Astronomy, rich in a history of more than 5000 years, is one of the oldest sciences. She has often been linked to religion. For several millennia she has been associated with astrology. In the eighteenth, the Enlightenment marked the separation of the two disciplines.
Deep Space, or simply Space, is the expanse that exists between celestial objects (also called celestial bodies in reference to the Latin corpus caelaste). Its physical exploration begins in the twentieth century with the use of balloons and continues during the race to the space between USA and USSR. The discovery of Space, in the sense in which we currently conceive it, has been the affair of multiple trials and errors.
In the Neolithic period (9000 to 3300 BC) most monumental megalithic sites were observatories. This is the case of Zorats Karer, Nabta Playa or Stonehenge. Astronomy has fascinated many civilizations. It is very much studied by the Mayans. In the Middle Ages are the Arab and Persian astronomers who develop it. Astronomy knowledge is essential to navigate or navigate the deserts.
Already in the fourth century BC, Aristotle relies on the teachings of Parmenides to explain that nature hates emptiness. In the 2nd century the Chinese astronomer Zhang Heng is convinced of its infinite character. Space is perceived as empty. Then the works of Copernicus, Galileo and Pascal and their successors helped to better understand how it works.
Contemporary times show the existence of stars as distant objects. We also discover the expansion of the universe. Photography allows astronomy to be much more precise. Already in 1870 the astronomer Hervé FAYE (1814-1902) prefers photos rather drawings. The end of the nineteenth century and the twentieth century saw astrophotography supplant other mediums of representation. It is from a photograph that in 1923 Edwin HUBBLE (1889-1953) determined the expansion of the Universe.
The interest of photography in astronomy was understood from the beginning. The daguerreotype, invented in 1839, was largely supported by François ARAGO (1786-1853), French astronomer and statesman, he was then director of observations at the Observatoire de Paris and a member of the Academy of Sciences. He immediately saw the potential of photography in the field of science, making it possible to record observations and then exploit them. His stance in favor of the DAGUERRE process led the State to buy the patent and offer it to the world.
In March of the following year, the Anglo-American John William DRAPER (1811-1882) made one of the first photographs of the Moon, and probably the first that showed so much detail. Draper is also recognized as the first astrophotographer. The first stellar photograph was made 10 years later, in 1850, at Harvard University, on the initiative of William Cranch BOND (1789-1859), George Phillips BOND (1825-1865) and John Adams WHIPPLE ( 1822-1891). The technique then limited shooting, especially because of the necessarily long exposure times. It was then necessary to compensate for the rotational movement of the Earth by shifting the photosensitive medium. The duration of exposure was a real challenge at the beginning of astrophotography. It later became an asset, making it possible to record luminous emanations that are very weak and imperceptible to the human eye, even equipped with telescopes.
Many astronomers subsequently turned photography into the service of science. We can mention the French Maurice LOEWY (1833-1907), Pierre Henri PUISEUX (1855-1928) and Jules JANSSEN (1824-1907), who contributed to the development of astrophotography. The first two are famous for their photographs of the Moon, while Jules JANSSEN made comet photographs and the surface of the Sun. At the same time the American Sherburne Wesley BURNHAM (1838-1921) mapped the surfaces of Mars and the Moon.
In 1887 a project of Carte du Ciel was born. It was at the instigation of the Henry brothers, famous French astronomers, that the director of the Paris Observatory: Ernest Amédée MOUCHEZ (1821-1892) launched this long-term project. The Paris Observatory managed to federate 17 other world observatories around this project. The photographic map was to identify the stars of the sky, more than 10 million. Each observatory covered by its observations a small part of the sky. The catalog was essentially completed in 1958.
Mount Wilson Observatory (MWO) is located northeast of Los Angeles. The site benefited from ideal weather conditions, which led to the construction of a first observatory in 1889. However, the harsh climatic conditions quickly led to its abandonment. It was not until 1904 and the patronage of George Ellery HALE (1868-1938) that the current observatory was built.
George Ellery HALE received a 1.5-meter mirror, made in France at Saint-Gobain, which was used to assemble the telescope. Its commissioning took place December 8, 1908, it was then the largest telescope in the world. This revolutionary instrument propelled astronomy into a new era, offering important breakthroughs. The telescope is also famous for the photographs of nebulae that it allowed. It is no longer used for scientific measurements but remains accessible to the public.
