0038-0946/05/3906- © 2005 Pleiades Publishing, Inc. 0489 Solar System Research, Vol. 39, No. 6, 2005, pp. 489–500. Translated from Astronomicheskii Vestnik, Vol. 39, No. 6, 2005, pp. 549–562. Original Russian Text Copyright © 2005 by Slemzin, Kuzin, Zhitnik, Delaboudinière, Auchere, Zhukov, Van der Linden, Bugaenko, Ignat’ev, Mitrofanov, Pertsov, Oparin, Stepanov, Afanas’ev. INTRODUCTION The SPIRIT telescopes (Zhitnik et al., 2002) onboard the CORONAS-F satellite (Oraevsky and Sobelman, 2002) have routinely observed the Sun in the EUV range 171–304 Å since August 2001. The most intense ion lines emitted from the transition region and the inner corona (T ~ 0.03–2 MK) lie in this spectral region. At present, these observations play a key role in studying a wide range of solar phenomena and are used to monitor the solar activity and forecast the space weather. The SPIRIT complex incorporates two telescopes: a Ritchey–Chretien telescope operating in the 171, 195, 284, and 304 Å bands and a Herschel telescope with two channels, 175 and 304 Å. The spectral bands of the SPIRIT telescopes were chosen to accomplish the main objective of the experi- ment—to study the structure and dynamics of the tran- sition region and the lower solar corona with a temper- ature of 0.05–2 MK (Oraevsky et al., 2002). The Ritchey-Chretien telescope (hereafter T1) is identical in optical design to the EIT instrument (Extreme-Ultra- violet Imaging Telescope) onboard the SOHO space- craft (Solar and Heliospheric Observatory; Moses et al., 1997). The main task for T1 is to carry out synoptic observations coordinated with the EIT instrument. The set of mirrors for T1 was produced at the Institut d’Astrophysique Spatiale (Orsay, France) and is a copy of the SOHO/EIT objective. The Herschel telescope (T2) is a third-generation solar telescope with multilayer normal-incidence optics and CCD detectors that have been designed at the Lebe- dev Physical Institute, Russian Academy of Sciences, for the past 20 years. The analogous (in optical design) TEREK telescope onboard the Phobos-1 spacecraft, 1988, (Sobelman et al., 1990) and the TEREK-C tele- scope onboard the CORONAS-I satellite, 1994, (Sobel- man et al., 1996) were the prototypes of this telescope. In comparison with their predecessors, T2 of the SPIRIT complex has a factor of 2.6 larger aperture as well as considerably higher sensitivity and angular and time resolutions. The main objective of the observations with T2 is to study various solar structures with the highest possible time resolution simultaneously in two spectral chan- nels, 175 and 304 Å. The wide dynamic range of the instrument makes it possible to perform observations at both maximum and minimum solar activity. Simulta- Observations of Solar EUV Radiation with the CORONAS-F/SPIRIT and SOHO/EIT Instruments V. A. Slemzin 1 , S. V. Kuzin 1 , I. A. Zhitnik 1 , J.-P. Delaboudinière 2 , F. Auchere 2 , A. N. Zhukov 3 , R. Van der Linden 3 , O. I. Bugaenko 4 , A. P. Ignat’ev 1 , A. V. Mitrofanov 1 , A. A. Pertsov 1 , S. N. Oparin 1 , A. I. Stepanov 5 , and A. N. Afanas’ev 5 1 Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia 2 Institut d’Astrophysique Spatiale, Orsay, France 3 Royal Observatory of Belgium, Brussels, Belgium 4 Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow, 119992 Russia 5 Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation, Russian Academy of Sciences, Troitsk, Moscow oblast’, 142190 Russia Received April 11, 2005 Abstract—The SPIRIT complex onboard the CORONAS-F satellite has routinely imaged the Sun in the 171, 175, 195, 284, and 304 Å spectral bands since August 2001. The complex incorporates two telescopes. The Ritchey–Chretien telescope operates in the 171, 195, 284, and 304 Å bands and has an objective similar to that of the SOHO/EIT instrument. The Herschel telescope obtains solar images synchronously in the 175 and 304 Å bands with two multilayer-coated parabolic mirrors. The SPIRIT program includes synoptic observations, stud- ies of the dynamics of various structures on the solar disk and in the corona up to 5 solar radii, and coordinated observations with other spaceborne and ground-based telescopes. In particular, in the period 2002–2003, syn- optic observations with the SPIRIT Ritchey–Chretien telescope were coordinated with regular 6-hour SOHO/EIT observations. Since June 2003, when EIT data were temporarily absent (SOHO keyholes), the SPIRIT telescope has performed synoptic observations at a wavelength of 175 A. These data were used by the Solar Influence Data Analysis Center (SIDC) at the Royal Observatory of Belgium for an early space weather forecast. We analyze the photometric and spectral parameters of the SPIRIT and EIT instruments and compare the integrated (over the solar disk) EUV fluxes using solar images obtained with these instruments during the CORONAS-F flight from August 2001 through December 2003.