18Feb2017

The False Southern Cross

False

The famous constellation Crux, the Southern Cross, is the jewel of the southern skies, the starting point for most observers who wish to learn the southern stars.

But in their search for Crux, many stargazers are tricked by the “False Cross”, a group of stars in the constellations Carina and Vela that resemble Crux.   The False Cross lies about 25 degrees west-northwest of the Southern Cross, and about 20 degrees north-northeast of the Large Magellanic Cloud. It’s not a constellation, merely an asterism of four stars: delta Velorum, kappa Velorum, iota Carinae, and epsilon Carinae (Avior).

The False Cross tends to grab the attention of new stargazers, possibly because it’s a little larger than Crux. (Many are surprised at the small size of Crux when they first see it… the long axis of Crux is just 6 degrees long). But here’s how to tell the difference: the False Cross has more of a diamond-shape, while Crux has more of a true cross (or kite) shape. Crux also has brighter stars, on average, and has two very bright stars alpha and beta Centauri to the southeast. Crux also has a fifth star, epsilon Crucis, between the stars Acrux and delta Crucis.

Grab a pair of binoculars and sweep the region around the False Cross. It is resplendent with fine open star clusters and emission nebulae. The cluster IC 2488 is a snap to find… it’s about halfway between kappa Vel and i Carinae, just east of the line joining the two stars. Here’s how to find the False Cross, and how to tell the difference from the real thing.

Locating The False Cross

At the lower edge of the Milky Way, about half way between the Cross and Canopus , is the “False Cross in Argo” which stands up at almost the s am e angle as the Southern Cross. itself. It is somewhat larger than and not quite as shapely as the Cross proper, from which it may be distinguished by the presence of two clusters of fine stars, one directly below the foot and the other to the right of the right arm. Parts of the Milky Way between the two crosses provide some of the most beautiful telescopic views in the sky. Source: One Minute Astronomer

http://www.oneminuteastronomer.com/wp-content/uploads/2012/02/False-Cross.jpg

The “False Cross” and the constellation Crux, the Southern Cross, as seen looking south in early March at 9 p.m. local time from 35S latitude

About The Southern Cross

The outstanding star formation and the one simplest to find in our southern skies is, of course, the Southern Cross, known as Crux. Around this constella­tion will be built our entire study of the southern skies. The Southern Cross can be seen throughout the year from all places at and south of Sydney ‘s latitude. It is formed by four main stars

The Southern Cross has been marked by observers in the Northern Hemisphere in pre-Christian times, and the four main stars were said to represent the four pagan virtues—Justice, Fortitude, Temperance and Prudence. Early Chris­tians naturally accorded it a religious significance, and some of the early emigrants to South America regarded it as a good omen planted before them in the sky as an emblem of their faith.

Like all constellations and other heavenly bodies, the Southern Cross also appears to alter its position in the skies; and observed at the sam e time-say 9 o’clock—each night, throughout the year, this change can be seen quite distinctly . In May it stands upright almost overhead to the south, in August it lies further to the west on its side pointing westwards, by November it stands on its head near the horizon and due south, and in February it lies on its side pointing to the east.

Next May it is back to its upright position again high overhead, thus com­pleting a circle in the southern sky. Always the head of the cross points out-wards. Observed at intervals during one night it will be seen to be following the sam e path, describing a circle in the sky like the hour hand of a clock travelling at half speed; but all the stars appear to complete a revolution in about four minutes less than a day.

Considered as a twenty-four-hour clock, then, the Cross gains about four minutes daily, which accounts for its being a little farther on each night round its clockwise circle. With this in mind, it is not difficult to tell the time by the Southern Cross. Source: Wonder Book of Knowledge

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