Yesterday the European Space Agency released the data collected by the Gaia satellite which sits in the 2nd Lagrange point. This data included positional information on about 1.7 billion stars, making this the most comprehensive map of the stellar neighbourhood ever conducted by humanity. Astrometry is the precise measurement of the position and movement of stars and other celestial bodies. Anyone with with a digital star map like Stellarium or Sky Safari relies on the details that these maps present with their richness of data about visible stars including distance from Earth and their relative positions. This information doesn’t just magically appear, it has to be collected and some of the biggest efforts in collecting astrometry data have be done by the European Space Agency. In December 2013 ESA launched the Gaia spacecraft to catalog around 1% of the estimated 100 billion stars in our galaxy. It’s not the first spacecraft to do this, Hipparcos was the first big effort in astrometry.
In 1989 ESA launched the Hipparcos satellite which operated until 1993. This satellite collected the positions of 118,218 stars and ESA released these as the Hipparcos catalog in 1997. The stars that were measured went out to about 300 light years from the Sun, so really just a small section of our galaxy. On board the spacecraft was another instrument called the Tycho-2 starmapper which was used to map about 2.5 million stars and these were later released by ESA as the Tycho-2 catalog. Many of the stars visible in the popular star maps applications are based on the data collected by the Hipparcos satellite. Hipparcos was good, but Gaia is even better with significantly more sensitive instruments, bigger mirrors and the advantage of the significantly larger processing power afforded by the later generation of software and hardware on the satellite. The instruments can collect 30 times more light than the Hipparcos instruments and get positional accuracy around 200 times better. This all means, for example, that where Hipparcos was able to collect data on a handful of white dwarf stars, Gaia was able to collect data on 35,000, greatly increasing our knowledge of these objects.
The Gaia satellite was launched in December 2013 on it’s mission to better the Hipparcos data and map an extraordinary number of stars, of which there have been two main data releases so far. The mission duration is 5 years. The spacecraft is in three parts, the bit with the instruments, the service part with the power and positioning bits and the sun shield. It needs the sun shield because unlike your backyard telescope there’s no large planet in the way to block out the Sun. It’s a heavy satellite weighing about 2030kg, including 710kg of payload, 910kg for the service module and 400kg for propellant. The instrument is basically a pair of space telescopes with three integrated functions including astrometry, photometry and spectrometry. The satellite sits in the L2 point at about 1.5 million km from the Earth, on the opposite side from the Sun and whizzes around the Sun with the Earth. From this fantastic vantage point Gaia can map the entire sky in a year.
The mission of Gaia has four main objectives. The first of these is to measure the positions of stars, both in this Galaxy and in the Local Group of galaxies to an accuracy or 24 microarcseconds. This is the astrometry mission of the satellite and it will measure about 3 million stars or more for every square degree of space. The second objective, which happens at the same time as the first, is to conduct photometry and spectrometry measurements of all objects Gaia sees. Another objective is to measure the velocities of the stars and the final objective is to stick all of that information together into a 3D map of the Galaxy.
With yesterday’s release of the data from Gaia we are now able to get a more detailed picture of the Galaxy than ever before. The release included data on 1.7 billion stars to make the amazing picture below. The data also included the parallax, motion and the colour of around 1.3 billion stars and the surface temperature of a 100 million different stars. Gaia was also able to identify 14,099 different Solar System objects.
The data has been made available by ESA to scientists all around the world and will no doubt be the subject of many published articles. We are looking forward to what may be discovered in this huge dataset. Thanks ESA!