Argelander

Today I’d like to introduce you to one of the famous historical figures in astronomy, Friedrich Wilhelm August Argelander. You just know he’s important because he has four names! Not only that, the crater Argelander on the Moon and the asteroid 1551 Argelander are named for him.

Argelander was important to astronomy in ways he could never have imagined. A lot of the things we know today, and many of the things we are still seeking answers to, Argelander was already working on in the 19th century. Friedrich Wilhelm August Argelander was a pioneer in astronomy.

Argelander was born March 22nd, 1799 in Memel, which at that time was in the kingdom of Prussia, now Lithuania. His father was a wealthy Finnish merchant and his mother was German. Not a lot is known about his early years, but he eventually came to study under the famous German mathematician and astronomer, Friedrich Bessel, and in 1822 he obtained a PhD at Königsberg University, famous for its School of Mathematics.

Argelander began his professional career in 1820 as an assistant in Bessel's Königsberg Observatory. A few years later, Bessel helped Argelander land a job as director of the Turku observatory in Finland and in 1828 he became professor of astronomy at the university there. Tragically, the observatory, and most of the university buildings, burned down in 1827 and Argelander began the design and construction of a new observatory in Helsinki, where the university was relocated. The new observatory was completed in 1832.

1836 he was appointed professor of astronomy at Bonn, where King Friedrich Wilhelm IV built Argelander an impressive new observatory. As it happens, the king and Argelander were actually old friends. In 1806, following Prussia's defeat by Napoleon, Friedrich Wilhelm, then the crown prince, had sought refuge in the Argelander home in Memel, East Prussia. It pays to have a rich father and friends in high places!

Argelander was very interested in the positions and motions of the stars, and in the direction the Sun and solar system were traveling through the stars. In 1837 he published his first results in a book, "About the Proper Motion of the Solar System", in which Argelander had come to the conclusion that he did not have enough data for the exact answers to his questions. This provided him with the incentive to begin mapping the exact positions of the stars in the Northern sky from 1852 on in Bonn, Germany, a monumental task before the use of photographic plates in astronomy.

Argelander's name is best known for this compilation, called the Bonner Dorchmusterung, the largest and most comprehensive of all the pre-photographic star catalogs. Under Bessel he had begun a survey of the sky from 15°S to 45°N. This was extended at Bonn to an area from 90°N to 2°S and when finally completed eleven years later, in 1863, it listed the positions of 324,198 stars down to ninth magnitude. Again, they did all this work without the use of photography…

Also in 1863, Argelander founded an international organization of astronomers named the Astronomische Gesellschaft, now the second oldest astronomical society after the Royal Astronomical Society.

Being a variable star enthusiast, I became interested in Argelander because he is generally considered the father of variable star astronomy. He was the first astronomer to begin a careful study of variable stars. One of them, epsilon Aurigae, is still a fascinating and challenging mystery to astronomers today.

At the time, only a handful of variables were known, and he was responsible for introducing the modern system of naming them using the capital letters R-Z. It was believed that variability was a rare phenomenon and that this would provide plenty of names for the variables yet to be discovered. In a few years this proved inadequate and the naming system was extended to double letters, and then a numbering system. Today, tens of thousands of variable stars are cataloged, with more being discovered all the time.

Argelander loved the stars, especially variable stars, and was one of the all-time great observers of the heavens. In 1844 he published "An Appeal to the Friends of Astronomy" in ‘Schumacher's Astronomical Year Book.’ This was translated to English and reprinted by Annie Jump Cannon, in Popular Astronomy in 1912.

“Therefore do I lay these hitherto sorely neglected variables most pressingly on the heart of all lovers of the starry heavens. May you become so grateful for the pleasure which has so often rewarded your looking upward, which has constantly been offered you anew, that you will contribute your little mite towards the more exact knowledge of these stars!

May you increase your enjoyment by combining the useful and the pleasant, while you perform an important part towards the increase of human knowledge, and help to investigate the eternal laws which announce in endless distance the almighty power and wisdom of the Creator! Let no one, who feels the desire and the strength to reach this goal, be deterred by the words of this paper.

The observations may seem long and difficult on paper, but are in execution very simple, and may be so modified by each one's individuality as to become his own, and will become so bound up with his own experiences that, unconsciously as it were, they will soon be as essentials.

As elsewhere, so the old saying holds here, "Well begun is half done," and I am thoroughly convinced that whoever carries on these observations for a few weeks, will find so much interest therein that he will never cease. I have one request, which is this, that the observations shall be made known each year. Observations buried in a desk are no observations. Should they be entrusted to me for reduction, or even for publication, I will undertake it with joy and thanks, and will also answer all questions with care and with the greatest pleasure.”

Yea, it’s a little wordy and flowery, but it’s obviously written by someone who loves observing and studying the stars.

The “Argelander Step Method” is a visual method of estimating the magnitude of a variable star. It involves comparing the variable with a comparison star of known constant magnitude, and assigning a step value that reflects the brightness of the variable as distinguished from that of the comparison star. Estimates of the form ‘A(3)V, V(1)B’ are the result, and the magnitude of the variable (V) can be calculated from the known magnitudes of the comparisons (A and B). This is very similar in practice to methods still used today by visual observers of variable stars.

Argelander died February 17th, 1875. But the body of astronomical knowledge that stands on the shoulders of this giant continues today, in the cataloging of the position and motion of the stars within our galaxy, and the study of variable stars, from supernovae and Cepheids used to determine the distances to far away galaxies to the transits of extra solar planets across the faces of stars. In 2006, the three astronomical institutes of the Bonn University were merged and renamed as the Argelander-Institut für Astronomie.

The lunar impact crater Argelander