Today the 69 jewel-like globular clusters that Harlow Shapley mapped to discover the shape of our Galaxy still yield new science and delight.
The heart of globular cluster M 13 “seethes with at least 100,000 stars” on the cover of Annals of the Deep Sky,Vol. 11 by Jeff Kanipe. M 13 was very important in Shapley’s discovery of our Galaxy.
From the Editor:
I am pleased to report on three recent projects by experts who are helping with the Harlow Shapley Project. Each Update shows how these rare and beautiful objects still reveal secrets of our Galaxy and the Universe. The last Update reports my meeting with Vatican astronomers who know another side of Shapley: his role in dialogues on how religion fits into the world of modern science.
Background: Globular clusters are aggregations of stars bound in round shapes by their mutual gravitational pull. Starting in 1893 on Harvard’s 13-inch telescope in Peru, Solon I. Bailey had found in globular clusters two kinds of variable stars: slow-period Cepheids and fast-pulsing RR Lyrae. In 1914 Bailey suggested to Shapley that he study them further with the 60-inch telescope at Mount Wilson.
Shapley - using Henrietta Swan Leavitt’s period-luminosity law and Ejnar Hertzsprung’s application of it - proceeded to measure distances to all the globular clusters he could find.
His papers from 1914 to 1918 revealed the 69 globular clusters formed a “skeleton” that must be the Galaxy. It was way bigger than anyone had thought and its center was from our sun in the constellation Sagittarius.
Globular clusters have remained important to astronomy. For starters they are the oldest stellar formations in the known universe. They are rare; Shapley’s 69 are about half of the well-established number of globular clusters today.
1. Important Shapley globular clusters in latest Annals guide
Astronomy author Jeff Kanipe describes four of Shapley’s 69 in the latest volume of his Annals series. Volume 11 covers myriad stars and deep sky objects in constellations starting with G and H (Gemini, Grus, Hercules, Horologium, and Hydra). The American Astronomical Society sponsors the A-to-Z Annals series, allowing the near-omniscient Kanipe to plough through “every corner of the known universe,” as its web page says. Throughout, Kanipe shares his encyclopedic knowledge in brief, readable profiles popular with amateurs, semi-pros, and general readers. 1/
Mighty M 13 in Hercules
M 13 in Hercules (NGC 6205) is one of the most impressive sights in the northern sky. The Hubble Space Telescope image on the book cover shows colors of old and some not-so-old stars, as well as the spaces between them.
In 1915 Shapley devoted an entire paper to 1,300 stars in M13, based on reviewing thousands of earlier sightings and new Mount Wilson data. He got the distance to M 13 ‘s Cepheid variables based on Leavitt’s law. He studied the RR Lyrae stars in M 13, which he could assume were at the same distance. So he made RR Lyrae another standard candle, or rung, reaching out to measure distances to globular clusters where no Cepheids could be seen.
Jeff Kanipe, author of the Annals of the Deep Sky series. Photo: American Astronomical Society.
Kanipe writes that in 1900 E.E. Barnard of Yerkes Observatory had found hot blue B-type stars in M 13. These blue stars helped Shapley lay out the color differences among stars in globular clusters - an important contribution. The blue stars became Shapley’s next rung outward to more globular clusters; they outlined an even larger galactic skeleton.
Three more clusters and one big dish
M 68 (NGC 4590) is in the constellation named for Hydra. The snake coils along the low northern sky under Hercules, who is attempting to slay it. Shapley found 28 variables in M 68. Most of them were RR Lyrae useful for his distance map
Stars give off their metals through time, so metal-poor stars are older; they are typically redder. The low metal content of M 68 was confirmed by P.T. Oosterhoff in 1939. M 68 is “primordial” from the early universe.”
Globular cluster M 68 in Hydra is a “seething globe of granular light” in this Hubble/ESA image.
Unique new image of M 92 combines the JWST resolving power in infrared to reveal stars on the outer fringes with HST’s image of the dense core. Credit for HST image: NASA, ESA, Gilles Chapdelaine; JWST image: NASA, ESA, CSA, Alyssa Pagan (STScI). The combined image processing was by Richard Berry for the Harlow Shapley Project. Full image is available on request.
M 92 (NGC 6341) Kanipe tells skywatchers that the M 92 globular cluster in Hercules is outshined by its neighbor M 13, but you should definitely take a look anyway! It is one of the brightest objects in the sky.
Like M 68 it has low, primordial metallicity, having given up most of its other elements long ago.
We are pleased to introduce this unique new image of M 92. It is the first of Shapley’s 69 from the James Webb Space Telescope (JWST).
The JWST and Hubble Space Telescope images was combined by Richard Berry with a Hubble Space Telescope image of its core. This Shapley globular cluster is yielding new science.
