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Episode Five: How to Time Travel to a Star




It’s one thing to collect and to generate data. It’s entirely another thing to make sense of it. 

Michael Shara Curator, Department of Astrophysics

Stargazing Across Time

Humans have spent eons looking up at the night sky with wonder and mapping it by creating constellations, gathering information, and using it to impose a sense of order on the vastness of space.

From the earliest days of astronomy, though, the answers we've found have served to create further questions, and with them the need for finer instruments that provide more complete data. The naked eye isn’t nearly sufficient for viewing stars closely or tracking their movements in detail, much less plumbing the depths of space. From early devices that used celestial bodies to tell travelers the time of day to the space-based telescopes now capturing images of the cosmos in unprecedented detail, ever-more intricate instruments have helped us get a better look at—and understanding of —the universe and our place in it.

Sundials

Prior to the development of reliable clocks, sundials, which tell the time of day by the position of the Sun, were a method of choice for determining lunch hour, coffee breaks, and quitting time for millennia. By the 17th century, portable dials became popular with people like soldiers and merchants, who were always on the go. Some, like the ivory-encased affair pictured above, could be adjusted to tell the correct time at a variety of different latitudes. 

 

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This portable sundial could tell time accurately from numerous European cities.

©AMNH


Dials

The Sun wasn’t the only heavenly body used for telling time. This rosewood dial crafted in 17th-century Italy was designed to align with the pointer stars of the Big Dipper, letting users determine the time of day even in the dead of night—provided they had a clear sky. 

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Time and other observations could be made with this dial using starlight using the positions of the stars.

©AMNH 


Astrolabes

Astrolabes, which could locate and predict the movement of heavenly bodies like the Moon, planets, and stars, were first developed in the 11th century BC and were refined throughout the ages. Examples like this bronze astrolabe, crafted in Persia during the 18th century, were variously used for surveying, telling time, and predicting and charting the movement of stars and planets. 

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This bronze astrolabe, made in Persia circa 1730–1775, has several inset plates for use by travelers at different latitudes.

©AMNH/D. Finnin


The reasons for gazing up weren’t always about terrestrial concerns like telling time or navigation. People all over the world made maps of the stars in an effort to better understand them. One of the earliest star atlases, Johann Bayer’s 1603 collection of engravings the Uranometria, detailed the known stars and constellations in the night sky. The work also enshrined Bayer’s method for naming stars by assigning them letters in the Greek alphabet in the order of their apparent brightness. While astronomers have developed new naming conventions—the number of stars in a constellation often far exceeds the 24 letters of the Greek alphabet—names like Alpha Centauri are still familiar today.   

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The early star atlas Uranometria depicted constellations such as Orion, above.

©AMNH/D. Finnin


Star Maps

Beginning in the 17th century, telescopes came into use, allowing astronomers to get closer looks at the sky, and the objects that populate it, than ever before. New and improving instruments spurred more detailed star mapping. 

In the 1800s, Connecticut schoolteacher Elijah Burritt brought astronomy to the masses when he published a popular volume of celestial maps, Burritt’s Atlas, to “illustrate Burritt’s geography of the Heavens.” The Museum’s holdings include an 1856 edition.

Ep 5 Burritt's Star Atlas

Burritt’s Atlas, designed to illustrate the geography of the heavens, featured celestial maps for the masses.

© AMNH/D. Finnin


Burritt had designed his atlas as a cheaper alternative to celestial globes, which illustrated the place of stars and constellations in the sky. While beautiful, globes were out of reach for most stargazers, including school teachers.

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Revolving the globe on its axis shows the stars’ daily rotation.

©AMNH/D. Finnin


Telescopes

in the late 19th century, photographic plates became the gold standard for capturing images that telescopes allowed astronomers to view. The images captured on these plates remain incredibly valuable to science, representing a century of data on stars and galaxies that can never be replaced. The Harvard Plate collection currently being digitized at the Museum consists of images of the sky taken beginning in the 1890s and continuing, uninterrupted, to the 1950s.

“[Harvard astronomers] would basically take a telescope that covered a large part of the sky and take pictures every night of the entire sky in an organized fashion,” says Ashley Pagnotta, a Kathryn W. Davis postdoctoral fellow at the Museum. The result was that about every week or two, the Harvard team would have a full picture of the sky, providing an excellent time lapse of how celestial objects changed over time.

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This spiral galaxy image, from the Harvard Plate collection, is one in a series of photos taken over decades.

©AMNH


From simple metal tubes with a series of lenses, telescopes have evolved into masterworks of engineering that dominate mountaintops and explore the depths of space with titanic mirrors and radio waves alike.

Today, high-powered digital telescopes, many of them traveling through the cosmos like the Hubble Space Telescope, give us a better look at the universe than ever before, providing answers to astronomical mysteries and introducing new questions.

Beginning in the 1970s, the move to digital imaging marked a revolution in photographing the cosmos. That’s because photographic plates have a quantum efficiency of just 1 percent, meaning that for every photon they record, 99 are going undetected. Modern digital detectors, says Astrophysics Curator Michael Shara, can achieve quantum efficiencies of more than 90 percent.

More sensitive digital detectors are key to the strides made in modern astronomy, but where those detectors are housed is just as important. Moving from Earth-based to space-based telescopes has further improved our ability to visualize the universe around us.

“With the launch of the Hubble Space Telescope, the Chandra X-Ray Observatory, and other infrared telescopes, we can do astronomy in space and see things 100 times fainter than we could before,” says Dr. Shara.  

Ep 5 Hubble Magellanic Cloud

The Hubble Space Telescope captured this image of stars forming in the Large Magellanic Cloud

© NASA/ESA


Coronograph

Among those new and improved devices is the Lyot Project Coronagraph, developed at the Museum. Curator Rebecca Oppenheimer has already used the coronagraph, which filters out light from distant stars and makes it easier to see dim objects nearby, to discover the first brown dwarf star ever observed. Future coronographs will aim to see even dimmer and dimmer objects. That's likely to be accomplished courtesy of coronagraphs mounted on space-based telescopes.

"The next goal is to use a coronagraph to see objects that are much fainter, that may just be reflecting light, not radiating it," says Dr. Oppenheimer. "To do that, we'll need better suppression of starlight. That's harder to do from the ground because of Earth's atmosphere, so we'll need to get into space."

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Viewed without a coronagraph, the Sun (left) is so bright that nothing can be seen around it. With a coronagraph in place, planets like Saturn and Jupiter (right) are visible.

©AMNH/R. Makidon, A. Sivaramakrishnan, B.R. Oppenheimer


 

Next-Generation Technology

As impressive as our tools for observing space are now, there is still plenty of room for improvement. Space-based and terrestrial telescope systems already in development will be able to give us images of the universe in unparalleled detail. One planned device, the Large Synoptic Survey Telescope, will use three huge mirrors and a 3.2-gigapixel digital camera to capture images of a huge swath of the sky every 20 seconds.

“In just a few years, we’re going to be photographing or imaging essentially the entire sky every two or three nights with the Large Synoptic Survey Telescope,” says Shara. “We will be imaging literally all hundred billion galaxies every night, and essentially seeing every supernova as it goes off…at least out to a distance of 10 million light years.”

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The Large Synoptic Survey Telescope is expected to be fully operational in 2022.

©LSST


 

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