Carte blanche. La mission spatiale européenne Gaia rend publics la position de 1 692 919 135 étoiles de notre galaxie, et le mouvement de la majorité de celles-ci. Un catalogue sans équivalent.

L’équipe scientifique de la mission spatiale Gaia publie, le 25 avril, le ­gigantesque catalogue issu de vingt-deux mois d’observation de ce satellite d’astrométrie développé par l’Agence spatiale européenne. Riche de plus de 1,69 milliard d’étoiles, ce qui représente 1 % de la population stellaire de notre galaxie, ce catalogue est l’ultime descendant de celui que l’astronome grec Claude Ptolémée inséra dans son Almageste au IIe siècle de l’ère chrétienne.

Fondé sur le catalogue établi par l’astronome grec Hipparque quatre siècles plus tôt, le catalogue de Ptolémée fit référence dans les mondes occidental et arabe pendant plus de mille ans. Il comptait 1 022 étoiles dont il indiquait la position céleste et l’éclat apparent. La taille et la qualité des catalogues d’étoiles se sont accrues au fil du temps mais ils restèrent longtemps incapables de ­décrire fidèlement notre environnement stellaire car il y manquait une information cruciale : la distance des étoiles. Cette question est longtemps restée irrésolue et polémique car liée à nos représentations du monde.

En décentrant la Terre pour en faire une planète comme les autres, Nicolas Copernic (1473-1543) provoqua un séisme intellectuel à portée cosmologique. En effet, si la Terre tourne autour du Soleil, alors la position ­apparente d’une étoile pourrait, au fil des mois, changer par rapport à celle d’une étoile d’éclat plus faible, supposée plus lointaine. N’ayant pas constaté cet effet de parallaxe des étoiles, le plus grand observateur du XVIe siècle, l’astronome danois Tycho Brahe (1546-1601), refusa de souscrire à l’hypothèse héliocentrique.

Pour échapper à cette objection et sauver le mouvement de la Terre autour du Soleil, Copernic déclara que les étoiles se trouvaient à une distance si considérable que le changement de position de la Terre sur sa trajectoire ne modifiait en rien le paysage stellaire. Autrement dit, alors que les Anciens tenaient la dernière sphère planétaire, celle de Saturne, pour voisine de celle des étoiles fixes, Copernic introduisit entre elles un immense espace vide de tout corps pour justifier l’absence d’observation de la parallaxe des étoiles.

Parallaxe d’une étoile

Pour observer ce qui fut considéré comme la preuve physique de l’héliocentrisme, les plus habiles astronomes se dotèrent d’instruments toujours plus précis. Mais il fallut ­attendre 1838 pour que l’astronome et mathématicien allemand Friedrich Bessel (1784-1846) mesure pour la première fois la parallaxe d’une étoile, la binaire 61 de la constellation du Cygne. Cet angle, égal à celui sous ­lequel on verrait le rayon de l’orbite terrestre depuis cette étoile, est extrêmement faible : Bessel obtint une parallaxe de 0,35 seconde d’arc (soit environ un cent millième de ­degré !), ce qui la situait à une distance 590 000 fois supérieure à celle du Soleil !</s>1.7 billion stars will be mapped from the Gaia space telescope that are as far as 8,000 light years away.

Tomorrow the European Space Agency will be publishing what is to date the largest 3D map ever created of the Milky Way galaxy thanks to the very unique and special Gaia space telescope.

As the Gaia space telescope has been in operation since 2013, it has had quite a lot of time to scan the Milky Way, and the upcoming map will include a whopping 1.7 billion stars on it, according to Gizmodo.

As Uwe Lammers, who is in charge of science operations for the Gaia, revealed, the new DR2 map created by the European Space Agency is the most exhaustive star map of the Milky Way ever released, and one that will astonish stargazers everywhere.

When the first star map of Gaia was officially launched in 2016, it contained figures relating to the brightness and location of 1.1 billion stars, which was an incredible feat at the time. But now with two extra years of data to collect which include 25 observations of these stars, it will be pushing up the amount of stars mapped considerably.

Another exciting thing about the new star map will be the enormous distance it will now cover, stretching from 500 to 8,000 light years away.

The new star map will also include precise information pertaining to velocities, stellar parallax, and the temperatures of the stars. As astronomer Emily Rice explained, a map of this kind with such a wealth of information is a rarity today.

