"polar axis" - Word of the Day from the OED

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polar axis, n.

DRAFT ENTRY June 2007

Brit. /plr akss/, U.S. /polr ækss/  [< POLAR adj. + AXIS n.¹] 

    1. Geogr. and Astron. The axis of rotation of the earth or other celestial object, passing through the two poles.

1724 J. SMEDLEY Petition to Duke of Grafton (title-page), One shivers with the Artick Wind, One hears the Polar Axis grind. 1814 J. PLAYFAIR Outl. Nat. Philos. II. I. ix. 179 Mars..is compressed at the poles, so that his equatorial diameter is to his polar axis as 16 to 15 nearly. 1939 E. D. LABORDE tr. E. de Martonne Shorter Physical Geogr. (rev. ed.) 9 Twice a year, at intervals of six months (June 21 and December 21), the straight edge of the sunlit portion [of the earth] makes an angle of 23° with the polar axis. 1984 C. R. KITCHIN Astrophysical Techniques v. 320 We..extend the polar axis, the equatorial and orbital planes of the Earth until these..meet the celestial sphere.

    2. Astron. An axis of an equatorially mounted telescope that is parallel to the earth's axis, and around which the telescope is turned to follow the apparent movement of stars resulting from the earth's rotation.

1753 Philos. Trans. 1751-2 (Royal Soc.) 47 163 When the great reflecting telescope..was nigh finished, it was proposed to support and direct it by means of a complicated machinery... This I strongly opposed in behalf of a polar axis. 1835 Mechanics' Mag. 24 210/2 The polar axis, of cast-iron, turning between the friction rollers.., and its lower part ending in a hardened steel pivot, turning in a block of..bell-metal. 1954 C. PAYNE-GAPOSCHKIN Introd. Astron. iii. 88 The instrument swings around an axis (the polar axis) directed towards the pole of the sky (and graduated in hour angles) and can pivot up and down perpendicular to the equator (in declination). 2003 J. SCALZI Universe ii. 28 An equatorial mount allows you to align your telescope with a celestial pole, so all you have to do is turn the telescope around the polar axis.

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