The word science comes from the Latin word for knowledge, and the extensiveness of its study reflects the pursuit of knowledge. Science effectively covers anything that can be quantitatively measured and tested. While no formal subdivisions exist, several recognized fields of science cover different realms of the physical world.
Physics
Physics, its name derived from the Greek word for "nature," is a broad study of how the universe works. Physics can also be thought of as a study of the unseen forces giving order to the universe, such as energy and gravity. Physics is often split into two categories: traditional physics, dealing with forces on a large scale level, like gravity; and quantum physics, focusing on the principles governing elementary particles, such as quarks and electrons.
Chemistry
Chemistry is the study of how matter combines to form compounds. Matter is effectively anything taking up space, and it is made up of elements. Elements are made up of atoms, which differ from one another based on the number of protons in their nuclei. When different types of atoms come together, they form compounds. The defining tool for chemistry is the periodic table of elements, a list of all known elements, their number of protons, and atomic weight. Chemistry is often divided into organic chemistry, focusing on compounds found in organisms, and inorganic chemistry.
Biology
Biology is an extensive subdivision of science dealing with the study of living things. Its name comes from Greek and means the science of life. Organisms are divided in to six kingdoms of life -- Archaea, Bacteria, Protista, Fungae, Plantae and Animalia -- with each kingdom having thousands of additional subdivisions. Biologists may focus on the specifics of an individual organism (e.g., physical traits) or how species organize themselves into a community. An important concept in biology is evolution, a complex theory explaining how organisms develop traits needed for survival.
Astronomy
Astronomy is the study of objects in space, including those in our solar system and beyond. Astronomers have several different tools for observing the cosmos, from different types of telescopes -- including use of X-rays or technology in the Earth's orbit -- to the observations of astronauts. Advances in physics have split astronomy effectively in two: astronomers who deal with observable objects, and those who work in theoretical objects that are scientifically possible, but not verified visibly. Two such theoretical objects are black holes and dark matter.
Tags: comes from, dealing with, different types, form compounds, from Greek