NGC 7006 (Caldwell 42). Shapley found this globular cluster to be the astonishing distance of 280,000 light years from earth; it was the farthest away in his “skeleton.” (This distance was revised along with all his galactic distances after 1930, when R. J. Trumpler showed that interstellar dust makes these objects look fainter than they are.)
NGC 7006 is part of the galactic halo or corona which Shapley discovered in 1939. 2/
NGC 7006 in the constellation Delphinius was the farthest from us of Shapley’s 69 globular clusters. Credits: Phil Plait, ESA/Hubble NASA
Arecibo radio telescope in Puerto Rico in 2018. The receiving dish was 1,000 feet across. Signals were sent from the transmitter slung 492 feet above the dish, The Arecibo Message sent in 1974 was omnidirectional but pointed at globular cluster M 13 in Hercules. Photo: Wiki
Arecibo Message aimed at M 13
The great globular cluster M 13 in Hercules was chosen as the target for the famous Arecibo Message sent November 16, 1974 from the radio telescope in Arecibo, Puerto Rico. The message was designed by the founders of SETI (Search for Extra-Terrestrial-Intelligence) Carl Sagan and Frank Drake and funded by the National Science Foundation.
All an alien needed was a receiver on the same band and then to be able to decode the strings of digits that earth-humans hoped would reveal their informative images of us. Kanipe points out, as others have, that the message would take 25,000 years to reach M 13 by which time the great globular cluster would have moved too far to be received by anyone there.
2. RR Lyrae aged very oddly over 120 years
Astronomer Horace A. Smith 3/ of Michigan State University, an expert on RR Lyrae variables, is a co-author on a Polish-led study of M 13’s evolution. Their new paper in Acta Astronomica dissects thousands of observations of ten RR Lyrae in M 13 over 120 years to find how each behaved. 4/ Astronomers have been using theoretical models of RR Lyrae evolution to estimate their ages. This study combines new CCD observations and archival data back to when Bailey and then Shapley began observations. (See Background.)
Data for V-8 RRab Lyrae in M 13 “showed an abrupt period decrease around 1970,” the authors write in Acta Astronomica, Credit: G. Kopacki, et al.
For these ten stars the study used all Charge Coupled Device (CCD) data from the Białków Station Observatory in Poland and from three US observatories. Fourier analysis was applied to standardize these data sets along with earlier observations.
Of the ten RR Lyrae, two (V7 and V 25) had period increases, making them redder and more evolved beyond theory predictions. One other (V 54) was bluer and younger than the model allowed. Four of the ten (V 9, V 31, V 34, V 36) have “rapid irregular period variations.” V 8 had an “abrupt decrease” which could not be attributed to evolution.
Horace A. Smith, astronomer and historian. Photo: Michigan State University
“The observed rates do not agree with predicted rates” in PISA, a principal model, the paper says. Odd behavior or “noise” has been found before. This thorough and back-looking study aimed to see if the noise would cancel out and if the “smooth evolutionary model” held up.
The study included Shapley’s data on RR Lyrae, then called “cluster variables,” in his big paper of 1915 on M13 and in his 1918 “Sixth Paper” where he mapped out the locations of all 69 globular clusters.
Helen Sawyer Hogg’s observations from the 1930s are included. In the 1920s at Harvard she worked with Shapley to update globular cluster data. She married Canadian Frank Hogg (also at Harvard) and continued this research in Canada at Dominion Astrophysical Observatory and David Dunlap Observatory.
3. New Tracking Database for Shapley's 69
Leila Belkora, teacher and author. Credit: National Association of Science Writers
Astronomy historian Leila Belkora is making a spreadsheet of the 69 globular clusters Shapley used to map our galaxy. The list will become an index linking to discoveries and news about each.
Dr. Belkora is the author of “Minding the Heavens: The Story of our Discovery of the Milky Way.” Despite its vast subject the book is manageable and constantly interesting - great for teachers and general readers. 6/
She has a PhD in astrophysics from the University of Colorado. She has taught physics, astronomy, and communication for engineers at the university level. Presently she’s completing a book about Robert Frost as an amateur astronomer.
New HSP database on “Shapley’s 69.”
4. Pope’s astronomer on science and faith
Br. Guy Consolmagno, S.J., presented his latest book A Jesuit’s Guide to the Stars, at a reception at the Apostolic Nunciature in Washington in February.
The Detroit native became as meteorite scientist with degrees from MIT. He then went to the University of Arizona in Tuscon, AZ, where he recalls being mentored by my aunt Mildred Shapley Matthews who edited books and papers there. 7/ He took orders as a Jesuit in 1989.
