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Measuring the Milky Way with radio waves

Pictured is one of the Very Large Baseline Array’s radio telescopes located in Pie Town. Los Alamos is also home to one of the telescopes. (Richard Pipes/Journal)

ALBUQUERQUE, N.M. — The Very Long Baseline Array, a group of radio telescopes that spans thousands of miles and is remotely operated near Socorro, just took a very long measurement of the galaxy we live in.

The VLBA directly measured a span of 66,000 light-years from Earth across the Milky Way’s center to a star-forming area near the edge of the other side, almost double the previous measurement record of an object in our galaxy.

One light-year is equal to 6 trillion miles.

Because the galaxy is essentially a flat disk that we can’t observe in its entirety from a distance, these measurements are the only way we are able to accurately map it.

Astronomers used a technique called trigonometric parallax.

Think back to your high school trigonometry class: Remember how you can use the angles of a triangle to obtain the lengths of the triangle’s sides?

Trigonometric parallax uses the same principles.

By measuring the angles between the sun, Earth and a distant object against celestial bodies in the background, and measuring it again six months later, once on each side of the sun, astronomers can calculate the object’s distance from Earth.

“This means that, using the VLBA, we now can accurately map the whole extent of our galaxy,” said Alberto Sanna of Germany’s Max-Planck Institute for Radio Astronomy in a news release.

Mark Reid, senior radio astronomer at the Harvard-Smithsonian Center for Astrophysics and who worked on the project, said they hope to be able to produce a map of the Milky Way — the first of its kind — within 10 years by measuring additional points around the galaxy.

So far, they’ve done around 200.

Reid said 100 or so observations must be done from the Earth’s southern hemisphere, so he will be traveling to Australia in the future to use telescopes there.

Although the data for the 66,000 light-year measurement was collected in 2014 and 2015, Reid said the team has spent the time since then analyzing it.

“It’s not like you get a Hubble (Space Telescope) space image,” he said.

While there are artistic renderings of what the Milky Way probably looks like, Reid said this will yield a highly accurate image.

Reid said they hope to use the technique to map the entire Milky Way within 10 years.