Sciences - Astronomy
Observing the Universe - The Universe
The Universe
Practise - Observing
Our Galaxy - The Milky Way
Galaxies
Quasars - Expansion of the Universe


Welcome to this site which presents a method of observing the deep sky, between visual observation and astrophotography.
Without having expensive and complex equipment, it is possible, even from the city, to observe very distant stars that make up our Universe.

1) Introduction



In my childhood, well before the digital age, I consulted books about astronomy which were illustrated with beautiful photographs of planets and nebulae. All this seemed inaccessible to me and I almost questioned the reality of what was being shown! “Who tells me it’s true?” I was interested in astronomy without being a great expert. One evening in August 1991, I was watching a live broadcast on the Antenne2 channel (France2) which dealt with the Sky, it was the first edition of the “Night of the (shooting) stars”, there was an eminent and charismatic astronomer professional with a white beard in the person of Hubert Reeves. In short, at the end of the show, motivated by everything that has been covered, I take out the family telescope in the garden, to try to observe something interesting. I point the instrument toward a moderately bright star.
I zoom in, I adjust the sharpness of the image, the star in question is special because it does not sparkle with a whole procession of aberrations of all colors like other stars that I have observed desperately by chance before! This one has fixed contours, it has an oval shape... I improve the magnification and amaze: "But it's Saturn, the famous planet with the rings!"... "We can see that, from home, without the need for 'a big observatory?'
"But if I can observe Saturn, I can observe lots of other things..."
The following nights, I noted the position of a constantly changing point around Saturn, I had confirmed the period of rotation of approximately 16 days of the Titan satellite... I could repeat the same experiments as the ancient astronomers like that of Christian Huygens more than 300 years later.
This is how I became passionate about amateur astronomy. Over the years, I learned to discover the sky. Digital technology has invaded our daily lives and of course our leisure activities. The amateur astronomer uses almost the same technologies as the professionals, allowing them to explore the cosmos further, which will allow them to realize for themselves the reality of the scientific world.


2) What is the Universe?




The definition of the Universe is the totality of everything that exists. When scientists talk about the Universe, they talk about our Universe resulting from the study of our observable Universe! The observable Universe is everything that exists and is observable. The “global” Universe would be enormously more important than “our Universe” with the impossibility of seeing it entirely. The "global" Universe can be infinite or be finite but without limit (for example, the surface of the Earth is finite but without limit: no obstacle prevents you from going around it an indefinite number of times)

“Two things are infinite: the Universe and human Stupidity, as far as the Universe is concerned, I have not acquired absolute certainty” Albert Einstein



What does our observable Universe look like?





Representation of the observable Universe, of logarithmic inspiration (As we move away from the center, the distances increase considerably)


It has the appearance of a sphere where the Earth is at the center, the radius is 13.8 billion light years (i.e. a distance traveled at the speed of light (300,000 km/s) for 13.8 billion years)
Attention! The Earth is not at the center of the Universe, it is just an appearance for the terrestrial observer. An inhabitant of a planet billions of light years away will have a similar perspective of being at the center of their own observable Universe.
The interior wall of this sphere represents the observational limit which is called the cosmic microwave background; it is the very first possible radiation, emitted approximately 380,000 years after the Big Bang, at a particular moment of fall in the temperature and density of the Universe, the photons were able to decouple from matter and begin to travel in space freely. This radiation, described as fossil, has only been mapped by observation satellites in the microwave domain Cobe, WMAP then Planck. This observational limit gives the appearance of a cosmological horizon, nothing can be observed beyond it whatever the power of the instrument. By analogy, from the Breton coast, you have no hope of observing the Statue of Liberty in New York with even a very powerful telescope because of the horizon produced by the curvature of the Earth.
The 6 meter diameter space telescope (the James Webb telescope) will look for the first stars and the first galaxies which must be close to the cosmic background, estimated to be a few hundred million light years away. The farther away we observe galaxies, the closer we observe them to the beginning of the Universe. The galaxies observed closest to Earth will be seen in more contemporary times. The closest astronomical object to us is the Moon, about 300,000 km away, the image of the Moon observed is that of the Moon one second ago (time taken by photons from the Sun reflected on the lunar surface to reach us). Light from the Sun takes 8 minutes to reach us and several years for the closest stars!
To observe from afar is to observe from the past!
With equipment described on the "Practical part equipment" page, we can explore part of our Galaxy, see the page "Our Galaxy The Milky Way", but also the galaxies that surround us, see the page "The extra-galactic environment" .
We can detect photons emitted long ago in the past, quasar like 3C273 when life on Earth was only present in the ocean in microscopic form 2 billion years ago; From a double quasar 7 billion years ago when the Earth and even the Sun did not yet exist or from a quasar more than 12 billion years ago when our Galaxy was perhaps also a quasar.