HALE began a second telescope in 1908 with funding from the Carnegie Foundation and philanthropist John Daggett HOOKER (1838-1911). Impressive in size, 2.5 meters in diameter, the mirror was once again built by Saint-Gobain. The Hooker telescope, named after the main donor, was commissioned on November 1, 1917. It was equipped in 1919 with an optical interferometer, an instrument exploiting the interferences between the waves developed by Nobel Prize winner Albert Abraham MICHELSON. This addition allowed for more accurate measurements of star distance and size.
It is from the measurements and photographs made from this second telescope that Edwin HUBBLE (1889-1953) proved that the Andromeda galaxy was outside the Milky Way in 1923. Later, in 1929, he demonstrated the expansion of the Universe from the data collected by this same telescope. Among the great discoveries made by the Mount Wilson Observatory we can also mention the discovery of evidence of the existence of dark matter by Fritz SWICKY in 1933, or the discovery of two satellites of Jupiter by Seth NICKOLSON in 1938.
Edwin HUBBLE managed to calculate the rate of expansion of the Universe from observations recorded by astrophotography. Edwin Hubble began working at the Mount Wilson Observatory in 1919, shortly after the starting of the Hooker telescope was then the largest in the world. His observations made between 1922 and 1924 made it possible to establish that the Universe extended beyond the Milky Way. He identified the presence of Cepheids, giant or supergiant stars whose luminosity varies in relatively close spiral nebulae. This is for example the case of the Andromeda Galaxy (Messier 31) and the Galaxy of the Triangle (Messier 33).
Thus, between 1922 and 1936 Edwin HUBBLE solved some of the great questions of cosmology, among which the speed of expansion of the Universe. By observing the brightness variations of the Cepheids he was able to determine the escape velocity of these galaxies. By his observations HUBBLE was able to establish that the galaxies were moving away, and this proportionally to their distance. In 1929 he published what is now called Hubble’s Law. This law is the first proof of the expansion of the Universe.
It is from empirical observations that Edwin HUBBLE made his calculations. A photograph in particular, taken at the observatory of Mount Wilson and drawn in negative, shows this work of calculations and the annotations of HUBBLE. Below we can see the Barnard Galaxy photograph annotated by HUBBLE and next to the same drawn in positive.
The Palomar Observatory is located near San Diego, California. The observatory building project was launched in 1928 by the California Institute of Technology (Caltech) with funding from the Rockefeller Foundation. The site of Mount Palomar was chosen in 1934. World War II postponed its commissioning until 1949. Successor of the Observatory of Mount Wilson, it was equipped with the largest telescope and kept status until 1976. This telescope 5.08 meters was named "Hale" in honor of astronomer George Ellery HALE, famous astronomer responsible for the creation of the Mount Wilson Observatory and instigator of Mount Palomar Observatory. The two institutions were linked for a long time. They were jointly managed before being separated in 1980.
In addition to the Hale telescope, smaller ones were installed, including a 122 cm (48 inch) in 1948, later baptized Schmidt in honor of Maarten SCHMIDT (1929-), and a 152.4 cm in diameter (60 inches) in 1970. The Palomar Observatory has many other instruments that have been improved as techniques evolve. It remains one of the most important places for the study of the stars.
In addition to the many discoveries allowed by the Palomar Observatory, a photography campaign began in 1949. They were made from the Schmidt telescope and published in 1958 in National Geographic. This study is called NGS-POSS (National Geographic Society - Palomar Observatory Sky Survey), later the images were used in many astronomical catalogs. A large number of discoveries were made by working from the photographs obtained during this study.
Since the end of the 1970s the importance of film photography has decreased in the field of astronomical research. It is gradually preferred CCD (Charge Coupled Device) sensors. This type of sensor is at the origin of digital photography. From the end of the 1970s it has an advantage over film photography: it can capture much weaker lights. The images do not need to be printed on paper to be studied or enlarged, so there is no loss of information.
In addition, the appearance of radio telescopes and radio astronomy in the twentieth century led to new measurements on celestial bodies. Spectroscopic analysis of atomic emissions and their different isotopes during quantum jumps becomes possible. A quantum leap is a change that occurs in the atom itself, at the level of the electrons. They are the source of electromagnetic emissions, including light. Changes in the state of atoms become identifiable, bringing astronomy into a new era.