A hidden star catalog on an ancient manuscript attributed to Hipparchus
Credit: Early Manuscripts Electronic Library/Lazarus Project, University of Rochester

Scholars studying Biblical texts have made an almost unimaginable find—fragments of a lost star catalog compiled by the ancient astronomer Hipparchus. Hipparchus’s work represents the earliest known project to catalog the entire night sky. The find is an example of a palimpsest—a manuscript that has been written over with other writings. The discovery was announced in the fall of 2022. 

The lost fragments were discovered by researchers examining a text taken from the library of St. Catherine’s Monastery, a Greek Orthodox monastery on the Sinai peninsula in Egypt. That text was written during the Middle Ages, a period of history that lasted form about the 400’s through the 1400’s. 

The text was written not on paper, but on a specially prepared animal skin called parchment. However, parchment and other materials could be rare in the Middle Ages. For this reason, scribes sometimes scraped the surface of the parchment, clearing the page for a new manuscript. In many cases, the scraped away writing can still be detected, forming a type of hidden manuscript called a palimpsest. 

In 2012, a biblical scholar asked his college students to study the text beneath the manuscript, hoping to find earlier Christian writings. But one student spotted an astronomical passage often attributed to the ancient Greek mathematician Eratosthenes. 

In 2017, researchers at the University of Rochester in New York analyzed the pages using multi-spectral imaging. They took 42 photos of each page at various wavelengths of light. A computer algorithm then combined the various images to search for hidden markings. The researchers discovered myths about the stars’ origins compiled by Eratosthenes, along with a poem about the constellations. 

During the COVID-19 pandemic, the house-bound scholar passed the time re-examining the images. He was surprised to find what appeared to be stellar coordinates, numbers that can be used to measure the position of a star in the night sky.  

Using radiocarbon dating, the coordinates were determined to be written in the 400’s or 500’s A.D. However, the way they were written suggested that they might have been copied from Hipparchus. Moreover, astronomers know that the stars appear to change position over time due to a wobble in Earth’s axis, an effect called precession. The coordinates were so detailed that scholars could thus determine that they were taken in 129 B.C., during Hipparchus’s life. 

The oldest surviving star catalog comes from a work called the Almagest by the astronomer Ptolemy, compiled in the 100’s A.D. Hipparchus’s earlier catalog is mentioned in ancient sources. But with no surviving evidence, it was thought to be lost forever or even never to have existed. 

The new discovery sheds an amazing light on Hipparchus’s work. Compiled nearly 2,000 years before the invention of the telescope, his catalog would have required countless hours of measurement with a sighting tube or a device called an armillary sphere. For now, only a few fragments remain, but scientists hope that they will help to identify other fragments of Hipparchus’s work in other manuscripts. 

March 2, 2017

Time operates on an epic scale among the stars and galaxies of outer space. Some stars exist for millions of years but then suddenly undergo rapid changes and explode within months. In October 2013, an international team of scientists led by Ofer Yaron, an astrophysicist at the Weizmann Institute of Science in Israel, detected and studied a supernova that occurred in a distant galaxy within three hours of the explosion’s light first reaching Earth. Thanks to the timely observations, the team was able to learn a lot about the star and the explosion that consumed it. The team published its findings in February 2017 in the journal Nature Physics.

Supernova 1604 was a star that exploded in our own galaxy. The supernova blasted off the shell of gas and dust seen in this false-color composite image. The shell continues to expand at around 2,000 kilometers (1,200 miles) per second. The German astronomer Johannes Kepler observed the explosion in 1604. Credit: NASA/ESA/JHU/R. Sankrit & W. Blair

A supernova is an exploding star that can become billions of times as bright as our sun before gradually fading from view. At its brightest, a supernova may outshine an entire galaxy. The explosion throws a large cloud of gas into space at speeds of up to 10 percent of the speed of light, which is 186,282 miles (299,792 kilometers) per second. The mass of the expelled material may exceed 10 times the sun’s mass. Most supernovae reach their peak brightness in one to three weeks and shine intensely for several months.