“Gaia is an unprecedented map of the Milky Way galaxy, fundamental astrophysics at its finest, laying the groundwork for decades of research on everything from the Solar System to the origin and evolution of the Universe. It is at once foundational and transformative, which is rare in modern astronomy.”

The European Space Agency map will also have detailed data on it pertaining to 14,099 asteroids within the Milky Way as well as the radial velocities of roughly 7 million stars, as Scientific American reports.

Learning more about stellar motions could prove a very useful tool when it comes to studying dark matter, and could even help with research revolving around different theories of gravity, according to astrophysicist Amina Helmi.

If you are interested in viewing the new Gaia 3D star map from the European Space Agency, it will be presented after a media briefing on Wednesday at 9:00 GMT.</s>We’re building a map of our galaxy, one star at a time. The European Space Agency’s Gaia satellite orbits Earth 1.5 million kilometres away, staring at millions of stars every day to make a 3D map of our galaxy. On 25 April it released its second batch of data.

In 2016, Gaia first released data from its star catalog spanning 14 months of constant observation. It included information about the brightness and positions in the sky of 1.1 billion stars, and more detailed data on the distances and motions of the brightest two million of those.

This new data release is even more robust, covering another 22 months of observation time. It includes more stars than the first release, and the colours, temperatures, and radii for some of those stars.

Here is the new Gaia release by the numbers:

In that 22-month timespan, Gaia looked at 1.7 billion stars up to 8,000 light-years away and measured their positions and brightness. Of those, 1.3 billion were bright enough for the satellite to measure their distances and motions. 161 million were bright enough to measure their surface temperature. This map shows the dust in our galaxy’s disk (pictured below). Dust between a star and the satellite dims the starlight and makes it seem redder, allowing Gaia to calculate how much dust is out there. Gaia measured the dimming and reddening of 87 million stars to construct this image.

Gaia measured the brightness and classified 500,000 variable stars, which are those whose brightness change over time. The length of these pulses is directly correlated to the stars’ average brightness, which we can compare to how bright they appear from Earth to figure out how far away they are. Because this process is so straightforward, these stars are used as “standard candles” to measure distances to other astrophysical objects.

While the satellite’s primary purpose is mapping stars, objects within our own solar system occasionally cross its cameras. Because of that, this data release included the positions of 14,099 objects – mostly asteroids – within our own solar system. We already knew that these asteroids existed, but for many, these are the most precise measurements of their positions. The video below shows the paths of the 200 brightest asteroids Gaia measured as they travel around the sun.

To place objects within our galaxy in a consistent frame of reference, Gaia peers into the distant universe at other galaxies, which do not appear to move across the sky because they are so far away. To find these other galaxies, it looks at quasars – supermassive black holes in the centres of other galaxies, each surrounded by a bright disk of material. It measured the brightness and positions in the sky of half a million quasars

Gaia also measured the orbits of 12 dwarf galaxies that revolve around the Milky Way, along with 75 compact clusters of stars. Because these celestial objects are nearby, they will help us understand our galaxy’s environment and evolution.

This huge pile of information will give us insight into how the Milky Way formed and evolved over time. Having extraordinarily precise measurements of so many stars may also help map the dark matter in our galaxy. It may also help us pin down how fast the universe is expanding.</s>Gaia’s all-sky view of our Milky Way Galaxy and neighbouring galaxies, based on measurements of nearly 1.7 billion stars. The map shows the total brightness and colour of stars observed by the ESA satellite in each portion of the sky between July 2014 and May 2016. ESA/Gaia/DPAC
• The European Space Agency's Gaia spacecraft just released its latest batch of data.
• The new data pins down the positions and brightness of almost 1.7 billion stars.
• That makes this the richest and most extensive map of the stars in our Milky Way galaxy to date.
• By mapping the location, brightness, and details of stars in our galaxy, Gaia helps us understand where and how our solar system fits into the greater whole.

It might be hard to find the "You Are Here" circle on this one.

The European Space Agency (ESA) just released the richest and most extensive map ever made of our Milky Way galaxy and stars beyond.

The map is based on the latest data from the ESA's Gaia mission, which was launched with the goal of creating the largest and most precise three-dimensional map of our galaxy.

So far, its results are stunning.

The latest data release pins down the positions of almost 1.7 billion stars. By mapping out the location, brightness, and details of the stars in our galaxy, Gaia helps us understand where and how our solar system fits into the greater whole.

