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Total eclipse, partial failure: Scientific expeditions don’t always go as planned
For centuries, astronomers have realized that total solar eclipses offer a valuable scientific opportunity. During what’s called totality, the opaque moon completely hides the bright photosphere of the sun – its thin surface layer that emits most of the sun’s light. An eclipse allows astronomers to study the sun’s colorful outer atmosphere and its delicate extended corona, ordinarily invisible in the dazzling light of the photosphere.
But total solar eclipses are infrequent, and are visible only from a narrow path of totality. So eclipse expeditions require meticulous advance planning to ensure that astronomers and their equipment wind up in the right place at the right time. As the history of astronomy shows, things don’t always go according to plan for even the most prepared eclipse hunters.
Into hostile territory, at the mercy of the map
Samuel Williams, the newly appointed professor of mathematics and natural philosophy at Harvard College, was eager to observe a total solar eclipse. He’d seen a transit of Venus in 1769, but had never had the chance to study the sun’s corona during an eclipse. According to his calculations, a total solar eclipse would be visible from Maine’s Penobscot Bay on Oct. 27, 1780.
But reaching Maine from Massachusetts would be something of a problem; the Revolutionary War was raging, and Maine was held by the British Army. The Massachusetts legislature came to Williams’ assistance; it directed the state’s Board of War to fit out a ship to convey the eclipse hunters. Speaker of the House John Hancock wrote to the British commander in Maine, requesting permission for the men of science to make their observations. When the astronomer-laden ship arrived at Penobscot Bay, Williams and his team were permitted to land but restricted to the island of Isleboro, three miles offshore from the mainland.
The morning of the big day was cloudless. As the calculated moment of totality approached, at half past noon, the excitement built. The sliver of uneclipsed sun became narrower and narrower.
Then, at 12:31 p.m., it started becoming wider and wider. Williams realized, to his frustration, that he wasn’t in the path of totality after all. They were 30 miles too far south.
After a subdued voyage back to Massachusetts, Williams tried to determine what had gone wrong. Some astronomers, at the time and in following centuries, suggested his calculations of the path of totality were inaccurate.
Williams, however, had a different explanation. In his report to the newly founded American Academy of Arts and Sciences, he blamed bad maps:
“The longitude of our place of observation agrees very well with what we had supposed in our calculations. But the latitude is near half a degree less than what the maps of that country had led us to expect.”
Since half a degree of longitude corresponds to 30 nautical miles, this could explain why Williams ended up too far south.
Although Samuel Williams missed seeing a total eclipse, his expedition was not a total failure. While watching the narrow sliver of sun visible at 12:31, he noted it became “broken or separated into drops.” These bright drops, known today as Baily’s Beads, are the result of the sun’s light shining through valleys and depressions along the moon’s visible edge. They’re named in honor of astronomer Francis Baily; however, Baily saw and described the beads in 1836, nearly 56 years after Williams observed them.
Hard to observe with smoke in your eyes
Almost a century later, in 1871, English astronomer Norman Lockyer was eager to observe a total solar eclipse.
Three years earlier, he and French astronomer Jules Janssen had independently measured the spectrum of the sun’s chromosphere; to their surprise, they found an emission line in the yellow range of the spectrum, not corresponding to any known element.
Lockyer boldly claimed that the emission line was from a new element that he named “helium,” after the sun god Helios. Realizing that eclipses offered a helpful opportunity to search for more undiscovered elements, Lockyer became a strong advocate of eclipse expeditions. He knew the total solar eclipse of Dec. 12, 1871 would pass across southern India and persuaded the British Association for the Advancement of Science to sponsor an expedition. Wishing to show that British rule in India was linked to scientific progress, the British government chipped in £2,000, and the P&O steamship company offered reduced fares to India for the eclipse hunters.
Lockyer’s voyage to India went smoothly. (This could not be taken for granted; in 1870, on his way to view an eclipse from Italy, Lockyer was aboard a ship that ran aground off the east coast of Sicily.) The team set up their instruments on a tower at Bekal Fort, on the southwest Indian coast. The morning of Dec. 12, 1871 was cloudless. Although Lockyer was suffering from a fever (and from the effects of the opium he was taking to treat it), he was ready.
