![]() The position and color of a star are in principle relatively easy to record. There are three main characteristics of a star, position, distance and color, from which these signatures emerge. Similarly, the difficult but seemingly mundane task of mapping stars provides a wealth of knowledge from the physical signatures that hide in such data. Today, highly accurate maps of our planet from orbiting satellites provide invaluable knowledge about the past, present and future of our home world. Exploratory voyages such as those undertaken by Ferdinand Magellan (1519–1522) and James Cook (1768–1799) revolutionized the understanding of Earth, bringing distant civilizations closer together. To understand the importance of mapping the Milky Way today, an analogy can be made to the importance of mapping Earth over the course of hundreds of years. Overall, the mission has, during the 15 years since it was approved, cost about €740 million, one-fiftieth of the current annual military budget of Germany alone. It took another 13 years before the project was finally authorized, and another seven before it was built and launched. Gaia was first proposed during the last year of the Hipparcos mission, given that a follow-up study would be necessary to further probe the Milky Way. The final Hipparcos Catalogue was published in 1997 and contained positions and distances for more than 118,200 stars. Hipparcos was the first satellite dedicated to the field of astrometry, the accurate measurement of the position and motion of astronomical objects. The spacecraft name is an acronym (HIgh Precision PARallax COllecting Satellite) but also a reference to Hipparchus of Nicaea, the ancient Greek astronomer who is credited with founding trigonometry and incidentally discovering the precession, or change, in Earth’s spin axis. The mission is the successor to the ESA Hipparcos mission, which operated from 1989 to 1993. To make their measurements as accurate as possible, researchers made at least 70 observations of presumed stars before including them in their data. To do this, Gaia was designed to be able to pinpoint object that are 400,000 times fainter than can be seen with the human eye. The latest Gaia release maps almost double the 1 billion stars of the mission’s original goal, roughly 1 percent of all stars in our galaxy. The spacecraft is expected to run out of propellant to adjust itself as needed in late 2025, the effective end to its mission. The orbit has the added benefit of minimizing fuel usage. This creates a very stable location for a space-based observatory to do precision work, a requirement for Gaia. It launched on Decemfrom the Guiana Space Centre in French Guiana and sits at the Earth-Sun Lagrange point 2, a point behind Earth from the perspective of the Sun where the gravitational forces of the two bodies are canceled out. Gaia was designed by the European Space Agency (ESA) and is operated by a team of more than 2,500 people from 15 countries. ![]() The third release also improves the accuracy and precision of the measurements over the second release. The specific findings of this data release were to explore the edge of the Milky Way, measure shifts in the Solar System’s orbit around the center of the galaxy, provide an updated census of nearby stars, and further characterize the two satellite galaxies of the Milky Way, the Large and Small Magellanic Clouds. ![]() The spacecraft has provided both a trove of data that will be studied for years, as well numerous jumping off points for further research. In short, the Gaia mission has provided the best map of the Milky Way to date, a tool which will be used in every field of astronomy. The findings, published or being reviewed in a series of papers in the journal Astronomy & Astrophysics, accurately mapped the position of 1,811,709,771 stars in our Milky Way galaxy, including the distances from Earth and relative motions of 1,467,744,818 of those stars. Astronomers from the Gaia Data Processing and Analysis Consortium have made public the first part of the third major data release from the European Space Agency’s Gaia spacecraft.
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