"Gaia will greatly advance our understanding of the universe on all cosmic scales," Timo Prusti, a Gaia project scientist at ESA, said in a news release announcing the discovery. "Even in the neighbourhood of the sun, which is the region we thought we understood best, Gaia is revealing new and exciting features."

The Gaia data provides an unprecedented level of detailed information about the stars in our galaxy, with precise distance, brightness, color, and motion indicators for more than a billion stars. The dataset also includes previously unknown information about asteroids hurtling through our solar system.

In maps created from the new data, it's possible to see the brightness and color of the stars, their density, and even the interstellar dust that fills the galaxy.

The maps show the total brightness and colour of stars (top), the total density of stars (middle) and the interstellar dust that fills the Galaxy (bottom). ESA/Gaia/DPAC

The Gaia spacecraft was launched in December of 2013 and began scientific operations the next year. Gaia's stunning first dataset, published in 2016, catalogued more than a billion stars and contained distance and motion data for 2 million stars.

The newly released information is far more exact and extensive.

"The new Gaia data are so powerful that exciting results are just jumping at us," Antonella Vallenari, from Astronomical Observatory of Padua, Italy, said in the release.

In our solar system, Gaia pinpointed 14,099 asteroids. The orbits of the 200 brightest ones are visible in an ESA animation.

Everything the spacecraft has observed and catalogued so far will eventually help build a detailed 3D map of our galaxy, which will give us a new understanding of its structure and evolution. You can already explore some 360-degree videos and virtual reality visualizations of the data using material released by the ESA.

According to the announcement about the new data, major discoveries are expected after scientists have taken time to pore over the data.

Gaia will continue to release new information about the approximately 100 billion stars in our galaxy over the next couple of years. The craft will most likely operate through the end of 2020.</s>Most of us have looked up at the night sky and wondered how far away the stars are or in what direction they are moving. The truth is, scientists don’t know the exact positions or velocities of the vast majority of the stars in the Milky Way. But now a new tranche of data from the European Space Agency’s Gaia satellite, aiming to map stars in our galaxy in unprecedented detail, has come in to shed light on the issue.

The Gaia Archive opened on April 25, making public Gaia’s second data release to everyone. To quote the character Dave Bowman in the sci-fi classic 2001: A Space Odyssey: “It’s full of stars”. In fact, it contains data on the distances to more than 1.3 billion stars.

The Gaia satellite was launched in 2013 and has been scanning the sky with its two telescopes continuously ever since, with the aim of deciphering how our Milky Way galaxy formed and evolved. To do this, it is measuring something called parallax. If you hold a finger at arms length and look at it with one eye and then the other, your finger appears to shift position compared to the background. The angular change is called parallax.

Being in space allows Gaia to see similar tiny shifts in star positions. Observations at different locations six months apart (half way of its orbit around the Earth) are akin to looking at your finger with one eye and then the other. When you know the parallax as well as the distance from Gaia to the sun (or the distance from your nose to your eye), you can use simple trigonometry to work out the distance to each star (or your finger).

Gaia also sees stars move in the plane of the sky over time. These units of “angle per time” can be converted to a physical unit of speed (for example kilometres per second) if we know the distance to the stars. However, to know how a star is moving in three dimensions in space requires that we also measure the speed perpendicular to the sky along the line-of-sight. This requires a galactic speed camera!

A normal radar speed camera uses the Doppler effect – the stretching or squashing of waves because of motion – by measuring the change in the radio frequency from signals bounced off cars to measure their speed. Similarly, Gaia measures the change in frequency in the light from stars to check their speed. The star light is bluer if the star is moving towards us or redder if the star is moving away from us. This is called radial velocity.

Gaia’s first data release in 2016 published the distances of around two million stars but did not include any radial velocities. However we already knew the radial velocity of less than 400,000 of these stars – measured from the ground by many different surveys.

Gaia’s second data release includes information on sky positions and brightness for nearly 1.7 billion stars and more than seven million radial velocities. Not only does this make Gaia the largest radial velocity survey ever – it increases the number of stars with accurate 3D space velocities by a factor of 18.

A series of Gaia science demonstration papers have also been published alongside the star catalogue. I was involved in the research behind one of these papers, constructing the most detailed map ever of 3D space velocities to date.

Excitingly, the map revealed that there’s a global arrangement of stars in the Milky Way, most of which reside in our galaxy’s thin disc. These are organised in thin substructures with the shape of circular arches. This is a vital clue to how the Milky Way formed and how it is still evolving. The baton now passes to the astronomical community to interpret this finding and explore the full potential of Gaia’s second data release.

