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What The Night Sky Would Look Like From Inside A Globular Cluster

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Globular clusters are incredibly dense structures often featuring hundreds of thousands of stars packed into a relatively small space. So what would it be like to live inside such a thing? A team of astronomers recently created a simulation to find out.

All images by William Harris and Jeremy Webb; used here with permission.

For their simulation, astronomers William Harris and Jeremy Webb designed a hypothetical Earth-like world orbiting a single main-sequence star — but one located smack-dab in the middle of 47 Tucanae, a globular cluster located 16,700 light-years from Earth. This cluster packs 570,000 stars in an expanse of space that's a "mere" 120 light-years across.


Harris and Webb sent me a sneak-preview of an article that's set to appear in the July edition of Astronomy. Here's what they have to say about the remarkable perspective from an Earth-like world:

At the center, our planet would be surrounded by a few hundred stars per cubic light-year (several thousand stars per cubic pc), which is thousands of times the stellar density of the Sun's neighborhood in the Milky Way's suburbs. The typical distance from our hypothetical planet to the closest star, however, still would be substantial — about 0.05 light-year (0.015 pc). In our solar system, this would place it beyond the inner edge of the Oort Cloud of comets.

Unless the closest stars happen to be red giants, none of them would have angular diameters large enough to resolve with the human eye, so all the stars still would appear as points of light. Across the entire sky, inhabitants of our hypothetical world would see 10,000 stars brighter than 1st magnitude — compared with just 29 in Earth's sky — and more than a thousand brighter than Earth's most brilliant nighttime star, Sirius. The brightest suns would blaze at apparent magnitudes brighter than –9, or 100 times more luminous than Venus appears from Earth. More than 130,000 stars would shine brighter than 6th magnitude, the naked-eye limit, compared with 6,000 from Earth.

Although it might sound like lots of empty space still exists at the cluster's center, the prospects for doing astronomy from there would be discouraging. The biggest problem would be the sheer amount of light from all those stars. The cluster's suns would combine to give an average sky brightness some 20 times brighter than Earth's night sky at Full Moon (or about 16.7 magnitudes per square arcsecond). In other words, the darkest night our viewers would ever see would be a strange sort of twilight that possesses a kind of grainy texture unlike the uniform sheet of light we see on Earth. The galaxy's disk — already hard to see from Earth at Full Moon except from isolated locations — would be visible in the background but hard to study. Astronomers on our hypothetical planet likely would favor telescopes with small fields of view and excellent baffling against scattered light.


Incredible. Our night sky suddenly seems thoroughly inadequate. Makes me wonder what kind of cosmology or metaphysics an alien civilization would develop when raised inside such a structure.

Harris and Webb are both in the Department of Physics and Astronomy at McMaster University in Hamilton, Ontario. Harris is a professor who has studied globular clusters over his career; Webb is completing his Ph.D. thesis on the orbital dynamics of star clusters in large galaxies.

An alternate perspective from inside 47 Tucanae.

Astronomy will be making the simulation available next month, where you can position yourself from anywhere inside the cluster. So cool.