Look south for globular star cluster in May

Good morning, fellow travelers. This month is mostly going to be devoted to one object, the giant globular in the far southern constellation of Centaurus in these May late evenings.

Globular star clusters are giant balls of stars, all bound by each other’s gravity. Omega Centauri (catalogued as NGC 5139, see my photo) is the largest such object by far known to mankind. From our latitude in Boerne, just under 30 degrees north, it barely skims the treetops to the south for about 45 days before dipping below the horizon. In other words, it’s actually a Southern Hemisphere object that we just get a glimpse of for a few weeks a year.

If we had excellent dark skies to the south from here, we could see it as a fuzzy star with the naked eye. From my hometown of Abilene in the 1960s and early ‘70s, I could see it easily with the naked eye to the south at Buffalo Gap State Park.

From the Southern Hemisphere, it is big, bright, and overhead on clear dark nights. The accompanying 15-minute image run was taken just after midnight on April 3. I was frankly amazed with the detail my little imaging telescope could pull out of the southern haze and light pollution looking over San Antonio.

There are many smaller globular star clusters generally orbiting the central portion of our Milky Way galaxy. Some of their million-year orbits take them well outside the Milky Way proper.

Modern professional astronomers have come up with the theory lately that Omega Centauri isn’t a globular cluster at all but the remnants of a dwarf galaxy that has been tidally disrupted and taken into our galaxy except for the core. So, what we’re seeing may be the exposed core of an alien galaxy.

This giant is 230 light years in diameter and 17,090 light years distant from Earth. It contains a minimum of 10 million stars packed into that 230 light years. That means the average distance between stars is 0.1 light year or a 10th of a light year.

By comparison, in our neighborhood of the Milky Way, the average distance is 5 light years, and then there is usually only one that close. The nearest star system to Earth is 4.25 light years (Alpha, Beta and Proxima Centauri), a triple system. Those are Southern Hemisphere objects which we never see from south Texas.

Here is a mind-boggling thought. If we lived on a planet orbiting a star in Omega Centauri, we would never know darkness. Our “nightime” sky would be continually bathed with the light of hundreds of very bright, nearby stars. We would have evolved thinking that was normal and would have no conception of the vast darkness and blackness of normal space.

The gravity well of Omega Centauri would be so great that we would likely never have the ability to break free and see any other part of the universe. No doubt alien civilizations have lived and died inside globular clusters in this manner. If possible, they would have evolved defenses against the intense radiation caused by all those bright, nearby stars.

A 2008 study with the Hubble space telescope and the Gemini Observatory in Chile found a midsize black hole at the center and contains 40,000 solar masses.

There is one other similar size globular cluster, called Mayall II, orbiting the Andromeda Galaxy (M31). Interestingly, the Andromeda Galaxy, which is the nearest nondwarf galaxy to the Milky Way, has two large orbiting companion galaxies just as our galaxy does.

Ours are named the Large and Small Magellanic “Clouds” easily visible with the naked eye from the southern hemisphere. They look like the small, broken off parts of the southern Milky Way.

Now for a May event to watch for. Much of North America will witness a total eclipse of the moon on the evening of May 15. May’s full moon is known as the Flower Moon coinciding with spring in the Northern Hemisphere.

The entire surface of the moon will be inside the inner shadow, perhaps giving it a deep reddish color at maximum eclipse. Totality will run from 10:29 to 11:54 p.m. on May 15. Mid-eclipse will be 11:12 p.m.

One final item, mark July 23, 2022, on your calendar. There will be a city of Boerne public star party at City Lake that night, weather permitting. More information later.