Eventually, the catalogue produced by Gaia could help us make many new discoveries – including mapping tens of thousands of asteroids in our solar system. By looking at dips in the stars’ brightness, we could also find exoplanets orbiting stars other than our own.

Perhaps more surprising, the measurements could even help us predict exactly where dark matter – an unknown, invisible substance thought to make up most of the matter in the universe – resides in the galaxy. Gaia has also found nearly 5,000 objects that can be followed by ground-based telescopes before they disappear. Most of these are supernovas, exploding stars, which may help to reveal the nature of dark energy that is causing the expansion of the universe to accelerate.

The next data release by Gaia will be in 2020. This is expected to boost the numbers of stars with known radial velocities from seven million today to around 30m – keeping our team busy for several years yet.</s>There are just so many stars. With around 300 billion stars across the entire Milky Way, making a detailed map of our entire galaxy is nearly impossible. But Europe’s space agency, the ESA, is doing it anyway.

On Wednesday, the released the largest map of the stars ever made. Their map, compiled over the past few years by the Gaia project, contains the precise locations of more than a billion stars.

The ESA’s mission began in 2013 with the launch of the Gaia spacecraft. Over the next two years, Gaia would routinely scan the entire sky twice per year, and use that information to create 3D images of the entire sky. Combining images taken about six months apart (meaning they were shot from opposite sides of our planet's orbit) can give the distances to these stars in much the same way that having two eyes gives you depth perception.

Now we have a database of the distances to around 1.3 billion stars located across a full quarter of our galaxy. That database was just made publicly accessible, so scientists from around the world can use it to make discoveries.

"Gaia is astronomy at its finest," says Fred Jansen, Gaia mission manager at ESA. "Scientists will be busy with this data for many years, and we are ready to be surprised by the avalanche of discoveries that will unlock the secrets of our Galaxy."

Although this database is already quite impressive on its own, Gaia actually gives much more information than that. In addition to distance, Gaia can track the movement of all of those stars, so we know where they’re headed and where they came from. The database also contains the color and brightness of almost every single star, which can tell astronomers a great deal of information about every one.

“The new Gaia data are so powerful that exciting results are just jumping at us,” says Antonella Vallenari from the Istituto Nazionale di Astrofisica (INAF) and the Astronomical Observatory of Padua. “It feels like we are inaugurating a new era of Galactic archaeology."

If you're interested in checking out Gaia's map for yourself, there are several different ways to explore the dataset at the ESA's website here.</s>How far is that star? Despite huge advances in technology, astronomers have always struggled with the basics of celestial geography.

That ended today when the European Space Agency (ESA) released its long-awaited , which reveals the exact distances and motions of the closest 1.3 billion stars to our solar system, plus data for hundreds of thousands more. Astronomy has changed forever.

Why, you may ask? Using those the exact positions, colors, motions, and brightness of stars, astronomers at ESA have been able to create a 3D map of the Milky Way that accurately shows how far stars are form us, but also a lot about their nature, and how they’re moving around our galaxy.

Gaia also mapped the proper motion of 14,000 asteroids in our solar system , revealed how fast seven million stars are moving either towards or away from us, and mapped the orbits of 75 globular clusters and 12 dwarf galaxies that orbit the Milky Way.

How important is the Gaia data?

A satellite that for almost five years has been anchored in an orbit of the sun about 1.5 million kilometres from Earth, the ESA’s €750 million (US$915 million) Gaia space observatory has been on a mission to produce a highly detailed star chart of our Milky Way and its neighboring galaxies that is 10,000 times more detailed than what we had before.

“Gaia is astronomy at its finest,” says Fred Jansen, Gaia mission manager at ESA. “Scientists will be busy with this data for many years, and we are ready to be surprised by the avalanche of discoveries that will unlock the secrets of our Galaxy.”

Astronomers know much about star formation in general, and a lot about some individual stars. However, they have always struggled to pinpoint exactly how far away they are from us, and how they move.

Stars more or less look the same in the night sky, but they do differ in brightness.

One star might be brighter because it’s very close, while another might be bright because it’s far away, but much larger.

"Gaia is rotating across the sky making one large circle every six hours, and it spins and covers the sky every two months," said Günther Hasinger, the Director of Science at the ESA. "In the five year mission we'll get 29 images of the whole sky."

