Astrophysik seit 1900 - Jubiläum von Karl Schwarzschild (1873-1916) und Ejnar Hertzsprung (1873-1967). Astrophysics since 1900 - Jubilee of Karl Schwarzschild and Ejnar Hertzsprung. E-Book

Gudrun Wolfschmidt

• Herausgeber: tredition
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Deutsch

Veröffentlichungsjahr: 2024

Beschreibung

Einleitend wird das Thema „Astrophysik seit 1900“ umrissen und die Entwicklung vom Ende des 19. Jahrhunderts bis zur Mitte des 20. Jahrhunderts wird in acht Kapiteln dargestellt. Bis zum 19. Jahrhundert basierte die klassische astronomische Forschung hauptsächlich auf auf der Messung von Stern- und Planetenpositionen zur Erstellung von Sternkatalogen. Um 1860 vollzog sich in der Astronomie eine Revolution. Anstatt nur die Richtung des Sternenlichts zu untersuchen, wurden erstmals auch die Quantität und Qualität der Strahlung untersucht. Dies war der Beginn der modernen (beobachtenden) „Astrophysik“; dieser Begriff wurde von Johann Karl Friedrich Zöllner (1834-1882). Die Astrophysiker begannen, die Eigenschaften der Himmelskörper mit physikalischen und chemischen Methoden zu untersuchen. Die neuen Themen waren Photometrie, Astrofotografie, Spektroskopie / Spektralanalyse und Sonnenphysik. Karl Schwarzschild (1873-1916) war der Pionier der theoretischen Astrophysik um 1900. Er führte neue theoretische Themen wie Sonnenphysik, Theorie der Sternatmosphären, Sternstruktur und Einsteins Allgemeine Relativitätstheorie. Ihm gelang der Durchbruch des Hertzsprung-Russell-Diagramms (HRD), das unabhängig voneinander von Ejnar Hertzsprung (1873-1967) 1905 und Henry Norris Russell (1877-1957) 1910/12 entwickelt wurde. Die HRD ist wesentlich für die Diskussion der Sternentwicklung. Der Beitrag von Markus Bautsch „Die von Johann Jakob Balmer (1825-1898) gefundenen Zahlenverhältnisse bei den Spektrallinien des Wasserstoffs“ ist der Rezeption dieser neuen Ideen (1884) gewidmet, die die Welt gleichermaßen in Erstaunen und und Verwirrung versetzte. Die Freundschaft des Mathematikers und Komponisten Hans Sommer (1837-1922) mit dem jungen Richard Strauss (1864-1949) führte 1893 zu einer Komposition unter Verwendung der Frequenzen der Balmerserie (Till-Eulenspiegel-Motiv). Xian Wu stellt Heinrich Kaysers (1853-1940) „Handbuch der Spectroscopie (1900-1934) und dessen Bedeutung für die Astrophysik“. Dieses achtbändige Werk wurde weltweit von Chemikern, Physikern und Astrophysikern enthusiastisch aufgenommen. Der Artikel „Karl Schwarzschild und Ejnar Hertzsprung in Potsdam (1910-1916)“ von Adriaan Raap ist ebenfalls dem Thema des Jubiläums 2023 gewidmet. Thematisiert wird Schwarzschilds Reise in die USA im Jahr 1910, wo er Henry Norris Russell (1877-1957) traf. Ein weiteres, etwas weniger bekanntes Thema ist die Meteorologie und die Navigation von Ballons und Zeppelinen, die 1914 zur Einrichtung einer Wetterstation in den belgischen Ardennen führte, wo Schwarzschild im Ersten Weltkrieg aktiv war. Der Artikel von Maik Schmerbauch beleuchtet „Hans Kienle (1895-1975) - Wissenschaftler zwischen Astrophysik und Politik im 20. Jahrhundert“. Der nächste Artikel von Stefan L. Wolff befasst sich mit Vertreibung und Emigration von Astrophysikern im Nationalsozialismus - insgesamt handelt es sich um 16 entlassene Wissenschaftler, ein Thema, das bisher kaum untersucht worden ist. Ralph N. & Dagmar L. Neuhäuser untersuchen „Die rasche Evolution von Beteigeuze durch die Hertzsprung-Lücke vom gelben zum roten Überriesen in historischer Zeit“. Abschließend berichtet Dietrich Lemke über „Erlebte Geschichte - Das James-Webb-Space-Telescope - Von der Idee zur Mission“.