Since then, Br. Guy has produced popular books and podcasts on faith and science. He has special authority as Director of the Vatican Observatory at Castel Gandolfo, which the Pope has visited often, and of the Vatican Advanced Technology Telescope (VATT) outside Tuscon. 8/
Vatican Advanced Technology Telescope (VATT) in Arizona. The red color is from the setting sun and an infrared lamp lit at night. Jesuit’s Guide p. 99.
Br. Guy Consolmagno, S.J., Deborah Shapley, and Fr. Chris Corbally, S.J. at reception at Apostolic Nunciature, Washington, DC. D. Shapley Photo.
At the reception I met Father Chris Corbally, S.J., Director of the VATT. He told me he was active for years in the Institute on Religion in the Age of Science (IRAS). Shapley co-founded IRAS in the 1950s to organize dialogues between religious and scientific leaders.
Fr. Corbally recalled colleagues who attended these meetings on Star Island, NH, in the years Shapley came regularly. Fr. Corbally said: “What an amazing man!”
Shapley would refer to himself as “unchurched.” Yet his medals and prizes included the Pius XI Prize of the Pontifical Academy of Sciences which was awarded by Pope Pius XII on Dec 1, 1941.
What I Am Reading
I recall my grandfather leaving their wooded “farm” in Sharon, N.H. for the annual Star Island meetings. We never discussed religion. Now, as I trace his writing and work, I see he was filled with wonder and love for ….his god? People asked him: Who was his god? he was asked. He said it’s spelled N-A-T-U-R-E.
So from the shelf I took down my father’s copy of Science Ponders Religion, a 1960 collection of essays by several IRAS luminaries Shapley edited. 9/
In his Preface Shapley posed questions for science and religion. By religion I’m sure he meant all faiths - Unitarian, Jewish, Catholic, and the fundamentalists he knew from his farm boyhood in Missouri.
“Are the great religions, the most widely spread cults, on their way to extinction because of the rise of science and naturalistic philosophy?
“Or rather, do religions have a validity and a capacity to revise that provide a continuing light unto men’s feet?”
Special thanks to those who are exploring the questions Shapley raised and the answers he offered.
Cover of Shapley’s book he sent to us in Washington. He inscribed “To the P Street heathen. Harlow Shapley.”
Notes & Credits
1/ Kanipe, Jeff, Annals of the Deep Sky: A Survey of Galactic and Extragalactic Objects, Volume 11: Gemini, Grus, Hercules, Horlogium, Hydra. American Astronomical Society, 2024.
Volumes 1-11 are available through shopatsky.com.
https://jeffkanipe.wordpress.com
2/ Shapley, Harlow, Galactic and extragalactic studies, I. On the corona of stars around the galactic system. PNAS, 25(8):423-428.1939.
3/ Smith, Horace A., RR Lyrae Stars, Cambridge Astrophysics Series 27, Cambridge University Press, 1995,
2003 paperback at https://www.google.com/books/edition/RR_Lyrae_Stars/dMv_r82moCQC?hl=en&gbpv=1
H.A. Smith at MSU: https://directory.natsci.msu.edu/Directory/Profiles/Person/102072
H.A.Smith, “Bailey, Shapley and Variable Stars in Globular Clusters,” JHA TK 2000.
4/ Variable Stars in M13. IV. The RR Lyrae Variable Stars G. Kopacki1 , W. Osborn2 , H. Smith3 , A. Layden4, B. Pritzl5 and C. Kuehn6, Acta Astromica, v. 74.
Shapley papers cited: Shapley, H. 1915, Contributions of the Mount Wilson Solar Observatory, 116. and Shapley, H. 1918, ApJ, 48, 89.
5/ Citations of Papers I, II and III in the series.
Paper I is Osborn et al
6/ Belkora, Leila, Minding the Heavens: The Story of Our Discovery of the Milky Way, CRC Press, Taylor & Francis Group, Second Edition, 2021. https://www.leilabelkora.space.
7/ From 1970 to 1993 Mildred Shapley Mattews was at the University of Arizona’s Lunar and Planetary Laboratory. She was scientific editor of the Space Science Series, which extended to some 30 volumes in her tenure. Her memoir of her father Shapley’s Round Table (2021) is summarized and updated on this blog at
https://harlowshapley.org/blog/close-up-life-with-the-director .
8/ Consolmagno, Guy, S.J. A Jesuit’s Guide to the Stars: Exploring Wonder, Beauty and Science, Loyala Press, 2025. Earlier books include as co-author with Dan Davis Turn Left at Orion and Would You Baptize an Extraterrestrial?
Main site: https://vaticanobservatory.org.
9/ Shapley, Harlow, Ed. Science Ponders Religion. Appleton-Century-Crofts, 1960.