3) History of the discovery of the Universe:

The most important dates (from my point of view) in the progress in understanding the Universe are cited there. What is extraordinary in man's intellectual abilities is the ability to construct step by step the description of the world around him based on the discoveries of the predecessor scientists of each era.

3.1) At the time when the Earth was at the center of the Universe but was no longer flat

More than 2,600 years ago, the Earth was considered flat, surrounded by an ocean and the passing of the stars was a projection of lights under the celestial vault. All physical phenomena were explained by the Gods... the stars were in close relationship with the divinities, for example for the Roman gods (and the Greek gods): the Sun (Helios), the Moon (Artemis goddess of the hunt) , Mercury (Hermes messenger of the Gods) Venus (Aphrodite goddess of love) Mars (Ares god of war) Jupiter (Zeus god of the gods) Saturn (Chronos god of time), even the Earth was Gaia goddess of the Earth. ..


In 570 years BC: the Greek philosopher Anaximander de Millet understands that the Earth floats in space, he answers that the Earth cannot fall because the objects that fall, fall towards the Earth... It's strange today to think that before him, no one had understood that the stars which set in the evening in the west were the same stars which rose several hours later in the east and so on... The earth imagined in the form of a cylinder (and without rotating on itself in 24 hours) is at the center of space in the middle of the stars which revolve around it. By analogy, the experience was simple and obvious: Anaximander, sitting on the steps of his home (facing the South) asks one of his students to turn around, the master sees his student go to the right (west side), disappear behind the walls, sees him reappear from the left (East side), he circulates in front of him and so on... The house is the Earth, Anaximander is an observer, his student is a star.
With Anaximander, it is the beginning of the study of natural phenomena without being explained by the will of the Gods.
(Carlo Rovelli, contemporary astrophysicist, wrote a remarkable and complete book on this first great event of explanation of the World "Anaximander of Miletus or the birth of scientific thought").

In 530 BC: The Earth is considered spherical, following in particular the observation of lunar eclipses: the Earth's shadow is projected onto the lunar surface. The diameter of the Moon is estimated to be 3 to 4 times smaller than the diameter of the Earth (considering that the Sun is at a distance much further than the Earth-Moon distance, the only conclusion drawn from the failure of the tests of the measurement of the Earth-Sun distance made in antiquity is that this distance must be very large)



Photo of a partial lunar eclipse, by matching the contour of the earth's shadow on the full Moon, we draw a circle which would roughly correspond to the size of the Earth. If you don't have the chance to one day travel into space to contemplate the Earth from afar, all that remains is to see ''part of'' its planet projected as a shadow puppet on our satellite.


- 273-192 BC: Erastosthenes precisely measures the circumference of the Earth: it is a historic measurement which was carried out at a time when many continents were unknown and no one had circumnavigated the world! The circumference of the Earth was deduced from the calculation of a meridian arc of a fiftieth of a circle between Syene (Aswan) and Alexandria. It is enough to know the distance between its two sites and to precisely measure the minimum length of the shadow of a vertical obelisk of a known height, on June 21 in Alexandria (On June 21, the Sun culminates at the zenith in the middle of during the day in Syène, there is no shadow in this place and at this moment). Trigonometry is the mathematical tool that allows you to calculate the angle of the shadow from the top of the Obelisk which is the same angle as that formed between Syène - The Center of the Earth - and Alexandria. The period unit of length used was the stadium equivalent to 157.5 meters. The known distance between Syène and Alexandria is 5000 stadia, this distance multiplied by fifty gives a terrestrial circumference of 250000 stadia or 38375 kms.


- 290 BC: Aristarchus of Samos describes the heliocentric system; More than 2,300 years ago, some scientists had already understood and considered that the Earth rotated on itself in one day but also around the Sun in 365 days. But to give importance to the existence of the human species, philosophers and religious people have focused on the geocentric system described by Aristotle and a geocentric system more precisely described (and complex) by Ptolemy.