Then, during the initial phases of the eclipse, he noted odd activity in the region below the fort. Local inhabitants were gathering a huge pile of brushwood to fuel a bonfire; apparently, by creating a bright fire on Earth, they hoped to encourage the darkening sun to become bright again. Lockyer was alarmed; the column of smoke would have risen directly between him and the eclipsed sun, ruining his observations.
Fortunately, the local superintendent of police happened to be present; he summoned a squadron of policemen who put out the fire and dispersed the crowd. During the now smoke-free eclipse, Lockyer made valuable observations of the structure of the sun’s corona.
To see an eclipse you must see the sun
Jump ahead to the early 20th century. The English Astronomer Royal Sir Frank Dyson was eager to view a total solar eclipse. He didn’t have to travel far, since the eclipse of June 29, 1927 had a path of totality cutting across northern England, from Blackpool in the west to Hartlepool in the east. As an eminent figure in the scientific establishment and a renowned expert on eclipses, Dyson had no trouble in commanding financial support for his eclipse observations.
What he could not command, however, was the famously fickle English weather. During the month of June, northern England averages about seven hours of direct sunlight per day; however, this comes from a mix of weather that includes completely overcast days and completely cloudless days. Dyson didn’t know what to expect.
After checking the weather records along the predicted eclipse path, Dyson decided to observe from the Yorkshire village of Giggleswick. As he and his team prepared for the eclipse, the location choice initially seemed dubious; for two weeks before the eclipse, the sky was completely cloudy every afternoon, at the time of day when totality would occur on June 29.
Despite the grimly unpromising weather, crowds of hopeful people converged on the widely publicized eclipse path. Railway companies ran special excursion trains, towns along the path of totality sponsored “eclipse dances” and newspapers offered “ecliptoglasses” to subscribers.
In the end, unfortunately, most viewers along the eclipse path were disappointed. From the errant cloud that blocked the totally eclipsed sun from Blackpool Tower to the unbroken overcast sky at Hartlepool, the weather did not cooperate.
Happily for Frank Dyson, however, the town of Giggleswick was nearly the only location along the eclipse path that had clear skies during totality. The estimated 70,000 people who converged there, following the lead of the astronomer royal, also benefited from Dyson’s good luck.
After the eclipse, Dyson’s public statement was, by British standards, positively bubbly:
“The photographs have come out extremely well. A very clear and striking eclipse. Our observations went off very well indeed.”
Despite the difficulties posed by weather… and smoky bonfires… and dodgy maps… astronomers have always persevered in their quest to view eclipses.
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Curious Kids: Why don’t the planets closest to the Sun melt or burn up?
This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!
Can you tell me why the planets closest to the sun don’t melt or burn up, please? – Sophie, aged 6, Brisbane.
Hi Sophie. That’s a good question.
The planets closer to the Sun than the Earth are indeed hotter than the Earth is. But that still doesn’t make them hot enough to melt the rocks that they are made from!
Mercury is the small, rocky planet nearest the Sun. The side that faces the Sun has a temperature of around 430℃. Remembering that 100℃ is the temperature at which water boils, that make 430℃ very hot indeed. In fact, it’s hot enough to melt some types of metal, like lead.
However, Mercury is not made of lead. It is made of rocky materials that have melting points above about 600℃.
So while Mercury is indeed very hot, it is not hot enough to melt. And certainly not hot enough to boil or turn into gas.
Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:
* Email your question to [email protected]
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Please tell us your name, age, and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.
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TRAPPIST-1 is Older Than Our Solar System
If we want to know more about whether life could survive on a planet outside our solar system, it’s important to know the age of its star. Young stars have frequent releases of high-energy radiation called flares that can zap their planets’ surfaces. If the planets are newly formed, their orbits may also be unstable. On the other hand, planets orbiting older stars have survived the spate of youthful flares, but have also been exposed to the ravages of stellar radiation for a longer period of time.
Scientists now have a good estimate for the age of one of the most intriguing planetary systems discovered to date — TRAPPIST-1, a system of seven Earth-size worlds orbiting an ultra-cool dwarf star about 40 light-years away. Researchers say in a new study that the TRAPPIST-1 star is quite old: between 5.4 and 9.8 billion years. This is up to twice as old as our own solar system, which formed some 4.5 billion years ago.
