ABSTRACT
This chapter deals with the Sun as observed in longer wavelengths in the infra-red (IR) and radio regimes. Of these, IR instrumentation is more difficult due to the observational and technical issues, but holds a lot of promise in the measurements of chromospheric magnetic fields and helioseismolo-gy. IR radiations can reach to the ground-levels only in certain bands due to molecular absorption by atmospheric water vapour, CO2, and O2, etc. The intense instrumental and surrounding emis-sions in IR overwhelm the emission coming from the source, that need to be removed. We discuss the new instruments for detection, imaging and polarimetry in IR, and in radio wavelengths. The radio window is accessible from ground, but was developed only after World War II, when radio emission from the Sun was serendipitously discovered using military radars. This discovery provid-ed a method to study the outer solar atmosphere that was so far not accessible by the optical solar telescopes. Following the early findings, radio observations have provided new insights in the un-derstanding of solar activity and of its link with the interplanetary medium. Advantage of radio emissions and bursts produced by thermal and non-thermal processes is discussed for remote detec-tion of sites of particle acceleration, release of magnetic energy, and the large scale coronal magnetic field patterns. Recent detections of solar coronal oscillations have developed as coronal seismology which helps in inferring the physical properties of corona. The chapter provides a brief introduction of solar MHD formulations governing the coronal plasmas.
