Search results
Results from the WOW.Com Content Network
Animation showing the difference between a sidereal day and a solar day. Sidereal time ("sidereal" pronounced / saɪˈdɪəriəl, sə -/ sy-DEER-ee-əl, sə-) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky.
Rotation period (astronomy) In astronomy, the rotation period or spin period[1] of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the sidereal rotation period (or sidereal day), i.e., the time that the object takes to complete a full rotation around its axis relative to the background ...
The anomalistic period is the time that elapses between two passages of an object at its periapsis (in the case of the planets in the Solar System, called the perihelion), the point of its closest approach to the attracting body. It differs from the sidereal period because the object's semi-major axis typically advances slowly.
Hour angle. The hour angle is indicated by an orange arrow on the celestial equator plane. The arrow ends at the hour circle of an orange dot indicating the apparent place of an astronomical object on the celestial sphere. In astronomy and celestial navigation, the hour angle is the dihedral angle between the meridian plane (containing Earth's ...
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 ...
A sidereal year (/ saɪˈdɪəri.əl /, US also / sɪ -/; from Latin sidus 'asterism, star'), also called a sidereal orbital period, is the time that Earth or another planetary body takes to orbit the Sun once with respect to the fixed stars. Hence, for Earth, it is also the time taken for the Sun to return to the same position relative to ...
At the equator, the solar rotation period is 24.47 days. This is called the sidereal rotation period, and should not be confused with the synodic rotation period of 26.24 days, which is the time for a fixed feature on the Sun to rotate to the same apparent position as viewed from Earth (the Earth's orbital rotation is in the same direction as ...
The United States Naval Observatory states "the Equation of Time is the difference apparent solar time minus mean solar time", i.e. if the sun is ahead of the clock the sign is positive, and if the clock is ahead of the sun the sign is negative. [6] [7] The equation of time is shown in the upper graph above for a period of slightly more than a ...