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parallax

[par´ah-laks]

an apparent displacement of an object due to change in the observer's position.

par·al·lax

(par'ă-laks),

1. The apparent displacement of an object that follows a change in the position from which it is viewed.

[G. alternately, fr. par-allassō, to make alternate, fr. allos, other]

Farlex Partner Medical Dictionary © Farlex 2012

par·al·lax

(par'ă-laks)

The apparent displacement of an object that follows a change in the position from which it is viewed.

[G. alternately, fr. par-allassō, to make alternate, fr. allos, other]

Medical Dictionary for the Health Professions and Nursing © Farlex 2012

parallax

Apparent displacement of an object viewed from two different points not on a straight line with the object.
binocular parallax The difference in angle subtended at each eye by an object that is viewed first with one eye and then with the other.
chromatic parallax Apparent lateral displacement of two monochromatic sources (e.g. a blue object and a red object) when observed through a disc with a pinhole placed near the edge of the pupil. When the pupil is centred on the achromatic axis (in some people the pinhole may have to be placed away from the centre of the pupil), the two images appear superimposed. The relative displacement of the two images becomes reversed when the pinhole is on the other side of that axis. This phenomenon is attributed to the chromatic aberration of the eye. See chromostereopsis; longitudinal chromatic aberration.
monocular parallax The apparent change in the relative position of an object when the eye is moved from one position to another.
motion parallax Apparent difference in the direction of movement or speed produced when the subject moves relative to his environment (Fig. P2). Example: when viewing the landscape through the window of a moving train near objects appear to move much more quickly than distant objects. See depth perception; stereopsis.
relative binocular parallax See stereoscopic visual acuity.

Fig. P2 An example of motion parallax

par·al·lax

(par'ă-laks)

The apparent displacement of an object that follows a change in the position from which it is viewed.

[G. alternately, fr. par-allassō, to make alternate, fr. allos, other]

Medical Dictionary for the Dental Professions © Farlex 2012

References in periodicals archive ?

Each one had been measured many times so that both proper motions and parallaxes could be determined.

The nearest stars: IS Glass, South African Astronomical Observatory

Note excessive horizontal parallaxes were introduced to some of these images when they were generated.

Visual fatigue reduction based on depth adjustment for DIBR system

It would be able to measure the parallaxes of infrared objects where that cannot be done now--in heavily obscured regions and in the center of our galaxy.

Star tracks

Multiple iterations of the above process converged on individual parallaxes for Venus and the Sun of 17.72 and 5.11 arcseconds, respectively (the expected values were 17.00 and 4.99 arcseconds).

Reliving history: the authors observed the 2012 transit of Venus to replicate experiments from past centuries

A new study published in 2007, which took into account an improved understanding of the spacecraft's motions, led key Hipparcos team member Floor van Leeuwen (Cambridge University, UK) to an improved catalog and a more accurate H-R diagram for the 17,502 stars whose parallaxes are known to better than 7%.

The H-R diagram's 100th anniversary: this year we celebrate the centennial of one of astronomy's cornerstone achievements

The accuracy of individual parallaxes will range from 20% for stars near the galactic center (26,000 light-years away) to a remarkable 0.001% for nearby dim stars.

Missions I Gaia launches to pinpoint a billion stars

Moreover, HST's parallaxes are "relative," meaning they're derived differentially against background stars within a small field, while Hipparcos's parallaxes are "absolute," the outcome of a global solution over the whole sky.

Hipparcos's star distances get better: the sphere of stars whose distances are known to 5% accuracy just grew from 200 to 600 light-years out

Radio observers are using the worldwide Very Long Baseline Array (VLBA) to measure parallaxes of a few objects to 10 microarcseconds, beating Hipparcos by a factor of 100.

Extreme parallax

As such, they could not be used to reveal parallaxes in the way Galileo --and Herschel--had intended.

The race to measure the cosmos

In 1973 Thomas Lutz and Douglas Kelker argued that star distances will be systematically underestimated when parallaxes are measured imperfectly.

Cosmological age crisis renewed?

Thus we want the parallaxes for each of the stars to be essentially identical, to the accuracy at which they can be observed.

Brocchi's cluster revealed

Parallaxes continue to be measured photographically today, chiefly by Ianna's group and by astronomers at the U.S.