Wonders of Space, Brain, Encyclopedia
The Wonders of Space can be found in the void that exists beyond any celestial body including the Earth. Outer Space contains a low density of particles, predominantly hydrogen plasma, as well as electromagnetic radiation, magnetic fields, and neutrinos. Theoretically, it also contains dark matter and dark energy. Space is the closest natural approximation of a perfect vacuum. It has effectively no friction, which allows stars, planets and moons to move freely along ideal gravitational trajectories. Some of the wonders of space include Nebulas which are clouds of gas and dust particles spread out through interstellar space. There are galaxies or enormous structures made up of stars, gas, and dust held together by the gravitational attraction between their individual parts. Star clusters which are groups of stars which are held together by their mutual gravitational attraction. There are many other wonders of space.
The center of the nervous system in all vertebrate and most invertebrate animals is the brain. In vertebrates the brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing, balance, taste, and smell. The brain controls the other organ systems of the body, by activating muscles or by causing a secretion of chemicals such as hormones and neurotransmitters. This centralized control allows rapid and coordinated responses to changes in the environment. Vertebrate brains are made of very soft tissue. Living brain tissue is pinkish on the outside and mostly white on the inside, with subtle variations in color. Vertebrate brains are surrounded by a system of connective tissue membranes called meninges that separate the skull from the brain. The cerebral cortex is the part of the brain that most strongly distinguishes mammals from other vertebrates, primates from other mammals, and humans from other primates.
An encyclopedia is a type of reference work holding a summary of information from either all branches of knowledge or a particular branch of knowledge. The word is also spelled encyclopaedia or encyclopædia. Encyclopedias are divided into subjects, articles or entries, usually accessed alphabetically. Encyclopedia entries are longer and more detailed than those in most dictionaries and focus on factual information to cover the subject or concept for which the article name stands. Encyclopedias have existed for around 2,000 years. Naturalis Historia is the oldest still in existence, written in ca. 77 CE by Pliny the Elder. The modern encyclopedia evolved out of dictionaries around the 17th century. Huge multi-volume works like the Encyclopaedia Britannica, were originally sold door-to-door. Some modern encyclopedias are electronic and are often freely available, for example Wikipedia and Citizendium. The free sites often contain un-documented information and should be checked for facts.