The Sun is the only star we can learn a great deal about, and Caltech possesses the best and most comprehensive facilities in the world for its study. Big Bear Solar Observatory (BBSO) resides in the middle of Big Bear Lake, in the San Bernadino mountains two hours from Caltech, to solve the special problems of solar observing. Because of the excellent seeing and transparency there, unique high-resolution observations are routinely carried out. An array of optical telescopes, ranging in size and including a 26-inch reflector, are available at BBSO for solar observations, along with three 0.25 A bandpass birefringent filters and an array of other instruments. Particularly important is the videomagnetograph, which was an developed at Caltech and allows the observation in real time of small-scale magnetic features on the solar surface. For the first time in history we can watch small magnetic dipoles emerge, move around, reconnect and cancel, and from these observations, we hope to learn more about the magnetohydrodynamics of the solar surface.

A vector magnetograph has been developed to examine the three-dimensional structure of the solar magnetic fields. With this it has been possible to record the changes of magnetic fields associated with the occurrence of solar flares. A second instrument, called thespectromagnetograph, has been developed to eliminate uncertainty over filling factors in solar fields. It is the only existing instrument with which the true field strength outside of sunspots can be directly determined.

Another aspect of the study of magnetic fields has been the study of the magnetic cycle. The observatory follows the fields close to the pole of the Sun to watch and understand how the poles change with the solar cycle; another target is the actual rotation rate at the pole, which is still unknown. A new program using magneto-optic atomic resonance cells to measure field vectors and small scale flows on the solar surface was recently begun.

Another telescope for solar research run by Caltech is the solar microwave facility at Owens Valley, which consists of a pair of dedicated 27-meter parabolic antennas, each equipped with a frequency-agile receiver capable of observing between 1 and 18 GHz. These are used with four smaller dishes to produce maps and spectra of the synchrotron emission from solar flares. This is one of the best ways to observe the acceleration of solar particles in flares. Interferometry provides high spatial resolution and suppresses background signal for high S/N observations of solar flares and active regions. A third antenna, 40-meters in diameter, is available about 20 days/year for solar observations, and with the third dish our spatial resolution increases to better than 2 arcseconds at 18 GHz.

By superposing the radio maps on the Big Bear images, we can determine the magnetic configurations in which particles are accelerated, and explore the mysterious mechanisms by which the acceleration is carried out.

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Ap.J., 329, 991, 1988 (with D. Gary), Cambridge University Press, 1988, ``Astrophysics of the Sun."

Solar Physics, 125, 45, 1990 (with H. Wang). ``Flows, Flares, Formation of Umbrae and Light Bridges in BBSO Region #1167."

Solar Physics, 144, 37, 1993 (with H. Wang), ``Strong Transverse Fields in Delta Spots."

Astrophysical Journal, 403, 426, 1993, (with M.W. Ewell, J. B. Jensen and T. S. Bastian), ``Submillimeter Observations of the 11 July 1991 Total Solar Eclipse"

Solar Physics, 144, 37, 1993, (with H. Wang), ``Strong Transverse Fields in Delta Spots"

Proc. IAU Colloquium No. 141, Astr Soc. Pac Conference series No. 46, 1993 (with Guoxiang Ai, and H. Wang), ``The Magnetic and Velocity Fields of Solar Active Regions."