| The starting principle is simple, then the scientists build a lot of clever stuff, the telescopes on Earth, the telescopes on the satellites and the remote controlled
radio telescopes... Parallax. Telescopes. https://medium.com/starts-with-a-bang/how-do-we-know-the-dis... "the same math that enables you to hold your thumb at arm’s length, close one eye and then switch eyes and watch your thumb appear to shift, allowed us to measure the distances to the stars." "Known as parallax, the fact that our planet’s orbit is some 300 million kilometers in diameter around the Sun means that if we view the stars today versus six months from now, we’ll see the closest stars appear to shift position in the sky relative to the other, more distant stars." There's more in the link above. Then... Satellites. http://news.nationalgeographic.com/2016/09/gaia-milky-way-ma... "For thousands of years, astronomers from the ancient Babylonians to Tycho Brahe had preoccupied themselves with noting the stars’ precise locations, a crucial foundation to understanding the cosmos. But the field sputtered in the 1960s, when scientists reached the smallest parallaxes that Earth-based telescopes could measure, stymied by interference from our rippling atmosphere. It wasn’t until the 1980s and 1990s that the ESA satellite Hipparcos took astrometry to space, where it ultimately measured the precise distances of more than 100,000 stars. Gaia is even better: Hipparcos’s gaze reached only as far as 1,600 light-years away, barely leaving our celestial backyard, but Gaia is able to spy on stars up to 30,000 light-years away." Remote controlled radio telescopes across the Earth, as in the article we comment to: https://science.nrao.edu/facilities/vlba "The Very Long Baseline Array (VLBA) is an interferometer consisting of 10 identical antennas on transcontinental baselines up to 8000 km (Mauna Kea, Hawaii to St. Croix, Virgin Islands). The VLBA is controlled remotely from the Science Operations Center in Socorro, New Mexico. Each VLBA station consists of a 25 m antenna and an adjacent control building. The received signals are amplified, digitized, and recorded on fast, high capacity recorders. The recorded data are sent from the individual VLBA stations to the correlator in Socorro." "Precision astrometry is a VLBA science centerpiece. The relative astrometric accuracy of ~ 10 micro-arcseconds achievable with the VLBA is better than what the Gaia satellite is designed to achieve for most stars in its catalog (scheduled for release after 2015" |
https://science.nrao.edu/facilities/vlba
"In 2010, the VLBA will begin a long-term program to determine the complete 3D structure of the Milky Way by measuring parallaxes with 10 mas accuracy or better to ~ 400 high-mass star-formation regions."
In order to achieve the stated accuracy using the radio telescopes around the world together is necessary.
http://www.vlba.nrao.edu/sites/