The "Second Uncle" in the scientific community: He turned a disaster into a blessing twice and eventually became a great scientist

A video describing the past half of the life of the "Second Uncle" has caused a sensation on the Internet. The protagonist of the video, the "Second Uncle", was disabled in his legs due to illness when he was a teenager, but he worked hard to overcome difficulties and lived his life. The protagonist of this article is also unfortunate - he was born with a disability in his legs and could not walk normally for the rest of his life. But with his own efforts and the help of others, he became a great scientist. The story of this "Second Uncle" in the scientific community repeats a truth for us: to get rid of suffering, one's own efforts and the timely help of others are equally important. I wish that all the "Second Uncles" in the world and all those who are suffering from other sufferings can get out of suffering with their own efforts and the help of others, and enjoy the sweetness of success and happiness.

Written by Wang Shanqin

A gifted boy with congenital disabilities

On March 24, 1893, Konrad Baade, a village schoolmaster in Schröttinghausen, Westphalia, northwestern Germany, and his wife Charlotte Baade had their first child.

The delighted couple named the child Wilhelm Heinrich Walter Baade. However, the child was later usually named Walter Baade. We will call him "Bad" below and his father "Old Baade".

Image: The house that the Budd family once lived in. Image source: Reference [1]

The Buds later had three more children. Of the four, Bud was their favorite because he was born with hip dysplasia , which made it difficult for the poor child to walk. Throughout his life, he would walk with a noticeable hop . [2]

Although Budd Sr. was a religious man, he also had a good scientific background. He gave Budd a lot of books to cultivate his interest in academics. When Budd was 14 years old, Budd Sr. brought Budd an astronomy book. The boy was deeply fascinated and read the whole book in one breath. [1]

From that day on, Bud knew what he wanted to do with his life. His love for astronomy was already rooted in his heart, and no one could shake it. After that, young Bud saved the money he earned from tutoring others and bought a 3-inch (7.6 cm) telescope to observe the stars. [1]

In January 1910, the famous "Great January Comet of 1910" approached the Earth. This comet was so spectacular that it could be seen even during the day, so it was also called the "Daylight Comet." Baade observed this great comet with his own telescope.

Image: The "daytime comet" that appeared in January 1910, photographed by Percival Lawrence Lowell (1855-1916). Image source: Reference [3]

In April of that year, the famous Halley's Comet returned. Baade observed it for several nights with his small telescope. He saw the head of Halley's Comet as a faintly glowing cloud. [1]

Image: Halley, photographed by Edward Emerson Barnard (1857-1923) in April 1910. Image source: Reference [4]

Baade's brother Martin Baade recalled: "When my brother was a little boy, he would wear winter clothes and sit by the window in his bedroom with a telescope in the winter, freezing for the science he loved..." [1]

Budd's obsession with astronomy worried his father. He just wanted Budd to learn a lot, but he didn't expect his son to become a scientist, especially an astronomer. Budd's younger brother recalled: "My father said that this (astronomy) is an art that can't make a living." [1] Budd and his wife both hoped that Budd would become a theologian in the future. This profession would definitely provide a good livelihood. [2]

University of Göttingen, World War I, and the Dream of the Wilson Observatory

In 1912, Bard entered the nearby University of Münster. A year later, he transferred to the University of Göttingen, a world-renowned university whose mathematics and astronomy were founded by the great mathematician Johann Carl Friedrich Gauss (1777-1855), who was known as the "Prince of Mathematics."

At the University of Göttingen, Baad studied mathematics with the world-renowned mathematicians David Hilbert (1862-1943) and Felix Klein (1849-1925), and astronomy with Leopold Ambronn (1854-1930) and Johannes Hartmann (1865-1936). The solid foundation of mathematics and physics laid at the University of Göttingen[1] enabled Baad to become an astronomer who was proficient in both theory and observation.

Figure: Hilbert (left) and Klein (right). Image source: Reference [5] (left); Reference [6] (right)

In addition to these subjects, Bud also showed a strong talent for languages. His native language was German, but he also mastered several foreign languages, including English, French, Latin, Greek, and Hebrew. [2] These foreign language skills were probably acquired during his university years.

After graduating from university, Baade studied the spectrum of Beta Lyrae, a binary star, under the guidance of Hartmann. In 1919, Baade received his doctorate from the University of Göttingen.

