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Chasing Shadows: Eclipses and Eclipse Observations in the Library of Congress Collections

This post was authored by Sean Bryant, Science Reference & Research Specialist in the Science, Technology, and Business Division of the Library of Congress. He recently authored the blog posts “The Last Man on the Moon? — The Story of Eugene Cernan in Two Parts” and “An American in Orbit: The Story of John Glenn.”

A partial solar eclipse, seen from NASA’s Solar Dynamics Observatory satellite in 2014. (NASA) https://www.nasa.gov/content/solar-dynamics-observatory-sees-lunar-transit

In a matter of days, the Moon will slip between the Earth and Sun. This has been happening every month or so, for more than four billion years, as the Moon orbits the Earth. If you imagine a line connecting the center of the Earth and the Sun, the Moon usually passes a bit above or below the line, and what we see is a new moon, which is to say we see nothing. The Sun’s light passes over or under the Moon and reaches the Earth normally. However, every so often the Moon passes nearer or directly through the line between the Sun and the Earth, casting a shadow on the Earth and briefly blocking much of the Sun’s light from reaching the Earth. This, we call a solar eclipse.

Humans have long been fascinated by solar eclipses.  We have developed myths, legends and stories around them, and celebrated them in poetry, art and, more recently, photography. Reports of occurrences appear in Chinese records from more than four thousand years ago, and come from other ancient civilizations, like the Maya, Babylonians and Greeks. Observers and astronomers of the time were able to use the reports and their own observations to predict the time and location of future eclipses.

Report of a Solar Eclipse seen in southern Spain. //lccn.loc.gov/06014356

Succeeding generations of astronomers would add their own records, refining their theories and models of celestial mechanics. As these predictions became more and more accurate, 17th and 18th century astronomers, such as Cassini and Halley, began to produce maps showing the predicted and actual paths of solar eclipses visible in their European locales. Due to the relative infrequency of solar eclipses, however, the science relating to them continued to proceed in fits and starts. By the 19th century though, astronomers were beginning to take note of more than just the Moon in their observations. With light from the center of the Sun blocked by the Moon, they were able see and measure the dimmer outer corona, a region of the Sun normally obscured by the brighter light at the heart of the Sun.

Astronomers, eager to observe more solar eclipses, began to travel farther from their European homes, traveling to far flung outposts of their colonial empires and then beyond in ever larger, more organized groups, observing from places like India, the East Indies and the Caroline Islands. They began to carry spectroscopes to search out chemical elements in the corona.  New observatories and societies, such as the US Naval Observatory, US Coast Survey and the National Geographic Society, sponsored expeditions to even more remote locations and began to contribute to their observations, many of which are included in the Library’s collections.

Report of an eclipse expedition to India, 1898. //lccn.loc.gov/s27000003

In recent years eclipse viewing has grown to encompass the scientific community in many more countries who contribute their reports to the collective body of scientific knowledge. The Library of Congress has copies of many of these reports in the general collections. Though totality – the portion of a solar eclipse when the Moon is directly in between the Sun and the Earth, lasts for no more than a few minutes in any one place, teams, working together while spread along the path of the eclipse, can make observations that run for hours. Observations have become ever more sophisticated, even moving into outer space, where the Earth’s atmosphere doesn’t interfere with observations. We continue to learn more each time the Moon passes directly between the Earth and the Sun.

Much of the information in this post was taken from the book Celestial shadows: eclipses, transits, and occultations, by John Westfall and William Sheehan. If you would like to learn more about solar eclipses, the Library of Congress has many resources available. The Library’s Science, Technology and Business Division, in partnership with NASA’s Goddard Space Flight Center, sponsored a lecture by Dr. C. Alex Young, the Associate Director for Science in NASA Goddard’s Heliophysics Science Division which is available via webcast.  Many of the items linked above are currently on display in the Science and Business Reading Room through the end of August, on the fifth floor of the Adams Building, where you are welcome to come and examine them. Many additional materials are available in the general and other collections of the Library of Congress.  You can start your own expedition at www.loc.gov.

Image from: https://eclipse2017.nasa.gov/sites/default/files/Twitter%201500×500.jpg

Venus-the Forgotten, Mysterious Planet: August 15 Lecture with NASA’s Dr. Lori Glaze

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. We’ve heard a great deal recently about Jupiter (Juno Mission) and Pluto (New Horizons), and soon the Science, Technology & Business Division will present a program on Saturn (Cassini), but what about Venus?  Except for programs on the […]

The 2017 Total Solar Eclipse: Through the Eyes of NASA, June 15 Lecture with Dr. C. Alex Young

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. The total solar eclipse on August 21, 2017 will be the first total solar eclipse visible in the contiguous United States since 1979 — and the first that has traversed the entire continent coast-to-coast since June 8, 1918. […]

Space Ethics: Ethical Implications of Commercial Space Projects: May 10th Lecture by Christopher Ketcham, Ph.D.

This post was authored by Tomoko Y. Steen, Ph.D., Science Reference & Research Specialist in the Science, Technology and Business Division of the Library of Congress. On Wednesday, May 10, 2017, Dr. Christopher Ketcham will discuss the need to balance the economic value of commercial ventures with safety and ethical concerns for life on Earth […]

Finding NEEMO at LC: Dr. Kelsey Young to Speak May 4 about NASA Extreme Environment Mission Operations

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. The Science, Technology and Business Division is presenting “NASA Extreme Environment Mission Operations (NEEMO): Preparing Astronauts for Space Exploration” with Dr. Kelsey Young in the Pickford Theater, third floor, Madison Building, Library of Congress, on Thursday, May 4, […]

What’s for Lunch: 2017 Earth and Space Science Talks at the Library of Congress, Sponsored by the NASA Goddard Space Flight Center and the ST&B Division

Lecture series coordinators Sean Bryant and Stephanie Marcus, Science, Technology and Business Division, contributed to this blog post. Spring has arrived, and with that, we are getting ready to kick off our annual Earth and Space Science lecture series, now in its eleventh year.  The series is a partnership between the NASA Goddard Space Flight […]

An American in Orbit: The Story of John Glenn

This post was authored by Sean Bryant, Science Reference & Research Specialist in the Science, Technology, and Business Division of the Library of Congress. Fifty five years ago this week John Hershel Glenn Jr. rode an Atlas rocket into a cloudy February morning. In his Mercury space capsule Friendship 7, Glenn became the third person, […]

Hidden Figures No More: African American Women in Space Exploration

Today’s post was written by Denise Dempsey a Science Reference Librarian. The recent release of the new film Hidden Figures, based on the book of the same name by Margot Lee Shetterly, presents a great opportunity to learn more about the contributions of African American women to the Space Race and to space exploration. The […]