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Crux: Difference between revisions
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[[Crux]] was visible to the Ancient Greeks; Ptolemy regarded it as part of the constellation [[Centaurus]]. It was entirely visible as far north as Britain in the fourth millennium BC. However, the precession of the equinoxes gradually lowered its stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes. By AD 400, most of the constellation never rose above the horizon for Athenians. <ref>[http://en.wikipedia.org/wiki/Crux Crux]</ref> | [[Crux]] was visible to the Ancient Greeks; Ptolemy regarded it as part of the constellation [[Centaurus]]. It was entirely visible as far north as Britain in the fourth millennium BC. However, the precession of the equinoxes gradually lowered its stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes. By AD 400, most of the constellation never rose above the horizon for Athenians. <ref>[http://en.wikipedia.org/wiki/Crux Crux]</ref> | ||
Like the Big Dipper ([[Ursa Major]] of the northern sky, the Southern Cross indicates the location of the pole and as such is often utilized by navigators. The longer bar of the Cross points almost exactly toward the south pole of the sky, which some aviators and navigators have named the "south polar pit" because, it is not marked by any bright star. According to the writings of Richard Hinckley Allen (1838-1908), an expert in stellar nomenclature, the Southern Cross was last seen on the horizon of Jerusalem around the time that Christ was crucified. But thanks to precession — an oscillating motion of the Earth's axis — the Cross ended up getting shifted out of view well to the south over the ensuing centuries. | Like the Big Dipper ([[Ursa Major]]) of the northern sky, the Southern Cross indicates the location of the pole and as such is often utilized by navigators. The longer bar of the Cross points almost exactly toward the south pole of the sky, which some aviators and navigators have named the "south polar pit" because, it is not marked by any bright star. According to the writings of Richard Hinckley Allen (1838-1908), an expert in stellar nomenclature, the Southern Cross was last seen on the horizon of Jerusalem around the time that Christ was crucified. But thanks to precession — an oscillating motion of the Earth's axis — the Cross ended up getting shifted out of view well to the south over the ensuing centuries. | ||
Immediately to the south and east of the Cross is a pear-shaped, inky spot, about as large as the Cross itself, that looks like a great black hole in the midst of the Milky Way. [[Crux]] is not visible north of +20° in the northern hemisphere, and it is circumpolar south of 34°S, which means that it never sets below the horizon. On the celestial sphere, Crux is exactly opposite the constellation [[Cassiopeia]]. It is the smallest constellation in the sky. <ref>[http://www.space.com/29445-southern-cross-constellation-skywatching.html Southern Cross]</ref> | Immediately to the south and east of the Cross is a pear-shaped, inky spot, about as large as the Cross itself, that looks like a great black hole in the midst of the Milky Way. [[Crux]] is not visible north of +20° in the northern hemisphere, and it is circumpolar south of 34°S, which means that it never sets below the horizon. On the celestial sphere, Crux is exactly opposite the constellation [[Cassiopeia]]. It is the smallest constellation in the sky. <ref>[http://www.space.com/29445-southern-cross-constellation-skywatching.html Southern Cross]</ref> | ||