On March 22, 2023, the European Solar Orbiter achieved a remarkable technical feat by observing the same region of the Sun at different wavelengths (ultraviolet and visible) while measuring the solar magnetic field and surface movements. The European Space Agency (ESA) has released a series of four images taken on the same day, showcasing the Sun's activity.
Launched in February 2020, Solar Orbiter follows an elliptical orbit around the Sun, with a perihelion of 42 million kilometers and an inclination exceeding 30° relative to the solar equator. This configuration allows for unprecedented observations with a resolution of 70 kilometers per pixel. The images, which depict a solar disk approximately 8,000 pixels in diameter, reveal an extraordinary level of detail.
The images are mosaics composed of 25 individual images captured over more than four hours. Two of the ten onboard instruments were utilized: the Polarimetric and Helioseismic Imager (PHI), which provides images of the photosphere while measuring the direction of the magnetic field and surface movements, and the Extreme Ultraviolet Imager (EUI), which captures high-resolution images of the solar atmosphere in non-visible light.
Although the published images are of low definition, scientists possess high-resolution photos that allow for substantial zooming on the solar surface. For instance, an enlargement of an image captured in visible light by the PHI instrument reveals the Sun's surface as a hot, luminous plasma made up of charged gas in perpetual motion. This layer, which emits nearly all solar radiation, exhibits temperatures ranging from 4,500 to 6,000 °C.
The most striking features of these images are undoubtedly the sunspots, appearing as dark areas on an otherwise smooth surface. These cooler regions emit less light than their immediate surroundings. The magnetic map provided by PHI, known as a magnetogram, shows that the solar magnetic field intensifies near sunspots, indicated by red (outward) and blue (inward) colors.
Furthermore, the velocity map from PHI, or tachygram, illustrates the speed and direction of material movement on the Sun's surface. Blue areas indicate movement towards the spacecraft, while red areas signify movement away from it. The EUI's image of the solar corona reveals phenomena occurring above the photosphere, with bright plasma rising above active sunspot regions, following magnetic field lines that often connect neighboring sunspots.