3.2) At the time when the Sun became the center of the Universe



Two famous travelers from the 15th and 16th centuries applied the knowledge of the ancients about the sphericity of the Earth. Wanting to reach the East Indies from the west, Christopher Columbus encountered the American continent in 1492. Continuing Columbus's unfinished project, the navigator Ferdinand Magellan undertook with 237 men and five ships on August 10, 1519, the epic the most extraordinary and dramatic of all time to have completed the first circumnavigation of the world. Only one ship "The Victoria" returned on September 6, 1522 to Seville and in total only 35 'surviving' men sailed around the world, even Magellan was killed during the expedition.



The Nao Victoria at the port of St-Raphaël (French Riviera) in March 2023,
replica of the Victoria ship which completed the first circumnavigation of the Earth (the greatest feat of all time!)


Ptolemy's system is criticized based on observational inconsistencies (how can we explain the variation in luminosity of the external planets which are supposed to be at equal distance throughout their rotations around the Earth?)
Nicolas Copernicus, in this context, will revolutionize his period, his work 'Revolutions of the Celestial Spheres' was printed in the year of his death in 1543. He exposed a heliocentric system which is simpler and more logical than the geocentric system.
We must recall the interesting remarks of Thomas Diggs around 1576, who thought that the stars are dispersed in infinite space (explanation of the difference in luminosity of the stars on the 'sphere of fixed objects'), in this case how can we imagine that a star located towards infinity can revolve around the Earth in 24 hours?
Tycho Brahé developed a more precise observation than his predecessors. He calls into question the immutability of Aristotle's supra-lunar world through observations of a supernova (why does a new star suddenly appear?) and a large comet which is not an atmospheric phenomenon. Tycho Brahé does not believe in Copernicus and he develops a 'hybrid' system where all the planets revolve around the Sun but the earth remains stationary.

The metaphysician Giordanno Bruno defends the Copernican system and the fact that the Universe is infinite... this does not please the church which will burn him alive in the Campio del fiori square in Rome in 1600.

Statue of Giordanno Bruno in Campo del Fiori square in Rome




- 1609 is the date that speaks the most to amateur astronomers: Galileo observes the stars behind a telescope. He is not the inventor of the telescope but he is the first recognized scientist to have studied the sky with this instrument. Only a little over four centuries ago, a man discovered new stars for the first time and saw objects never seen before. These observations will provide proof of the falsity of Ptolemy's model.
The observation of the phases of the planet Venus proves that the latter revolves around the Sun.
The discovery of the Galilean satellites around Jupiter proves that small bodies gravitate around large ones.




These 3 photos taken with a compact digital camera with 30X zoom, represent the estimated appearance of the lunar landscapes, the 4 satellites orbiting Jupiter and the phases of Venus that Galileo observed behind his first glasses at the beginning of the 17th century. Today, even the smallest beginner's glasses are of much better quality!


As instruments become more and more perfect and observers become more and more numerous, the Universe will continue to expand in the sight of astronomers...

By studying the movement of Jupiter's satellites, Olaüs Roemer notes that satellite eclipses occur with a delay of several minutes depending on whether the Earth is located more or less far from Jupiter. This time difference comes from the distance that the light information takes to reach the observer if the Earth is closest to Jupiter or furthest away.
The Danish astronomer demonstrated that light is not instantaneous and that it has a finite speed estimated at the time around 230,000 kms/sec. (The real speed of light in a vacuum is 300,000 kms/sec, so the light from the stars takes time to travel to us)



The Englishman Isaïc Newton describes the law of universal gravitation which can explain both the fall of an object towards the ground (like the apple which is the Newtonian fetish object) and the revolution of a satellite around its planet (like the Moon around the Earth).


The distances of the planets of the Solar system are well known in the astronomical unit (the AU which is the distance of the semi-major axis of the earth from the sun). But what is the precise distance from the Earth to the Sun?
The transits of Venus in front of the Sun seen from several different points on Earth will make it possible to obtain an interesting value of the Astronomical Unit.


Photo of the transit of Venus in front of the Sun on June 8, 2004 in Lyon (France) (canon 350D at the focus of an 80mm telescope and 480mm focal length protected by a solar filter)

The observation of the transit of Venus in front of the Sun is a rare phenomenon because the last transits took place in 2004 and 2012 and we will have to wait until 2117 and 2125 for the next transits...


