NGC 6250 is an open cluster right at the Ara-Scorpius border. Small scopes show about a dozen stars in this magnitude 5.9 object, but an 11-inch instrument will let you see dozens more. The five brightest form a rough, wide M. (Credit: Adam Block (Data provided by Jose Joaquin Perez))
The constellation ARA (pronounced AIR-uh) the Altar was one of the “original” constellations of the Greeks. It appeared in Phaenomena, a 3rd-century-b.c. work by the Greek poet Aratus. He based it on a work written a century earlier by Eudoxus of Cnidus. The constellation’s position is easy to locate directly beneath the tail of Scorpius. Making an altar out of the stars is more difficult.
Ara is visible May through July in the Northern Hemisphere, the time Scorpius hangs directly in the south. Its center lies at right ascension 17h18m and declination –56°30′.
Ranking 63rd in size out of the 88 constellations, Ara covers 237.06 square degrees (0.575 percent) of the sky. And while its size is nearer to the bottom than the top of that category, it fares somewhat better (34th) in terms of overall brightness.
The best date to see Ara is June 10, when it stands opposite the Sun in the sky and reaches its highest point at local midnight. Your location will make a difference, however: The constellation is completely visible from latitudes south of 22° north and completely invisible from latitudes north of 45° north.
Although this star pattern isn’t huge or bright, it offers some worthy treats for observers. Among them are open and globular clusters, an emission nebula, and a couple nice galaxies. So, consider heading south if necessary to reach the Altar and all the under observed deep-sky objects it holds. Good luck!