Leseprobe

Astrophysik seit 1900 Jubiläum von Karl Schwarzschild (1873–1916) und Ejnar Hertzsprung (1873–1967)

Astrophysics since 1900Jubilee of Karl Schwarzschild (1873–1916)and Ejnar Hertzsprung (1873–1967)

Abbildung 0.1: Karl Schwarzschild & Ejnar Hertzsprung in Göttingen (1909)

Cod. Ms. K. Schwarzschild 23: 1,13 (Nachlass K. Schwarzschild; SUB Universität Göttingen)

Nuncius Hamburgensis

Beiträge zur Geschichte der Naturwissenschaften Band 59

Wolfschmidt, Gudrun (Hg.)

Astrophysik seit 1900

Jubiläum von Karl Schwarzschild (1873–1916) und Ejnar Hertzsprung (1873–1967)

Proceedings der Tagung des Arbeitskreises Astronomiegeschichte in der Astronomischen Gesellschaft in Berlin 2023.

Astrophysics since 1900 – Jubilee of Karl Schwarzschild (1873–1916) and Ejnar Hertzsprung (1873–1967)

Ahrensburg bei Hamburg: tredition 2024

Nuncius Hamburgensis Beiträge zur Geschichte der Naturwissenschaften

Hg. von Gudrun Wolfschmidt, Universität Hamburg, AG Geschichte der Naturwissenschaft und Technik (ISSN 1610-6164).

Dieser Titel wurde inspiriert von „Sidereus Nuncius“ und von „Wandsbeker Bote“.

Wolfschmidt, Gudrun (Hg.): Astrophysik seit 1900 – Jubiläum von Karl Schwarzschild (1873–1916) und Ejnar Hertzsprung (1873–1967). Astrophysics since 1900 – Jubilee of Karl Schwarzschild (1873–1916) and Ejnar Hertzsprung (1873–1967). Proceedings der Tagung des Arbeitskreises Astronomiegeschichte in der Astronomischen Gesellschaft in Berlin, Sept. 2023. Ahrensburg: tredition (Nuncius Hamburgensis – Beiträge zur Geschichte der Naturwissenschaften, Band 59) 2024.

Cover vorne und Frontispiz: Karl Schwarzschild & Ejnar Hertzsprung in Göttingen (1909), (Cod. Ms. K. Schwarzschild 23: 1,13, Nachlass K. Schwarzschild; SUB Universität Göttingen)Cover hinten: HRD (Riesen- und Zwergsterne) (CC3, HR-sparse-de.svg, Rursus)

AG Geschichte der Naturwissenschaft und Technik, Hamburger Sternwarte, Bundesstraße 55 – Geomatikum, 20146 Hamburg, Germany https://www.fhsev.de/Wolfschmidt/GNT/home-wf.htm, [email protected]

Dieser Band wurde gefördert von der Hans Schimank-Gedächtnisstiftung und dem Arbeitskreis Astronomiegeschichte in der Astronomischen Gesellschaft.

Das Werk, einschließlich seiner Teile, ist urheberrechtlich geschützt. Jede Verwertung ohne Zustimmung des Verlages und des Autors ist unzulässig. Dies gilt insbesondere für Vervielfältigungen, Übersetzungen, Mikroverfilmungen und die Einspeicherung und Verarbeitung in elektronischen Systemen. Die Publikation und Verbreitung erfolgen im Auftrag von tredition GmbH.

Verlag: tredition GmbH, An der Strusbek 10, 22926 Ahrensburg, Germany ISBN – 978-3-384-44634-3 (Softcover), 978-3-384-44635-0 (Hardcover), 978-3-384-44636-7 (e-Book), © 2024 Gudrun Wolfschmidt.

