Exploring the Famous Southern Cross Constellation
The four main stars of the famous Southern Cross constellation are Acrux (Alpha Crucis), bottom; Becrux (Beta Crucis), left; Gacrux (Gamma Crucis), top; and Delta Crucis, right.
Credit: European Southern Observatory

In some strange and mysterious way, the four stars that comprise the constellation Crux — better known as the Southern Cross — have come to represent the lands that lie below the equator.

Indeed, travelers in the Southern Hemisphere eagerly look for their first glimpse of the Cross, as I did in April 1986 when I led a tour to Easter Island and the Chilean Andes for a view of Halley's Comet. Up until then, the Cross was always out of sight from my home location in the New York City area, hidden below the southern horizon. But that all changed when our tour group spent our first night on Easter Island, and at long last I could finally see the four stars of the famed Southern Cross.

Crux certainly looks like an almost perfect small cross, perhaps marred to a slight degree by a dim, superfluous fifth star. (Two of the main four stars, Acrux and Becrux, are of first-magnitude brightness.) [See Saturn's Rings and More: May 2015 Skywatching Video]

From top to bottom, Crux measures just 6 degrees — only a little taller than the distance between the pointer stars of the Big Dipper. (Reminder: Your clenchd fist held at arm's length is 10 degrees wide.) In fact, the Southern Cross is the smallest (in area) of all the constellations.

Like the Big Dipper of the northern sky, the Southern Cross indicates the location of the pole and as such is often utilized by navigators. The longer bar of the Cross points almost exactly toward the south pole of the sky, which some aviators and navigators have named the "south polar pit" because, unfortunately, it is not marked by any bright star.

It is believed that Amerigo Vespucci was the first European explorer to see the "Four Stars," as he called them, while on his third voyage in 1501. Yet, Crux was plainly visible everywhere in the United States some 5,000 years ago, as well as in ancient Greece and Babylonia.

According to the writings of Richard Hinckley Allen (1838-1908), an expert in stellar nomenclature, the Southern Cross was last seen on the horizon of Jerusalem around the time that Christ was crucified. But thanks to precession — an oscillating motion of the Earth's axis — the Cross ended up getting shifted out of view well to the south over the ensuing centuries.

Immediately to the south and east of the Cross is a pear-shaped, inky spot, about as large as the Cross itself, that looks like a great black hole in the midst of the Milky Way. Legend holds that, when Sir John Herschel first saw this feature from the Cape of Good Hope in South Africa in 1835, he wrote his Aunt Caroline about this "hole in the sky." [Stunning Photos of Our Milky Way Galaxy (Gallery)]

Indeed, few stars are seen within this hole, and it soon became popularly known as the "Coalsack." People initially thought the Coalsack was some sort of window into deep space, but today we know that it's really a great cloud of gas and dust that absorbs the light of the stars that must lie beyond it.

Interestingly, the Southern Cross has been depicted on the flags of several different antipodean countries.

Crux can be found on the national flags of Australia, New Zealand, Papua New Guinea, Samoa and Brazil. The New Zealand flag depicts only the four brightest stars of the Cross, while the banners of the other nations also include the faintest fifth star (known as Epsilon Crucis).

Additionally, Crux is not the only constellation that is represented on the Brazilian flag. This banner holds a total of 27 stars, each representative of a Brazilian state or its federal district. All of these stars are depicted on a globe, with their positions plotted for 20:30 local time on Nov. 15, 1889 over Rio de Janeiro, to commemorate the date when Emperor Dom Pedro II was deposed and Marechal Deodoro Da Fonseca declared Brazil a republic.

In addition to Crux, the stars on the flag are from eight other constellations: Canis Major, the Big Dog; Canis Minor, the Little Dog; Virgo, the Virgin; Scorpius, the Scorpion; Hydra, the Water Snake; Triangulum Australe, the Southern Triangle; Carina, the Keel of Argo, the Ship; and Octans, the Octant. A banner across the sky reads Ordem e Progresso, which means "Order and Progress" in Portuguese.

There are likely a number of readers who have never seen the Southern Cross and might wonder about how far they might have to travel in order to get a view of the constellation.

At this time of the year, Crux is reaching its highest position in the night sky right after sunset in late May and early June. To see Crux, one must go at least as far south as 25 degrees north latitude. For example, you could head to the Florida Keys, where you'll see it just lifting fully above the southern horizon. The Cross appears noticeably higher from Puerto Rico and the islands of the Caribbean, as well as Hawaii.

Admittedly, Crux is far from being the most beautiful of all the constellations; in fact it lacks the beauty of the much larger Northern Cross, known also as Cygnus, the Swan. And yet, the Southern Cross has made its mark on those who have seen it for the first time — one of the novel sights that can best be seen from the southern hemisphere.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.