In astronomy, the argument of periapsis (ω) is a way of talking about the orbit of a planet, asteroid or comet. It is also known as the argument of perihelion or the argument of perifocus. It is the angle (starting from the center of the orbit) between an orbiting body's periapsis and its ascending node. Periapsis is the point when the orbiting object comes the closest to the thing it is orbiting around; for example, the moon is at periapsis when it is closest to the Earth. The ascending node is one of two places where an orbiting object passes through the reference plane, an imaginary flat surface which runs through the object being orbited around. The size of the angle depends on which way the object is orbiting.
The angle is measured in the orbital plane and in the direction of motion. For specific types of orbits, words such as "perihelion" (for Sun-centered orbits), "perigee" (for Earth-centered orbits), "pericenter" (general), etc. may replace the word "periapsis".
An argument of periapsis of 0° means that the orbiting body will be at its closest approach to the central body at the same moment that it crosses the plane of reference from south to north. An argument of periapsis of 90° means that the orbiting body will reach periapsis at its northmost distance from the plane of reference.
Argument of perihelion and Longitude of ascending node of planets.
Longitude of the ascending node
The longitude of the ascending node (☊ or Ω) is one of the orbital elements used to specify the orbit of an object in space. It is the angle from a reference direction, called the "origin of longitude", to the direction of the ascending node, measured in a reference plane.
Mean anomaly
In the study of orbital dynamics the mean anomaly of an orbiting body is the angle the body would have traveled about the center of the orbit's auxiliary circle. Unlike other measures of anomaly, the mean anomaly grows linearly with time. Because of the linear growth with time, the mean anomaly makes calculating the time of flight between two points on the orbit very easy. The mean anomalies for the two points are calculated and their difference is found. Knowing this, the ratio of this difference relative to the entire formula_1 encompassing one orbit is simply equal to ratio of the time of flight to the orbital period of one whole orbit (i.e. formula_2).
Orbital period
The orbital period is the time taken for a given object to make one complete orbit around another object. The year and month are orbital periods.
When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars. Other periods include the synodic period, which is the interval between conjunctions.
Orbital speed
The orbital speed of a body, usually a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. It can be used to refer to either the mean orbital speed, the average speed as it completes an orbit, or instantaneous orbital speed, the speed at a particular point in its orbit.
The orbital speed at any position in the orbit can be computed from the distance to the central body at that position, and the specific orbital energy, which is independent of position: it equals the kinetic energy plus the potential energy, divided by the mass. It is also given by Kepler's Second Law.
101
Year 101 was a common year starting on Friday of the Gregorian calendar.
Continental drift
Continental drift is a historical, scientific theory. The theory was first proposed by Abraham Ortelius in 1596. It was fully developed by the German geologist and meteorologist Alfred Wegener in 1915.
The theory said that parts of the Earth's crust move slowly on top of a liquid mantle of higher density. The theory has now been included in the wider theory of plate tectonics.
The theory was supported by finding the same minerals and fossils in western Europe and eastern North America. There are also similar fossils on the western coast of Africa and the eastern South America. The shapes of these continents nearly fit together. The theory was plausible (believable), but there was no known mechanism to drive these great movements. This problem was later solved by plate tectonics.
The pattern of volcanic activity, mountain building (orogeny) and earthquakes is explained by continental drift. The existence of identical rocks widely apart supports the theory.
Examples (there are hundreds):
The basic machine driving continental movement is heat moving from the Earth's mantle through the crust and out of the planet. The effect of this it to cause convection, and plate movement.
Two events in particular are of huge importance:
Saxe-Altenburg
Saxe-Altenburg () was one of the Ernestine duchies of the House of Wettin.
Altenburg was independent for most of the 1600s until 1672. This is when the last male ruler died. Because only men could rule the Ernestine duchies Altenburg began to be ruled by the Duke of Saxe-Gotha, who had married the last ruler’s daughter.
In 1825 the ruler died, and he also had no male heirs. Saxe-Gotha-Altenburg was split up. Gotha was given to the Duke of Saxe-Coburg-Saalfeld and Altenburg to the Duke of Saxe-Hildburghausen, who in exchange gave up Saalfeld and Hildburghausen to the Duke of Saxe-Meiningen. This family ruled in the duchy until the end of the monarchies in 1918. Saxe-Altenburg became part of the new state of Thuringia in the Weimar Republic in 1920.
Saxe-Altenburg had an area of and a population of 207,000 (1905). Its capital was Altenburg.
The Saxe-Altenburg line became extinct following the death of Prince George Moritz in 1991.
In 1991 the Saxe-Altenburg line became extinct.
Two branches descend from duke Ernest the Pious, the father of the progenitor of this Saxe-Altenburg branch: Saxe-Meiningen and Saxe-Coburg-Gotha; according to old Wettin family law, they would have divided the actual territories between them (as happened to Gotha and Altenburg in 1826). The senior male agnate descending from duke Ernest the Pious, in 1991 , was prince Frederick-Alfred of Saxe-Meiningen (a monk, 1921-1997), and thus technically succeeded then as titular duke of Saxe-Altenburg and head of the whole branch; but, because he renounced all his succession rights in favor of his uncle Bernhard, was him instead Frederick-Alfred the general heir of the line of Saxe-Meiningen. His successor was Konrad, Duke of Saxe-Meiningen, the present head of that branch.
Porcupine
A porcupine is a rodent with a coat of sharp spines, or quills, that defend them from predators. The porcupine is the third biggest rodent, after the capybara, and beaver, and are not to be confused with hedgehogs. Most porcupines are about 60–90 cm long, with a 20–25 cm long tail. Weighing between 12-35 pounds (5–16 kg), they are rounded, large and slow. Porcupines come in various shades of brown, grey, and the unusual white. The name "porcupine" comes from Middle French "porc d'épine" "thorny pork", hence the nickname "quill pig" for the animal. The correct term for a baby porcupine is a porcupette. A porcupette has soft quills made of hardened hair. This protects the mother from injury as she gives birth.
The animal's quills or spines take on many forms, depending on the type, but all are hairs coated with thick plates of keratin, and they are in the skin musculature. Old World porcupines (Hystricidae) have quills in clusters, whereas in New World porcupines (Erethizontidae) single quills are mixed with bristles, underfur, and hair.