A red supergiant called V838 Monocerotis glows at the center of a dust cloud in this photograph taken by the Hubble Space Telescope. In 2002, the star gave off a brilliant flash of light, becoming 600,000 times as bright as the sun. The flash illuminated dust thrown off the star during a previous outburst. Credit: NASA/ESA/H.E. Bond (STScI)

The exploding star examined by Yaron and his associates was a red supergiant. Such stars are dozens of times larger than our sun, which is a main sequence star or yellow dwarf. Red supergiants have relatively short life spans, however, existing for “only” millions of years. In contrast, our sun is expected to live some 10 billion years. All stars produce energy through the process of nuclear fusion, a joining of two atomic nuclei (cores) to produce a larger nucleus. Fusion releases a huge amount of energy. Most stars fuse hydrogen or helium, but a supergiant quickly (over millions of years) burns through its fuel supply and begins to fuse heavier elements together in its core. At this point, a supergiant’s days are numbered. Each new level of fusion chips away at its core, slowly killing the star. At a critical point, the star quickly fuses its available silicon into iron. Once the core fills with iron, the star will collapse and rebound in an explosive supernova.

Click to view larger image
A huge star creates chemical elements by nuclear fusion, the joining of two atomic nuclei to make a larger nucleus. In the outermost shell, hydrogen nuclei fuse, creating helium. In the next shell, helium fuses to make carbon and oxygen. Fusion creates successively heavier elements in shells closer to the core, where iron is produced. The shells in this diagram are not drawn to scale. Credit: WORLD BOOK diagram

Based on the patterns of light emitted by the supernova in question, Yaron and the team discovered that the star had blown off a layer of material into space about a year before the explosion. They suspect that this layer has to do with a change in fusion fuel at the star’s core shortly before it went supernova. The transition itself was violent, setting off a chain reaction within the star that shot a layer of star matter into space ahead of the supernova.

The discovery was made with the help of an ever-improving array of automated survey telescopes. Such telescopes capture images of a certain portion of the night sky. A computer then compares the images against earlier pictures of the same section of sky, looking for changes. If it detects any, the computer alerts a human astronomer to investigate the findings.

Astronomers are eagerly awaiting the next supernova to occur in the Milky Way. They estimate that a supernova occurs once every 100 years or so in our galaxy, but they are not always visible to Earth-bound observers. The last local supernova seen on Earth occurred in 1604, when German astronomer Johannes Kepler observed what he thought was a new star in the night sky. The most recent intragalactic (within our galaxy) supernova occurred around 1900, but its light was obscured by dust. Scientists were only able to study it 100 years later with instruments such as the orbiting Chandra X-Ray Observatory and the National Radio Astronomy Observatory’s Very Large Array near Socorro, New Mexico. If we’re lucky enough for the next supernova to be close (but not too close), we can learn more about the largest stars and the brilliant ends of their lives.

October 26, 2015

The space telescope Kepler (Credit: NASA/Kepler mission/Wendy Stenzel)

We’re not saying it’s aliens…but it could be aliens. Astronomers Tabitha Boyajian and colleagues published a paper in the Monthly Notices of the Royal Astronomical Society in which they describe a star that was found to dim in a mysterious fashion over the course of their study. The star, named KIC 8462852, is 1,400 light-years from Earth. A light-year is the distance light can travel in one year, about 5.88 trillion miles (9.46 trillion kilometers).

Why is this star so puzzling to astronomers? Stars can vary in brightness slightly over time. Such objects as planets can pass in front of stars,  in an event called a transit, reducing the light visible to an observer. Astronomers can use telescopes to detect such dimming, helping them to find planets orbiting distant stars. In fact, the space telescope Kepler was observing KIC 8462852 for that very reason. But the star dimmed by as much as 20 percent, far more than what would be expected from the transit of even the largest planet. Furthermore, the dimming was not regular and periodic, as would be expected from the transit of an orbiting planet. A protoplanetary disk (a disk of dense gas circling around a young star) could cause such  significant dimming. But KIC 8462852 is a mature star, so any disk that once revolved around it should have formed planets and other orbiting bodies by now.

So, what explanations are left? Boyajian and her colleagues propose that an orbiting cloud of dust from an exocomet (a comet outside the solar system) is the most likely explanation. But others have weighed in as well. Some scientists have suggested that the star could be spinning very rapidly, causing it to become stretched and producing strange dips in brightness. Others suggested that dust and debris from a major collision between two planets could be the culprit.

A few scientists and others note that alien technology cannot yet be ruled out as a cause of the dip. They propose that an advanced alien civilization could be building huge groups of solar panels or other gigantic structures around the star. These structures would presumably be built to supply the enormous energy needs of such an advanced civilization. Such huge buildings, termed megastructures, could block out a portion of the star’s light to observers on Earth.

