2023-10-07 17:50:14
On October 14, 2023, the next annular solar eclipse will take place, where the Moon will partially hide the Sun. If the eclipse will not be visible in France, it will nevertheless be easily observable in North America, and NASA intends to take advantage of it to launch its mission Atmospheric Perturbations around the Eclipse Path (Apep). Using three probes, the latter aims to study the effects of the sudden drop in the Sun’s brightness during an eclipse on the atmosphere, and more particularly on the ionosphere, whose dynamics are governed by the rays ultraviolet rays coming from the Sun.
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It’s an anticipated event for Americans who love the sky: on October 14, the Earth, the MoonMoon and the SunSun will be perfectly aligned. This alignment will temporarily eclipse the Sun which will find itself hidden behind the Moon. This phenomenon is called an annular solar eclipse, which differs from a total solar eclipse. During a solar eclipsetotal solar eclipse, the Moon completely hides the solar disk, so that the latter is replaced by a very dark lunar silhouette, revealing only the solar coronasolar crown.
During an annular solar eclipse, on the other hand, the apparent size of the Moon in the sky is slightly smaller than that of the Sun: observers looking at the sky then see a very bright ring appear around the disk during the peak of the eclipse. lunar, which is also called “ring of firefire”. The annular solar eclipse on October 14 will only be visible from the American continent, where the apparent brightness of our Sun will drop to 10% of its usual brightness.
Effects on the ionosphere, an atmospheric layer controlled by sunlight
The ionosphere of a planet corresponds to the part of its atmosphereatmosphere where gases are ionized, that is to say, atoms and moleculesmolecules lose or gain one or more electronselectrons, thus becoming charged particles (ions) . On Earth, the ionosphere ionosphere occupies a large part of the atmosphere, and is located approximately between 60 and 1,000 kilometers in altitude.
It is the ultraviolet radiation coming from the Sun which is at the origin of the ionosphere: the latter react with atmospheric molecules, sometimes allowing them to be dissociated (for example, ultraviolet radiation can separate a dioxygen molecule into two oxygen atoms), but also to ionize them. Ultraviolet radiation can indeed strip an electron from a molecule or atom, producing a soup composed of ions (which are missing an electron) and free electrons, in equal quantities. Through these processes, gases in the ionosphere act as an absorbing filter, helping to limit the amount of ultraviolet radiation reaching the Earth’s surface. During the day, constant solar radiation allows these particles to remain separated; but when night falls, many recombine into neutral molecules or atoms, before breaking away once more at daybreak.
A dynamic still poorly understood during a solar eclipse
During a solar eclipse, the Sun’s light disappears and reappears almost immediately on a small part of the Earth’s surface. In a very short time, the temperature and density of the ionosphere drop only to rise once more, producing kinds of waves moving through matter, like a body of water in which a boat is moving. , creating waveswaves (or waves) in its wake.
To study these phenomena, NASA plans to launch its program Atmospheric Perturbations around the Eclipse Path (Ape)carried out jointly with researchers from theEmbry-Riddle Aeronautical University, in Florida. Small anecdote, the acronym “Apep” refers to the Egyptian god Apophis (Apep in Egyptian), a deity represented as a serpent who, according to mythology, would have pursued the sun god Ra to the point of almost completely making him disappear, producing a solar eclipse.
The American Space Agency therefore plans to launch three probes into the ionosphere, the first 35 minutes before the peak of the eclipse, the second during the peak of the eclipse, and the last 35 minutes following. They will travel through our atmosphere at altitudes between 70 and 325 kilometers to deploy four scientific instruments that will measure variations in the electric and magnetic fields of the ionosphere, as well as changes in temperature and density. During their trajectories (ascending then descending), these probes will be able to precisely measure changes that occur at different altitudes. The probes will be recovered at the end of the mission to be launched once more during the next total solar eclipse on April 8, 2024.
The influence of the ionosphere on telecommunications satellites
At the same time, several ground observations will complete the mission. Researchers from the Haystack Observatory, led by the Massachusetts Institute of Technology (MIT) will use their instruments to measure ionospheric disturbances a little further from the path of the eclipse. A team of students fromEmbry-Riddle Aeronautical University will deploy probe balloons at high altitude to measure weather changes as the eclipse passes.
All of these measurements will help to establish a precise model of the dynamics of the ionosphere. Its understanding is increasingly necessary because all of our satellite communications pass through the ionosphere before reaching Earth. It therefore appears essential to fully understand the behavior of the ionosphere and to be able to predict the disturbances that may occur there.
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