It was less than a century ago, in 1920, that astronomers were famously debating the nature of so-called spiral nebulae. Some believed they lay inside our own Milky Way galaxy and were, perhaps, forming solar systems. Others thought they were large and distant separate galaxies. Thus the wisest astronomers of yesteryear couldn’t be sure of the true nature of our home galaxy, the Milky Way. They couldn’t know it is indeed one galaxy of billions in the universe. And they couldn’t have imagined that now, just 100 years later, we’d have a space observatory like Gaia, whose goal is nothing less than to provide a 3D map of our galaxy. This mission had its second data release this week, along with a host of virtual reality resources for scientists and the public. The European Space Agency (ESA) said Gaia’s data makes possible:
… the richest star catalog to date, including high-precision measurements of nearly 1.7 billion stars and revealing previously unseen details of our home galaxy.
The new data, which ESA called phenomenal, is based on 22 months of Gaia’s charting of the sky. Günther Hasinger, ESA’s director of science, said:
The observations collected by Gaia are redefining the foundations of astronomy.
Why all the superlatives? What’s so amazing about Gaia’s data?
Gaia gathers its phenomenal data in the most unglamorous of ways, via what’s called astrometry. Okay, now, hang in there with me. Think about this. Gaia’s job is to scan the sky repeatedly, observing each of its targeted billion stars an average of 70 times over its five-year mission. So, for example, we know our sun and all the stars in the Milky Way are moving continuously in great orderly masses around the center of our galaxy. We know that … but we didn’t have many details about how each star moves. How could we? The data for so many stars would be (are) massive; collecting the data, storing it and analyzing it requires today’s spacecraft and computer technologies.
Over its five years, again and again and again, Gaia will acquire data points on the positions of Milky Way stars. Thus astronomers have already been able to produce an illustration like the very wonderful one below, which shows median velocities (the distances and directions traveled by each star per unit of time) of stars in our Milky Way.
And so we begin to see – not just see in our minds, but actually see via Gaia’s actual data – that, due to the movements of its stars, our Milky Way galaxy is rotating, with us in its midst. You can see that in one illustration of Gaia’s data, below:
And that’s just one example of the type of insight Gaia’s data can provide. ESA said:
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 July 25, 2014, and May 23, 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.
Gaia is also gathering other types of data. The illustration below shows some of the ways in which Gaia sees our Milky Way:
Virtual Reality Resources. Also, along with this second data release by Gaia, ESA has released several virtual reality resources to help visualize Gaia’s extraordinary data set, both for public outreach and for scientific purposes.
One of the public offerings is Gaia Sky, a real-time, 3D astronomy visualisation software that runs on Windows, Linux and MacOS, developed in the framework of ESA’s Gaia mission by the Gaia group at the Astronomisches Rechen-Institut (Zentrum für Astronomie Heidelberg, University of Heidelberg, Germany). It contains a simulation of our solar system, a view of the second Gaia data release (with different selections based on parallax relative errors, ranging from a few million to hundreds of millions of stars), and additional astronomical and cosmological data to visualize star clusters, nearby galaxies, distant galaxies and quasars, and the Cosmic Microwave Background. The data are extensive, and you’ll want to explore them yourself here. ESA also offered this fun trailer for Gaia Sky:
So you can see … there’s really a lot here to think about and explore, both for the public and for scientists. And maybe you can begin to see that – to those astronomers debating the nature of spiral nebulae in 1920 – Gaia’s data might have seemed nothing short of miraculous!
The video below shows a comparison between Gaia’s first and second data releases:
Bottom line: The Gaia space observatory’s mission is to create a 3D map of our Milky Way galaxy. This week was its 2nd data release, consisting of high-precision measurements of some 1.7 billion stars. ESA also released a host of virtual reality resources, based on Gaia data.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.