Inhalt

Cover

Halbe Titelseite

Titelblatt

Urheberrechte

Vorwort – Preface

Einführung: Astrophysik seit 1900 – zum Jubiläum von Schwarzschild und Hertzsprung

1.1 Introduction: The Rise of Astrophysics

1.1.1 Transition from Classical Astronomy to Observational Astrophysics

1.1.2 New Instrumentation for Astrophysics

1.1.3 Centers of Astrophysics until around 1900

1.1.4 New Observatory Layout – Astronomy Park

1.2 Biographical Notes on Karl Schwarzschild (1873–1916) – Places of Activity

1.3 Biographical notes on Ejnar Hertzsprung (1873–1967) – places of activity

1.3.1 Ejnar Hertzsprung and his Colour-Brightness Diagramme

1.4 Transition from Visual to Photographic Photometry

1.5 Theoretical Optics

1.6 Planning a Southern Observatory

1.7 Spectral Classification and Hertzsprung-Russell-Diagram (HRD)

1.8 Solar Eclipse Expedition (1905) and the Rise of Solar Physics

1.9 Theory of Stellar Structure

1.10 Analysing Stellar Spectra – Theory of Stellar Atmospheres

1.11 General Theory of Relativity (Tests, Schwarzschild Radius, Black Holes)

1.11.1 Einstein’s Three Tests for the General Theory of Relativity

1.11.2 First Solution of Einstein’s Equation – Schwarzschild Radius

1.12 Conclusion and Aftermath – Schwarzschild as Pioneer of Theoretical Astrophysics

1.13 Archive Material and Bibliography

1.13.1 Archive Material

1.13.2 Bibliography

Die von Johann Jakob Balmer gefundenen Zahlenverhältnisse bei den Spektrallinien des Wasserstoffs

2.1 Spektrallinien

2.1.1 Die Entdeckung der Absorptionslinien im Sonnenspektrum

2.1.2 Spektroskopische Messungen

2.1.3 Künstliche Lichtquellen mit Spektrallinien

2.1.4 Wellenlängenmessung mit Transmissionsgittern

2.1.5 Nachweis von Spektrallinien im Sternenlicht

2.1.6 Weitere Spektrallinien des Wasserstoffs

2.2 Die Balmer-Serie

2.2.1 Verallgemeinerung durch die Rydberg-Formel

2.3 Musikalischer Exkurs

2.4 Quantenphysik

2.4.1 Die Naturkonstante h

2.4.2 Weitere Wasserstoffserien

2.4.3 Das Bohrsche Atommodell

2.4.4 Die Schrödinger-Gleichung

2.5 Wasserstofflinien in der Astronomie

2.6 Literatur

Heinrich Kaysers „Handbuch der Spectroscopie“ (1900–1934) und dessen Bedeutung für die Astrophysik

3.1 Einleitung

3.2 Heinrich Kayser – der Meister der klassischen Spektroskopie

3.3 Kaysers Meisterwerk – Handbuch der Spectroscopie

3.3.1 Vorbereitungen

3.3.2 Handbuch der Spectroscopie Band I

3.3.3 Handbuch der Spectroscopie Band II

3.3.4 Handbuch der Spectroscopie Band III und Band IV

3.3.5 Handbuch der Spectroscopie Band V und Band VI

3.3.6 Handbuch der Spectroscopie Band VII und Band VIII

3.3.7 Fazit

3.4 Schlusswort

3.5 Literatur

Karl Schwarzschild and Ejnar Hertzsprung in Potsdam (1910–1916)

4.1 Introduction

4.1.1 The Scientific Curriculum Vitae of Karl Schwarzschild (1873–1916)

4.1.2 The Scientific Curriculum Vitae of Ejnar Hertzsprung (1873–1967)

4.2 Director of the Astrophysical Observatory in Potsdam

4.2.1 Problems with the appointment of Karl Schwarzschild

4.2.2 The Great Double Refractor – Combined guiding and photographic telescopes

4.2.3 The Comet-Fever of the year 1910

4.2.4 The empress and the crown princess visit the Great Refractor

4.3 Karl Schwarzschild as Balloon- and Zeppelin-aeronaut

4.3.1 Astronomical navigation with a Balloon-Sextant at night

4.3.2 The “Internationale Luftschiffahrt-Ausstellung”

4.4 The large Observatories of the United States

4.4.1 Atlantic Crossing with the s. s. “AMERICA”

4.4.2 Observatories and Institutes at the Eastcoast

4.4.3 Observatories and institutes at the Westcoast

4.4.4 The Mount Wilson Conference of the Solar Union, August 1910

4.5 Karl Schwarzschild during the World War I

4.5.1 The establishment of a Zeppelin weather station in Namur (Ardennes-Belgium)

4.5.2 The Heavy Artillery Staff of Major-General Johannes von Schabel

4.5.3 The Head Quarters during the Winter of 1915/16: Mulhouse and Stenay

4.5.4 “On the Gravitation on the Battlefield and in Spacetime”