3.3) When the Milky Way was the Universe - the beginning of the study of stars



The Sun is seen at the center of the Galaxy which is considered to be the Universe. Astronomers have no idea of ​​the dimensions of the Galaxy or the Milky Way.

The 19th century will be marked by great scientific and technological progress which will see the birth of astrophysics.

1838 was the year of the first measurements of the distance to stars using the annual parallax method. Finally, a distance is assigned to the fixed ones. The nearest stars are at extremely farther distances than the farthest planet from Earth. After the visual discovery of Uranus by William Herschell in 1781, Neptune was discovered at the coordinates given by Urban LeVerrier in 1846, thanks to long calculations carried out following the laws of gravitational mechanics (observations of the disturbance of the trajectory of Uranus suggested the presence of an 8th planet).

Bessel was the first to calculate the first distance of a star, that of 61 Cygnus with 0.37''; Struve determined 0.1'' for Vega. It was at the Cape Town Observatory that the largest parallax for Alpha Centauri was known with 0.76'' which gives a distance from Earth of 271,400 AU (The most distant planet in the solar system Neptune is approximately 30 AU from the Sun).

The beginning of the measurement of the Universe has also begun. The first observations are that the stars are very far from each other and that space is made up essentially of vacuum or ether, a fine substance which is capable of propagating light: this was a fashionable hypothesis before the beginning of the 20th century.

Joseph van Fraunhofer was a German optician-physicist who invented the spectroscope. He discovers dark lines in the spectrum of the sun. It observes spectra of bright stars, which are different from the Sun. He observes the spectra of the planets which are almost identical to the Sun, this is proof that the planets reflect solar light.

Kirschoff and Bunsen describe the chemical elements seen in the Sun, using spectra of chemical elements reproduced in the laboratory.

As early as 1848, Doppler and Fizeau discovered, through the shift of spectral lines, the speed of movement away or approach of a source thus measured.

Physicists Kirchoff, Stephan, Boltzmann, Wien and then Max Planck will make it possible, thanks to the analysis of the intensity of the spectrum in different wavelengths, to measure the surface temperature of a star, thus creating a new discipline: astrophysics.

The instruments will be perfected and improved. Foucault would invent the modern telescope; in 1862 he built an equatorial telescope equipped with a more efficient silver glass mirror 80cm in diameter which replaced the metal mirror, which was difficult to cut and maintain.

The revolution will be the invention of photography. The moon was photographed in 1840, the star Vega in 1850 and a spectrum in 1880.
The Harvard Observatory was at the forefront in producing photographic plates of star fields and spectra. Picking will organize an efficient and profitable female team to analyze and catalog the entire sky. A main sequence of stars will be defined as OBAFGKM.

After synthesis of distance measurements by annual parallax, production of spectra, determination of surface temperatures and then luminosity; Hertzprung and Russell will create a diagram that will allow us to study star populations.

Since Charles Messier and his first catalog of around a hundred deep sky objects, Herschell has pushed the collection to 2,500 objects. The increasingly detailed photos of nebulae make it possible to identify spiral nebulae, especially present in regions less populated by stars (away from the Milky Way).

3.4) At the time when the Milky Way became one galaxy among billions of others



Henrietta SwanLeavitt was the woman who started it all. Working at the Harvard Observatory, she published a paper in 1912 which provided the solution for measuring the distance of objects located well beyond the nearest stars around the Earth. During the twentieth century, the Universe will immediately be much larger!

Its job is to detect variable stars on photographic plates. By studying photos of the Small Magellanic Cloud, she discovered Cepheid variables and noted that the brightest ones had the longest periods. Considering all the stars in the Small Cloud equidistant from Earth, his paper demonstrates a relationship between the luminosity and period of these variable stars. It even suggests that if we know the distance of a star of this type closer to Earth (measurable by parallax), it would be possible to know the distance of any Cepheid star spotted and studied. A Cepheid would be a “standard candle”, very useful for fixing the intrinsic luminosity of the star (because otherwise, there is no possibility of knowing if a star is faint but close, or bright but distant!).

