the United States will be in 2024, when the path of totality will stretch in a northeasterly direction from Texas through Maine. Not until 2045 will another total solar eclipse cross the continent from the Pacific to Atlantic oceans.

 By Kevin Schindler, Lowell Observatory Public Information Officer and Historian

What is a Total Solar Eclipse?

We can see total solar eclipses thanks to a couple of phenomena: orbital motions of Earth and the Moon, and a cosmic coincidence that renders the Sun and Moon to appear similar in size.


Solar eclipses can only happen during the new phase of the Moon, when the Moon lines up between Earth and the Sun. If the three bodies are not quite aligned correctly, then the Moon may block part of the Sun in what is called a partial solar eclipse; if the three are perfectly aligned, then the Moon can completely cover the Sun, creating a total solar eclipse.

However, because the distance between the Moon and Earth varies, the Moon will sometimes appear a little larger or smaller than usual. Occasionally, even when the three bodies are perfectly aligned, the smaller-than- usual Moon won’t completely block the Sun, leaving a ring, or annulus, of the Sun showing. This is known as an annular eclipse.


But there is more to the story and in order to understand it, a look at one of space’s curiosities is necessary. The Sun has a diameter about 400 times greater than that of the Moon, but it also happens to be 400 times further from Earth than the Moon. This means that the two bodies, as seen from Earth, appear to be about the same size. If the Moon was farther away from Earth, then the Sun would appear larger and thus could never be covered by the Moon. In that case, total solar eclipses wouldn’t be visible from Earth; the best we could hope for would be annular ones. This will eventually become the case; with the Moon moving away from Earth at a rate of 1.5 inches per year (about the same rate that our fingernails grow), in several hundred million years it will be too small to completely block the Sun.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian

Why The Great American Eclipse of 2017 Will Be So Great

Professional and amateur astronomers alike are gearing up for what may become the most viewed sky event in history.

On August 21, 2017, the Moon will pass in front of the Sun during the first total solar eclipse visible from the continental United States in 38 years. The last solar eclipse occurred February 26, 1979, but was only visible from five states in the Northwest.

The Great American Eclipse will hit land in Oregon and travel across the country to South Carolina where it will then only be visible from the Atlantic Ocean – making the U.S. the only country that will be lucky enough to experience this historic event.


The entire country will see a partial eclipse, but only people in the “Path of Totality” will experience a total eclipse, view the iconic two diamond rings, and revel at the 360 º corona.

Because the moon’s shadow is round, those viewers nearest the center line of the Path of Totality will experience a longer eclipse. Madras, Oregon is a prime location not only for being on the center line, but also because, based on past weather patterns, it has a high probability of clear skies on August 21.


The solar totality will last a brief, but amazing 2 minutes and 40 seconds. The next total solar eclipse to fall across the United States won’t occur until April 8, 2024.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian