"With coal gone, oil gone, high-grade metallic ores gone, no species however competent can make the long climb from primitive conditions to high-level technology. This is a one-shot affair. If we fail, this planetary system fails so far as intelligence is concerned. The same will be true of other planetary systems. On each of them there will be one chance, and one chance only."
Because of the slow change in our orientation to the stars, the position of the Sun on the first the day of spring (the vernal equinox) slowly shifts westward around the sky, which also moves it around our calendar. That is why we refer to the effect as the precession of the equinox. The rate of the shift is 1 day every 71 years.
From the start of the building of the Stonehenge monument around 3,800 BC, to well past the building of the great pyramids in Eqypt in 2500 BC, a star named Thuban in the constellation Draco must have been perceived as the north star. Around the cave-dwelling mammoth-hunting time of 12,000 BC, the bright star Vega in the constellation Lyra was the north star, and will be again around the year 14,000 AD.
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