The Polarimetric and Helioseismic Imager (PHI) on ESA’s Solar Orbiter measures the magnetic field at the Sun’s surface and allows the investigation of the Sun’s interior via the technique of helioseismology.
The top left image is a view of the Sun taken by PHI’s Full Disc Telescope on 18 June 2020. This is a visible light image and represents what we would see with the naked eye. There are no sunspots visible because the Sun is displaying only low levels of magnetic activity at the moment. Below this is a close-up image taken by PHI’s High Resolution Telescope on 28 May 2020. The area is approximately 200 000 km x 200 000 km across and is centred on the middle of the Sun. It shows the Sun’s granulation pattern that results from the movement of hot plasma under the Sun’s visible surface.
The top image of the middle column reveals the magnetic properties of the same region. Dark and light areas show the north and south magnetic polarities of those areas. The full disc image below shows a similar magnetic map but for the whole Sun. Taken on 18 June 2020, there is a large magnetically active region in the lower right-hand quadrant of the Sun.
The top image of the right-hand column is a ‘tachogram’ of the Sun, again taken with the PHI Full Disc Telescope on 18 June 2020. It shows the line of sight velocity of the Sun, with the blue side turning to us and the red side turning away. The close-up image below is a similar tachogram but for the close-up area of the Sun that PHI imaged on 28 May 2020. Here, the granulation pattern can be seen as well as the change from blue to red, which signifies the overall rotation of the Sun. In this image, yellow (rather than white) denotes the zero line-of-sight velocity.
Solar Orbiter is a space mission of international collaboration between ESA and NASA.