For most of us, the countless bright spots in the nighttime sky all seem to be stars. But in fact, some of those spots are actually planets, or distant suns, or even entire galaxies located billions of light years away. Just what you’re looking at depends on how far it is from Earth. That’s why measuring the exact distance to celestial objects is such an important goal for astronomers – and one of the biggest challenges they’re currently tackling.

It was with this in mind that the European Space Agency (ESA) launched the Gaia mission ten years ago. Data collected by the Gaia satellite are opening up a window into the near Universe, providing astronomic measurements – such as position, distance from the Earth and movement – on nearly two billion stars.

At EPFL, the Standard Candles and Distances research group headed by Prof. Richard Anderson is aiming to measure the current expansion of the Universe and sees Gaia as a valuable tool. “Gaia increased by a factor of 10,000 the number of stars whose parallaxes are measured thanks to a massive gain in accuracy over its predecessor, the ESA Hipparcos mission,” he says. Today, scientists use parallaxes to calculate the distance to stars. This method involves measuring parallax angles, with the help of the satellite, through a form of triangulation between Gaia’s location in space, the Sun and the star in question. The farther away a star, the more difficult the measurement because parallax gets smaller the larger the distance.

Despite the resounding success of Gaia, the measurement of parallax is complex, and there remain small systematic effects that must be checked and corrected in order for Gaia parallaxes to reach their full potential. This is what scientists from EPFL and the University of Bologna, in Italy, have been working on, through calculations performed on over 12,000 oscillating red giant stars* – the biggest sample size and most accurate measurements to date.

“We measured the Gaia biases by comparing the parallaxes reported by the satellite with parallaxes of the same stars that we determined using asteroseismology,” says Saniya Khan, a scientist in Anderson’s research group and the lead author of a study published today in Astronomy & Astrophysics.