The seven wonders of TRAPPIST-1 were revealed earlier this year in a NASA news conference, using a combination of results from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, NASA’s Spitzer Space Telescope, and other ground-based telescopes. Three of the TRAPPIST-1 planets reside in the star’s “habitable zone,” the orbital distance where a rocky planet with an atmosphere could have liquid water on its surface. All seven planets are likely tidally locked to their star, each with a perpetual dayside and nightside.
At the time of its discovery, scientists believed the TRAPPIST-1 system had to be at least 500 million years old, since it takes stars of TRAPPIST-1’s low mass (roughly 8 percent that of the Sun) roughly that long to contract to its minimum size, just a bit larger than the planet Jupiter. However, even this lower age limit was uncertain; in theory, the star could be almost as old as the universe itself. Are the orbits of this compact system of planets stable? Might life have enough time to evolve on any of these worlds?
“Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago,” said Adam Burgasser, an astronomer at the University of California, San Diego, and the paper’s first author. Burgasser teamed up with Eric Mamajek, deputy program scientist for NASA’s Exoplanet Exploration Program based at NASA’s Jet Propulsion Laboratory, Pasadena, California, to calculate TRAPPIST-1’s age. Their results will be published in The Astrophysical Journal.
It is unclear what this older age means for the planets’ habitability. On the one hand, older stars flare less than younger stars, and Burgasser and Mamajek confirmed that TRAPPIST-1 is relatively quiet compared to other ultra-cool dwarf stars. On the other hand, since the planets are so close to the star, they have soaked up billions of years of high-energy radiation, which could have boiled off atmospheres and large amounts of water. In fact, the equivalent of an Earth ocean may have evaporated from each TRAPPIST-1 planet except for the two most distant from the host star: planets g and h. In our own solar system, Mars is an example of a planet that likely had liquid water on its surface in the past, but lost most of its water and atmosphere to the Sun’s high-energy radiation over billions of years.
However, old age does not necessarily mean that a planet’s atmosphere has been eroded. Given that the TRAPPIST-1 planets have lower densities than Earth, it is possible that large reservoirs of volatile molecules such as water could produce thick atmospheres that would shield the planetary surfaces from harmful radiation. A thick atmosphere could also help redistribute heat to the dark sides of these tidally locked planets, increasing habitable real estate. But this could also backfire in a “runaway greenhouse” process, in which the atmosphere becomes so thick the planet surface overheats – as on Venus.
“If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years,” Burgasser said.
Fortunately, low-mass stars like TRAPPIST-1 have temperatures and brightnesses that remain relatively constant over trillions of years, punctuated by occasional magnetic flaring events. The lifetimes of tiny stars like TRAPPIST-1 are predicted to be much, much longer than the 13.7 billion-year age of the universe (the Sun, by comparison, has an expected lifetime of about 10 billion years).
“Stars much more massive than the Sun consume their fuel quickly, brightening over millions of years and exploding as supernovae,” Mamajek said. “But TRAPPIST-1 is like a slow-burning candle that will shine for about 900 times longer than the current age of the universe.”
Some of the clues Burgasser and Mamajek used to measure the age of TRAPPIST-1 included how fast the star is moving in its orbit around the Milky Way (speedier stars tend to be older), its atmosphere’s chemical composition, and how many flares TRAPPIST-1 had during observational periods. These variables all pointed to a star that is substantially older than our Sun.
Future observations with NASA’s Hubble Space Telescope and upcoming James Webb Space Telescope may reveal whether these planets have atmospheres, and whether such atmospheres are like Earth’s.
“These new results provide useful context for future observations of the TRAPPIST-1 planets, which could give us great insight into how planetary atmospheres form and evolve, and persist or not,” said Tiffany Kataria, exoplanet scientist at JPL, who was not involved in the study.
Future observations with Spitzer could help scientists sharpen their estimates of the TRAPPIST-1 planets’ densities, which would inform their understanding of their compositions.
Provided by: Jet Propulsion Laboratory
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