From the June 2023 issue

Learn all about the constellation Ara the Altar

This small, often-overlooked constellation contains several observing treasures worth your while.
By | Published: June 7, 2023 | Last updated on June 13, 2023

NGC 6250
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))
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Key Takeaways:

  • Ara, an ancient Greek constellation documented in the 3rd-century-B.C. *Phaenomena*, is positioned directly beneath the tail of Scorpius. It is visible from May through July in the Northern Hemisphere, with optimal viewing south of 22° North latitude around June 10th.
  • Occupying 237.06 square degrees (0.575% of the celestial sphere), Ara ranks 63rd among 88 constellations in size, while achieving a higher rank of 34th in overall brightness.
  • The constellation hosts a variety of deep-sky objects, including several open and globular star clusters, the combination emission/reflection nebula NGC 6188, and the barred spiral galaxy NGC 6300.
  • Notable observational targets include the magnitude 5.3 globular cluster NGC 6397, ranked as the fourth-brightest in the sky and visible to the naked eye, and the magnitude 5.2 open cluster NGC 6193, also discernible without optical aid under dark conditions.
Key takeaways sponsored by The Space Store

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!

NGC 6188
NGC 6188 is a combination emission/reflection nebula. Even a 4-inch scope will reveal a faint haze measuring 20′ by 12′ that interacts with open cluster NGC 6193. Larger scopes will reveal a dark region separating the eastern and western halves. Gerald Rhemann
NGC 6300
Barred spiral galaxy NGC 6300 glows at magnitude 10.1 and measures 5.2′ by 3.3′. Of interest are the four 13th-magnitude foreground stars: two over the core, and one each on the northern and southern ends. (Credit: ESO/C. Snodgrass)
NGC 6397
As the sky’s fourth-brightest globular cluster (tied for that honor with NGC 6752 in Pavo), magnitude 5.3 NGC 6397 certainly would have earned a Messier designation if it were in the northern sky. Keen observers see it easily with their naked eyes as a fuzzy star. An 8-inch telescope at 200x reveals 50 stars.(Credit: Michael Sidonio)
NGC 6362
Globular cluster NGC 6362 glows at magnitude 7.5. Because it lies in a rich field of faint stars, it’s quite easy to spot. The cluster has a diameter of 10.7′ and responds well to high magnifications. Use 250x or more through an 11-inch scope. (Credit: ESO)
IC 4651
Magnitude 6.9 IC 4651 is a gorgeous open cluster with a rough arrowhead shape pointing west-northwest. Even a 3-inch telescope will resolve 50 points across its 12′ diameter that stand out nicely from the surrounding star field. (Credit: ESO)
NGC 6193
At magnitude 5.2, open cluster NGC 6193 is bright enough for sharp-eyed observers to spot beneath a dark sky without optical aid. This quarter-degree-wide stellar wedge, also known as Caldwell 82, contains two relatively bright stars and about a dozen faint ones. (Credit: Gerald Rhemann)
NGC 6352
Peer at globular cluster NGC 6352 through binoculars and you’ll see that it lies in a really bright star field. The cluster stands out well because it glows at magnitude 8.1. A telescope shows a hazy object with a slightly brighter core. (Credit: NASA)

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