One of the new images, taken by the Extreme Ultraviolet Imager (EUI) aboard the ESA/NASA Solar Orbiter spacecraft on March 7, 2022, is the highest resolution image of the Sun’s full disk and its outer atmosphere, the corona, ever taken. Another image, taken by Solar Orbiter’s Spectral Imaging of the Coronal Environment (SPICE) instrument, represents the first full Sun image of its kind in 50 years, and by far the best one, taken at the Lyman-beta wavelength of ultraviolet light that is emitted by hydrogen gas.
The Sun as seen by Solar Orbiter in extreme ultraviolet light from a distance of roughly 75 million km. The image is a mosaic of 25 individual images taken on March 7, 2022 by the high resolution telescope of the Extreme Ultraviolet Imager (EUI) instrument. Taken at a wavelength of 17 nanometers, in the extreme ultraviolet region of the electromagnetic spectrum, this image reveals the Sun’s upper atmosphere, the corona, which has a temperature of around a million degrees Celsius. Image credit: ESA / NASA / Solar Orbiter / EUI Team / E. Kraaikamp, ROB.
Solar Orbiter is a collaborative mission between the ESA and NASA to study our Sun.
The spacecraft views some of the never-before-seen regions of the Sun, including the poles, and sheds new light on some of the little understood aspects of the star’s activity, such as the formation of the solar wind. It also provides data about the Sun’s magnetic field and how it arises.
Launched on February 10, 2020, Solar Orbiter carries ten scientific instruments, four of which measure properties of the environment around the spacecraft, especially electromagnetic characteristics of the solar wind, the stream of charged particles flowing from the Sun.
The new images of the Sun were taken when the spacecraft was at a distance of roughly 75 million km, half way between Earth and our star.
The high-resolution telescope of EUI takes pictures of such high spatial resolution that, at that close distance, a mosaic of 25 individual images is needed to cover the entire Sun.
Taken one after the other, the full image was captured over a period of more than four hours because each tile takes about 10 min, including the time for the spacecraft to point from one segment to the next.
In total, the final image contains more than 83 million pixels in a 9,148 x 9,112 pixel grid.
EUI images the Sun at a wavelength of 17 nm, in the extreme ultraviolet region of the electromagnetic spectrum. This reveals the Sun’s upper atmosphere, the corona, which has a temperature of around a million degrees Celsius.
At the 2 o’clock and 8 o’clock positions on the edges of the Sun, dark filaments can be seen projecting away from the surface.
These ‘prominences’ are prone to erupt, throwing huge quantities of coronal gas into space and creating ‘space weather’ storms.
Solar Orbiter took images of the Sun on March 7, 2022 from a distance of roughly 75 million km, using its Spectral Imaging of the Coronal Environment (SPICE) instrument. SPICE takes simultaneous spectral images at several different wavelengths of the extreme ultraviolet spectrum by scanning its spectrometer slit across a region on the Sun. The different wavelengths recorded correspond to different layers in the Sun’s lower atmosphere. Purple corresponds to hydrogen gas at a temperature of 10,000 degrees Celsius, blue to carbon at 32,000 degrees Celsius, green to oxygen at 320,000 degrees Celsius, yellow to neon at 630,000 degrees Celsius. Each full-Sun image is made up of a mosaic of 25 individual scans. It represents the best full Sun image taken at the Lyman beta wavelength of ultraviolet light that is emitted by hydrogen gas. Image credit: ESA / NASA / Solar Orbiter / SPICE Team / G. Pelouze, IAS.
In addition to EUI, the SPICE instrument was also recording data during the crossing. These too needed to be pieced together as a mosaic.
SPICE is designed to trace the layers in the Sun’s atmosphere from the corona, down to a layer known as the chromosphere, getting closer to the surface.
The instrument does this by looking at the different wavelengths of extreme ultraviolet light that come from different atoms.
In the SPICE sequence of images purple corresponds to hydrogen gas at a temperature of 10,000 degrees Celsius, blue to carbon at 32,000 degrees Celsius, green to oxygen at 320,000 degrees Celsius, yellow to neon at 630,000 degrees Celsius.
This will allow solar physicists to trace the extraordinarily powerful eruptions that take place in the corona down through the lower atmospheric layers. It will also allow them to study one of the most puzzling observations about the Sun: how the temperature is rising through the ascending atmospheric layers.
Usually the temperature drops as you move away from a hot object. But above the Sun, the corona reaches a million degrees Celsius whereas the surface is only about 5,000 degrees Celsius. Investigating this mystery is one of the key scientific objectives of Solar Orbiter.
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