Mk II Coronal Activity Monitor White Light Polarization Brightness Scans

The MK II Coronal Activity Monitor was the second K-coronameter developed by the High Altitude Observatory. The design drew heavily from the Mk I K-coronameter. Like the Mk I, the Mk II was an internally occulted white light coronameter designed to record the polarization brightness (pB) of the Thomson scattered K-Corona continuum emission. The Mk II had a larger aperture than the Mk I and took advantage of newer (1960s) photo-multiplier tubes that were more sensitive to red wavelengths (620 nm) where the sky brightness is lower, reducing background noise. The Mk II did not acquire images of the corona but collected brightness scans at various heights between 1.125 and 2.0 solar radii. A cone with a small hole drilled along its axis isolated the region of the corona for scanning around the Sun. It was designed to scan more quickly than the Mk I in order to detect rapid changes (a few minutes) in the solar corona to meet the science objective of studying solar transients, i.e. coronal mass ejections (CMEs). The Mk II was capable of continuous scanning around the Sun but unlike the Mk I, it was also capable of scanning back and forth over small regions of interest in the corona where solar activity was more likely to occur. It detected signatures of Coronal Mass Ejections (CMEs) before CME coronagraph images were available. When not in activity monitor mode, the Mk II scanned the entire corona at eight heights between 1.125 and 2 solar radii in height increments of 0.125 solar radii. It took 2 to 3 hours to acquire 360 degree scans at all 8 heights. Mk II digital synoptic maps at 1.5 solar radii are available from May 1969 through September 1978.