position angle

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position angle

(PA; p.a.)

1. The direction in the sky of one celestial body with respect to another, measured from 0° to 360° in an easterly direction from north. It is used, for example, to give the position of the fainter component of a visual binary with respect to the brighter component.

2. The angle at which the axis of a planet or star, or some other line on a celestial body, is inclined to the hour circle passing through the center of the body; it is measured eastwards from 0° to 360° from north.

Position Angle

an angle on the celestial sphere between a direction given at some point and the hour circle through this point; it is measured counterclockwise from 0° to 360° from the northern sector of the hour circle. Position angles are used to determine the relative position of the components of binary stars and multiple systems and the directions of the proper motions of stars. They are measured with a position micrometer.

position angle

[pə′zish·ən ′aŋ·gəl]

(astronomy)

The angle formed by the great circle running through two celestial objects and the hour circle running through one of the objects.

In measuring double stars, the angle formed between the great circle running through both components and the hour circle going through the primary measured from the north through the east from 0 to 360°.

(navigation)

That angle of the navigational triangle at the celestial body having the hour circle and the vertical circle at its sides. Also known as parallactic angle.

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