Now, telescopes all over the world—and in space—are trained on KIC 8462852. The next time the star dims, astronomers will be able to better track the dimming to reveal its cause. The Allen Telescope Array has focused in on the system, looking for characteristic radio transmissions that should “leak” from any advanced civilization. Soon, scientists should know more about this mysterious star. The odds that the star’s light is being blocked by alien megastructures are extremely small. But aliens or no, the unusual KIC 8462852 will help astronomers learn more about the nature of star systems.

Other World Book articles

• Astronomy
• Extraterrestrial intelligence
• SETI Institute

April 8, 2015

An artist’s impression of protostar W75N (B)-VLA-2. The blue, oval-shaped region represents the shockwaves observed by scientists in the protostar’s evolution in 2014. (Credit: Wolfgang Steffen, Instituto de Astronomic/UNAM)

In the astronomical blink of an eye, a protostar underwent a significant change in how energy flows from its core. A team from the Centre of Radio Astronomy and Astrophysics (Centro de Radioastronmía y Astrophysíca) in Michoacán, Mexico, led by Carlos Carrasco-González, discovered the event and published their findings in the journal Science.

A star develops from a giant cloud of gas and dust. Under the influence of its own gravity, the cloud begins to collapse inward, becoming smaller. The collapsing material becomes warmer, and its pressure increases. But the pressure tends to counteract the gravitational pull that is responsible for the collapse. Eventually, therefore, the collapse slows to a gradual contraction. The inner parts of the clump form a protostar, a ball-shaped object that is no longer a cloud but is not yet a star. Surrounding the protostar is an irregular sphere of gas and dust that had been the outer parts of the cloud.

Carrasco-González and colleagues studied the massive protostar W75N(B)-VLA 2, located 4,200 light-years from our solar system. (One light-year equals the distance light travels in a vacuum in a year, about 9.46 trillion kilometers.) When the protostar was first examined in 1996, it was releasing shockwaves in a spherical formation from its center. Astronomers could detect these shockwaves because they excited particles in the protostar’s surrounding cloud of gas, causing them to glow. When the team looked at the star in 2014, they noticed that the shockwave-containing region had changed from a sphere to an elongated oval. The scientists think this will be a short-lived event in the protostar’s formation, ending after 25 years or so.

Such a quick change is rarely detected when studying the stars. Stars live for millions or billions of years, so scientists piece together their life cycles by comparing and contrasting thousands of stars, rather than by directly observing transformations. Examining other such rapid changes in the future may help scientists better understand the nature of star and planet formation.

Other articles and links:

• Astronomy
• Centro de Radioastronmía y Astrophysíca

February 27, 2014

The number of known exoplanets in the Milky Way Galaxy has nearly doubled, thanks to a new method of confirming planet candidates discovered by the Kepler space telescope. Mission control officials at NASA‘s Ames Research Center in Moffett Field, California, announced that they had identified 715 new planets, which raises the total number of alien planets to some 1,700. The research has also significantly increased the number of smaller exoplanets. About 95 percent of the new planets are smaller than Neptune, which is about 17 times as massive as Earth. Many exoplanets found previously were at least as massive as Jupiter, which is 318 times as massive as Earth. All of the newly discovered planets orbit one of 305 stars in a multiplanet system like the solar system.

Although Kepler’s original planet-hunting days are over–the telescope has been nonoperational since May 2013–mission scientists are still on the job. The new exoplanets were found in data collected during the telescope’s first two years in orbit, from 2009 to 2011. Kepler’s main mission was to search one section of the Milky Way for Earth-like planets in the “habitable zone.” The habitable zone, also called the Goldilocks zone, is the region around a star that scientists believe is neither too hot nor too cold to support life as we know it. In this zone, the temperature is cool enough to let liquid water form and warm enough to prevent water from freezing. Earth orbits in the habitable zone of the solar system. Although Kepler searched over 150,000 stars for signs of orbiting planets, its search zone was actually quite small. Scientists estimate that the Milky Way alone has up to 200 billion stars.

All of the newly identified planets orbit a star in a multiplanet system, like the solar system. (NASA)

The new method of identifying planets is called validation by multiplicity. This method, which relies on the logic of probability, allows scientists to identify exoplanets in groups, rather than one by one. NASA officials compared the technique to the behavior of lions and lionesses living on the savannah. “In our imaginary savannah, the lions are the Kepler stars and the lionesses are the planet candidates,” the agency explained in a press release. “If you see two of the big cats it could be a lion (star) and a lioness (planet) or two lions. But if more than two large felines are gathered, then it is very likely to be a lion and his pride (star and its planets).”

Additional World Book articles:

• Binary star
• In Search of Other Worlds (a special report)
• Space exploration (2011) (a Back in Time article)