Earth's rotation period relative to the International Celestial Reference Frame, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86 164.098 903 691 seconds of mean solar time (UT1) (23 h 56 m 4.098 903 691 s, 0.997 269 663 237 16 mean solar days). Earth's rotation period relative to the precessing mean vernal equinox, …

Rotation, or spin, is the circular movement of an object around a central axis. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. ... The speed of rotation is given by the angular frequency (rad/s) or frequency (turns per time), or period (seconds, days, etc ...

Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure).It may also describe other motions such as precession or nutation of an object's rotational axis. Prograde or direct motion is more normal motion in the same direction as the primary rotates.

A rotation can be represented by a unit-length quaternion q = (w, r →) with scalar (real) part w and vector (imaginary) part r →. The rotation can be applied to a 3D vector v → via the formula = + (+). This requires only 15 multiplications and 15 additions to evaluate (or 18 multiplications and 12 additions if the factor of 2 is done via ...

In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbital plane. It differs from orbital inclination.At an obliquity of 0 degrees, the two axes point in the same direction; that is, the rotational axis is ...

The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars.. For celestial objects in general, the sidereal period (sidereal year) is referred to by the orbital ...

Solar rotation varies with latitude.The Sun is not a solid body, but is composed of a gaseous plasma.Different latitudes rotate at different periods. The source of this differential rotation is an area of current research in solar astronomy. The rate of surface rotation is observed to be the fastest at the equator (latitude φ = 0°) and to decrease as latitude increases.

The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from each side are averaged to create the curve.

Menstruation, also called a "period" Unit of time or timeframe Period (geology), a subdivision of geologic time; Period (physics), the duration of time of one cycle in a repeating event; Orbital period, the time needed for one object to complete an orbit around another; Rotation period, the time needed for one object to complete a revolution

Rotational frequency (also known as rotational speed or rate of rotation) of an object rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second (cps), etc. The symbol for rotational frequency is (the Greek lowercase letter nu).