Crux the Southern Cross is the smallest of the 88 constellations in the sky. It was unknown to the ancient astronomers as Crux its four brightest stars were noted by Ptolemy as being part of Centaurus.
There are reports that it was known to Pliny as Thronos
Caesaris in honour of the emperor Augustus. It may have been named by someone
wishing to court favour from the emperor.
The Arab astronomer Al Biruni wrote that the stars could be
seen from Multan in India, one star was recorded as being named Sula, The Beam
of Crucifixion. This is a reference to the cross.
It’s invention as a constellation is often attributed to
Augustin Royer in 1679, however the constellation had been referred to for
about two hundred years before Royer, meaning that his claim to inventing the
constellation is not accurate.
As it became a separate constellation during the Middle Ages
it comes under the classification of a modern constellation.
There appears to be some suggestions that it was observed by
Amerigo Vespucci (1454 – 1512) during his voyage of 1501-1502, however the
first time that Crux appears separately on a star chart was one made by the Dutch map maker Petrus Plancius (1552
-1622) and the English maker of star globes Emery Molyneux (d1594) on a star
globe of 1592.
Not surprisingly there are four stars that form the shape of
the southern cross when Johann Bayer produced his Uranometria star atlas in
1603, he labelled these four stars as epsilon, zeta, nu and Xi Centaurus, today
we know these four stars as alpha, beta, gamma and delta Crux.
In 1624 Jakob Bartsch (c1600-1633) showed the constellation
separately from Centaurus. Bartsch married Johannes Kepler’s daughter Susanna
in 1630 and helped Kepler with some of his calculations.
The names of the stars in Crux are either modern, or they
don’t have any names.
Alpha or Acrux which is a 19th century name and has no ancient meaning. It has a magnitude of 0.8, it is B class star with a surface temperature of 22,500’C compared to the 5,800’C for the Sun. It lies at a distance of 320 light years.
Beta is a star of magnitude 1.2 lying 280 light years away
it’s another B class giant star also with a temperature of 25,000’ C
Gamma is 87 light years away and has a magnitude of 1.6 it’s
a red M giant class star with a temperature of 3,300, C. It is the nearest red
giant to the Sun.
Delta at magnitude 2.8 is the faintest of the four stars
that make the Southern Cross. It lies 345 light years away; it is a B class
star with a temperature of 22,000’C
The Kappa Crucis Cluster or NGC 4755, also known as the
Jewel Box (or Herschel’s Jewel Box), is an open star cluster in Crux. It is one
of the youngest clusters ever discovered, with an estimated age of only 14
million years. Kappa is one of the brightest members of the cluster.
The 19th century English astronomer Sir John Herschel
described the cluster as “a casket of variously coloured precious stones,”
which is how the cluster appears in a telescope and how it subsequently got the
name the Jewel Box.
To the naked eye, the cluster appears like a star near beta,
the brightest stars in the Jewel Box Cluster are super giants. The three
brightest stars got the nickname “traffic lights” because of their different
colours.
The cluster has a visual magnitude of 4.2 and contains about
one hundred 100 stars. It is approximately 6,440 light years distant from the
solar system.
The cluster can only be observed from the southern
hemisphere. It was discovered by the French astronomer Nicolas Louis de
Lacaille on his trip to South Africa in 1751-52.
The Coalsack Nebula is located about 600 light-years away.
This huge, dusky object 35 light years across was seen around 1500 by Ferdinand
Magellan on his trip around the world. It was called at that time Macula
Magellan or Magellan’s Spot.
The Coalsack like other dark nebulae, it is an interstellar
cloud of dust so thick that it prevents most of the background starlight from
reaching observers.
It forms a conspicuous silhouette against the bright, starry
band of the Milky Way and for this reason the nebula has been known to people
in the Southern Hemisphere for as long as our species has existed.
The Southern Cross appears on the national flags of
Australia, Brazil, New Zealand, Papua New Guinea and Samoa.
www.theramblingastronomer.co.uk
No comments:
Post a Comment