INTRODUCTION

In September 1926, Helen Sawyer arrived at the Harvard College Observatory to work with the eminent astronomer, Harlow Shapley. It was the beginning of a distinguished career that lasted more than 65 years.

Helen was a native New Englander who received her early education in Lowell, Massachusetts. She then attended Mount Holyoke College with the intention of becoming a chemist. However, that plan was revised after she went on an expedition to observe a total solar eclipse in her junior year. It was a life-changing experience for her. As a result, she switched her major in chemistry to one in astronomy and never looked back. When she graduated, she was awarded a fellowship to go to Harvard.

Shapley was famous for his seminal research on the size and structure of the Milky Way galaxy. It was published a decade earlier when he was working at the Mount Wilson Observatory in California. By mapping the three-dimensional distribution of globular clusters over the sky, he had shown that the Sun was not at the centre of the Milky Way. In fact, it was far from it. With this breakthrough, he accomplished for our perception of the Galaxy what Copernicus had done for the Solar System centuries earlier.

In 1921, Shapley moved to the east coast to become director of the Harvard College Observatory. In making this transition, he gave up access to the clear California skies and the largest telescopes in the world. In return, he gained access to Harvard's extensive photographic plate collection that covered the entire southern sky. This included numerous globular cluster photographs which provided him with an opportunity to expand his research on establishing the size of the Milky Way. While Helen was at Mount Holyoke, she had developed a great interest in globular clusters; they were her favourite celestial objects. So it was decided that she was the ideal person to assist with the project.

As soon as she arrived at Harvard, Helen began to study the globular cluster plates. Then over the next three years, she co-authored a series of papers with Shapley. Their aim was to derive distances. In those days, the most accurate method for calculating cluster distances was to study their variable stars. Unfortunately, this was a complicated task that required a great deal of data and analysis. Because of this limitation, the method could be applied to only a small fraction of the 93 clusters in their sample. For the others, indirect methods had to be employed. This involved measuring general properties of the individual clusters as well as the brightnesses of their most luminous stars.

By the time Helen finished this work, she had become a world expert on globular clusters and in subsequent years she was often invited to write reviews on the subject. She also recognized the need to obtain more data on variable stars. Because of this, she set up her own program to observe globular cluster variable stars as soon as the opportunity arose. Another one of Helen's assignments while she was at Harvard was to compile a list of references for Shapley. In the course of this work, she realized that bibliographies were valuable resources for researchers and, for the duration of her career, she published catalogues and bibliographies.

After Helen completed her PhD in 1931, she moved to Canada with her husband Frank Hogg, whom she had met while she was at graduate school. They spent a few years at the Dominion Astrophysical Observatory in Victoria, British Columbia and then relocated to Richmond Hill, Ontario in 1935 when the University of Toronto's David Dunlap Observatory opened. At both institutions, she established a globular cluster observing program and continued observing until 1971. During this time, she published many research papers, reviews and reports that, along with her catalogues and bibliographies, were of fundamental importance to researchers in the field. In 1972, an international conference was held in Toronto to honour her contributions. It brought together observers and theorists and demonstrated the importance of research on variable stars in clusters for understanding stellar evolution and stellar pulsation.

Meanwhile, Helen's professional activities had greatly expanded. She was a highly respected and skilled administrator who, over the years, held leadership roles in numerous scientific organizations. In addition, she had developed an interest in communicating astronomy to a wider audience and this was the area where she had her greatest impact. She became well known through her weekly astronomy columns in the Toronto Star and her interviews for radio and television.

I first met Helen when I was an undergraduate at the University of Toronto in the early 1960s. For me, and other women of my generation, she was an important role model. In those days, the post World War II societal values prevailed. Successful women were expected to marry after graduation and seek fulfilment through the lives of their husbands and children. Helen showed us that women could have their own satisfying lives. I have a special memory from the summer of 1963 when Helen invited the female astronomy students to her home. She showed us slides from some of her travels. Among these were pictures from a 1958 visit to Samarkand in Central Asia where she visited the observatory of the 15th century astronomer Ulugh Beg. I was amazed. The evening had a profound effect on me. After that, Helen became my friend and mentor. Even now, she continues to inspire me.

All her life, Helen was a meticulous record keeper and when she died in 1993, her personal and professional papers were donated to the University of Toronto Archives. The collection comprises 90 boxes of correspondence, diaries, notes, photographs and slides. It is a valuable resource for anyone who would like to learn more about Helen's life and work.

In addition, there is a Helen Sawyer Hogg webpage on the website of the University of Toronto's David A. Dunlap Department of Astronomy and Astrophysics - https://www.astro.utoronto.ca/about/history/helen-sawyer-hogg/

Of particular interest on this page are tributes to Helen by some of her colleagues when the University of Toronto Southern Observatory was named in her honour in 1992.