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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeOct 31st 2013
    • CommentRowNumber2.
    • CommentAuthorTobyBartels
    • CommentTimeNov 1st 2013

    I added a bit more to the Idea section. This should be a familiar concept to anybody who's used light to observe the world.

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeNov 1st 2013

    Thanks, I like the bit about the birds!

    • CommentRowNumber4.
    • CommentAuthorTobyBartels
    • CommentTimeNov 1st 2013

    Unfortunately, Wikipedia (my source) didn't say which birds (or cite a source of its own).

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeNov 1st 2013
    • (edited Nov 1st 2013)

    One could go on and consider the stunning view of the celestial sphere which one has on a cloudness night in a remote place in, say, the African savannah. The heavenly sphere that the ancients saw is still with us, we just have to find a dark enough spot on Earth to see it. :-)

    • CommentRowNumber6.
    • CommentAuthorUrs
    • CommentTimeAug 6th 2015
    • (edited Aug 6th 2015)

    finally added a reference to celestial sphere (lecture notes which appeared today on the preprint server)

    • CommentRowNumber7.
    • CommentAuthorTodd_Trimble
    • CommentTimeAug 6th 2015

    I added Moebius transformation as a related concept, as the “heavenly sphere” had been mentioned there too.

    The celestial sphere can also been seen in the Australian outback on suitable nights. :-)

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