cross-staff

[kraws-staf, -stahf, kros-]

noun

Astronomy.

plural

cross-staffs, cross-staves 

1. an instrument for measuring the angle of elevation of heavenly bodies, consisting of a calibrated staff with another shorter staff perpendicular to and sliding on it.

Word History and Origins

Origin of cross-staff¹

1400–50, for an earlier sense; late Middle English

Example Sentences

So Tycho worked out a table of corrections for the instrument from which he could read off the correct measurement corresponding to the incorrect reading obtained by the cross-staff for any observation he made.

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Although the details of the instruments he used are not crucial to my story, it is worth mentioning one, called a cross-staff or radius, which Tycho had made for him early in 1564.

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Cross-staff being used for surveying and astronomy—from the title page of Petrus Apianus, Introductio geographica, 1533.

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You can use a cross-staff, for example, to measure the angle between the horizon and the sun at midday.

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The cross-staff is merely one of a series of instruments, such as the quadrant and the sextant, designed for measuring angles by taking sightings.

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