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46          Sidereal Explorations

Metagalaxy. Progress can be claimed in all territories, but
not conquest. Our acquisitions are small compared with the
unfolding unknown. Some parts of the program may be
satisfactorily completed in ten or twenty years ; other phases
extend indefinite decades into the future. Meanwhile we
shall approach understanding through sampling processes
and through reasonable extrapolation, leaving to future
astronomers the pursuit of detailed studies in fields now but
provisionally explored.

Limitations of space will prevent full discussion of the
work in all eight regions. Previous studies are summarized
very briefly, and current investigations are only partially re-
ported; but throughout the discussion many results hereto-
fore unpublished are given in text and diagram.

The eight territories, in order of distance, are the follow-
ing:

1. The Solar Neighborhood, out to a distance of fifty
light years, explored chiefly through studies of the motions
ofnearbystars.

2. The Sphere of Lucid Stars, extending five hundred
light years from the solar system, and studied by us mainly
through that joint agency of photometry and spectroscopy—
the method of spectroscopic parallax.

3. The Local System, out to five thousand light years or
so, investigated statistically, for the most part, on the basis
of the spectral classifications, magnitudes, and positions of
tens of thousands of faint stars; but also explored by means
of spectroscopic parallaxes, star counts, and studies of vari-
able stars and galactic clusters.

4. The Milky Way, with a radius in excess of fifty thou-
sand light years, and yielding its secrets very slowly to our
probing by means of variable stars.

5. The System of Globular Clusters, coextensive with the

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