Image: Ann Brown (left) and Hartmann (right). Image source: Reference [7] (left); Reference [8] (right)

While Bader was studying at the University of Göttingen, World War I broke out in 1914 and ended in 1918. Bader was exempted from conscription and death because of his disability. His disability likely saved his life and prevented him from becoming cannon fodder for the German army. It was the first blessing in disguise in his life.

After graduating with a doctorate, Baade planned to apply for a position as an assistant at the Mount Wilson Observatory, the most powerful observatory in the world at that time. The Mount Wilson Observatory was established in 1904, and the Carnegie Institution for Science, which was established by a foundation under the name of steel tycoon Andrew Carnegie (1835-1919), was responsible for all expenses. [Note 2] (hereinafter referred to as the "Carnegie Institution").

Image: Carnegie Institution’s office building in Washington, DC. Image source: Reference [9]

Wilson Observatory is 1742 meters above sea level, which can avoid most of the cloud cover and has good observation conditions. At that time, it had a 100-inch (254 cm) diameter Hooker telescope, and a gathering of talents, and its overall strength was the best in the world.

Image: A distant view of the Wilson Observatory on the top of Mount Wilson. Image source: Reference [10]

However, Hartmann told Baade that it was less than a year since the end of World War I, and as a citizen of the defeated country Germany, it was unlikely to succeed in applying for such a position in the enemy and victorious countries that had fought bloody battles. Baade accepted this advice and soon found a position as an assistant at the Hamburg Observatory in Bergedorf, and started working there in October 1919. [Note 3]

Two flowers, two flowers

Although he did not go to the Wilson Observatory, the Hamburg Observatory where Baade worked was also a good choice. It had a 40-inch (102 cm) reflecting telescope, which was not only the largest telescope in Germany at the time, but also one of the best in the world.

Image: 102 cm telescope at Hamburg Observatory. Image source: Reference [11]

Budd's boss, the director, Richard Schorr (1867-1951), was very interested in celestial bodies such as comets and asteroids. Budd was very interested in celestial systems such as variable stars (stars with obvious changes in brightness) and globular clusters. As an assistant hired by the director, Budd must of course first complete the tasks assigned by the director.

Image: Shore. Image source: Reference [12]

Fortunately, since Shore was busy with administrative affairs, he handed the telescope, which was originally his, directly to Budd. While completing his tasks, Budd had enough observation time to observe what he wanted to observe. Therefore, Budd adopted the " two blossoms " model to balance the director's tasks and his own interests, and study two major directions at the same time.

Baade quickly became a world-class expert in astronomical photography and photometry. He could quickly solve problems in both observation and theory. Baade was born for astronomy . He was highly regarded by Shore for his outstanding work.

In 1920 and 1921, Baade discovered six asteroids, the first of which was Hidalgo 944, which was between the orbits of Jupiter and Neptune when it was farthest from the Sun. This type of asteroid is collectively called "Centaurs", and Hidalgo 944 was the first Centaur to be discovered.

A few years later, despite the conventions of the time, Baad named one of the two asteroids he discovered in 1921 "Muschi 966". [Note 4] Muschi was the nickname of Johanna Bohlmann, a female technical assistant at the Hamburg Observatory. She was born in the same year as Baad, on September 1, a few months younger than Baad. The two were in a passionate love relationship at the time. During this period, Baad was also in a period of " both blossoming " in his career and love.

Baade discovered a total of 10 asteroids in his lifetime. In addition to the above 6, the other 4 were discovered by him in 1924, 1928, 1948 and 1949. Among them, the asteroid 1036 Ganymed discovered by Baade in 1924 is the largest "near-Earth asteroid" discovered so far. Fortunately, its orbit does not intersect with the Earth's orbit, but only "grazes" the outside of the Earth's orbit.

Figure: The appearance of 1036 Ganymed simulated based on observational data. Source: Reference [13]

In terms of stars and star clusters, Baade observed many variable stars in the globular clusters M53, M92, the Orion Nebula (M42), and NGC 5053, achieving high observational accuracy. At the time, the "RR Lyrae variable stars" were of particular interest because they could be used to measure the distances to star clusters in the Milky Way. The number of such variable stars discovered by Baade was more than twice the number previously discovered by Harvard Observatory.

