Aerospace engineering

Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It is divided into two major and overlapping branches: aeronautical engineering and astronautical engineering.

Aeronautical engineering was the original term for the field, but as flight technology advanced to include craft operating in outer space, the broader term "aerospace engineering" has largely replaced it in common usage. Aerospace engineering, particularly the astronautics branch, is often referred to as "rocket science".

Overview

Flight vehicles are subjected to demanding conditions such as those produced by changes in atmospheric pressure and temperature, with structural loads applied upon vehicle components. Consequently, they are usually the products of various technological and engineering disciplines including aerodynamics, propulsion, avionics, materials science, structural analysis and manufacturing. The interaction between these technologies is known as aerospace engineering. Because of the complexity and number of disciplines involved, aerospace engineering is carried out by teams of engineers, each having their own specialized area of expertise.

Rocket

A rocket (Italian rocchetta‚ "little fuse") is a missile, spacecraft, aircraft or other vehicle that obtains thrust from a rocket engine. Rocket engine exhaust is formed entirely from propellant carried within the rocket before use. Rocket engines work by action and reaction and push rockets forward simply by expelling their exhaust in the opposite direction at high speed, and can therefore work in the vacuum of space.

In fact, rockets work more efficiently in space than in an atmosphere. Multi-stage rockets are capable of attaining escape velocity from Earth and therefore can achieve unlimited maximum altitude. Compared with airbreathing engines, rockets are lightweight and powerful and capable of generating large accelerations. To control their flight, rockets rely on momentum, airfoils, auxiliary reaction engines, gimballed thrust, momentum wheels, deflection of the exhaust stream, propellant flow, spin, and/or gravity.

Rockets for military and recreational uses date back to at least 13th century China. Significant scientific, interplanetary and industrial use did not occur until the 20th century, when rocketry was the enabling technology for the Space Age, including setting foot on the moon. Rockets are now used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight, and space exploration.

Randomness

Randomness is the lack of pattern or predictability in events. A random sequence of events, symbols or steps has no order and does not follow an intelligible pattern or combination. Individual random events are by definition unpredictable, but in many cases the frequency of different outcomes over a large number of events (or "trials") is predictable. For example, when throwing two dice, the outcome of any particular roll is unpredictable, but a sum of 7 will occur twice as often as 4. In this view, randomness is a measure of uncertainty of an outcome, rather than haphazardness, and applies to concepts of chance, probability, and information entropy.

The fields of mathematics, probability, and statistics use formal definitions of randomness. In statistics, a random variable is an assignment of a numerical value to each possible outcome of an event space. This association facilitates the identification and the calculation of probabilities of the events. Random variables can appear in random sequences. A random process is a sequence of random variables whose outcomes do not follow a deterministic pattern, but follow an evolution described by probability distributions. These and other constructs are extremely useful in probability theory and the various applications of randomness.

Scientist

A scientist is a person engaging in a systematic activity to acquire knowledge. In a more restricted sense, a scientist may refer to an individual who uses the scientific method. The person may be an expert in one or more areas of science. This article focuses on the more restricted use of the word. Scientists perform research toward a more comprehensive understanding of nature, including physical, mathematical and social realms.

Philosophy is a distinct activity that is not generally considered science. Philosophers aim to provide a comprehensive understanding of intangible aspects of reality and experience that cannot be physically measured.

Scientists are also distinct from engineers, those who design, build, and maintain devices for particular situations; however, no engineer attains that title without significant study of science and the scientific method. When science is done with a goal toward practical utility, it is called applied science. An applied scientist may not be designing something in particular, but rather is conducting research with the aim of developing new technologies and practical methods. When science is done with an inclusion of intangible aspects of reality it is called natural philosophy.

Guest appearance

In show business, a guest appearance is the participation of an outsider performer (such as a musician or actor) in an event such as a music record or concert, show, etc., when the performer does not belong to the regular cast, band or other performing group. In music, such an outside performer is often referred to as a guest artist. In performance art, the terms guest role or guest star are also common, the latter term specifically indicating the guest appearance of a celebrity. The latter is often also credited as "special guest star" or "special musical guest star" by some production companies. A guest character is a character being portrayed within a fictional entertainment setting who is only involved as part of the plot once or a few times at most. A guest character has fewer appearances than main characters, supporting characters, and recurring characters.

In pop music, guest appearances are often described with the words featuring, with, or and. It is abbreviated in credit lists as feat., ft., f/, f.. In a television series, a guest star is an actor who appears in one or a few episodes. In radio and television shows, a guest star is a guest of the show who is a celebrity.