In 1913, the Danish Ejnar Hertzsprung, then Harlow Shapley in 1918, attempted to determine the distance of several Cepheid variables to calibrate the Leavitt luminosity-period relationship. Due to the difficulty of the task, the calibration was poor until 1952 when the calibration was revised by Walter Baade.

While waiting for the time for more precise calibrations to arrive, Edwin Hubble detected a Cepheid in a photograph of the great Andromeda nebula M31 in 1923, taken at the focus of the brand new 100-inch Hooker telescope (2.54 meters in diameter ) of Mount Wilson, which is the largest instrument of the time. It will determine the distance of M31 at 900,000 light years which is very distant and becomes a spiral galaxy distinct from ours. There are a number of other galaxies even more distant.





Hubble will study the galaxies to classify them and measure their distances by methods other than the Cepheids because the stars are no longer discernible on the images of more distant galaxies. By producing spectra of galaxies, identified absorption lines shift towards the red (Redshift). By the Doppler-Fizeau effect, we conclude that the galaxies are moving away from us. In 1929, this was confirmation for Hubble, who relied on the observations of Vesto Slipher from 1912 (4 galaxies are approaching and 21 are fleeing us), and then of Humason, his assistant (with 38 additional fleeing galaxies). .

Hubble will publish its famous law linking the escape speeds of galaxies as a function of their distances. By measuring the Redshift of a galaxy spectrum, we can know its distance. Due to the poor initial calibration of the Cepheid method, the Hubble constant which allows the distance of galaxies to be calculated is worth 500 Km/s/Mpc. After 1952, the constant H0 will be estimated between 50 and 100 Km/s/Mpc then close to 70 Km/s/Mpc in 1990.

3.5) At the time when the model of evolution of the dynamic Universe became the Big Bang



During the year 1905, Albert Einstein (1879-1955) published 5 articles, one of which was the theory of special relativity: space is linked to time, the speed of light is an absolute value, nothing Not even a light emitted from a moving vehicle can exceed it.

He shows that if a body releases energy in the form of light then its mass decreases by an amount E/C² and publishes his famous equation of E=mC².


Wax of Albert Einstein at Chaplin's World, Veuvey in Switzerland


In 1907, he had his 'happiest idea of ​​his life': he understood that a body in free fall does not feel its own weight.

He will then write the principle of equivalence: the effect of gravitation on a body is the same as a continuous acceleration of this body. In 1911 he did a thought experiment where he imagined himself in a cabin accelerating in space, he opened a small opening which let a beam of light pass through the cabin, the light having a finite speed reached the other side not exactly opposite but at a lower point, the light is seen curved!

Using the principle of equivalence, he deduces that gravitation must bend light, which nevertheless has no mass! Gravitation caused by mass bends space-time and light then follows its path over the altered space-time.

With the precious help of a mathematician friend Marcel Grossmann who mastered non-Euclidean geometries, Einstein was able to publish in 1915 the theory of general relativity which replaced Newton's mutual forces (which cannot be exerted at a distance at an infinite speed ) by a geometry of space-time modeled by the mass which will be the actor of the effects of gravitation.

In 1917, Einstein described with general relativity a model of a closed universe within a static hyper-sphere!

This theory was validated thanks to the measurement of the deviation (small in the order of an arc second!) of stars passing very close to the Sun, which was totally eclipsed in 1919 by Eddington's expedition. The effect of the deviation of light rays is also the prediction of gravitational mirages which will be observable much later from 1979.


Solar Eclipse of March 29, 2006 in Niger



Alexandre Friedmann (1888-1925) is a brilliant Russian mathematician, who after learning general relativity, will apply it to describe different dynamic theoretical universes, such as a universe in expansion then in contraction in 1922 or a universe in infinite expansion in 1925 , year of his disappearance.

Abbot Georges Lemaître, canon, astronomer and Belgian physicist (1894-1966) carried out the same work as Friedmann, but upon learning of the latest astronomical discoveries in 1927, he was the first to explain the constant relationship between distance and escape velocity of galaxies discovered by Hubble.

At this time, the most distant galaxies reach a tenth of the speed of light. How can we explain the extremely rapid movement of an immense cluster of stars in a theory of Newtonian gravitation where space is absolute? With General Relativity, the container of the universe (space) can vary in size, if it increases then the objects present inside will follow the course of expanding space!

