parallacticadj.
/ˌparəˈlaktɪk/, U.S. /ˌpɛrəˈlæktɪk/ Chiefly Astronomy.
Of, relating to, or resulting from parallax.
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the world > physical sensation > sight and vision > [adjective] > parallax
parallactic1630
parallactical1670
1630 R. Norton tr. W. Camden Hist. Princesse Elizabeth ii. 53 Thomas Digsey, and Iohn Dey..haue learnedly proued by Paralactic Doctrine [L. Parallactica doctrina], that it [sc. a new star in Cassiopeia] was in the celestiall, not in the Elementary Region.
1670 T. Blount Glossographia (ed. 3) Parallactic, pertaining to the difference between the true and apparent place of any Planet or Comet.
1763 Philos. Trans. 1762 (Royal Soc.) 52 567 The tangent of the sum or distance, which may be called the parallactic arch.
1869 Jrnl. Royal Geogr. Soc. 39 92 At Kerguelen's Island the altitude of the sun at the ingress will be about 12°, while the parallactic value is large (about 0·97).
1988 Nature 28 July 331/1 Absolute scales of stellar brightness have been constructed like pyramids, founded on parallactic measurements of distance.
2001 O. Sacks Uncle Tungsten xii. 142 If one moved the camera more than this, the parallactic differences were exaggerated, and the two pictures, when fused, gave an exaggerated sense of depth.
Compounds
parallactic angle n. the angle formed at a celestial object by the intersection of arcs drawn on the celestial sphere to the observer's zenith and to the celestial pole.
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1668 H. Oldenburg Let. 3 Jan. in J. Wallis Corr. (2003) II. 377 To subtend the parallactic angle.
1681 J. Flamsteed Gresham Lect. (1975) 108 Therefore the parallactick Angle 37°–44' [sic].
1789 Philos. Trans. (Royal Soc.) 79 59 I have calculated them two different ways, viz. by the method of parallactic angles, and by the method of the nonagesimal.
1994 J. North Fontana Hist. Astron. & Cosmol. iv. 103 (caption) The parallactic angle clearly increases to a maximum when the object is near our horizon and we are at B in the figure.
parallactic ellipse n. an elliptic curve traced by the apparent position of a star as a result of the observer's motion as the earth moves around the sun.
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1826 Philos. Trans. (Royal Soc.) 116 272 It is obvious then that a will represent the major semi-axis of the star's parallactic ellipse, and a. sin. λ the minor.
1871 J. F. W. Herschel Familiar Lect. Sci. Subj. v. 203 Each of them, microscopically watched, appears to describe the same minute annual parallactic ellipse.
1978 J. M. Pasachoff & M. L. Kutner University Astron. iii. 50 For a star that is far from the plane of the earth's orbit..the parallactic ellipse will be almost a circle.
parallactic inequality n. an inequality in the moon's orbit caused by the gravitational attraction of the sun, in which the moon in its first quarter is ahead of its position as calculated assuming uniform motion, and in its last quarter lags behind the calculated position.
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1831 Philos. Trans. (Royal Soc.) 121 233 (note) Parallactic inequality.
1861 G. F. Chambers Handbk. Descr. Astron. i. vii. 43 The Parallactic Inequality, which arises from the difference in the influence of the Sun's attraction when the Moon traverses that part of its orbit nearest the Sun.
1974 Proc. Royal Soc. A. 338 406 The Society desired Newton to determine the solar parallax from the parallactic inequality of the Moon's motion.
parallactic instrument n. historical an instrument invented by Ptolemy, consisting of three hinged rods (one vertical, one aligned along the observer's line of sight, and the third fixing the angle between the first two), used for calculating the parallax of the moon.
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1687 Philos. Trans. 1686–7 (Royal Soc.) 16 404 The Meridian Altitude of the Sun in the summer Solstice was observed by the Parallactick instrument of Ptolemy.
1779 Philos. Trans. (Royal Soc.) 69 164 A parallactic instrument, with a common telescope five feet long, and a reticule rhomboide.
1990 Jrnl. Hist. Ideas 51 356 Of Copernicus in particular Tycho cherished the parallactic instrument which an assistant had brought back from an observing expedition to Frauenburg.
parallactic motion n. the change in the apparent position of a celestial object resulting from change in the observer's position.
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1804 Philos. Trans. (Royal Soc.) 94 360 The motion of the solar system, towards this assumed point, will produce an opposite parallactic motion, in every star that is not too far from us to be sensibly affected by it.
1938 R. L. Waterfield Hundred Years of Astron. vii. 126 Although we cannot find the parallactic motions and hence the distances of individual stars, we can find the average parallactic motions and hence the average distances of large groups of stars.
1998 Proc. National Acad. Sci. U.S.A. 95 9/1 In ground-based parallax measurement, one can measure only the parallactic motion of a nearby star relative to the positions of fainter background stars in the same field.
parallactic telescope n. now historical a telescope mounted equatorially, used for measuring stellar parallax.
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1765 Philos. Trans. 1764 (Royal Soc.) 54 363 The parallactic telescope ought to be nearly of equal goodness with the transit telescope.
1870 J. Thomas Universal Pronouncing Dict. Biogr. & Mythol. 961/2 He [sc. Fraunhofer]..constructed the great parallactic telescope of Dorpat.
1935 M. S. Libby Attitude Voltaire to Magic & Sci. iii. 98 He [sc. Voltaire] explains..the measuring of the parallax of the fixed stars by Bradley using the parallactic telescope invented by Molineux and Graham in 1725.
This entry has been updated (OED Third Edition, June 2005; most recently modified version published online March 2022).
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adj.1630