4.6 Literatur

Hans Kienle (1895–1975) – Wissenschaftler zwischen Astrophysik und Politik im 20. Jahrhundert

5.1 Einleitung

5.2 Kindheit und Jugend

5.3 Ein Studium während des Ersten Weltkrieges 1915–1918

5.4 Wechsel an die Universität nach Göttingen

5.5 Die Machtübernahme der Nationalsozialisten

5.6 Heidelberg – DDR – Heidelberg: Kienles Zeit 1945 bis 1962

5.7 Ruhestand und Tod

5.8 Literatur

Vertreibung und Emigration von Astrophysikern im Nationalsozialismus

6.1 Literatur

Die rasche Evolution von Beteigeuze durch die Hertzsprung-Lücke vom gelben zum roten Überriesen in historischer Zeit

7.1 Literatur

Erlebte Geschichte – Das James-Webb-Space-Telescope – Von der Idee zur Mission

Links – Astronomie, Museen in Berlin

9.1 Allgemeine Links zur Astronomie und Astronomiegeschichte

9.2 Links zur Astronomie und ihrer Geschichte in Berlin

9.3 Museen in Berlin

Tagung des Arbeitskreises Astronomiegeschichte in Berlin 2023

10.0.1 SOC – Scientific Organizing Committee

10.0.2 LOC – Local Organizing Committee

10.1 Sonntag, 10. September 2023, 15 Uhr, Berlin AKAG Tagung – Exkursion: Archenhold-Sternwarte Berlin

10.2 Berlin, Montag, 11. September 2023

List of Participants – Astrophysik seit 1900 – AKAG Berlin 2023

Autoren

Nuncius Hamburgensis

Personenregister

Astrophysik seit 1900 - Jubiläum von Karl Schwarzschild (1873–1916) und Ejnar Hertzsprung (1873–1967)

Cover

Titelblatt

Urheberrechte

Einführung: Astrophysik seit 1900 – zum Jubiläum von Schwarzschild und Hertzsprung

Personenregister

Astrophysik seit 1900 - Jubiläum von Karl Schwarzschild (1873–1916) und Ejnar Hertzsprung (1873–1967)

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Abbildung 0.2: Brandenburger Tor Berlin

(Foto: Gudrun Wolfschmidt)

Vorwort – Preface

Astrophysik seit 1900 – Astrophysics since 1900

Wolfschmidt, Gudrun (Hamburg)

Astrophysik seit 1900 – Astrophysics since 1900 – this conference of the Arbeitskreis Astronomiegeschichte in der Astronomischen Gesellschaft took place in Bremen from 10–11 September 2023.1

Introduction: From classical astronomy to theoretical astrophysics

The topic, astrophysics since 1900, is outlined by way of introduction, and the development from the end of the 19th century to the middle of the 20th century is presented in eight chapters.

Until the 19th century, classical astronomical research was mainly based on measuring stellar and planetary positions for compiling star catalogues, and astronomers were mathematicians.

Around 1860, astronomy underwent a revolution. Instead of only studying only the direction of star light, the quantity and quality of radiation were studied for the first time. This was the beginning of modern (observational) “astrophysics”; this term was introduced by Johann Karl Friedrich Zöllner (1834– 1882). The astrophysicists began to investigate the properties of the celestial bodies with physical and chemical methods. The new topics were photometry, astrophotography, spectroscopy / spectralanalysis, and solar physics.

Astrophysics in the 1st half of the 20th century

The first article focuses on the 150th anniversary of Schwarzschild and Hertzsprung. Karl Schwarzschild (1873–1916) was the pioneer of theoretical astrophysics around 1900. He introduced new theoretical topics like solar physics, theory of stellar atmospheres, stellar structure, and Einstein’s General Theory of Relativity. He achieved the breakthrough of the Hertzsprung-Russell-Diagram (HRD), developed independently by Ejnar Hertzsprung (1873–1967) in 1905, and Henry Norris Russell (1877–1957) in 1910/12. The HRD is essential for the discussion of stellar evolution.

Schwarzschild was convinced that the interplay with other areas of exact sciences was of great importance for the development of astrophysics.