Image: Globular clusters M53 (upper left), M92 (upper right), NGC 5053 (lower left) taken by the Sloan Digital Sky Survey telescope and a local area of ​​the Orion Nebula (lower right) taken by the Hubble Space Telescope. Image source: Reference [14] (upper, lower left); Reference [15] (lower right)

Baade's outstanding work in this area was highly praised by world-class authorities in the field of variable stars, such as Solon Irving Bailey (1854-1931) and Harlow Shapley (1885-1972), the former being the former executive director of Harvard Observatory and the latter being the director of Harvard Observatory at that time.

Figure: Bailey (left) and Shapley (right). Source: References [16] (left); [17] (right)

In 1923, Edwin Powell Hubble (1889-1953) of the Wilson Observatory used the Hooker telescope to distinguish Cepheid variables in the Andromeda Galaxy and calculated that its distance was about 900,000 light years, which was larger than the Milky Way. This meant that the Andromeda Galaxy was a galaxy outside the Milky Way. Hubble thus pioneered galactic astronomy.

Baade naturally soon learned of this great news that shocked the astronomical community. However, he could not have predicted at that time that he would improve Hubble's results more than 20 years later.

In 1925, at Shapley's suggestion and strong recommendation, Baade received the Rockefeller International Education Board Fellowship, which allowed him to visit Harvard Observatory, Yerkes Observatory, Dominion Observatory, Lick Observatory and Wilson Observatory within a year.

Figure: A photo of Baade visiting Yerkes Observatory in 1926. Source: Reference [18]

During his visit, Baade made full use of the various resources of the observatories and discussed and exchanged ideas with his colleagues there, and was very popular. In particular, during his visit to Wilson Observatory, he was warmly received by the director, Walter Sydney Adams (1876-1956). He admired Baade very much and would become the most important person in changing Baade's life .

Image: Adams (left) and a photo of Adams and Einstein at the Wilson Observatory (right). Image source: Reference [19] (left); Reference [20] (right)

A job offer from Wilson Observatory

After returning to Germany, Baade continued to work at the Hamburg Observatory. At that time, inflation was severe in Germany. Although Shor continued to increase Baade's salary, the rate of increase could not keep up with inflation.

In 1929, 36-year-old Bud married his girlfriend Muschi (Johanna Bohlmann).

In the same year, Hubble used the Hooker telescope to observe the distances of some galaxies. Combining the velocities of these galaxies obtained by Vesto Melvin Slipher (1875-1969), he announced an extremely important conclusion: the recession velocity of galaxies is proportional to the distance, and the proportionality constant (the "Hubble constant") is about 550. [21]

Hubble's discovery meant that the universe was expanding. But Hubble's work left an embarrassing loophole: taking the inverse of the Hubble constant, the age of the universe was about 1.7 billion years; however, the age of the earth measured at that time and later based on radioactive elements was 3-3.5 billion years. It was absurd that the age of the universe was younger than the age of the earth. This is the "universe age problem."

In 1930, Adams asked Baade through a third person if he would like to work at Wilson Observatory. Baade was overjoyed and immediately wrote to Adams to express his infinite joy. Adams offered Baade an annual salary of $3,300. At that time, $1 was equivalent to $14.5 today. [22]

However, due to long-term inflation, Budd no longer had the savings to buy a ship ticket to go abroad, and the Carnegie Association did not provide travel expenses. He had no choice but to write to Adams, telling him the truth and asking Adams to advance part of his salary to buy a ship ticket.

After receiving Baade's letter, Adams was shocked by Baade's situation. He was deeply saddened that a world-leading astronomer at the time, who Adams considered to be the " future of Wilson Observatory ", had fallen into such poverty.

At that time, what Adams thought of was probably the thin figure of the young man who could only walk in a hopping manner due to congenital disability. His "mental exhaustion" might have been cured by this young German "second uncle"...

On the one hand, Adams reported the situation to the Carnegie Association, requesting special treatment and promising that it would not happen again. [Note 5] On the other hand, Adams paid Budd an advance of $900 from other funds. Then, Budd and his wife bought a boat ticket and arrived at the Wilson Observatory, starting the second half of his brilliant academic career. The Wilson Observatory's world-class telescope and stable and abundant income brought Budd extra great pleasure and made his work more efficient.

Figure: Bud in his prime. Source: Reference [23]

In May 1934, Baade and Fritz Zwicky (1898-1974) published three papers [24-26] , studying topics related to supernova explosions. They emphasized that novae can be divided into "ordinary novae" and "supernovae", and proposed three core ideas: supernovae are produced by the collapse and explosion of stars; the collapse process will compress a dense "neutron star" in the core; the shock wave of the supernova accelerates the particles in the supernova, turning them into high-energy cosmic rays.

