Tuesday 17th July 7:30 PM at Pedros Castle
CAYMAN ISLANDS ASTRONOMICAL SOCIETY
NEWSLETTER JULY 2007
The viewing session this month will be on Tuesday 17th, 7.30 p.m. at Pedro Castle.
Last months illustration showed, as well as the featured constellation Crux, Centaurus (Latin for centaur). One of the 48 constellations listed by Ptolemy, it counts also among the 88 modern constellations. This southern constellation is one of the largest in the sky. This half man, half horse marked the southernmost constellation visible to astronomers of classical times.
The constellation, as depicted above, represents the death of Lupus, the wolf, on the spear of a heavenly centaur. Early representations of the two constellations actually reveal the figure of a centaur holding a staff called the thyrsus and a wolf. The thyrsus is covered with ivy and grape vines and tipped with a pine cone. These are the ingredients of the godly drink called nectar. The she-wolf is Selene, the moon, who helps in the preparation of the drink.
Centaurus contains the closest star to the Sun, Alpha Centauri, 4.4 light years away. Alpha Centauri is also known as Rigil Kentaurus, from the Arabic meaning ‘centaur’s foot’. To the naked eye it appears as the third-brightest star in the sky, but a small telescope reveals it to be double, consisting of two yellow stars like the Sun. A third, much fainter companion star is called Proxima Centauri because it is slightly closer to us than the other two. Beta Centauri is called Hadar, from an Arabic name signifying one member of a pair of stars. Alpha and Beta Centauri mark the front legs of the centaur, and they act as pointers to Crux, the Southern Cross, which lies under the centaur’s rear quarters. Centaurus also contains the largest and brightest globular star cluster visible from Earth, Omega Centauri.
Gamma Centauri, Muhlifain, is a double star approximately 130 light years from Earth, which consists of two spectral type A0 stars each of apparent magnitude +2.9. For the resolution of the double star system a telescope of at least 15 centimeters in aperture is necessary. They have an orbital period of 83 years.
The star forms the hip or backside of the Centaur and is found directly north of the Southern Cross.
Saturn and Venus will be low in the west on viewing night, close to the crescent moon. Both will disappear from the night sky at months end, leaving brilliant Jupiter to shine alone.