Ejnar Hertzsprung (1873–1967), after having studied studied chemical engineering, was interested in photochemistry. In 1905 and 1907, Hertzsprung published now classic articles Zur Strahlung der Sterne (On the Radiation of Stars) about his attempts to measure the luminosity of stars on the basis of their spectra. 50 years after Kirchhoff and Bunsen, the development of astrophysics reached a peak with Schwarzschild and Hertzsprung. Modern theoretical astrophysics began through the inclusion of important physical topics in astronomy.

The contribution of Markus Bautsch Die von Johann Jakob Balmer (1825–1898) gefundenen Zahlenverhältnisse bei den Spektrallinien des Wasserstoffs is dedicated to the reception of these new ideas (1884), which astonished and perplexed the world likewise. It was not until 1926 that the mystery of the Balmer series was solved with the help of quantum mechanics.

Very interesting is the information that through the friendship of the mathematician and composer Hans Sommer (1837–1922) in the early 1890s with the young composer Richard Strauss (1864–1949) created a composition that used the frequencies of the Balmer series in 1893 to create the pitches of a composition (Till-Eulenspiegel motif).

Xian Wu presents Heinrich Kayser’s (1853–1940) “Handbuch der Spectroscopie” (1900–1934) und dessen Bedeutung für die Astrophysik (“Handbook of Spectroscopy” (1900–1934) and its significance for astrophysics). This eightvolume work was enthusiastically received and favourably reviewed worldwide – by chemists, physicists and especially astrophysicists. This is characterised in the article by impressive quotes.

The article Karl Schwarzschild and Ejnar Hertzsprung in Potsdam (1910– 1916) by Adriaan Raap is also dedicated to the topic of the 2023 anniversary. Schwarzschild ’s trip to the USA in 1910 on the occasion of the International Solar Union meeting in Los Angeles is interesting. He not only visited all the major observatories, but in particular met Henry Norris Russell (1877–1957) at Princeton University, to whom he reported on Hertzsprung’s research, which pointed to a relationship between the luminosity and colour temperature of a star, which eventually led to today’s Hertzsprung-Russell diagram. Another, somewhat less well-known topic is meteorology and navigation of balloons and zeppelins, which led to a weather station in the Belgian Ardennes in 1914, where Schwarzschild was active in the First World War. However, he also remained constantly connected to current physics, and made remarkable contributions to Einstein’s general theory of relativity.

The article by Maik Schmerbauch sheds light on Hans Kienle (1895–1975) – Scientist between astrophysics and politics in the 20th century, based on archive material. The stages of his scientific life in various observatories took place under different political systems.

The next article by Stefan L. Wolff deals with displacement and emigration of astrophysicists under National Socialism – a total of 16 dismissed scientists, a topic that has hardly been investigated so far.

Modern Astrophysics

Ralph N. & Dagmar L. Neuhäuser investigate The rapid evolution of Betelgeuse through the Hertzsprung gap from a yellow to a red supergiant in historical times (Die rasche Evolution von Beteigeuze durch die Hertzsprung-Lücke vom gelben zum roten Überriesen in historischer Zeit). Historical reports on the colours of stars are also compiled and critically evaluated. Due to the colour change of Betelgeuse to a red supergiant in the last millennia, the mass of Betelgeuse can be precisely determined by the historically documented colour change – and thus also its remaining lifetime until the supernova in only about 1.5 million years.

Finally, Dietrich Lemke reports on Experienced history – The James Webb Space Telescope – From idea to mission (Erlebte Geschichte – Das James-Webb-Space-Telescope – Von der Idee zur Mission).

Excursion

It was a successful conference, complemented by a visit to the Archenhold Observatory in Berlin-Treptow, founded in 1896 by Friedrich Simon Archenhold (1861–1939), cf. p. 205. The impressive large 68 cm-refractor (21 m focal length), the giant telescope, made by Steinheil of Munich, and by C. Hoppe of Berlin, is the longest fully movable refracting telescope in the world.

Figure 0.3: An observational Hertzsprung-Russell diagramme with 22,000 stars plotted from the Hipparcos Catalogue and 1,000 from the Gliese Catalogue of nearby stars. One recognizes clearly the main sequence, the white dwarfs, and the giants.

(CC2.5, Richard Powell)

1 Website of the conference of the AKAG: https://www.fhsev.de/Wolfschmidt/ events/akag-berlin-2023.php. There you will also find the link to the Booklet of Abstracts: https://www.fhsev.de/Wolfschmidt/events/pdf/ Booklet-AKAG-Berlin-2023-Abstract+Cover.pdf.

