Astronomy and Related Fields

Astronomy - The study of phenomena outside of the earth's atmosphere (also includes the study of the earth as a
        planet).  Astronomy includes the study of stars and their associated planetary systems, galaxies, the interstellar
        and intergalactic mediums, and the universe as a whole.

Astrophysics - The study of the physics associated with and required for an understanding of astronomical
        phenomena.  Astrophysics is not a fundamental branch of physics in the sense that mechanics or
        thermodynamics is, but includes many concepts from many of those fundamental branches, e.g., astrophysics
        includes contributions from mechanics, electromagnetism, statistical mechanics, thermodynamics, plasma
        physics, optics, particle physics, nuclear physics, atomic and molecular physics, quantum mechanics, and
        relativity.

Space Science - The study of phenomena outside the earth's atmosphere, but within the solar system.

Planetary Science - The study of planets and planetary systems.

Geophysics - The study of the physical phenomena of the earth's atmosphere, surface and interior.

Cosmology - The study of the universe as a whole.

Cosmogony - The study of the origin of the universe.  Historically the term has also been used to describe the study
        of the origin of the solar system.

Astrobiology - The study of all topics relevant to the question of whether life exists elsewhere in the universe.  This
        very broad field is a blend of astrophysics, biology, chemistry and even social sciences.

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There are obviously no sharp distinctions between many of these fields and many interesting questions and phenomena lie within more than a single field.  Usage of many of these terms has not been consistent, e.g., the term "space science" is sometimes used much more broadly than indicated above, almost synonymously with "astronomy."