In 1938, Baade studied 18 supernovae discovered between 1885 and 1937 and found that the brightness of their brightest stars was relatively small, so they could be used as "standard candles" to measure the distances of distant galaxies. [27] This article pioneered supernova cosmology. In 1998, two international collaboration groups realized Baade's idea and used Type Ia supernovae to measure the distances of distant galaxies, confirming that the universe was expanding at an accelerating rate. [28-29] This made humans realize that there is dark energy in the universe. The first reference in one of the groups' papers [29] was Baade's paper.

Figure: An artistic conception of a Type Ia supernova exploding in the universe. In 1938, supernovae had not yet been divided into Type I and Type II, let alone Type Ia. However, Baade's estimate of the uniformity of the luminosity of supernovae as a whole was correct. Image source: Reference [30]

Surprise after house arrest

On December 7, 1941, the Japanese army attacked Pearl Harbor and the United States declared war on Japan. Four days later, Japan's ally Germany declared war on the United States. Bud was from Germany, and although he was not thrown into a concentration camp like the local Japanese expatriates, his travel was also restricted to a certain extent: except for going to work, he could not leave his home more than 5 miles away.

In April 1942, the military issued a curfew for German expatriates, prohibiting them from leaving their homes between 8 p.m. and 6 a.m. This ban prevented Baade, who lived in Pasadena, from going to Wilson Observatory to conduct observations.

Director Adams and others immediately came forward and wrote letters to plead for Bud and guarantee him. In May, they asked Milton Humason (1891-1972) to accompany Bud to meet the military police commander and let Humason guarantee Bud. Humason assured the military police commander that Bud would not help Germany spy on military secrets. Therefore, the military police commander allowed Bud to go to the observatory at night. This matter only wasted Bud's time for one month.

During the war, astronomers at Wilson Observatory left the observatory one after another to participate in military projects. In particular, Hubble also left the observatory in June 1942. Baade was not qualified to access any military projects or information, let alone participate in military projects, so he continued to work at the observatory.

After a brief period of depression, Baade experienced a second blessing in disguise : due to the departure of several colleagues, especially Hubble, Baade was able to use the Hooker telescope for a much longer and almost unlimited time.

Another surprise that made Baade very happy was that in order to prevent ships near the west coast from being bombed by the Japanese, cities near the observatory had to obey the light control order. As a result, the light pollution near Mount Wilson was greatly reduced, and the observation conditions were better than when the observatory was first built. Baade could even use the Hooker telescope to distinguish a large number of stars near the center of the Andromeda Galaxy. In contrast, Hubble and others could only distinguish the bright stars at the edge of the Andromeda Galaxy.

In addition, Baade used a photographic plate that was sensitive to red light, which helped him discover those reddish stars.

Baade carefully observed many stars in the core region of the Andromeda Galaxy, M32 (NGC 221), and M110 (NGC 205). [31] After analyzing the photographic plates, Baade found that the stars in the galaxy can be divided into two types: one type is mainly located in the spiral arms of the galaxy, with a blue color, and are young stars; the other type is mainly located in the central region of the galaxy and in globular clusters, with a red color, and are old stars.

Image: Image of the Andromeda Galaxy M31, M32 (above and to the left of the M31 core in the image), and M110 (below the M31 core in the image). Image source: [32]

Baade called these two types of stars "Population I stars" and "Population II stars". The RR Lyrae variable stars that Baade has studied for many years and other stars in globular clusters belong to Population II stars.

After this major discovery was published in 1944, all astronomers who studied stars at the time realized that this core field of astronomy had been completely reshaped by Baade . [Note 6] From that time to the present, Baade's great discovery has been written into the constantly updated textbooks and has become one of the foundations of astronomy. Baade has therefore become a master of the generation who is famous in the history of astronomy.

In the fall of 1945, Baade observed a relatively dust-free area near the center of the Milky Way to search for RR Lyrae variables. This area was later called "Baade's Window". Baade soon confirmed a large number of RR Lyrae variables there, 152 of which were obtained by comparing the first 10 photographic plates. The number of RR Lyrae variables in this batch was several times the total number before.

