CAYMAN ISLANDS ASTRONOMICAL SOCIETY
NEWSLETTER JUNE 2007
We will aim to meet this month on Monday, 18th June, 7.30.p.m. at Pedro Castle, weather permitting.
Crux, the Southern Cross will be visible for the rest of this month. On the night of the 18th, the constellation will be more upright than in the diagram above, hanging above the southern horizon.
Crux is the smallest constellation in the sky, but one of the most celebrated. The early Portuguese navigators saw it as a symbol of their faith, and the mystery of the unknown lent it an additional charm in the minds of those from whom the southern skies were hidden. There are other cross patterns formed by stars, but the distinguishing feature of the two bright pointers alpha and beta Centauri make Crux unmistakable.
Crux lies in a dense and brilliant part of the Milky Way, which makes the famous dark nebula known as the Coalsack striking in silhouette against the star background.
This is the head of the Emu to the native aborigines of Australia. The rest of the Emu is made from the dark lanes in the Milky Way.
Alpha Crucis was too far south to have been given an ancient name so Acrux is simply a combination of the A in alpha and Crux. Being of first magnitude (0.83), it is the 12th brightest star in the sky and 321 light years distant from us. Under high power, a telescope reveals it to be a binary system with two very similar B type stars having magnitudes of 1.33 and 1.73 separated by 4 arc seconds. With surface temperatures of around 27,000K they are highly luminous, the brightest 25,000 time more luminous than our Sun. In fact, the brighter star is itself a double, the two component stars orbit each other every 76 days but are too close to split with a telescope. So Acrux is a triple star system. A further, type B4, star lies 90 arc seconds away and may belong to the system as well. It has a similar proper motion - that is, its direction of motion through space - but is probably a more distant star that just happens to lie in the same direction.
NGC 4755 (k, kappa Crucis) is an open cluster of stars, that contains about 100 stars and is about 10 million years old. It lies some 7500 light years away and spans a 10 arc minutes field of view so filling a volume of space about 20 light years across. Lying close to Beta Crucis, it is easy to find and best seen with binoculars or a telescope at low power. It contains many highly luminous blue-white stars along with a central red supergiant that makes a beautiful colour contrast. It was named the Jewel box by Sir John Herschel who called it a "casket of variously coloured precious stones". It can easily be seen by the unaided eye as a star, and indeed was originally catalogued as such in pre-telescope times.
The three day crescent Moon will be very close to Venus and Saturn on viewing night, with Jupiter risen in the east.
NEWSLETTER JUNE 2007
We will aim to meet this month on Monday, 18th June, 7.30.p.m. at Pedro Castle, weather permitting.
Crux, the Southern Cross will be visible for the rest of this month. On the night of the 18th, the constellation will be more upright than in the diagram above, hanging above the southern horizon.
Crux is the smallest constellation in the sky, but one of the most celebrated. The early Portuguese navigators saw it as a symbol of their faith, and the mystery of the unknown lent it an additional charm in the minds of those from whom the southern skies were hidden. There are other cross patterns formed by stars, but the distinguishing feature of the two bright pointers alpha and beta Centauri make Crux unmistakable.
Crux lies in a dense and brilliant part of the Milky Way, which makes the famous dark nebula known as the Coalsack striking in silhouette against the star background.
This is the head of the Emu to the native aborigines of Australia. The rest of the Emu is made from the dark lanes in the Milky Way.
Alpha Crucis was too far south to have been given an ancient name so Acrux is simply a combination of the A in alpha and Crux. Being of first magnitude (0.83), it is the 12th brightest star in the sky and 321 light years distant from us. Under high power, a telescope reveals it to be a binary system with two very similar B type stars having magnitudes of 1.33 and 1.73 separated by 4 arc seconds. With surface temperatures of around 27,000K they are highly luminous, the brightest 25,000 time more luminous than our Sun. In fact, the brighter star is itself a double, the two component stars orbit each other every 76 days but are too close to split with a telescope. So Acrux is a triple star system. A further, type B4, star lies 90 arc seconds away and may belong to the system as well. It has a similar proper motion - that is, its direction of motion through space - but is probably a more distant star that just happens to lie in the same direction.
NGC 4755 (k, kappa Crucis) is an open cluster of stars, that contains about 100 stars and is about 10 million years old. It lies some 7500 light years away and spans a 10 arc minutes field of view so filling a volume of space about 20 light years across. Lying close to Beta Crucis, it is easy to find and best seen with binoculars or a telescope at low power. It contains many highly luminous blue-white stars along with a central red supergiant that makes a beautiful colour contrast. It was named the Jewel box by Sir John Herschel who called it a "casket of variously coloured precious stones". It can easily be seen by the unaided eye as a star, and indeed was originally catalogued as such in pre-telescope times.
The three day crescent Moon will be very close to Venus and Saturn on viewing night, with Jupiter risen in the east.
No comments:
Post a Comment