As soon as darkness falls this Easter weekend, step outside and look skyward. What is the most prominent and easiest star pattern to recognize?
If you live in the Northern Hemisphere, you only need to look overhead and toward the north where you will find the seven bright stars that comprise the famous Big Dipper. For most sky gazers, the Big Dipper is probably the most important group of stars in the sky. For anyone in the latitude of New York or at points northward, it never drops below the horizon. The Big Dipper is one of the most recognizable patterns in the sky and thus one of the easiest for the novice to find.
People in other parts of the world know these seven stars not as "the Dipper" but as some sort of a wagon. In Ireland, for instance, sky watchers recognize this pattern as "King David's Chariot," named for one of that island's early kings, and in France, it is the "Great Chariot." And in the British Isles, people widely recognize these seven stars as "The Plough." [See amazing photos taken by stargazers in April 2014]
Stargazers can use the Big Dipper to locate Polaris, the North Star. The two bright stars that mark the outer edge of the bowl of the Big Dipper make this possible. These two stars, Dubhe and Merak, are known as "the Pointers," because they always point to Polaris. Just draw an imaginary line between these two stars and stretch it out to about five times its length. It will ultimately hit a moderately bright star: Polaris.
The Southern Cross
Those in the Southern Hemisphere don't use the Big Dipper as their guide to the night sky, instead relying on the constellation known as Crux, the Southern Cross.
Sky watchers south of the equator (where the season is autumn), need only cast a glance toward the south, where they'll see the distinctive shape of the Cross hanging well up in the sky. To some, it looks more like a kite, though the Cross is outlined by four bright stars.
From top to bottom, Crux measures just 6 degrees — only a little taller than the distance between the Pointer stars of the Big Dipper. 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 so navigators often use it. 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 thought that Amerigo Vespucci was the first of the European voyagers to see the "Four Stars," as he called them, while on his third voyage, in 1501. Actually, Crux was plainly visible everywhere in the current United States some 5,000-years ago, as well as in ancient Greece and Babylonia. [Best night sky events of April 2014 (photos)]
According to Richard Hinckley Allen (1838-1908), an expert in stellar nomenclature, the Southern Cross was last seen on the horizon of Jerusalem about the time that Christ was crucified. But thanks to precession — an oscillating motion of Earth’s axis — through the centuries, the Cross shifted out of view, well to the south.
Immediately to the south and east of the Cross is a pear-shaped, inky spot, about as large as the Cross itself, looking like a great black hole in the midst of the Milky Way. When John Herschel first saw it from the Cape of Good Hope, South Africa in 1835, it is said that he wrote his aunt, Caroline, about this "hole in the sky." Indeed, few stars appear within this hole, and it soon became popularly known as the "Coalsack," initially thought to be some sort of window into outer space. Today, astronomers know that the celebrated Coalsack is really a great cloud of gas and dust that absorbs the light of the stars that must lie beyond it.
A number of flags have also depicted the Big Dipper and the Southern Cross. Crux appears on the flags of several different nations, while the Alaskan State flag features the Dipper.
Limits of visibility
Coincidentally, this time of year, the Southern Cross and Big Dipper both reach their highest positions in the sky at the same time: around midnight local time. To see Crux, one must go at least as far south as 25 degrees north latitude. That means heading to the Florida Keys in the continental United States, where you'll see the constellation just lifting fully above the southern horizon. A slightly better view is afforded to those living in Hawaii, where the Cross appears a few degrees higher.
For the Big Dipper, you must go north of 25 degrees south latitude to see it in its entirety. Across the northern half of Australia, for instance, you can now just see the upside-down Dipper virtually scraping the northern horizon about an hour or two after sundown. In fact, those latitudes experience just the opposite effect as those in north, temperate latitudes (like New York). In these northern spots, inhabitants see the Dipper at a similar altitude above the northern horizon on early evenings in late November or early December, except the Dipper appears right side up.
Editor's Note: If you have an amazing skywatching photo you'd like to share for a possible story or image gallery, please contact managing editor Tariq Malik at firstname.lastname@example.org.
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, Facebookand Google+. Original article on Space.com.
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Joe Rao is Space.com's skywatching columnist, as well as a veteran meteorologist and eclipse chaser who also serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Joe is an 8-time Emmy-nominated meteorologist who served the Putnam Valley region of New York for over 21 years. You can find him on Twitter and YouTube tracking lunar and solar eclipses, meteor showers and more. To find out Joe's latest project, visit him on Twitter.