There are three main divisions of science: physical science, life science, and earth science. However, there are many subdivisions that also overlap, such as physical chemistry, astrophysics, organic chemistry, and astrogeology. These sub divisions overlap because they are require a knowledge of at least two main divisions of science.
Science is defined as a branch of knowledge about the study of the natural world through observation and scientific method. Although observations seen on a daily basis are broken down into three main divisions, they are also categorized in different ways. For example, a science can be categorized as pure or theoretical. Pure science explains a phenomenon while theoretical science is based on hypothetical deductive methods.
Physical sciences, such as physics and chemistry, are related to matter and energy and describe the physical universe in objective measurements. Earth sciences, geology and astronomy, are related to earth, its geological and atmospheric phenomena, and its solar system. Life sciences, biology and botany are related to all living organisms and their relationship to one another and their environment.
Each main division of science is categorized as a pure science, however, when subdivisions overlap and new compound sciences emerge, theoretical sciences are created to form studies such as paleontology and astronautics.