Abbildung 1.1: Karl Schwarzschild (1873–1916), pioneer of astrophysics, and Black Hole with accretion disk

(© Leibniz-Institut für Astrophysik Potsdam (AIP))

Einführung: Astrophysik seit 1900 – zum Jubiläum von Schwarzschild und Hertzsprung

Gudrun Wolfschmidt (Hamburg)

Abstract: Astrophysics since 1900 – Jubilee of Schwarzschild and Hertzsprung

Karl Schwarzschild (1873–1916) began his astrophysical studies in Strasbourg in the field of variable stars. At the Kuffner Observatory in Vienna, he created photographic photometry. In Munich he devoted himself to the orbit determination of spectroscopic binaries and stellar statistics. As director of the Göttingen Observatory in 1901, he started theoretical optics and instrument development. Inspired by the total solar eclipse in Algeria (1905), he began working on solar physics, which led him to the theory of stellar atmospheres in 1906. As director of the Potsdam Astrophysical Observatory (1909 to 1916), Schwarzschild was particularly concerned with the emerging General Theory of Relativity.

Ejnar Hertzsprung (1873–1967), former professor in Göttingen from 1909, recognised that “giant stars” and “dwarf stars” can occur in stars with the same surface temperature, and as early as 1905 he conceived a colour-magnitude diagramme – decisive for stellar evolution. Henry Norris Russell (1877–1957) learned of this through Schwarzschild in 1910, and presented his diagram in 1912. Fifty years after Kirchhoff & Bunsen (1859), the development of astrophysics reached a climax with Schwarzschild and Hertzsprung; modern theoretical astrophysics began by incorporating important physical subfields into astronomy.

Zusammenfassung

Karl Schwarzschild (1873–1916) begann seine astrophysikalischen Studien in Straßburg auf dem Gebiet der Veränderlichen Sterne. In der Wiener Kuffner-Sternwarte schuf er die photographische Photometrie. In München widmete er sich der Bahnbestimmung spektroskopischer Doppelsterne und Stellarstatistik. Als Direktor der Sternwarte Göttingen 1901 widmete er sich der theoretischen Optik und Instrumenten-Entwicklung. Angeregt durch die Sonnenfinsternis in Algerien (1905) begann er mit Sonnenphysik, was ihn ab 1906 zur Theorie der Sternatmosphären führte. Als Direktor des Astrophysikalischen Observatoriums Potsdam (1909 bis 1916) beschäftigte sich Schwarzschild besonders mit der gerade entstehenden Allgemeinen Relativitätstheorie.

Ejnar Hertzsprung (1873–1967), ab 1909 a.o. Professor in Göttingen, erkannte er, dass bei Sternen gleicher Oberflächentemperatur „Riesensterne“ und „Zwergsterne“ auftreten können und konzipierte bereits 1905 ein Farben-Helligkeits-Diagramm – entscheidend für die Sternentwicklung. Henry Norris Russell (1877–1957) erfuhr durch Schwarzschild 1910 davon und stellte sein Diagramm 1912 vor. 50 Jahre nach Kirchhoff und Bunsen (1859) erreichte die Astrophysik seit 1900 mit Schwarzschild unter Mitwirkung von Hertzsprung einen Höhepunkt; durch Einbeziehung wichtiger physikalischer Teilgebiete in die Astronomie begann die moderne theoretische Astrophysik.

1.1 Introduction: The Rise of Astrophysics

Until the 19th century, classical astronomical research was based on measuring stellar and planetary positions for compiling star catalogues, in addition, since Newton’s gravitational theory also celestial mechanics, and astronomers were mathematicians. Around 1860, astronomy underwent a revolution. Instead of only studying the direction of star light, the quantity and quality of radiation were studied for the first time. This was the beginning of modern (observational) “astrophysics”. The astrophysicists began to investigate the properties of the celestial bodies with physical and chemical methods. The new topics were photometry, photography, spectroscopy/spectralanalysis, and solar physics.

