If the mass of the smaller body (e.g. Earth) is m, and it orbits a heavier body (e.g. Sun) of mass M with a semi-major axis a and an eccentricity of e, then the radius r of the Hill sphere for the sma ...
Eclipses only occur in the eclipse season, when the Sun is close to either the ascending or descending node of the Moon. Each eclipse is separated by one, five or six lunations (synodic months), and t ...
There are four types of solar eclipses:A total eclipse occurs when the dark silhouette of the Moon completely obscures the intensely bright light of the Sun, allowing the much fainter solar corona to ...
The shadow of the Earth can be divided into two distinctive parts: the umbra and penumbra. Within the umbra, there is no direct solar radiation. However, as a result of the Sun's large angular size, s ...
The motions as described above are simplifications. Due to the movement of the Earth around the Earth-Moon barycenter, the apparent path of the Sun wobbles slightly, with a period of about one month. ...
Before clocks were commonplace, the terms "sunwise" and "deasil", "deiseil" and even "deocil" from the Scottish Gaelic language and from the same root as the Latin "dexter" ("right") were used fo
The north celestial pole currently is within a degree of the bright star Polaris (named from the Latin stella polaris, meaning "pole star"). This makes Polaris useful for navigation in the northern he ...
This is the average period of the Moon's revolution with respect to the line joining the Sun and Earth. The synodic month is the period of the Moon's phases, because the Moon's appearance depends on t ...
The concept of "center of mass" in the form of the "center of gravity" was first introduced by the ancient Greek physicist, mathematician, and engineer Archimedes of Syracuse. He worked with simplifie ...
A meridian is the great circle passing through the celestial poles and the zenith of a particular location. Consequently, it also contains the horizon's north and south points and it is perpendicular ...
Approximating Earth's orbit around the sun to be an ellipse with semimajor axis of 1 au and eccentricity of 0.0167, the distance Earth travels in one year is roughly 940 million kilometers (584 millio ...
The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space. As a ...
Sidereal time /sa??d??ri?l/ is a time-keeping system astronomers use to keep track of the direction to point their telescopes to view a given star in the night sky. Briefly, sidereal time is a "t ...
When Julius Caesar established his calendar in 45 BC he set 25 March as the spring equinox. Because a Julian year (365.25 days) is slightly longer than an actual year the calendar drifted with respect ...
In astronomy, precession refers to any of several gravity-induced, slow and continuous changes in an astronomical body's rotational axis or orbital path. Precession of the equinoxes, perihelion preces ...