Image: The location of the Baade Window in the Milky Way (left, the area where the light yellow "Baade's Window" is located) and two globular clusters (NGC 6522, upper right; GC 6528, lower left) in the Baade Window and the surrounding stars (right) captured by the camera on the 32-inch (81 cm) Schulman telescope. Image source: Reference [33] (left); Reference [34] (right)

Baade used these variables to determine the distance to the globular cluster NGC 6522 (see above) in the Baade Window, which is why the cluster is called "Baade's Cluster".

Solving the puzzle of the age of the universe

After the end of World War II, Baade had been waiting to use the 200-inch (508 cm) telescope at the Palomar Observatory. It had been planned since 1928, but due to the huge scale of the project and the impact of World War II, it had not been fully completed until then.

One of the reasons why Baade was looking forward to this telescope was that he and Hubble had previously realized that there might be different types of "Cepheid variables" in the Andromeda Galaxy, and those Cepheid variables located in globular clusters might be very different from other Cepheid variables; he had already discovered several Cepheid variables belonging to Population II in the Andromeda Galaxy with the Hooker telescope, but he needed a more powerful telescope to observe many more Cepheid variables in the Andromeda Galaxy to verify this idea.

In 1948, the 200-inch telescope was finally turned on. It was named the Hale telescope, or P200. Its diameter was twice that of the Hooker telescope. Baade became one of the main users of the Hale telescope because of his previous outstanding work.

Image: Hale Telescope. Image source: Reference [35]

He first used this telescope to search for RR Lyrae variable stars in the Andromeda Galaxy. However, he found nothing. If the distance to the Andromeda Galaxy was correct, they would have been visible with a 200-inch telescope at the time.[Note 7] Baade's failure to find them meant that the distance to the Andromeda Galaxy was underestimated. This also meant that the brightness of the Cepheid variables in it was underestimated.

Starting in the fall of 1950, Baade used the Hale telescope to identify more than 300 Cepheid variables in the Andromeda Galaxy. After careful analysis, Baade confirmed his previous speculation: Cepheid variables do have two types, belonging to Population I and Population II. [36][Note 8] The brightness of the first type of Cepheid variable is about 4 times that of the second type of Cepheid variable.

The Cepheid variables observed by Hubble in the Andromeda Galaxy belonged to the first type, but he treated them as the second type, thus underestimating their true brightness to 1/4 of their true brightness, and thus underestimating the distance of the Andromeda Galaxy by half.

Image: Humason, Hubble, Baade and Rudolph Minkowski (1895-1976) (from left to right) checking the telescope's photographic plates in 1950. Image source: Reference [37]

After Baade corrected Hubble's error, he calculated that the Andromeda Galaxy was about 1.9 million light-years away[36], twice the previous distance. The Hubble constant was thus reduced by half, and the age of the universe doubled, finally exceeding the age of the Earth. The problem of the age of the universe was thus solved.

Because he expanded the age and "size" of the universe to twice the original, he saved the confidence of astronomers who believed in the theory of cosmic expansion and became the "second savior" of the universe at that time.

Baade did not publish this important result immediately, but announced it at the 1952 annual meeting of the International Astronomical Union. Shapley was also present at the time, but he doubted Baade's result. What shocked Baade was that Shapley suddenly announced to the media in 1953 that he had doubled the distance of the universe, and did not mention Baade's contribution at all. The usually mild-mannered Baade was furious and severely condemned Shapley, calling him a shameless person. Fortunately, the astronomical community recognized Baade's priority. [2]

Later, Allan Rex Sandage (1926-2010), a doctoral student under the guidance of Bader, continued the research and reduced the proportional constant to about 70, thus obtaining the age of the universe to be more than 10 billion years.

Clearly distinguishing between the two types of Cepheid variables not only solved the problem of the age of the universe, but also ensured the reliability of a large number of subsequent research, and played a decisive role in subsequent celestial distance measurement and cosmology research.

The fall of a scientific giant

Because of his important contributions in many aspects, Baade was awarded the Gold Medal of the Royal Astronomical Society (1954), the Bruce Prize (1955) and the Henry Norris Russell Lecture (1958).

Baade retired in 1958. After that, he was invited to visit Harvard University, the Institute for Advanced Study in Princeton, the Australian National University Observatory and other institutions, and then returned to the University of Göttingen as "Gauss Professor".

