![]() ![]() The solar corona appeared as a highly inhomogeneous X-ray source with 80% of the emission coming from 5% or less of the area of the solar disk (Blake et al. The X-ray image of the Sun, obtained by the Naval Research Laboratory scientists during a sub-orbital rocket flight on April 19, 1960, in the form of a crude low-resolution photograph, revealed for the first time the hottest layers of the solar atmosphere against the bright disk. These events are characterized by the emission of highly energetic electromagnetic radiation and particle acceleration, frequently associated with huge plasma ejections, inducing transient changes and a reorganization of the structure of the corona. When the level of activity increases, magnetic energy is sporadically released in sudden and powerful reconnection events occurring at coronal heights. Coronal holes and quiescent streamers, reflecting long-lived large-scale patterns, are prevalent in the declining to minimum phase of solar activity when the magnetic field becomes organized according to lower order multipoles. Active regions are dominant in the ascending phase of the solar cycle and at solar maximum when the relatively simple poloidal configuration of the solar magnetic field typically observed at solar minimum is disrupted by the emergence of the toroidal field of the new cycle. Solar Orbiter is a space mission of international collaboration between ESA and NASA.The picture of the solar corona derived from ground-based and space observations is that of a hot inhomogeneous magnetized atmosphere, which is constantly evolving and consisting of features developing on different scales in the various phases of the solar activity cycle. During its nominal mission, Solar Orbiter will venture much closer to the Sun (up to 0.28 AU), providing even more detailed images. Better resolution in visible light can only be achieved during the few minutes of the natural total eclipse of the Sun, while the UV images have no match. Already at this distance, the spatial resolution of these images is comparable or better than any coronagraph on ground or in space. The instrument field-of-view covers heights from 3.2 to 5.8 times the solar radius from the Sun’s centre. ![]() These are shown in the right-hand column. Metis also captured simultaneously visible and UV images on 21 June 2020, soon after Solar Orbiter’s first perihelion (approaching the Sun from 0.52 AU on 15 June). ![]() When Metis took these images, Solar Orbiter was at a distance of 0.6 astronomical units (AU one AU is equivalent to the average distance from Earth to the Sun, about 150 million kilometres) from the Sun and the instrument field-of-view covered heights from 3.8 to 7.0 times the solar radius from the Sun’s centre. This is the first UV image of the extended solar corona ever obtained. The ultraviolet image (shown in red) records emission from neutral hydrogen atoms in the corona. The visible light image (shown in green) clearly shows the two bright equatorial streamers and fainter polar regions, which are characteristic of the solar corona during times of minimal magnetic activity. Its first light images, taken on, and displayed here in the left hand column, are the first simultaneous images of the corona taken in both visible light (580-640 nm) and ultraviolet light (UV, 121.6 nm). Metis is a coronagraph, which blocks out the dazzling light from the solar surface, allowing the fainter outer atmosphere of the Sun, the corona, to be seen. The Metis coronagraph on ESA’s Solar Orbiter scored a couple of ‘world firsts’ with its first light image. ![]()
0 Comments
Leave a Reply. |