The Jewel Box Cluster (NGC 4755), spiral galaxy M102, and globular cluster Palomar 5

June 23–30, 2016: The Jewel Box Cluster (NGC 4755) in Crux is an excellent target for naked-eye and binocular observers, spiral galaxy M102 (NGC 5866) in Draco offers small-telescope owners stunning views, and large-telescope owners can seek out globular cluster Palomar 5 in Serpens.
By | Published: June 23, 2016 | Last updated on May 18, 2023
This week’s small-telescope target, spiral galaxy M102, lies 4.1° south-southwest of magnitude 3.3 Iota (ι) Draconis.
Astronomy: Roen Kelly
Each week, Astronomy magazine Senior Editor Michael E. Bakich, a master at explaining how to observe, posts a podcast about three objects or events you can see in the sky.

Targets for June 23–30, 2016
Naked eyes:
The Jewel Box Cluster (NGC 4755)
Small telescope: Spiral galaxy M102 (NGC 5866)
Large telescope: Globular cluster Palomar 5

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Jewels on black velvet
This week’s naked-eye object is the fabulous Jewel Box Cluster, also known as NGC 4755, in the constellation Crux.

Many amateur astronomers consider the Jewel Box the sky’s finest open cluster. It’s not the biggest. It measures 10′ across. And it’s not the brightest. Actually, it’s the 12th-brightest open cluster. It shines at magnitude 4.2, making it a naked-eye object from a dark site. But the reason NGC 4755 stops so many observers in their tracks is its colorful stars.

Almost all open clusters contain hot, recently formed stars. Most of them are blue, but they appear white through a telescope because they’re not bright enough to trigger our eyes’ color receptors. The Jewel Box, however, contains about a dozen stars of various shades of blue, yellow, and orange.

French astronomer Nicolas Louis de Lacaille discovered NGC 4755 during his trip to South Africa in 1751-2. English astronomer Sir John Herschel’s eloquent 19th-century description led other astronomers to coin the popular name “Jewel Box.”

NGC 4755’s alternate proper name, the Kappa Crucis Star Cluster, does not derive from a single star because no star in the cluster is bright enough to have garnered such attention. So the designation “Kappa,” which usually would indicate a single star, instead refers to the entire cluster.

To find the Jewel Box, look 1° southeast of magnitude 1.3 Mimosa (Beta [β] Crucis). A 6-inch telescope and an eyepiece that yields a magnification of 50x may be the best combination with which to view NGC 4755. Through this setup, you’ll see nearly a dozen stars that exhibit color, 20 additional white stars, and a faint backdrop composed of some 200 cluster members.

Messier, or no?
This week’s small-telescope target is spiral galaxy NGC 5866 in Draco, and it always generates a question among observers. Is this Messier’s 102nd object? That depends on who you ask. Some astronomical historians argue that M102 is a duplicate observation of spiral galaxy M101 in Ursa Major. Others say the evidence points to this galaxy, NGC 5866.

Well, whether or not Messier meant NGC 5866 to be his 102nd entry, this lens-shaped galaxy shows up nicely through a 4-inch telescope as a bright streak with a brilliant center. It shines at magnitude 9.9 and measures 6.6′ by 3.2′. On the best nights, larger scopes reveal a thin dust lane extending almost as long as the galaxy.

To find NGC 5866, point your scope 4.1° south-southwest of magnitude 3.3 Iota (ι) Draconis.

Astronomy magazine Contributing Editor Stephen James O’Meara makes a good case that M102 is simply a more refined observation of M101. He therefore calls M102 the Fool’s Gold Galaxy because, if you think you’ve found it when you’re observing NGC 5866, the joke’s on you.

A nice large-scope test
This week’s large-telescope target is globular cluster Palomar 5 in Serpens. This faint object lies 9° west-northwest of magnitude 3.5 Mu (μ) Serpentis. You also can start at the bright globular cluster M5 and move 2.3° to the south-southwest.

Palomar 5 glows softly at magnitude 11.8 and measures 6.9′ across. It is the fifth entry on a list of only 15 mostly difficult-to-see globular clusters. German-born American astronomer Walter Baade discovered it in 1950, but it was American astronomer George Abell who gave them their “Palomar” designations. Astronomers discovered them on photographic plates taken during the first National Geographic – Palomar Observatory Sky Survey in the 1950s.

Seeing Palomar 5 is a good test of the darkness of your site and your patience. It’s a bit tough because this object has a low surface brightness. Through an 11-inch telescope, use an eyepiece that magnifies 75x. The globular cluster will appear as a subtle brightening against a darker sky. Larger telescopes make this observation much easier.

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