2024-04-07 20:33:34
For most of history, a total eclipse—the period when the Moon covers the entire disk of the Sun—was the only time humans could see the faint outer layer of the Sun. This envelope of plasma, called the corona, has been an important factor behind many scientific breakthroughs in the study of eclipses.
The Sun’s corona is home to many interesting solar phenomena, including coronal mass ejections (CMEs), which occur when the Sun’s magnetic field ejects material from the Sun into space. CMEs that reach Earth can damage satellites and power grids, and can be extremely dangerous to astronauts in space outside Earth’s atmosphere.
“The Sun’s magnetic activity changes over time and changes over the entire surface of the star,” says Meredith MacGregor from Johns Hopkins University (USA). We do not yet have a good way to predict this activity. However, we may be able to begin to do so by exploring the Sun’s corona.
A total solar eclipse isn’t the only way to look at the outer layers of the Sun—there’s also a device called a coronagraph that casts a shadow over the Sun’s disk, creating a kind of artificial eclipse. These instruments are important not only for the study of our star, but also for the study of other, more distant stars, as well as for the search for planets orbiting them, which would otherwise be hidden in the brightness of the star. “The inspiration for using coronagraphs to block the light of other stars so we can search for their exoplanets came from natural eclipses,” says m. McGregor.
The same blurring that makes the corona difficult to observe outside of totality also makes it an excellent target for spectroscopy. Spectroscopy works by splitting light into separate wavelengths. This allows scientists to determine which elements are present in a material based on the unique pattern of wavelengths emitted or absorbed by each element. During 1868 Helium was detected by spectroscopy during the eclipse, the first time any element had been detected by studying the sky.
Soon after, astronomers discovered another new element in the corona, which they named coronium – but it turned out to be simply iron heated to an unusual temperature of millions of degrees. Although this was not a new element, the finding was surprising – the surface temperature of the Sun is only about 5600 °C, so how could the outer layer be so hot?
“Imagine that you are at a fire and start to move away from it. It should be colder, but it’s getting much hotter, says Frederic Bertley from the Center for Science and Industry in Ohio (USA). “That’s what’s happening in the corona, and nobody knows why.”
Solar eclipses even became one of the first pieces of evidence for Albert Einstein’s theory of general relativity, which governs how gravity works on a large scale. One of the key predictions of general relativity is that massive objects should bend the path of light as it passes through them. A. Einstein first presented his theory in 1915, and proved its correctness in 1919, when astronomer Arthur Eddington observed how starlight bends around the Sun during a solar eclipse.
Next Monday, when a total solar eclipse will pass through Central and North America (it will not be visible in Lithuania), astronomers will continue the long-standing tradition of using the total eclipse to make accurate observations of the Sun and its effects on the space around it.
The Sun still has many unsolved secrets, and the eclipse is one of the best times to study them, writes New Scientist.
2024-04-07 20:33:34