Sky & Telescope - July 2021 - 4

SPECTRUM

by Peter Tyson

A Tremendous Blaze

The Essential Guide to Astronomy
Founded in 1941 by Charles A. Federer, Jr.
and Helen Spence Federer

STAR CLUSTERS PLEASURABLY WORK YOUR BRAIN . As with cross-

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EDITORIAL
Editor in Chief Peter Tyson
Senior Editors J. Kelly Beatty, Alan M. MacRobert
Science Editor Camille M. Carlisle
News Editor Monica Young
Associate Editor Sean Walker
Observing Editor Diana Hannikainen
Consulting Editor Gary Seronik
Editorial Assistant Sabrina Garvin
Senior Contributing Editors
Dennis di Cicco, Richard Tresch Fienberg,
Robert Naeye, Roger W. Sinnott
Contributing Editors
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John E. Bortle, Ronald Brecher, Greg Bryant, Thomas
A. Dobbins, Alan Dyer, Tom Field, Tony Flanders, Ted
Forte, Steve Gottlieb, David Grinspoon, Shannon Hall,
Ken Hewitt-White, Johnny Horne, Bob King, Emily
Lakdawalla, Rod Mollise, James Mullaney, Donald W.
Olson, Jerry Oltion, Joe Rao, Dean Regas, Fred Schaaf,
Govert Schilling, William Sheehan, Mathew Wedel, Alan
Whitman, Charles A. Wood, Richard S. Wright, Jr.
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word puzzles, give them time, and satisfying surprises often await.
Consider the open cluster Messier 7 in Scorpius (see image on
page 38). Certain aspects jump out as soon as you have it in your
eyepiece: shape, size, differing magnitudes, how well the cluster
stands out from background stars. But dally a bit and you begin to discern
subtleties: suns of varying colors, dark dust lanes seemingly weaving between
the stars, asterisms you've heard of or invent yourself on the spot.
Sometimes the unexpected occurs. While on TravelQuest's annual observing trip to Costa Rica in 2017, I was enjoying M7 in my 10×42 binoculars when
the cluster suddenly popped into 3D, like a Magic Eye image. It almost felt like I
could project myself into its very midst. When I shifted my gaze to nearby M6,
the Butterﬂy Cluster, the sensation vanished, but
it returned the moment I swung back to M7.
Globular clusters can tickle your mind, too. On
that same trip, I lingered often on Omega Centauri, which many consider the ﬁnest globular of
all. But each viewing featured the same tease. As I
scribbled in my notebook while observing Omega
Cen one night, " Want to resolve stars more clearly
than can, like getting head around a new but elusive idea. Just out of reach, that clariﬁcation. "
S Panoramic Hubble Telescope view of 100,000 stars in
The cores of globular clusters appear so comthe core of Omega Centauri
pressed that they can fool you into thinking stars
there must collide all the time. The cores are crowded: As long-time S&T editor
Walter Scott Houston once wrote of Omega Cen, " If we were located inside this
cluster, we would see the night sky ablaze with many thousands of 1st-magnitude stars, and it would be twilight all night long. " (So much for stargazing.)
But in reality, space abounds in globular cores. The average distance between
any two stars in the heart of Omega Cen, for example, is about one-third of a
light-year, or roughly 3 trillion kilometers (2 trillion miles).
Throughout this special issue on star clusters, you'll ﬁnd articles on a variety
of subjects: how globulars formed billions of years ago (page 14); what exoplanets in open clusters can teach us about how planetary systems evolve (page 22);
how to photograph star clusters (page 28); and which open clusters we recommend observing in the summer sky (page 34).
In all these pieces, you can savor photos of star clusters that Houston once
called, while referring to the Double Cluster, " a tremendous blaze of scintillating suns. " While you're at it, be
prepared for a blaze of scintillating thoughts as well.

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SOCIETY
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Institute of Technology
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Kelsey Johnson, University of Virginia; Tereasa Brainerd,
Boston University; Hannah Jang-Condell, University of
Wyoming; Edmund Bertschinger, MIT

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Sky & Telescope - July 2021

Table of Contents for the Digital Edition of Sky & Telescope - July 2021