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  2. Photometry (astronomy) - Wikipedia

    en.wikipedia.org/wiki/Photometry_(astronomy)

    A CCD (charge-coupled device) camera is essentially a grid of photometers, simultaneously measuring and recording the photons coming from all the sources in the field of view. Because each CCD image records the photometry of multiple objects at once, various forms of photometric extraction can be performed on the recorded data; typically ...

  3. Spacetime diagram - Wikipedia

    en.wikipedia.org/wiki/Spacetime_diagram

    A spacetime diagram is a graphical ... It says that any observer in an inertial reference frame measuring the vacuum speed of light relative to themself obtains the ...

  4. Multiple time dimensions - Wikipedia

    en.wikipedia.org/wiki/Multiple_time_dimensions

    Dunne suggested that, in the context of a "block" spacetime as modelled by General Relativity, a second dimension of time was needed in order to measure the speed of one's progress along one's own timeline. This in turn required a level of the conscious self existing at the second level of time.

  5. List of spacetimes - Wikipedia

    en.wikipedia.org/wiki/List_of_spacetimes

    This is a list of well-known spacetimes in general relativity. [1] Where the metric tensor is given, a particular choice of coordinates is used, but there are often other useful choices of coordinate available.

  6. Spacetime - Wikipedia

    en.wikipedia.org/wiki/Spacetime

    Likewise, a timelike spacetime interval gives the same measure of time as would be presented by the cumulative ticking of a clock that moves along a given world line. A timelike spacetime interval hence provides a measure of the proper time = s 2 . {\displaystyle {\sqrt {s^{2}}}.} [ 3 ] : 220–221

  7. Four-velocity - Wikipedia

    en.wikipedia.org/wiki/Four-velocity

    The history of an object traces a curve in spacetime, called its world line. If the object has mass, so that its speed is necessarily less than the speed of light, the world line may be parametrized by the proper time of the object. The four-velocity is the rate of change of four-position with respect to the proper time along the curve. The ...

  8. Coordinate time - Wikipedia

    en.wikipedia.org/wiki/Coordinate_time

    A fuller explanation of the concept of coordinate time arises from its relations with proper time and with clock synchronization. Synchronization, along with the related concept of simultaneity, has to receive careful definition in the framework of general relativity theory, because many of the assumptions inherent in classical mechanics and classical accounts of space and time had to be removed.

  9. World line - Wikipedia

    en.wikipedia.org/wiki/World_line

    time-like curves, with a speed less than the speed of light. These curves must fall within a cone defined by light-like curves. In our definition above: world lines are time-like curves in spacetime. space-like curves falling outside the light cone. Such curves may describe, for example, the length of a physical object.