DATA FROM THE PRECISION SOLAR PHOTOMETRIC TELESCOPE (PSPT) IN HAWAII FROM MARCH 1998 TO MARCH 1999 ORAN R. WHITE (orw@ucar.edu), PETER A. FOX (pfox@ucar.edu), RANDY MEISNER (meisner@ucar.edu), MARK P. RAST (mprast@ucar.edu), ERIC YASUKAWA (yasukawa@ucar.edu), DARRYL KOON (koon@ucar.edu) and CRYSTAL RICE (crice@hao.ucar.edu) High Altitude Observatory, National Center for Atmospheric Research, Box 3000 Boulder, Colorado 80307 USA HAOSHENG LIN (lin@nso.noao.edu) U.S. National Solar Observatory, Sunspot, New Mexico 88349 USA JEFF KUHN (kuhn@ifa.hawaii.edu) and ROY COULTER (coulter@ifa.hawaii.edu) University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822 USA Received: 13 October 1999; Accepted in final form: 10 March 2000 Abstract. Two Precision Solar Photometric Telescopes (PSPT) designed and built at the U.S. National Solar Observatory (NSO) are in operation in Rome and Hawaii. A third PSPT is now in operation the NSO at Sunspot, NM. The PSPT system records full disk solar images at three wave- lengths: K line at 393.3 nm and two continua at 409 nm and 607 nm throughout the observing day. We currently study properties of limb darkening, sunspots, and network in these images with particular emphasis on data taken in July and September 1998. During this period, the number of observations per month was high enough to show directional properties of the radiation field surrounding sunspots. We show examples of our PSPT images and describe our study of bright rings around sunspots. 1. Rationale for Development of a Precision Photometric Solar Telescope Impetus for development of a solar disk imager for high precision photometry of photospheric structure came from the NSF program to study Radiative Input from the Sun to the Earth (RISE). Under the leadership of Dr. Peter Foukal, the RISE steering committee recommended initiation of this new NSF program for measure- ment and analysis of solar images to determine basic properties of radiation from the Sun in the direction of the Earth. Program objectives included estimation of irradiance changes from solar images, determination of directional properties of radiation from surface structures, and resolution of the question about changes in the solar luminosity. The nature of energy transport through the convection zone remains a fundamental question that requires precision measurements of radiation from magnetic and non-magnetic regions on the solar disk over a solar cycle. Space Science Reviews 94: 75–82, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.