speed
An object's average speed is the distance it moves during a given period of time, divided by the length of the time interval. If you make the time interval infinitely small, the result is the object's speed at one particular moment in time. The notion of ...
speed of light
The speed at which light or, more generally, electromagnetic radiation propagates through space (especially: through empty space). Central quantity in special relativity: There, the constancy of the speed of light is a basic postulate: every observer (more ...
spectrum
The electromagnetic radiation reaching us from an astronomical object or other source is a mix of electromagnetic waves with a great variety of frequencies. The spectrum lists the composition of this mix: For every frequency, it states the amount of radiation ...
special relativity
Albert Einstein's theory of the fundamentals of space, time, and movement (but not gravity). For a brief introduction, check out the chapter Special relativity of Elementary Einstein. Selected aspects of special relativity are described in the category ...
space
In a strict sense: Space as we know it from everyday life: the totality of all locations in which objects can sit, with three dimensions. In a more general sense used by mathematicians, all kinds of sets of points are spaces - a line for instance, which ...
spacetime
Already in special relativity, observers in motion relative to each other will not, in general, agree as to whether two events happen simultaneously, or as to how great is the distance between two objects. They do, however, agree as to what events there are, ...
Space Telescope Science Institute
The institute operating the Hubble space telescope; located in Baltimore, USA. Space Telescope Science Institute website ...
