A planet (or asteroid or comet) is said to be "in opposition" or "at opposition" when it is in opposition to the Sun. Because most orbits in the Solar System are nearly coplanar to the ecliptic, this occurs when the Sun, Earth, and the body are configured in an approximately straight line, or syzygy; that is, Earth and the body are in the same direction as seen from the Sun. Opposition occurs only for superior planets (see the diagram).
The instant of opposition is defined as that when the apparent geocentric celestial longitude of the body differs by 180° from the apparent geocentric longitude of the Sun.[1] At that time, a body is:
at the place where the opposition effect increases the reflected light from bodies with unobscured rough surfaces[6]
The Moon, which orbits Earth rather than the Sun, is in approximate opposition to the Sun at full moon.[7] A more exact opposition occasionally occurs with mathematical regularity if the Moon is at its usual sun and Earth-aligning point so that it appears full and happens to be aligning with the ecliptic (Earth's orbital plane) during the descending or ascending phase of its 5° inclined (tilted) orbit, which is more concisely termed at a node of its orbit, in which case, a lunar eclipse occurs. A more exact, shaded form is when a central area of the earth aligns more precisely: a central lunar eclipse, of which there were 14 in the 50 years to 2000, others being penumbral.
Seen from a superior planet, an inferior planet on the opposite side of the Sun is in superior conjunction with the Sun. An inferior conjunction occurs when the two planets align on the same side of the Sun. At inferior conjunction, the superior planet is "in opposition" to the Sun as seen from the inferior planet (see the diagram).
When two planets are on the same side of the Sun then from the point of view of the interior planet the other planet is in opposition with the Sun. When two planets are on opposite sides of the Sun, there is an opposition from the point of view of the Sun. In either case, the interval between two such occurrences involving the same two planets is not constant because the orbits are not circular and because the planets perturb one another. But the average interval between them can be calculated from the periods of the two planets. The "speed" at which a planet goes around the Sun, in terms of revolutions per time, is given by the inverse of its period, and the speed difference between two planets is the difference between these. Since the time interval between two oppositions is the time it takes for 360° to be covered by that speed difference, the average interval is:
The following table gives these average intervals, in Julian years (of 365.25 days), for combinations of the nine traditional planets. Since Pluto is in resonance with Neptune the period used is 1.5 times that of Neptune, slightly different from the current value. The interval is then exactly thrice the period of Neptune.
^ U.S. Naval Observatory Nautical Almanac Office (1992). P. Kenneth Seidelmann (ed.). Explanatory Supplement to the Astronomical Almanac. University Science Books, Mill Valley, CA. p. 733. ISBN0-935702-68-7.
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In positional astronomy two astronomical objects are said to be in opposition when they are on opposite sides of the celestial sphere as observed from a given body usually Earth Diagram of positional astronomy A planet or asteroid or comet is said to be in opposition or at opposition when it is in opposition to the Sun Because most orbits in the Solar System are nearly coplanar to the ecliptic this occurs when the Sun Earth and the body are configured in an approximately straight line or syzygy that is Earth and the body are in the same direction as seen from the Sun Opposition occurs only for superior planets see the diagram The instant of opposition is defined as that when the apparent geocentric celestial longitude of the body differs by 180 from the apparent geocentric longitude of the Sun 1 At that time a body is in apparent retrograde motion 2 visible almost all night rising around sunset culminating around midnight and setting around sunrise 3 at the point in its orbit where it is roughly closest to Earth making it appear larger and brighter 4 nearly completely sunlit the planet shows a full phase analogous to a full moon 5 at the place where the opposition effect increases the reflected light from bodies with unobscured rough surfaces 6 The Moon which orbits Earth rather than the Sun is in approximate opposition to the Sun at full moon 7 A more exact opposition occasionally occurs with mathematical regularity if the Moon is at its usual sun and Earth aligning point so that it appears full and happens to be aligning with the ecliptic Earth s orbital plane during the descending or ascending phase of its 5 inclined tilted orbit which is more concisely termed at a node of its orbit in which case a lunar eclipse occurs A more exact shaded form is when a central area of the earth aligns more precisely a central lunar eclipse of which there were 14 in the 50 years to 2000 others being penumbral The astronomical symbol for opposition is U 260D Seen from a superior planet an inferior planet on the opposite side of the Sun is in superior conjunction with the Sun An inferior conjunction occurs when the two planets align on the same side of the Sun At inferior conjunction the superior planet is in opposition to the Sun as seen from the inferior planet see the diagram Contents 1 Average interval between oppositions 2 See also 3 References 4 External linksAverage interval between oppositions editWhen two planets are on the same side of the Sun then from the point of view of the interior planet the other planet is in opposition with the Sun When two planets are on opposite sides of the Sun there is an opposition from the point of view of the Sun In either case the interval between two such occurrences involving the same two planets is not constant because the orbits are not circular and because the planets perturb one another But the average interval between them can be calculated from the periods of the two planets The speed at which a planet goes around the Sun in terms of revolutions per time is given by the inverse of its period and the speed difference between two planets is the difference between these Since the time interval between two oppositions is the time it takes for 360 to be covered by that speed difference the average interval is 1 1 p 1 1 p 2 displaystyle frac 1 1 p 1 1 p 2 nbsp The following table gives these average intervals in Julian years of 365 25 days for combinations of the nine traditional planets Since Pluto is in resonance with Neptune the period used is 1 5 times that of Neptune slightly different from the current value The interval is then exactly thrice the period of Neptune Average interval between oppositions Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Period 0 241 0 615 1 000 1 881 11 863 29 447 84 017 164 791 247 187 Mercury 0 241 0 396 0 317 0 276 0 246 0 243 0 242 0 241 0 241 Venus 0 615 0 396 1 599 0 914 0 649 0 628 0 620 0 618 0 617 Earth 1 000 0 317 1 599 2 135 1 092 1 035 1 012 1 006 1 004 Mars 1 881 0 276 0 914 2 135 2 235 2 009 1 924 1 903 1 895 Jupiter 11 863 0 246 0 649 1 092 2 235 19 865 13 813 12 783 12 461 Saturn 29 447 0 243 0 628 1 035 2 009 19 865 45 338 35 855 33 430 Uranus 84 017 0 242 0 620 1 012 1 924 13 813 45 338 171 406 127 277 Neptune 164 791 0 241 0 618 1 006 1 903 12 763 35 855 171 406 494 374 Pluto 247 187 0 241 0 617 1 004 1 895 12 461 33 420 127 277 494 374See also edit nbsp Mars in opposition 2016 8 Conjunction Phase angle Spherical astronomy SyzygyReferences edit U S Naval Observatory Nautical Almanac Office 1992 P Kenneth Seidelmann ed Explanatory Supplement to the Astronomical Almanac University Science Books Mill Valley CA p 733 ISBN 0 935702 68 7 Newcomb and Holden 1890 p 115 Newcomb Simon Holden Edward S 1890 Astronomy pp 115 273 Moulton Forest Ray 1918 An Introduction to Astronomy pp 255 256 Newcomb and Holden 1890 p 334 see references at opposition surge Moulton 1918 p 191 Close up of the Red Planet Retrieved 20 May 2016 External links editAsteroids around opposition British Astronomical Association Computing Section Portals nbsp Astronomy nbsp Stars nbsp Spaceflight nbsp Outer space nbsp Solar System Retrieved from https en wikipedia org w index php title Opposition astronomy amp oldid 1216978184, wikipedia, wiki, book, books, library,
