Measuring the distance to the stars was a problem that plagued astronomy for centuries and it was solved with a clever geometrical trick known as parallax. Astronomers first measure the position of a star on a certain day and then six months later when the Earth is on the other side of the Sun. The changes to the position and a bit of trigonometry provide a measurement of the distance.
This is been a highly successful method but the changes measured are tiny. They can’t be appreciated without specialist tools. To make it clear to our naked eye, we need a much larger shift, one more than Earth’s journey around the Sun can deliver. That’s where NASA’s New Horizons comes in.
The spacecraft has already flown by Pluto and the Kuiper Belt object Arrokoth and is currently 7 billion kilometers (4.3 billion miles) from Earth. The spacecraft was used to take pictures of Proxima Centauri and Wolf 359, two of the closest stars to the Sun, at the same time as observatories on Earth view them. Proxima is located 4.3 light-years away and Wolf 359 is 7.86 light-years away.
The results of the experiment are 3D images that can be appreciated using the classic red and green glasses or using a stereoscopic viewer. At the very least, you can appreciate just how far New Horizons must be in order to see a star light-years away separated from the background of more distant stars. Involved in the project with the science team was Dr Brian May, astrophysicist, stereo images enthusiast, and legendary Queen guitarist.
"It could be argued that in astro-stereoscopy – 3D images of astronomical objects – NASA's New Horizons team already leads the field, having delivered astounding stereoscopic images of both Pluto and the remote Kuiper Belt object Arrokoth," May said in a statement. "But the latest New Horizons stereoscopic experiment breaks all records. These photographs of Proxima Centauri and Wolf 359 – stars that are well-known to amateur astronomers and science fiction aficionados alike – employ the largest distance between viewpoints ever achieved in 180 years of stereoscopy!"
One of the images collected on Earth was achieved with the Las Cumbres Observatory, which was operating a remote telescope at Siding Spring Observatory in Australia. The other was taen by astronomers John Kielkopf and Karen Collins operating a remote telescope at Mt. Lemmon Observatory in Arizona.
"The professional and amateur astronomy communities had been waiting to try this, and were very excited to make a little space exploration history. The images collected on Earth when New Horizons was observing Proxima Centauri and Wolf 359 really exceeded my expectations," added Tod Lauer, New Horizons science team member who coordinated the parallax demonstration.
Parallax is still the method of choice when it comes to establishing most stellar distances. The European Spacy Agency’s Gaia observatory is currently mapping the Milky Way and is capable of measuring stellar distancing with unprecedented precision.