Many cairns or quoits are in the shape of the star groups they represent. The shape of many stones shows the appropriate part of the heavens explicitly. Ancient earthworks also served astronomical purposes. Tumuli and barrows mark specific stars or nebulae. A cursus at a site may, e.g., mark the Milky Way. Earthwork mounds may form the shape of a celestial object, e.g. the Large Magellanic Cloud. The ancients - as shown on Megaliths.net - knew the southern skies and left us evidence carved in stone that they traveled as far as e.g. Africa, where we still find megaliths in the Central African Republic, megaliths now easily explained by geodetic survey and astronomy. That some ancient seafarers knew the southern heavens is recorded in an ancient legend from Sri Lanka, as found In Richard Hinckley Allen's book, Star Names. Quoting from my Ancient World Blog:
"Richard Hinckley Allen in his book, Star Names, Dover Publications, N.Y. 1997, reports of ancient legends that the southern stars were initially created by ancient seafarers to approximate the shape of Northern constellations in similar positions. Allen writes (p. 436) as follows:
"Before the observations of the navigators of the 15th and 16th centuries the singular belief prevailed that the southern heavens contained a constellation near the pole similar to our Bear or Wain; indeed it is said to have been represented on an early map or globe. Manilus wrote:
'The lower Pole resemblance bears
To this Above, and shines with equal stars;
With Bears averse, round which the Draco twines;'
and Al Biruni repeated the Sanskrit legend that at one time in the history of the Creation an attempt was made by Visvamitra to form a southern heavenly home for the body of the dead king, the pious Somadatta; and this work was not abandoned till a southern pole and another Bear had been located in positions corresponding to the northern, this pole passing through the island Lunka, or Vadavamukha (Ceylon). The Anglo-Saxon Manual made distinct mention of this duplicate constellation 'which we can never see.'...
And, quoting from Francisco Lopes of 1552: [our comment: the spelling is original!]
'Abowt the poynt of the Southe or pole Antartike, they sawe a lyttle whyte cloude and foure stars lyke unto a crosse with three other joynynge thereunto, which resemble oure Septentrion, and are judged to bee the signes or tokens of the south exeltree of heaven.'
What is referred to here is not known, for although the figure represented is that of the Southern Cross this constellation always is upright when on the meridian, and, as the observation was made in latitude 14° or 15°, its base star was plainly visible."