April 18, 2019

AstroChallenge: Bagging Omega Centauri from Mid-Northern Latitudes.

Omega Centauri as seen from Arizona. (Image Credit: Mike Weasner/Cassiopeia Observatory).

The Magellanic Clouds. The Tarantula Nebula. Sure, the Southern Hemisphere skies have all the “good stuff…” but did you know that in the summer months, YOU may be able to nab one of its crowning glories? This week, we here at Astroguyz challenge observers in the southern part of the northern hemisphere to try and spot Omega Centauri, a fine globular cluster located in the constellation Centaurus about 15,800 light years distant. Also known as NGC 5139, this +3.7 magnitude gem beats out the best the northern hemisphere has to offer in the form of M3 and M13. At a declination of -47° 32.5’, it transits the southern sky at 5 degrees or higher for viewers south of 37° North latitude, roughly the latitude of Washington D.C. I’ve seen it from both the current Astroguyz HQ in Hudson Florida, and the site formerly known as the Very Small Optical Observatory in Vail, Arizona. Make sure you have clear skies and an uncluttered southern horizon to catch this gem. At a Right Ascension of 13 hours and 27.5 minutes, I always think of Omega Centauri as due south of the bright star Spica in the constellation Virgo. Can you spot it with binocs? The naked eye? Image it? The cluster transits around 10PM local for the month of June, and even this week’s 1st quarter Moon shouldn’t hamper efforts to spot it too much… let us know what you see!

(Cool extra credit for those in the extreme south; can you catch the top of the Southern Cross? OK, I’ve yet to accomplish this myself from US climes…)

The astronomy word of the week is Globular Cluster. These are immense swarms of stars, intermediate in size between dwarf galaxies and open clusters. These are also some of the most ancient structures in the universe known, dating in many cases from the 1st billion years of the universe’s existence. Omega Centauri is the largest known cluster of its kind, and hosts a bevy of Population II stars. What would a sky on a world within a globular cluster look like? Well, the stellar population density within such clusters sets average distance between star systems at about a tenth of a light year; compare that with the distance of about four light years to Alpha Centauri, the nearest star system to our own… such a night sky scene would be dappled with hundreds of stars, all brighter than Sirius. (Read Asimov’s classic Nightfall to appreciate such awesomeness)…

Wanna really spark a debate in astro-linguistics? It’s been suggested that the proper pronunciation of the term is GLOBE-ular as opposed to GLOB-ular… try bringing THAT one up at the next astronomy meeting and watch the slide-rules fly!


  1. Steve Kudlak says:

    Have you seen the Southern Cross from Florida? It in theory should be visible under good conditions from the Florida Keys. the co latitude for Key West ends up being 65 or 66 South Declination. I assume people in Florida see Canopus regularly. It can if you are at just the right place and time able to see it as a second magnitude star. The guy who wrote “Skywatchers of Ancient Mexico” claims that 1st or 0 magitude stars under ideal conditions are visible to the horizon. Here Omega nCenturi should be about 4 or 5 degrees above the horizon.

    Have FUN,
    sENDS steve

  2. David Dickinson says:

    Never seen the Southern Cross from Florida, but have heard folks make mention of seeing the very top star of the Cross from the Florida Keys.


  1. [...] observadores en el sur de los EE.UU. no se dan cuenta que los sitios del hemisferio sur como Omega Centauri , en la constelación de Centaurus son visibles en la noche baja hacia el sur en esta época del [...]

  2. [...] Though Nova Cen 2013 technically peeks above the southern horizon from the extreme southern United States, the viewing circumstances aren’t great. In fact, the nova only rises just before the Sun as seen from Miami in December, at 25 degrees north latitude. The Centaurus region is much better placed in northern hemisphere during the springtime, when many southern tier states can actually glimpse the celestial jewels that lie south, such as Omega Centauri. [...]

  3. [...] talking about Omega Centauri in the constellation Centaurus.  At a declination of -47 degrees south, it clears 5 degrees above [...]

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