00:00Locating the Polar Star is relatively easy by a clear night.
00:04You just have to identify the Big Bear.
00:07The two stars located at the end of the pot of this constellation serve as landmarks
00:11and indicate the direction of the Polar Star.
00:13Do you see it? It's the tip of the pot handle.
00:16Or, if you prefer, the tail of the Little Bear, right there.
00:21For centuries, the Polar Star has fascinated observers.
00:25Also called Polaris, it shines almost exactly above the Northern Pole,
00:30which makes it a precious landmark for any traveler without a compass or GPS on his phone.
00:37It is also the closest CFI to our planet,
00:39a type of star that oscillates periodically in brightness and size.
00:44In addition, Polaris belongs to a binary system.
00:47It has a more discreet companion, named Polaris B.
00:51From Earth, we can observe the latter in orbit around the Polar Star.
00:57But as astronomers scrutinize Polaris, their perplexity grows.
01:01The main obstacle lies in the inability to adapt to its size and distance.
01:06To estimate its parameters, as well as its age, scientists use several techniques.
01:12One of them is based on stellar evolution.
01:15After studying the brightness, color and frequency of pulsations of a star,
01:20experts can deduce its brightness, size and stage of evolution.
01:25Once these parameters are established, it becomes relatively easy to calculate its distance.
01:30This is a mathematical operation based on the comparison between its intrinsic brightness
01:35and the intensity with which it is perceived from Earth.
01:39These models are particularly reliable for stars like Polaris,
01:43whose pulsation is directly related to brightness.
01:47This relationship allows to estimate their distance with precision.
01:50Astronomers are so confident in this approach that they use it
01:54to measure distances on a large scale in the universe,
01:57making cepheids a fundamental tool in astronomy.
02:00However, other methods of analysis of the Polar Star contradict these models.
02:05Polaris is an astrometric binary star,
02:08which means that its companion star gravitates around it following a well-defined trajectory.
02:14From Earth, this orbit gives the impression of a circle drawn around the main star.
02:19The complete revolution of the secondary star takes about 26 years.
02:23Although astronomers have not yet observed in detail the entire orbit of Polaris B,
02:28they have enough elements to deduce its trajectory.
02:32By applying Newton's laws of gravitation, they can thus calculate the masses of the two stars.
02:38These calculations, crossed with the recent measurements of the Hubble Space Telescope,
02:43provide very precise estimates.
02:45They indicate that Polaris has a mass of about 3.45 times that of the Sun.
02:52However, this value is much lower than that advanced by stellar evolution models,
02:57which suggests a mass 7 times that of the Sun.
03:01There is another strange peculiarity in this stellar system.
03:05By calculating the age of the stars,
03:07researchers have discovered that Polaris B was much older than its companion.
03:11This is very rare in a binary system, because in general the two stars are the same age.
03:17One possible explanation would be that one of the measures used to determine this age is incorrect.
03:23Polaris remains a difficult star to study.
03:26Because of its position above the North Pole, it escapes the view of most telescopes.
03:31Those who have the equipment necessary to measure its properties with great precision
03:36are generally used to observe stars that are farther away and less luminous.
03:41Polaris, with its intense light, dazzles these instruments, preventing them from studying it correctly.
03:47An interesting theory suggests that the main star of the Polaris system
03:51was once a binary system, but that the two stars merged several million years ago.
03:57This collision could have rejuvenated them by bringing them additional matter,
04:01which makes them look younger than they really are.
04:04This phenomenon could also explain other anomalies,
04:07because the stars from such collisions do not correspond to the classical evolution model.
04:12However, it is important to note that none of these hypotheses have yet been confirmed.
04:17The polar star is of paramount importance.
04:20Because of the incessant rotation of the Earth, the stars seem to move through the sky.
04:25And this movement, combined with the inclination of the planet, is at the origin of the seasons.
04:30If we drew a straight line extending the axis around which the Earth rotates,
04:34and if we extended it over more than 300 light years beyond the North Pole,
04:38we would end up with the polar star.
04:41Polaris remains practically immobile in the sky, constantly pointing north.
04:45This makes it an essential navigation tool,
04:48especially before the appearance of GPS systems.
04:51If you were at the equator, the polar star would be just above the horizon,
04:55while at the North Pole, it would be directly above you.
04:59By measuring the height of the star in the sky,
05:02it is possible not only to orient yourself,
05:05but also to determine your position on Earth with great precision.
05:09It is curious to note that there are no stars equivalent to the South Pole,
05:13because there are no stars bright enough directly above this region.
05:18However, it is possible that such a star will appear one day.
05:22This phenomenon could be linked to the precession,
05:25the movement similar to that of a spinning top,
05:28which leads to a progressive change in the orientation of the Earth's poles.
05:32Thus, in the next 26,000 years, it is possible that the North Star changes,
05:37going from Polaris to other stars.
05:39One day, Vega will take the place of the Polar Star.
05:43It is the fifth brightest star in the night sky
05:46and the second brightest in the northern celestial hemisphere.
05:49Vega is also called Alpha Lyrae,
05:52the main star of the Lyra constellation.
05:55It has played a central role for civilizations since Antiquity,
05:59thanks to its great luminosity and its blue color,
06:02which make it very recognizable.
06:04Vega was already the Polar Star several thousand years ago
06:08and should find this title in about 12,000 years.
06:11This star is only 25 light-years from Earth
06:15and is only 450 million years old,
06:18much less than our solar system,
06:21aged 4.6 billion years.
06:24Astronomers study it to better understand the stellar systems in formation.
06:29Vega is almost directly above our heads in summer,
06:33or the Middle North latitude.
06:35It hides behind the horizon for only 7 hours a day
06:38and is visible every night of the year.
06:41Traveling further south,
06:43we see that Vega disappears under the horizon for longer periods,
06:46but in Alaska, in northern Canada and in certain regions of Europe,
06:50it never sets.
06:52Its blue-white light has been noticed in many cultures,
06:55including the oldest,
06:57from the Chinese to the Polynesians and the Hindus.
07:00The name Vega can be translated as
07:02Chute or Rapt,
07:04referring to the period when this constellation was seen
07:07as a flying vulture rather than a lyra.
07:09Vega was also the first star to be photographed,
07:13after the sun, of course.
07:15In 1850, astronomers from Harvard's observatory
07:19used a 38-centimeter refractor to capture it in image.
07:24Twenty years later,
07:26an amateur astronomer analyzed Vega's light,
07:29thus revealing the different elements that make up the star.
07:32In 2006, thanks to telescopic observations,
07:35scientists discovered that Vega rotated at a speed such that
07:39its poles were several thousand degrees warmer than its equator.
07:43The star rotates every 12 and a half hours,
07:46reaching 90% of its critical rotation speed,
07:50i.e. the speed at which an object may disintegrate.
07:53In 2013, researchers announced the discovery
07:57of an asteroid belt around Vega,
07:59suggesting the possibility of planets among these space rocks.
08:02This belt is divided into two areas,
08:04an exterior region composed of icy asteroids
08:07and an interior region with warmer rocks.
08:10Scientists can study bright stars like Vega
08:13thanks to NASA's TSS mission,
08:16whose name means Transiting Exoplanet Survey Satellite.
08:20Launched in 2018,
08:22this satellite dedicated to observing the entire sky
08:25has as its main objective the search for exoplanets.
08:28But it also allows to analyze stellar variability.
08:32By studying stars like Vega,
08:34TESS helps scientists better understand
08:36the first stages of star evolution.
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