- published: 13 Dec 2013
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An apsis (Greek ἁψίς, gen. ἁψίδος), plural apsides ( /ˈæpsɨdiːz/; Greek: ἁψίδες), is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system. Historically, in geocentric systems, apsides were measured from the center of the Earth.
The point of closest approach (the point at which two bodies are the closest) is called the periapsis or pericentre, from Greek περί, peri, around, and κέντρον kentron. The point of farthest excursion is called the apoapsis (ἀπό, apó, "from", apocentre or apapsis [from ἀπ-, ap-, before an unaspirated, or ἀφ-, aph-, before an aspirated vowel, respectively]), (the latter term, although etymologically more correct, is much less used). A straight line drawn through the periapsis and apoapsis is the line of apsides. This is the major axis of the ellipse, the line through the longest part of the ellipse.
Derivative terms are used to identify the body being orbited. The most common are perigee /ˈpɛrɨdʒiː/ and apogee /ˈæpɵdʒiː/, referring to orbits around the Earth (Greek γῆ, gê, "earth"), and perihelion /ˌpɛrɨˈhiːliən/ and aphelion /əˈfiːliən/, referring to orbits around the Sun (Greek ἥλιος, hēlios, "sun"). During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon.
William Thomas "Tommy" Emmanuel AM (born 31 May 1955) is an Australian guitarist and occasional singer, best known for his complex fingerstyle technique, energetic performances and the use of percussive effects on the guitar. In the May 2008 and 2010 issues of Guitar Player Magazine, he was named as "Best Acoustic Guitarist" in their readers' poll. In June 2010 Emmanuel was appointed a Member of the Order of Australia (AM).
Emmanuel was born in Australia in 1955. He received his first guitar in 1959 at age four, being taught by his mother to accompany her playing lap steel guitar. At the age of 7 he heard Chet Atkins on the radio. He vividly remembers this moment and says it greatly inspired him.
By the age of 6, in 1961, he was a working professional musician. Recognizing the musical talents of Tommy and his brother Phil, their father created a family band, sold the family home and took his family on the road. With the family living in two station wagons, much of Emmanuel’s childhood was spent touring Australia with his family, playing rhythm guitar, and rarely going to school. The family found it difficult living on the road; they were poor but never hungry, never settling in one place. His father would often drive ahead, organize interviews, advertising and finding the local music shop where they'd have an impromptu concert the next day. Eventually the New South Wales Department of Education insisted that the Emmanuel children needed to go to school regularly.