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Figure 8.- The apparent change in cycle of asteroid rotation at various longitudes, plotted for four values of the latitude of the pole, 90° longitude of pole; asteroid is on the ecliptic.

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Figure 9.—Same as figure 8 except asteroid is 20° above the ecliptic.

precision is needed in the timing of lightcurves to establish precise epochs of maximum or minimum light. Without precise timing, it is impossible to have high precision when comparing epochs from different oppositions.

ACKNOWLEDGMENT The asteroid program at the University of Arizona is supported by the National Aeronautics and Space Administration.

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*The numbers in brackets are as used in table I.

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SUMMARY ON ORIENTATIONS OF ROTATION AXES

CARL D. VESELY
University of Arizona

To evaluate the precision of the previously determined coordinates of the rotation axes (table I) we should review the methods (originally developed for 433 Eros) and logic of the various authors. Table II contains pole coordinates of Eros and the sources of these data. A critical summary of the work will enable us to make some conclusions concerning the poles presented.

EARLY RESEARCH ON THE POLE OF EROS

There is general agreement that greatest rotational amplitude is observed when an asteroid is viewed equatorially, and we can detect three approaches to the determination of the Eros pole: the micrometer position angles observed by van den Bos and Finsen (1931); the graphic presentations used by Watson (1937), Stobbe (1940), and Rosenhagen (1932); and the mathematical model developed by Krug and Schrutka-Rechtenstamm (1936). These initial attempts yielded only approximate values, but the approximations were sometimes refined by analytical methods.

Micrometer Measurements of Position Angles

Eros is the only asteroid to have directly observed micrometer measurements of the position angles of the projection of its long axis. Van den Bos and Finsen (1931) found the position angle rotating over 360° in 5h 17m and a separation of “about 0.18.” The precision of the measurements of the position angle may be +5° (Van Biesbroeck, personal communication).

In 1931, W. Zessewitsche (1932, 1937) graphically determined the equator of Eros from the observations of van den Bos and Finsen (1931). He determined an average position angle of the line of intersection of the projection of the long axis of Eros with the projection plane perpendicular to the line of sight at a given time and assumed the pole to be this position angle plus 90°. Zessewitsche calculated a value for the inclination of the equator of Eros to the projection plane at that time and determined the pole coordinates. The pole determination enabled him to calculate the Erocentric right ascension

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