Several visits after retirement drained his strength and exacerbated his hip disease. After returning to Germany, bone spurs on Bader's spine compressed his nerves and caused him severe pain. By the end of 1959, he could no longer sit, stand, or write... To relieve the pain, he could only lie on his bed. [2]

On January 27, 1960, Bader underwent major surgery at one of Germany's best hospitals. The operation itself was a success. But afterward, he had to lie prone. During those months, his recovery was slow. It was almost five full months before doctors allowed Bader to use a wheelchair, but only for a few minutes at a time. [2]

On June 25, 1960, Bader, who was in a wheelchair for the third time after surgery, suddenly collapsed and died at the age of 67. Nearly five months of lying in bed damaged Bader's circulatory system, and blood clots may have formed in his blood, which eventually took the life of this scientific giant. [2]

His wife, Muschi, died in a nursing home on August 31, 1988, one day before her 95th birthday. [2]

One of the most important astronomers of the 20th century

In addition to the many outstanding achievements mentioned above, Baade also made important contributions to the study of radio sources, supernova remnants, etc. Throughout Baade's brilliant academic career - from asteroids and comets in the solar system, to variable stars and ordinary stars outside the solar system, to supernovas, supernova remnants, radio sources and the universe - he made indelible and significant contributions to human understanding of the universe and the universe itself with his extraordinary ability and perseverance.

Because of his many outstanding achievements, Baade is recognized as one of the most important astronomers of the 20th century . In his memory, there are "Baade Crater" and "Baade Valley" on the moon, asteroid 1501 is named "Baade Asteroid", the pulsar in the center of the Crab Nebula is named "Baade Star" - because Baade once made detailed observations of the Crab Nebula, and one of the two 6.5-meter Magellan telescopes established by the Carnegie Association in Chile is named "Magellan-Baade Telescope".

Image: Magellan-Bade Telescope in the night sky. Image source: Reference [38]

In the 1950s, after Bud became famous, a female playmate of Bud's recalled the time when they played together when they were six or seven years old: those boys always liked to brag, and the most outrageous time was when they even said they would go to the moon in the future. [1] She and Bud's other playmates could not have predicted that one day, the name of the disabled boy among them who walked in a hopping manner would actually appear on the moon .

Image: Baader Crater on the Moon. Image source: Reference [39]

Born with a disability and tormented by leg problems all his life, this "Second Uncle" in the scientific community is unfortunate. On the road to his growth and success, he has received the appreciation and help of many elders and peers, and this "Second Uncle" in the scientific community is lucky.

Bud's success was not only due to his intelligence and hard work, but also to the timely help of others. Even Shapley, who later hurt him, had strongly supported him when he was young; Adams, who protected and helped him until his death, and Shor, who still cared for him after he left Germany, were even more selfless mentors of Bud, the swift horse.

Image: A plaque in memory of Bard in the museum of the city where he was born. Image source: Reference [40]

The story of Bud, the "Second Uncle" in the scientific community, repeats for us an obviously correct truth: to get rid of suffering, one's own efforts are as important as timely help from others. I wish that all the "Second Uncles" in the world and all those who are suffering from other sufferings can get out of suffering through their own efforts and with the help of others, and enjoy the sweetness of success and happiness.

Questions and Answers

Q: "Why does Adams admire Bud so much? Is there no other reason besides Bud's talent and character?"

▼

A: "The other reason is probably that they are all named Walter..."

Notes

[Note 1] During his time at the University of Münster and the University of Göttingen, Bard told his father that he was studying theology, mathematics, physics, and astronomy. In fact, he did not take any theology courses at all, but instead studied courses related to mathematics, physics, geophysics, and astronomy. He said that he studied theology only to appease his father.

[Note 2]CIS’s office is located in Washington, D.C., and its official name is the Carnegie Institution of Washington.

[Note 3] The University of Hamburg was founded in Hamburg in 1825 and moved to Bergedorf in 1912 without changing its name.

[Note 4] According to the convention at the time, asteroids could only be named after goddesses or women in ancient Greek mythology (only a few were named after male gods). In fact, Hidalgo 944 did not follow this convention. Hidalgo was the father of Mexico, Miguel Hidalgo Costilla (1753-1811). In 1923, German astronomers were allowed to observe a total solar eclipse in Mexico. In order to express their gratitude to Mexico, the asteroid was named "Hidalgo 944" after approval by the Mexican president.

[Note 5] Original text: [c]ertainly...need not be taken as a precedent for the future.

[Note 6] Although, as Baade himself said, Jan Hendrik Oort (1900-1992) proposed this idea as early as 1926, Baade used rich observations to fully establish a reliable classification.

