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Cosmic Challenge: NGC 1851

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Cosmic Challenge: NGC 1851


January 2024

Phil Harrington

This month's suggested aperture range:

Binoculars and 3- to 5-inch (7.6- to 13-cm) telescopes












NGC 1851


05h 14.1m

-40° 02.8'





I thought I'd welcome in the new year with a target that is not challenging due to its faintness, but rather due to its southern location far from any bright stars. NGC 1851 is a 7th-magnitude globular cluster in the constellation Columba, the Dove.


Above: Evening star map showing the location of this month's Cosmic Challenge.


Credit: Map adapted from Star Watch by Phil Harrington


Above: Finder chart for this month's Cosmic Challenge.


Credit: Chart adapted from Cosmic Challenge by Phil Harrington
Click on the chart to open a printable PDF version in a new window



Depending on your latitude, the toughest test may be finding a clear enough view to the south to spot it. NGC 1851 is located some 40° south of the celestial equator.  As a result, it never crests more than 20° above the southern horizon from most of North America . Thats undoubtedly why it was missed by Messier and the Herschels. NGC 1851 was first discovered by James Dunlop, a Scottish astronomer based in Australia on May 29, 1826.


Our southern hemisphere colleagues remark that they easily see NGC 1851 through 10x50 binoculars and that it is one of the showpieces of January and February skies.  Our view up north, however, is hampered by horizon-hugging haze and light pollution.  The result is merely a dim glimmer of the globular's true self.


The easiest way that I have found to locate Columba is to imagine a large equilateral triangle between Rigel, Sirius, and the dove's brightest star, Phact [Alpha (α) Columbae].  Each is separated from the others by between 23° and 26°.  Aim your binoculars or finderscope at Phact, and then look to its southeast for Wazn [Beta (β) Columbae] and to its southwest for Epsilon (ε) Columbae.  Shifting about a field due south of Epsilon should bring a right triangle of three 6th-magnitude stars into view.  The star at the triangle's right angle, SAO 195807, glows with a reddish tinge and is a little less than 2° to the east-northeast of NGC 1851.


NGC 1851 is a globular for all telescopes and all magnifications.  At 45x, my 4-inch (10.2-cm) refractor reveals an unresolved, nebulous glow punctuated by a brighter, almost starlike central core.  In many ways, it resembles the coma of a tailless comet.  But then, increase the magnification and that allusion begins to change.  At 143x, the edges of the cluster begin to take on a graininess, as if on the brink of resolution.  A 4-inch (10.2 cm) scope doesn't have quite enough oomph to take that final step, but upping the aperture just 2 inches (5 cm) will show some of NGC 1851's 13th-magnitude stars around its fringe.


Above: NGC 1851 through the author's 4-inch (10.2-cm) f/9.8 refractor.


Below: New Zealand CN member RMS82 took this image of NGC 1851 using a 6" (15.2 cm) f/5 Newtonian and a Player One Saturn-C SQR (IMX533) camera. Be sure to visit his CN profile page for full information on this as well as his other spectacular images.


NGC 1851 also challenges theories about globular cluster formation. Globulars typically consist of stars of similar ages, suggesting a common formation period. NGC 1851, however, challenges this trend by exhibiting stellar populations of varying ages. Additionally, the cluster is surrounded by a diffuse halo of stars. The exact origins of these features remain uncertain, but one hypothesis posits that NGC 1851 could be the result of the collision between two clusters within a dwarf galaxy. Following the merger, interactions with more massive galaxies may have stripped away the outer regions of the original host galaxy, leaving behind only the stellar nucleus and the observed halo. To learn more about this atypical globular, read the study The Halo+Cluster System of the Galactic Globular Cluster NGC 1851 by A.F. Marino, et al, published in the Monthly Notices of the Royal Astronomical Society, June 28, 2014.


Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's challenge.  Contact me through my website or post to this month's discussion forum.


Until next month, remember that half of the fun is the thrill of the chase.  Game on!

About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2024 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.


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