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  2. Solar System - Wikipedia

    en.wikipedia.org/wiki/Solar_System

    That is, counter-clockwise, as viewed from above Earth's north pole. [48] There are exceptions, such as Halley's Comet . [ 49 ] Most of the larger moons orbit their planets in prograde direction, matching the direction of planetary rotation; Neptune's moon Triton is the largest to orbit in the opposite, retrograde manner. [ 50 ]

  3. Rotation matrix - Wikipedia

    en.wikipedia.org/wiki/Rotation_matrix

    where for every direction in the base space, S n, the fiber over it in the total space, SO(n + 1), is a copy of the fiber space, SO(n), namely the rotations that keep that direction fixed. Thus we can build an n × n rotation matrix by starting with a 2 × 2 matrix, aiming its fixed axis on S 2 (the ordinary sphere in three-dimensional space ...

  4. Universe - Wikipedia

    en.wikipedia.org/wiki/Universe

    The physical universe is defined as all of space and time [a] (collectively referred to as spacetime) and their contents. [10] Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.

  5. List of time periods - Wikipedia

    en.wikipedia.org/wiki/List_of_time_periods

    Ancient history – Aggregate of past events from the beginning of recorded human history and extending as far as the Early Middle Ages or the Postclassical Era. The span of recorded history is roughly five thousand years, beginning with the earliest linguistic records in the third millennium BC in Mesopotamia and Egypt .

  6. Solar time - Wikipedia

    en.wikipedia.org/wiki/Solar_time

    On a prograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the Sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 = one sidereal day). But it is not until a little later, at time 3, that the Sun is overhead again (1→3 = one solar day). More simply, 1→2 is a complete ...

  7. Antikythera mechanism - Wikipedia

    en.wikipedia.org/wiki/Antikythera_mechanism

    The mean Sun position is, by definition, the current date. It is speculated that since significant effort was taken to ensure the position of the Moon was correct, [ 17 ] : 20, 24 there was likely to have also been a "true sun" pointer in addition to the mean Sun pointer, to track the elliptical anomaly of the Sun (the orbit of Earth around the ...

  8. Physics - Wikipedia

    en.wikipedia.org/wiki/Physics

    Physics is the scientific study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. [1] Physics is one of the most fundamental scientific disciplines. [2] [3] [4] A scientist who specializes in the field of physics is called a physicist.

  9. Science - Wikipedia

    en.wikipedia.org/wiki/Science

    Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. [1] [2] Modern science is typically divided into two or three major branches: [3] the natural sciences (e.g., physics, chemistry, and biology), which study the physical world; and the social sciences (e.g., economics, psychology, and sociology), which ...