Jack B. Zirker

The spectrum of the inner corona observed during the total solar eclipse of 30 May 1965

A series of spectrograms of the inner solar corona were obtained at the total solar eclipse of 30 May 1965 using a fast spectrograph with a circular slit that recorded the spectrum from λ3000 to λ9000 at all position angles around the limb simultaneously. In this paper absolute intensity is given as a function of position angle for the stronger lines and the continuum. In the coronal enhancement or condensation centered at heliocentric position angle 293°, absolute intensity is given for 34 forbidden emission lines and the continuum.

Flows in quiescent prominences

Earlier studies of quiescent prominences claim that there is a systematic downward directed motion of the small-scale structure. Disk observations, on the other hand, have detected mass motions both upwards and downwards. The earlier high-resolution observations of limb prominences have been re-examined using local cross-correlation techniques for measurements of motion perpendicular to the line of sight. The new measurements reveal flow speeds and directions that are in good agreement with current Doppler measurements on the disk.

Why is the Sun’s corona so hot? Why are prominences so cool?

Over the past several decades, solar physicists have made steady progress in answering the two long-standing questions, but puzzles remain.

A model for X-ray emission from loop prominences

A study is made of X-ray line emission observed during the developing stages of a set of post-flare loop prominences. The time behaviour of the line emission can be described by a model consisting of two flux tubes containing plasma heated impulsively at the flash phase; the plasma cools by radiation and by conduction to the chromosphere. These ideas are extended to the possible formation of Hα prominences from low-lying hot loops.

The interpretation of total line intensities from optically thin gases: II. The coronal forbidden lines

We discuss the application of a general diagnostic procedure, developed in the preceding paper of this series, to the inference of the physical state of coronal condensations from a knowledge of their forbidden line emission. We consider the limitations set on such an analysis by inadequacies in existing data and indicate the additional observations in the infrared and ultraviolet, as well as the visible, which will be needed for development of the full power of the diagnostic method.

Searching for nanoflares

The evolution of hydrodynamic shocks generated by nanoflares in coronal loops is investigated in order to suggest requirements for future observations. The shocks produced by nanoflares of 1024 ergs decay within a few seconds, which sets stringent requirements for Doppler or transverse velocity measurements. With feasible improvements, the Normal Incidence X-ray Telescope could observe the time-averaged emission from a nanoflare, however. We also consider collisions between shocks and show that these could also be observed.

The Parallel Worlds of Christoph Scheiner and Galileo Galilei

Galileo Galilei and Christoph Scheiner, working independently, discovered many of the properties of sunspots that we accept as valid today. Using his precise drawings of sunspots, Scheiner discovered seasonal variations in the slope of sunspot tracks. These led him to measure a small inclination of the solar axis with respect to the ecliptic plane. Galileo interpreted the variations of sunspot tracks as strong evidence in support of the Copernican model of the planets and Sun. Scheiner, in contrast, sought to reconcile his discoveries with his belief in Church dogma. He rejected the Copernican model and adopted instead Tycho Brahe’s hybrid geocentric model, which was consistent with all pertinent observations.