Measuring the Milky Way

This illustration shows the vastly increased number of stellar objects that will be provided by the Gaia satellite following its launch projected for about 2011. Click on the stars under Hipparcos or under Gaia to see the relative radius of measurement and number of objects that each satellite collects.

Hipparcos: 1989
Number of stars: 120 000
Magnitude limit: 12
Complete to magnitude: 8-9
Accuracy: 1-2 milliarcsec


Gaia: about 2011
Number of stars: 1 billion
Magnitude limit: 21
Complete to magnitude: 19-20
Accuracy: 0.02 milliarcsec