In 1901, Heegaard's childhood stargazing experience matured in the form of a series of popular articles that appeared in a Danish weekly magazine. In book form, under the title ``Popular Astronomy'' (1902), it became very popular and it was later translated into Swedish and German. Moreover, it became the starting point for a long series of popular lectures on astronomy, often accompanied by small publications.
During his visit with Dehn in Kiel, Heegaard participated in professor Schur's seminar on astronomy, and also otherwise
``I had the opportunity to cultivate my old love, astronomy. In Copenhagen I had often wanted to to get this opportunity, at times I had even had plans to study astronomy. After my dissertation I went so far as to lecture on astronomy at Copenhagen Unversity. But this crossed Professor [of astronomy] Thiele's plans, and I never got any further. Especially, I never had the opportunity to learn observation skills. But here, I was met favourably by Professor Harzer, the Director of the Kiel observatory. On the one hand, I performed observations with the observer, Professor Kobold, using the big meridian instrument, along with a sister instrument in South Africa the largest on Earth. On the other hand, I worked with a Swedish astronomer, Dr. StrømgrenA year after Heegaard's visit to Kiel, in 1906, Professor Thiele retired from the astronomy chair at University of Copenhagen, and several friends urged Heegaard to apply.I recall an experience, which really throughout the years contributed to the cooling of my desire to be an observing astronomer. One starry night at around 2 - 3 o'clock I was sitting in the meridian house, assisting Professor Kobold. He would give the times for the star passages, and I would record them. Then he got tired and wanted to take a break. We were both looking through the slit in the roof where innumerable stars sparkled in the dark night. Then he suddenly said: `Eigentlich ein lächerliches Geschäft'. Here sat a man, who had reached all I longed for, the insight, the position, and one of the world's best instruments - and then basically he found the work `a ridiculous business'. I began to fear that it might turn out the same way for me.''
``Zeuthen spoke very diplomatically when he answered one of my most insistent friends: `Dr. Heegaard is probably the best judge of his own qualifications'. In that he was right. For although I did not have a bad standing concerning theoretical knowledge, I lacked sufficient experience in observation and I completely lacked scientific publications. It therefore never occurred to me to apply.''However, this did not mean that Heegaard gave up his interest in astronomy. He became a cofounder and the first chairman of the Astronomy Society in Denmark in 1916, and his popularizing lectures continued, also after he went to Norway. So did the small accompanying publications, including one called `The Childhood of Astronomy. Lectures for prisoners of war' published 1917 by University of Copenhagen and The Danish Red Cross and translated into French, Italian, Russian and German, [Hee1917]