Gaia's 3D map of the Milky Way

The new data includes positions and brightness for nearly 1.7 billion stars, and the distances, proper motions and colors for 1.3 billion of them.

"It's not a photograph, it's made from the positions of 1.3 billion stars," said Anthony Brown, Gaia Data Processing and Analysis Consortium at Leiden University, of the first accurate map of our own galaxy.

"You should download the high-res version from ESA and go to a dark place and study it."

In the image it's possible to see the plane of the Milky Way and its dust bands, and over a billion stars. "It's so hi-res that that every single dot we have a distance for," said Brown.

Gaia stands for Global Astrometric Interferometer for Astrophysics. Astrometry is the science of measuring the positions and movements of stars.

The core problem is that it's very difficult to study the distance between two objects when you’re on one of the. Luckily, the Earth travels about 584 million miles / 940 million km in one year on its orbit of the sun.

So, astronomers measure exactly where a star appears to be in the night sky twice, six months apart, therefore getting a measurement from two different places in space. Knowing the distance from the Earth to the sun is always roughly the same, astronomers then use triangulation.

The closer the star, the more it will appear to move. This is called stellar parallax.

However, it only really works for stars that are close to us. So, astronomers have sent various satellites into space to take measurements from greater distances.

The most famous was Hipparcos (named after the founder of trigonometry), which spent three and a half years in the late 1990s accurately measuring the positions of 118,000 stars, and getting a general position for 2.5 million.

The Hipparcos catalogue is still used to point ground-based telescopes and to navigate spacecraft. Gaia’s scope is far wider than Hipparcos, and its tech is much more accurate. Its billion-star catalogue is from today the definitive star catalogue, if it wasn’t already.

What tech is Gaia using?

Gaia’s instruments are thousands of times more sensitive than Hipparcos’. It is able to detect stars down to magnitude 20, which is around 400,000 times fainter than the human eye can see.

Flying on Gaia is a video camera – the biggest astronomical camera ever built – and a couple of telescopes that sweep across the whole of the sky as the satellite slowly spins.

The light they collect is funneled to three instruments, and its astro-metric detector records stars as they cross its field of view, calculating positions, proper motion and parallax.

Meanwhile, Gaia’s radial velocity spectrometer susses out how fast a star is moving towards or away from Earth, and its photometric instrument collects data on the color and brightness of each star. Gaia is filming each star 70 times.

More work to do

We now know our place in the Milky Way with unprecedented precision. With Gaia’s data, astronomers will be creating models of exactly how stars will move, and have moved, essentially rewinding and fast-forwarding time to unlock how the Milky Way developed.

But however advanced Gaia may appear, it's only the beginning. The data released today took 22 months to collect, and represents only 50% of the official five-year mission's total data.

And while the Milky Way is 100,000 light years across, Gaia has only been able to look to 8,000 light years.

Scientists are hoping to extend the mission by at least two years, and possibly until 2024, to get even more precise measurements.

"1.7 billion is only about 1% of the stars in the Milky Way," said Brown. Just 180 billion (or so) to go…
• The giant telescopes that will change what we know about the universe</s>The European Space Agency just released a new catalog, but it's not full of the latest fashions. It's full of stars.

The star catalog comes from data collected by the ESA's Gaia satellite and it includes a mind-blowing 1.7 billion stars, most of which are measured with precision as to their positions and motions. It covers stars in our home Milky Way Galaxy and beyond.

Gaia launched in late 2013. The ESA released its first Gaia catalog of 1 billion stars in 2016 with data on the distances and motions of around 2 million of those stars. This new round of data covers Gaia's surveys from mid-2014 to early 2016.

The current map is even more precise about star positions than the first release. "For some of the brightest stars in the survey, the level of precision equates to Earth-bound observers being able to spot a euro coin lying on the surface of the Moon," says the ESA.

The Gaia mission also examines the brightness, colors and surface temperatures of some stars, and the amount of space dust between us and them.

Looking beyond stars, the data includes the positions of over 14,000 asteroids. You can check out a fascinating video visualizing the orbits of those asteroids.

"The observations collected by Gaia are redefining the foundations of astronomy," says ESA director of science Günther Hasinger.

While 1.7 billion stars may be hard to wrap your head around, NASA says scientists estimate there are at least 100 billion stars (and maybe as many as 400 billion) in the Milky Way alone.

