Sunspot Telescope

[Sunspot Telescope]
Sunspot observations at Mitaka have been conducted with a 20cm aperture refractor made by Zeiss (installed in 1938). The solar image with a diameter of 24cm is projected onto a sheet of paper, and sunspots and faculae are sketched. The sunspot relative numbers are published in Monthly Bulletin on Solar Phenomena, NAOJ.
Visual sunspot observations at Mitaka have now accumulated data over 60 years. Because large-format CCDs are becoming available, we decided that it is time to make a transition to a digital system. The new system constructed in 1997 is made of a 10cm refractor equipped with a 2K X 2K format CCD. Parallel observing runs with the old 20cm telescope for half a year showed the reliability of the new system. Since the spring of 1998, sunspot observations have been transferred to the new system, while the old 20cm refractor is still used occasionally.