The next step was the introduction of theoretical astrophysics around 1900. Karl Schwarzschild (1873–1916), born 150 years ago (jubilee 2023), started with observational astrophysics by introducing photographic photometry. With his pioneering research as director of Göttingen and Potsdam observatories, he introduced new theoretical topics like solar physics, theory of stellar atmospheres, stellar structure, and Einstein’s General Theory of Relativity. He achieved the breakthrough of the Hertzsprung-Russell-Diagram (HRD), developed independently by Ejnar Hertzsprung (1873–1967) in 1905, and Henry Norris Russell (1877–1957) in 1910/12. The HRD is essential for the discussion of stellar evolution. Modern theoretical astrophysics began through the inclusion of the important new physics (quantum theory) in astronomy.

1.1.1 Transition from Classical Astronomy to Observational Astrophysics

This topic was introduced and discussed by me since 2008, when I organized the ICOMOS conference Cultural Heritage of Astronomical Observatories – From Classical Astronomy to Modern Astrophysics in Hamburg. Here I would like to give only a short summary.

The emphasis in classical astronomy was on astrometry, timekeeping, especially for navigation, and surveying, and providing the time to the public clocks as well as to the timeballs, celestial mechanics, calculation of ephemeris and calendars. The most important topic of research until the first half of the 19th century was positional astronomy with meridian circles for compiling star catalogues by the observation of star transits with meridian circles.

Around 1860 astronomy underwent a revolution. In the context of “classical astronomy”, only the direction of star light was studied. In the 1860s quantity and quality of radiation were studied for the first time. This was the beginning of modern “astrophysics”. Simon Newcomb (1835–1909) wrote: “that the age of great discoveries in any branch of science had passed by, yet so far as astronomy is concerned, it must be confessed that we do appear to be fast reaching the limits of our knowledge.” (Newcomb 1888). But he was wrong. In the second half of the 19th century a new, revolutionary branch of astronomy began to be practised – the “New Astronomy” – as Newcomb later called it, in contrast to positional astronomy.

The main topic of research had crossed over from classical astronomy to the new astrophysics. Concerning the change of the research field, Johann Karl Friedrich Zöllner (1834–1882) introduced the term “astrophysics” in 1865. Instead of combining astronomy with mathematics with compiling large star catalogues and the calculation of orbits of the planets and comets, astronomers – or better astrophysicists – began around 1860 to investigate the properties of celestial bodies with physical and chemical methods.

The new topics were photometry (1860), astrophotography (1839, 1880s), spectroscopy/spectral analysis (Fraunhofer 1814, Kirchhoff & Bunsen 1859), and solar physics. In the laboratory, the collected data were analysed and the photographic plates are measured. Julius Scheiner (1858–1913), one of the first professors at Astrophysical Observatory Potsdam, wrote about the research topics of astrophysics in 1890:1

“There can be no doubt that spectral analysis occupies the first place here and will continue to do so for the foreseeable future, all the more, so as the latter research has opened up a new field of observational activity that promises to yield extensive results in the future.”2

Astrophysics started with amateur astronomers in private observatories. Seven pioneers of astrophysics can be presented: William Huggins (1824–1910), and Joseph Norman Lockyer (1836–1920) near London, Angelo Secchi (1818–1878) in Rome, Pierre Jules César Janssen (1824–1907) in Paris, Nikolaus von Konkoly (1842–1916) in O’Gyalla, Hungary, and in addition the two early professional astrophysicists in German countries: As the cradle of astrophysics, the Observatory Bothkamp near Kiel (1869–1914) in the middle of a lake (IAU code 603, IAU List OAH: id 146) should be mentioned. Hermann Carl Vogel (1841– 1907), scholar of Johann Karl Friedrich Zöllner (1834–1882), Professor for Astrophysics in Leipzig, started his career here, before he became director of the first Astrophysical Observatory Potsdam, Telegraphenberg (1874), 1882 to 1907.

1.1.2 New Instrumentation for Astrophysics

This new field of astrophysics caused, and was caused by, new instrumentation: spectrographs and object lens prisms, instruments for astrophotography (portrait lenses, astrographs), photometers for measuring the brightness of stars (starting with the visual Zöllner comparison photometer in 1860, later photographic and photoelectric photometry), solar physics instruments (since 1868, photoheliograph, spectroheliograph, later coronograph), and laboratory equipment for analysing the photographic plates and spectra (cf. blink comparator, spectrum comparator, measuring devices for getting the stellar magnitudes like iris diaphragm photometer, etc.).

Figure 1.2: Spectral classification with five classes, spectra of comets, Uranus, nebulae, and solar spectrum – Spectral table (1898)

Meyer, Max: Das Weltgebäude (1898), after p. 52.