Astronomers will be busy for years working with Gaia's data, which can give us clues to the formation and evolution of the Milky Way. The ESA plans more releases and expects to issue a final star catalog in the 2020s.

You can access the publicly available Gaia information through the ESA's Gaia Archive.

Cambridge Analytica: Everything you need to know about Facebook's data mining scandal.

Tech Enabled: CNET chronicles tech's role in providing new kinds of accessibility.</s>After 22 months spend charting the night skies, the European Space Agency (ESA) has revealed the most detailed star map of the Milky Way ever created.

The ESA's Gaia mission has catalogued the positions, distance indicators and motions of over one BILLION stars in our galaxy.

It has also recorded high-precision measurements of asteroids within the solar system.

“The observations collected by Gaia are redefining the foundations of astronomy,” says Günther Hasinger, ESA Director of Science.

By looking at the information collected, researchers at the ESA are learning more about how stars move during their formation and lifespan - possibly revealing clues about the formation of the galaxy itself.

“Gaia is an ambitious mission that relies on a huge human collaboration to make sense of a large volume of highly complex data," explained Hasinger.

"It demonstrates the need for long-term projects to guarantee progress in space science and technology and to implement even more daring scientific missions of the coming decades.”

According to the ESA, the mission is able to pin down the location of some of the brightest stars in the Milky Way with a level of precision that equates to Earth-bound observers picking out a euro coin on the surface of the moon.

The amount of data captured by the Gaia mission doesn't just stop at the location of stars.

As well as positions, the data include brightness information of all surveyed stars and colour measurements of nearly all, plus information on how the brightness and colour of half a million variable stars change over time.

It also contains the velocities along the line of sight of a subset of seven million stars, the surface temperatures of about a hundred million and the effect of interstellar dust on 87 million.

Gaia also observes objects in our Solar System: the second data release comprises the positions of more than 14 000 known asteroids, which allows precise determination of their orbits.

“Gaia will greatly advance our understanding of the Universe on all cosmic scales,” says Timo Prusti, Gaia project scientist at ESA.

“Even in the neighbourhood of the Sun, which is the region we thought we understood best, Gaia is revealing new and exciting features.”</s>A multitude of discoveries are on the horizon after this much awaited release, which is based on 22 months of charting the sky. The new data includes positions, distance indicators and motions of more than one billion stars, along with high-precision measurements of asteroids within our Solar System and stars beyond our own Milky Way Galaxy.

Preliminary analysis of this phenomenal data reveals fine details about the make-up of the Milky Way's stellar population and about how stars move, essential information for investigating the formation and evolution of our home Galaxy.

"The observations collected by Gaia are redefining the foundations of astronomy," says Günther Hasinger, ESA Director of Science.

"Gaia is an ambitious mission that relies on a huge human collaboration to make sense of a large volume of highly complex data. It demonstrates the need for long-term projects to guarantee progress in space science and technology and to implement even more daring scientific missions of the coming decades."

Gaia was launched in December 2013 and started science operations the following year. The first data release, based on just over one year of observations, was published in 2016; it contained distances and motions of two million stars.

The new data release, which covers the period between 25 July 2014 and 23 May 2016, pins down the positions of nearly 1.7 billion stars, and with a much greater precision. For some of the brightest stars in the survey, the level of precision equates to Earth-bound observers being able to spot a Euro coin lying on the surface of the Moon.

With these accurate measurements it is possible to separate the parallax of stars – an apparent shift on the sky caused by Earth's yearly orbit around the Sun – from their true movements through the Galaxy.

The new catalogue lists the parallax and velocity across the sky, or proper motion, for more than 1.3 billion stars. From the most accurate parallax measurements, about ten per cent of the total, astronomers can directly estimate distances to individual stars.

"The second Gaia data release represents a huge leap forward with respect to ESA's Hipparcos satellite, Gaia's predecessor and the first space mission for astrometry, which surveyed some 118 000 stars almost thirty years ago," says Anthony Brown of Leiden University, The Netherlands.

Anthony is the chair of the Gaia Data Processing and Analysis Consortium Executive, overseeing the large collaboration of about 450 scientists and software engineers entrusted with the task of creating the Gaia catalogue from the satellite data.

"The sheer number of stars alone, with their positions and motions, would make Gaia's new catalogue already quite astonishing," adds Anthony.

"But there is more: this unique scientific catalogue includes many other data types, with information about the properties of the stars and other celestial objects, making this release truly exceptional."

