History of Astronomy
- Written by michaeloconnell
- Parent Category: Astronomy
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Hertzsprung was born on the 8th of October 1873 in Frederiksberg, Denmark. His
father had obtained a degree in astronomy in the local university. Although awarded
a gold medal for some of his work in astronomy, his father gave up science due to
the poor financial returns involved and eventually became director of the Denmarks
national life insurance company.
In 1893, when Ejnar was 20 years old, his father died. After this, his fathers books
were sold as there was nobody in the family, including Ejnar, who had an interest in
astronomy. His father never wanted his son to study astronomy or insurance or
mathematics. As a result, Ejnar himself went to university and graduated with a
degree in chemical engineering and never studied astronomy.
Between 1899 and 1901, Ejnar was employed as an engineer at St. Petersburg and
studied photochemistry at Leipzig. In 1902, Hertzsprung returned to Denmark after
the death of his mother and started working as an amateur astronomer at the
Copenhagen University Observatory and the Urania Observatory in Frederiksberg,
which belonged to a well-known amateur astronomer Victor Neilsen. Victor is quoted
as saying to a fellow amateur; Hertzsprung is a clever young man who intends to
measure star colours photographically. Little did they know that this was to start a
life-long interest in stellar measurement and lead to ground-breaking research in
In 1905 Hertzsprung published Zur Strahlung der Sterne (Radiation of Stars) in the
periodical "Zeitschrift fr Wissenschaftliche Photographie" (Magazine for Scientific
Photography). What was unusual about this was that he did not publish them in an
astronomical journal. This paper made the following conclusions:
Stars in the spectral-classes G, K and M are divided into two series with different luminosity.
Luminous red stars must be massive.
The small number of red giants indicates that that these stars are in a stage of fast evolution.
In 1907 Hertzsprung published "Zur Bestimmung der Photographischen
Sterngrssen" (Determination of the Photographic Star Sizes) in the same journal
with his follow-on results.
Karl Schwartzchild was the leading astronomer in Germany at the time and was the
director of Gttingen Observatory. Upon reading Hertzsprungs papers he secured a
post for him firstly at Gttingen Observatory and later took him to Potsdam, where
Schwartzchild also moved. Within seven months, Hertzsprung become a senior staff
member at one of Europes premier observatories.
Meanwhile, across the Atlantic and one year later, Henry Norris Russell came to
conclusions very similar to those determined by Hertzsprung but was completely
unaware of the Danish mans work, partly due to the unusual nature of the
publication of Hertzsprungs work.
The graphical form of both Hertzsprungs and Russells work wasnt published until
1911 by Hertzsprung in the paper "Publikationen des Astrophysikalischen
Observatorium zu Potsdam" (Astrophysical Publications of Potsdam Observatory).
Figure 1 Charts from Hertzsprungs Paper of 1911
Figure 2 Hertzsprung-Russell Diagram
Both astronomers became attributed to this common piece of work. However, there
was no animosity between the two gentlemen. Russell, when asked about the
diagram, was quick to point out that it was Hertzsprung who started work on
developing it. Hertzsprung, for his part, is quoted as saying It is Russells merit that
he presented this complex of problems in a spirited, easily understood form in
In 1919, Hertzsprung became Adjunct Director of the University Observatory of
Leiden, Holland and was promoted to rank of associate professor in 1920.
In 1922, Hertzsprung published his catalogue of data representing 734 stars, all ofwhich were brighter than 5th magnitude. At the time, accurate information was not
available on star parallax so he used data from stars proper motion to calculate
absolute magnitude and thence construct a diagram showing a relationship between
colour and luminosity.
However, Hertzsprung also undertook research in others areas of stellar
measurement. In 1911 he developed a light curve for Polaris. Shortly after, he
determined the distance of the Small Magellanic Cloud using Cepheid variable stars.
In 1926, he undertook further work on Cepheid variable stars and developed a
relationship between period length and light curve shape based on photographs he
took at an observatory in South Africa during an 18-month trip there in 1923-1925.
However, he undertook extensive work in the measurement of double stars. He
developed techniques which would allow him to measure relative positions between
stars to an accuracy of a few thousandths of an arc second.
During his work, he also discovered two asteroids; 1627 Ivar in the year 1929 and
the asteroid 1702 Kalahari 5 years earlier.
During his time, Hertzsprung received many awards, including doctorates from the
universities of Utrecht (1923), Copenhagen (1946) and Paris (1949). He also
received the Gold Medal from the Royal Astronomical Society in 1929 and the Bruce
Medal in 1937 from the Astronomical Society of the Pacific. In 1959, the city of
Copenhagen gave him its Ole Roemer Medal.
Hertzsprung continued to take measurements long after his retirement and only
slowed down 2 to 3 years before his death. He is quoted as saying I cannot
compete with Dr. Strand any longer!; Dr. Strand being a former student of his who
was Director of the US Naval Observatory.
Hertzsprung died in 1967 in Roskilde, Denmark, at the age of 94 and his papers
(12,153 pages with original measurements) were given to the USNO Library.
Michael OConnell 2006