1.1.3 Centers of Astrophysics until around 1900

In the last quarter of the 19th century only a few centres of astrophysics existed in the world.3 Besides the Astrophysical Observatory Potsdam, where astrophysics was born, one should mention Göttingen, Heidelberg, Bonn, Bamberg, and Hamburg in Germany, then two observatories in Hungary, Italy (Collegio Romano Rome in the 1870s), England (Greenwich Astrophysical Department, 1873), France (Meudon Solar Observatory 1876), Russia (Pulkovo Astrophysical Department, 1882), and South America (La Plata, Argentina, 1886), also in the United States (Harvard College Observatory, Cambridge, Mass., (*1839), astrophysics with Edward Charles Pickering (1846–1919), director of HCO from 1877 to 1919, Lick, Mt. Hamilton, 1888, Yerkes, Wisconsin, 1897, Mount Wilson (1905), and India (Kodaikanal Solar Observatory, 1899 (since 1972, field station of the Indian Institute of Astrophysics in Bangalore).

Karl Schwarzschild was to play a special role in this phase of blossoming astrophysics.

1.1.4 New Observatory Layout – Astronomy Park

Around 1900, in addition, a revolution in observatory layout took place. This changed the architecture of the observatory building to the idea of an “Astronomy Park” with many different buildings and domes, as in the case of Nice Observatory (1879, id 225), EAO Kazan, Russia (1901, id 158), La Plata (1885, id 122), US Naval Observatory Washington D.C., 1887, id 116), Remeis Observatory Bamberg (1889, id 143), Uccle Observatory Bruxelles (1891, id 153), Heidelberg-Königstuhl (1896, id 141), and in Hamburg-Bergedorf (1906/12, id 92). The idea of an astronomy park observatory is performed in Hamburg in a perfect and consistent manner with a strict separation of observatory domes on one side, and the main building with the library, administration and offices, the workshop, and the residential buildings on the other side.

1.2 Biographical Notes on Karl Schwarzschild (1873–1916) – Places of Activity

Karl Schwarzschild (1873–1916) was born as the eldest of seven children in a German-Jewish upper middle-class family in Frankfurt am Main, where the proportion of Jews was 10% – the highest in Germany. He was the eldest son of his parents, Henrietta Ottilie Sabel (1852–1922) and Moses Martin Schwarzschild (1837–1916), a successful businessman. Karl attended the Philanthropin,4 the primary school of the Israelite community. Then, he visited the Städtisches Gymnasium (Municipal Latin School, founded in 1519 during the Reformation movement) Frankfurt, a “Humanistic Gymnasium” (High School with Greek, Latin, and exact sciences), where he graduated in 1891. Karl and his friend Paul Epstein (1871–1939), the later mathematician, built a telescope, and they occupied themselves with mathematical and astronomical problems. At the age of 16, Schwarzschild published an article in Astronomische Nachrichten (1890) on determining the orbits of double stars using three measurements.

Figure 1.3: Karl Schwarzschild (1873–1916), (photo 1900) Observatoire de Strasbourg, Refracting telescope

(Photo: Göttingen SUB Archive, “Cod. Ms. K. Schwarzschild – 23: 1,2”). (Top right: CC3, Ji-Elle, 2010), bottom: CC3, Pethrus, 2010)

Figure 1.4: Photometrische Beobachtungen: Light curves of the eclipsing binaries η Aquilae (δ Cephei-Star) and β Lyrae

(Schwarzschild (1900a), VII. Capitel, C 123, Fig. 5+6)

Karl Schwarzschild5 began his physics degree studies with Ernst Becker (1843–1912) in Straßburg/Strasbourg University. His first work concerned the observation of variable stars, Schwarzschild (1892).

He obtained his doctorate in Munich under Hugo von Seeliger (1849–1924) in 1896 with a mathematical thesis on Poincaré. During his time in Munich, from 1899 to 1901, he began to work on stellar statistics, an important field of research of Hugo von Seeliger.6

Figure 1.5: Hugo von Seeliger (1849–1924), director 1882 to 1924. Top right: 28.5 cm-Refractor, Fraunhofer, Merz of Munich (1835), Bottom: Observatory Munich-Bogenhausen (1817), Refractor Dome

(Top left: © University Observatory Munich, Top right: CC3, Michael Florian Schönitzer, Bottom: © University Observatory Munich)