Something for everyone

The comprehensive dataset provides a wide range of topics for the astronomy community.

As well as positions, the data include brightness information of all surveyed stars and colour measurements of nearly all, plus information on how the brightness and colour of half a million variable stars change over time. It also contains the velocities along the line of sight of a subset of seven million stars, the surface temperatures of about a hundred million and the effect of interstellar dust on 87 million.

Gaia also observes objects in our Solar System: the second data release comprises the positions of more than 14 000 known asteroids, which allows precise determination of their orbits. A much larger asteroid sample will be compiled in Gaia's future releases.

Further afield, Gaia closed in on the positions of half a million distant quasars, bright galaxies powered by the activity of the supermassive black holes at their cores. These sources are used to define a reference frame for the celestial coordinates of all objects in the Gaia catalogue, something that is routinely done in radio waves but now for the first time is also available at optical wavelengths.

Major discoveries are expected to come once scientists start exploring Gaia's new release. An initial examination performed by the data consortium to validate the quality of the catalogue has already unveiled some promising surprises – including new insights on the evolution of stars.

"The new Gaia data are so powerful that exciting results are just jumping at us," says Antonella Vallenari from the Istituto Nazionale di Astrofisica (INAF) and the Astronomical Observatory of Padua, Italy, deputy chair of the data processing consortium executive board.

"For example, we have built the most detailed Hertzsprung-Russell diagram of stars ever made on the full sky and we can already spot some interesting trends. It feels like we are inaugurating a new era of Galactic archaeology."

Named after the two astronomers who devised it in the early twentieth century, the Hertzsprung-Russell diagram compares the intrinsic brightness of stars with their colour and is a fundamental tool to study populations of stars and their evolution.

A new version of this diagram, based on four million stars within five thousand light-years from the Sun selected from the Gaia catalogue, reveals many fine details for the first time. This includes the signature of different types of white dwarfs – the dead remnants of stars like our Sun – such that a differentiation can be made between those with hydrogen-rich cores and those dominated by helium.

Combined with Gaia measurements of star velocities, the diagram enables astronomers to distinguish between various populations of stars of different ages that are located in different regions of the Milky Way, such as the disc and the halo, and that formed in different ways. Further scrutiny suggests that the fast-moving stars thought to belong to the halo encompass two stellar populations that originated via two different formation scenarios, calling for more detailed investigations.

"Gaia will greatly advance our understanding of the Universe on all cosmic scales," says Timo Prusti, Gaia project scientist at ESA.

"Even in the neighbourhood of the Sun, which is the region we thought we understood best, Gaia is revealing new and exciting features."

For a subset of stars within a few thousand light-years of the Sun, Gaia has measured the velocity in all three dimensions, revealing patterns in the motions of stars that are orbiting the Galaxy at similar speeds.

Future studies will confirm whether these patterns are linked to perturbations produced by the Galactic bar, a denser concentration of stars with an elongated shape at the centre of the Galaxy, by the spiral arm architecture of the Milky Way, or by the interaction with smaller galaxies that merged with it billions of years ago.

At Gaia's precision, it is also possible to see the motions of stars within some globular clusters – ancient systems of stars bound together by gravity and found in the halo of the Milky Way – and within our neighbouring galaxies, the Small and Large Magellanic Clouds.

Gaia data were used to derive the orbits of 75 globular clusters and 12 dwarf galaxies that revolve around the Milky Way, providing all-important information to study the past evolution of our Galaxy and its environment, the gravitational forces that are at play, and the distribution of the elusive dark matter that permeates galaxies.

"Gaia is astronomy at its finest," says Fred Jansen, Gaia mission manager at ESA.

"Scientists will be busy with this data for many years, and we are ready to be surprised by the avalanche of discoveries that will unlock the secrets of our Galaxy."

Explore further: How many stars to expect in Gaia's second data release

More information: A series of scientific papers describing the data contained in the release and their validation process will appear in a special issue of Astronomy & Astrophysics.

A series of 360-degree videos and other Virtual Reality visualisation resources are available at sci.esa.int/gaia-vr

Gerard Gilmore. Gaia: 3-dimensional census of the Milky Way Galaxy, Contemporary Physics (2018). DOI: 10.1080/00107514.2018.1439700
The European Space Agency releases the largest-ever 3D map of stars in our galaxy from the Gaia spacecraft.