More than 350 keywords from relativity and related topics, from "absolute zero" to "X-rays" - please use the menu on the left to choose a letter.
In physics, velocity is a combination of two aspects: First of all, how fast an object is, in other words: how long a distance it moves in a given time (its "speed"). Secondly, the direction in which an object moves. Physicists combine these two informations into a single mathematical object, called a "vector", and this is what is called the velocity. For instance, when a car goes around a curve with 100 miles per hour, its speed is constant, but as it changes its direction of movement, its velocity changes correspondingly.
- virgo cluster
- visible light
In astronomy, the word light is often used to denote any kind of electromagnetic radiation, from infrared radiation to X-rays and beyond. If, in contrast, an astronomer is talking about the ordinary light to which our eyes are susceptible - electromagnetic radiation with wavelengths between about 400 and 700 nanometers (400 to 700 billionths of a meter) - he or she will use the expression "visible light".