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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

    From the rule for reading off coordinates in coordinate system with tilted axes follows that the two world lines are the angle bisectors of the x - and ct-axes. As shown in Fig 4-5, the Minkowski diagram illustrates them as being angle bisectors of the x′ - and ct′-axes as well. That means both observers measure the same speed c for both ...

  4. Time of flight - Wikipedia

    en.wikipedia.org/wiki/Time_of_flight

    A time-of-flight camera (ToF camera), also known as time-of-flight sensor (ToF sensor), is a range imaging camera system for measuring distances between the camera and the subject for each point of the image based on time-of-flight, the round trip time of an artificial light signal, as provided by a laser or an LED.

  5. Pulsar timing array - Wikipedia

    en.wikipedia.org/wiki/Pulsar_timing_array

    The pulsars P1 ... Pn are sending signals periodically, which are received on Earth. A gravitational wave (GW) perturbs spacetime in between the pulsar and Earth (E) and changes the time of arrival of the pulses. By measuring the spatial correlation of the changes in the pulse parameters of many different pulsar pairings, a GW can be detected.

  6. 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 ...

  7. 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.

  8. 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.

  9. Frame-dragging - Wikipedia

    en.wikipedia.org/wiki/Frame-dragging

    A useful metaphor is a planetary gear system with the black hole being the sun gear, the ice skater being a planetary gear and the outside universe being the ring gear. See Mach's principle . Another interesting consequence is that, for an object constrained in an equatorial orbit, but not in freefall, it weighs more if orbiting anti-spinward ...