He then puts forward the hypothesis of the primitive Atom to describe the birth of the Universe. He even suspects that cosmic radiation would carry traces of the initial events.
In 1951, he distanced himself from the speech of Pope Pius XII who evoked the theory of the original explosion of the Universe as the Flat Lux of the creation story. It should be noted that many astronomers have had preconceptions regarding this theory, which is considered a little too biblical.

The discovery of the cosmic microwave background will have a significant and decisive impact. Planned in 1948 by Georges Gawmow, Ralph Alphs and Robert Hermann, they predict an important stage in the evolution of the very young Universe which is a phase of decoupling between light and matter. This is the existence of the cosmic microwave background, the first detectable radiation from the Universe emitted 380,000 years after its birth. It is very homogeneous, diffuse and observable in all directions in the sky. In 1964 the Americans Arno Penzias and Wilson discovered it by chance while developing a Cornet-type antenna in New Jersey, working for Bell Laboratories.

Supporters of the steady state theory doubt the explanation of the background noise, but the analysis of the thermal spectrum of the diffuse background removes the doubts by wonderfully identifying it with that of a black body. The spectral red shift of galaxies has also been criticized by explaining a theory of tired light through its travel in space, but the analysis of the brightness curves of distant supernovas among others has demonstrated the veracity of the spectral shift.

This scientific confrontation was healthy: if propositions contrary to a theory fail to prevail, then this further strengthens the criticized theory.
The British Fred Hoyle is known for having participated in the writing of the B2FH article (Margaret and Geoffrey Burbidge, William Fowler and Fred Hoyle) which describes nucleosynthesis processes (production of chemical elements in stars). Fred Hoyle, the most famous supporter of the stationary state theory against the model of dynamic evolution of the Universe, will nevertheless invent the Big Bang!

Indeed, during a radio broadcast, he uses the expression ''Grand Boum'' in order to ridicule the theory being fought!

The term Big Bang will remain the definitive and impactful term to describe the expansion of the Universe since its beginnings, the Big Bang model will definitively establish itself in the 1970s. The term Big Bang is not the best chosen to popularize this theory because we can imagine an explosion of a firecracker which extends into a void initially present. The universe is not a content which extends in a container (reference to Newtonian mechanics) but a content (energy-matter) and a container (space – time) which extend mutually ( reference to general relativity).


Many other arguments for the Big Bang exist such as primordial nucleosynthesis (alpha, beta, gamma article for which Georges Gamow is still well illustrated), the explanation of the greater presence in the past of radio galaxies, of which the quasars, discovered in the 60s are part of it and of course the absence of any object having an age greater than that of the Universe....


3.6) At the time when the Solar System ceased to be the only planetary System in the Universe



It was not until the 1990s that the first planets from other stars were detected. They are called Exoplanets. Before this period, many astronomers believed that they existed but there was no observational technology to prove it.

Some astronomers even claimed to consider that the Solar System was unique and that the formation of a planetary system around a star was improbable...

In 1995, Michel Mayor and Didier Queloz, Swiss astrophysicists, proved the opposite by identifying the first planet around another star, 51 Pegasi b using the Elodie spectrograph installed at the Haute-Provence Observatory.



Observatoire de Haute-Provence (OHP) in St-Michel-l'Observatoire, where the first exoplanet was detected in 1995 at T193



28 years later, the sum of exoplanet discoveries amounts to several thousand...



Four centuries earlier, Giordano Bruno had the idea that all stars were Suns that sheltered inhabited worlds... It was his concept of the plurality of inhabited worlds...

Programs searching for extraterrestrial signals discovered that there was no There are no traces of technological civilizations around us. After the exploration of the Solar System during the 20th century, there is no life on the surface of the Moon, Venus and Mars...

The discovery of traces of life elsewhere than on Earth will be a major event. Scientists believe that a trace of life can be indirectly detected by the spectral analysis of the atmosphere of an exo-planet (example: if O2 is detected, it is because a form of microbial life is proliferating on this planet like the stromatolites which helped to enrich the Earth's atmosphere 3.5 billion years ago).

Research has so far only led to the discovery of a single planet that is home to life: it is the planet that draws us to the ground every day!