[Note 7] The ability to observe celestial bodies of a certain brightness is not only related to the telescope aperture and exposure time, but also to the technology of different eras. Baade did not discover RR Lyrae variable stars in the Andromeda Galaxy using a 5-meter telescope, but in the 1980s, Pritchet and van den Bergh observed RR Lyrae variable stars in the Andromeda Galaxy using the 4-meter Canada-France-Hawaii Telescope.

[Note 8] The first category is relatively massive stars whose brightness changes over a long period, and they are classified as Type I Cepheid variables, also known as "classical Cepheid variables." The second category is low-mass stars whose brightness changes over a short period, and they are classified as Type II Cepheid variables.

References & Image Sources

[1]https://www.astronomie.de/astronomische-fachgebiete/geschichte/walter-baade/

[2](a)Osterbrock, DE Walter Baade, Observational Astrophysicist, (1): The Preparation 1893-1931, 1995, JHA, 26, 1; (b) Osterbrock, DE Walter Baade, Observational Astrophysicist, (2): Mount Wilson 1931-1947, 1996, JHA, 27, 301; (c) Osterbrock, DE Walter Baade, observational astrophysicist, (3): Palomar and Göttingen 1948-1969 (Part A), 1997, JHA, 28, 283; (d) Osterbrock, DE Walter Baade, observational astrophysicist, (3): Palomar and Göttingen 1948 - 1960 (Part B).

[3]Percival Lowell - Lowell Obscurity, publ. 1910

[4]Professor Edward Emerson Barnard at Yerkes Observatory, in Williams Bay, Wisconsin. - Published in the New York Times on July 3, 1910.

[5]American Journal of Mathematics, 29(1)

[6]Gebruder Noelle (m. 1917, attivo a Gottingen) - Archivio storico dell'Accademia delle Scienze

[7]Liber Amicorum HG van de Sande Bakhuyzen (1908)

[8]Niedersächsische Staats - und Universitätsbibliothek Göttingen

[9]Popular Science Monthly Volume 76

[10]Georgia State University

[11]Leuband (Diskussion)

[12] Max Liebermann

[13]Astronomical Institute of the Charles University: Josef Ďurech, Vojtěch Sidorin - DAMIT – Database of Asteroid Models from Inversion Techniques: for (1036) Ganymed

[14]Sloan Digital Sky Survey

[15]NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team

[16]National Academy of Sciences – Annie J. Cannon - National Academy of Sciences Biographical Memoir of Solon Irving Bailey (1854–1931), Annie J. Cannon, National Academy of Sciences, Volume XV – sixth memoir, p. 2, 1932

[17] Armagh Observatory

[18]Yerkes Observatory Photography

[19]http://phys-astro.sonoma.edu/brucemedalists/walter-adams

[20] The Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, California

[21]Hubble, E. A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae, 1929, PNAS, 15, 168

[22]https://stats.areppim.com/calc/calc_usdlrxdeflator.php

[23]https://www.mtwilson.edu/mount-wilson-astronomomers-2/

[24]Baade, W., Zwicky, F. On Super-novae, 1934, PNAS, 20, 254

[25]Baade, W., Zwicky, F. Cosmic Rays from Super-novae, 1934, PNAS, 20, 259

[26]Baade, W., Zwicky, F. Remarks on Super-Novae and Cosmic Rays, 1934, PhRv, 46, 76

[27]Baade, W. The Absolute Photographic Magnitude of Supernovae, 1938, ApJ, 88, 285

[28]Riess, AG, et al. Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant, 1998, AJ, 116, 1009

[29]Perlmutter, S., et al. Measurements of Ω and Λ from 42 High-Redshift Supernovae, 1999, ApJ, 517, 565

[30] ESO

[31]Baade, W. The resolution of Messier 32, NGC 205, and the central region of the Andromeda nebula, 1944, ApJ, 100, 137

[32]Robert Gendler (2008)

[33]NASA, ESA, Z. Levay (STScI) and A. Fujii

[34]Adam Block/Mount Lemmon SkyCenter/University of Arizona

[35] Palomar/Caltech

[36]Baade, W. The period-luminosity relation of the Cepheids, 1956, PASP, 68, 5

[37]Hamburg Observatory

[38]https://obs.carnegiescience.edu/Magellan

[39]James Stuby based on NASA image - Reprocessed Lunar Orbiter 4 image cropped in Gimp to show Baade crater and surrounding terrain.

[40]Grunswiki

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