Alphard (or Alpha Hydrae), the Twenty Fifth star in the Nautical Almanac, is, at Magnitude 2, the brightest star in the constellation Hydra.
The modern constellation of Hydra is the largest segment of the sky, at 1303 degrees square. It is also the longest constellation at over 100 degrees in length. It is an ancient constellation, having been one of the most important asterisms in the science and legend of the Mesopotamian serpent-worshiping cultures of 4000-6000 years ago. The Greeks imagined Hydra as a curled water snake or a sea serpent. (It should not be confused with the constellation Hydrus). In Greek mythology, Hydra was a multiheaded snake that, when decapitated, grew multiple heads to replace the severed one. Hydra was finally killed by Hercules as part of his labors.
Alphard is a name derived from Arabic, "Suhail al-Fahrd" meaning "Glorious Solitary" due to its isolated position in the sky. Since there are no close by stars, and no other bright stars in Hydra, Alphard appears brighter and is easier to find, making it a very helpful star to navigators. It is also known as Cor Hydrae, "The Heart of the Sea-Snake."
Alphard glows a dull orange, meaning that it has left its Main Sequence. It is estimated at 400-500 million years old. It is 800 times as luminous as the Sun, has three times the mass of the Sun and fifty five times the Sun's radius, lying about 180 light years away from us. It burns at 7000 degrees F., 3000 degrees less than our Sun. Scientists have discovered that Alphard has a large amount of barium within its chemical make-up. This is unusual, and indicates that when Alphard left its Main Sequence and expanded it most likely swallowed up its companion white dwarf star or perhaps a huge gas giant planet.
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