Following the study of the development of life, it appeared quite early and this suggests that if all the elements are present then the appearance of microscopic life is easy to cause.
However, it took a few billion years to develop to become a more complex multi-cellular organism. This step seems much more difficult to achieve and for some biologists it is almost a miracle!
Then, over the last hundreds of millions of years, life has exploded in size and shape, from the seas to the air...
Very recently (on the scale of the 4.5 thousand years of the Earth), a mammal has become a primate developing like a very intelligent monkey which ended up conquering its entire territory and now perceives the entire Universe surrounding it as infinite!

So, the idea that a single and unique planet out of all the X billion planets in the universe (statistical basis built on the study and inventory of exoplanets discovered), has seen all the stages of the evolution of living things and that no other planet has even seen the threshold of the first stage crossed... is illogical or incomprehensible...

Almost all specialists agree in thinking that life necessarily exists elsewhere, that it remains be discovered to be scientifically validated, but we should not expect it to resemble extra-terrestrials resembling characters from science fiction films!
In this regard, concerning the appearances of flying saucers at night, it is curious to note that no amateur or professional astronomer has had this type of encounter? However, it is this type of individual who spends a lot of time observing the sky outside and understanding a little bit of what he sees!

3.7) Today, at a time when knowledge about the Universe is considerable and yet...



Since the 1990s, telescopes have moved from 3-4-5 meter diameter telescopes to 8 meter telescopes (like the 4 8 meter telescopes of a single mirror, the Very Large Telescope at Cerro Paranal in Chile ) or 10-meter telescopes (like the 2 10-meter Keck telescopes composed of several mirrors, located at the summit of Mauna Kea in Hawaii); Technologies have been developed to make it possible to increase the size of mirrors.

Active optics makes it possible, thanks to the action of actuators on the primary mirror, to correct mechanical deformations caused by gravity.

Adaptive optics makes it possible to perform actions always via actuators, up to 1000 times per second on the secondary mirror, the actions caused were calculated directly after analysis of an artificial star constructed from lasers, to compensate the harmful effects of air turbulence (a sworn enemy with the pollution of artificial lights for any high resolution observation).

To completely eliminate turbulence, telescopes must be put into orbit, this was achieved with the launch of a 2.5 meter telescope known as the Hubble Space Telescope in 1990 and then a more ambitious 6 meter telescope launched 31 years ago. later. The other great advantage of space telescopes is to observe the stars at wavelengths which are not absorbed by the Earth's atmosphere such as gamma rays, X, UV, infrared and radio microwaves.



Visit of the VLT in 2000, Very Large Telescope, ESO, Cerro Paranal in Chile
Network of 8 telescopes, including 4 telescopes of 8.2 meters in diameter


Another type of observatory which has emerged recently, does not observe electro-magnetic radiation but very minute deformations of space caused by black hole mergers, the event is so cataclysmic that part of the energy released distorts space-time which propagates to the Earth!
The observations collected are colossal, astrophysicists and cosmologists have recently entered into precision astronomy which must manage colossal Big Data.

Fritz Zwicky (1898-1974), Swiss astronomer, raised in 1933 the fact that there is not enough mass in galaxy clusters to hold all the galaxies together.

Vera Rubin (1928-2016), exposed in 1978 with other specialists, following the measurement of rotation of stars at different distances from the galactic center, that they all rotate at approximately the same speed, while depending on of the estimated mass of the number of stars, the rotation speed should decline with distance from the center of the galaxy. At the periphery of galaxies, a halo of matter must exist to explain the stability of rotation speeds.

Dark matter, now named, is the still unknown type of matter that is missing around galaxies and galaxy clusters. It does not interact with baryonic matter (atomic nuclei) and with any type of radiation.

In 1998, two international teams, engaged in the study of supernovas (type Ia whose absolute magnitude is known), precisely measured the distances of distant galaxies and they came to the conclusion that for several billion years, the expanding universe is accelerating! The energy called “dark” because it is not yet known, further increases the repulsion between galaxies.

A final assessment states that the universe is made up of only nearly 5% known matter, approximately 27% unknown dark matter and 68% equally unknown dark energy...
All physics professionals of all ages disciplines (from particles to cosmology) still have a lot of work to do!

A certain modesty must seize us to understand that despite the fantastic discoveries made since antiquity, everything cannot yet be understood and that the Universe still retains many mysteries!





| The Universe | Practise - Observing | Our Galaxy - The Milky Way | Galaxies | Quasars - Expansion of the Universe |

Observing the Universe - The Universe (Sciences - Astronomy)    -    Author : Frédéric - France



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