NASA probe captures images of our nearest stars appearing to be in different positions than seen from Earth
Speeding through interstellar space, from its unique vantage point of over 4 billion miles from Earth, NASA's New Horizons spacecraft has sent back pictures of the sky from so far away that some stars appear to be in different positions than what we would see from Earth.
New Horizons — which flew by Pluto in 2015, and the remote Kuiper Belt object Arrokoth in January 2019 — recently photographed our nearby stars Proxima Centauri and Wolf 359. The images show the two sitting in different parts of the sky than they do from our point of view on Earth.
According to NASA, on April 22-23, the spacecraft turned its long-range telescopic camera to the pair of stars, showing just how they appear in different places than we see from Earth. According to experts, this is New Horizons' first interstellar "parallax experiment" in which stars appear to be in different locations due to the "parallax effect." Scientists have long used this parallax effect — implying how a star appears to shift against its background when seen from different locations — to measure distances to stars.
"It's fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth. And that has allowed us to do something that had never been accomplished before — to see the nearest stars visibly displaced on the sky from the positions we see them on Earth,” said Alan Stern, New Horizons principal investigator from Southwest Research Institute (SwRI) in Boulder, Colorado, in a statement.
At the time of the observations, New Horizons was more than 4.3 billion miles (about 7 billion kilometers) from Earth, where a radio signal, traveling at the speed of light, needed a little under 6 hours and 30 minutes to reach home. Launched in 2006, New Horizons will eventually leave the solar system, joining the Voyagers and Pioneers on their paths to the stars.
An easy way to see parallax is to place one finger at arm’s length and watch it jump back and forth when you view it successively with each eye, explain scientists. Similarly, as Earth makes its way around the Sun, the stars shift their positions. But since even the nearest stars are hundreds of thousands of times farther away than the diameter of Earth’s orbit, the parallax shifts are tiny, and can only be measured with precise instrumentation. The human eye cannot detect these shifts. But when New Horizons images are paired with pictures of the same stars taken on the same dates by telescopes on Earth, the parallax shift is instantly visible. “The combination yields a 3D view of the stars "floating" in front of their background star fields," said NASA.
The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, designed, built and operates the New Horizons spacecraft, and manages the mission for NASA's Science Mission Directorate.
Navigators have used measurements of the stars throughout history to establish their position on Earth. Interstellar navigators can do the same to establish their position in the galaxy, using the technique that New Horizons has demonstrated for the first time. While radio-tracking by NASA’s Deep Space Network is far more accurate, its first use is a significant milestone in what may "someday become human exploration of the galaxy," say experts.
"The New Horizons experiment provides the largest parallax baseline ever made — over 4 billion miles — and is the first demonstration of an easily observable stellar parallax," said Tod Lauer, New Horizons science team member from the National Science Foundation's National Optical-Infrared Astronomy Research Laboratory, who coordinated the parallax demonstration.
Lauer, along with New Horizons deputy project scientist John Spencer from SwRI and science team collaborator, astrophysicist and stereo imaging enthusiast Brian May created the images that clearly show the effect of the vast distance between Earth and the two nearby stars. "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," said May.
The companion images of Proxima Centauri and Wolf 359 were provided by different institutes. The Proxima Centauri image was obtained on April 22 by a remotely operated 0.4-meter telescope at the Siding Spring node of the Las Cumbres Observatory in Australia. This is nine minutes earlier than the New Horizons image, relative to Proxima Centauri time. The timing accounts for New Horizons being nearly three light hours closer to Proxima Centauri than Earth when the images were taken. The Wolf 359 image was obtained on April 23 with the University of Louisville 0.6-meter telescope located at Mt. Lemmon Observatory, near Tucson, Arizona, operated remotely by John F. Kielkopf (University of Louisville) and Karen A. Collins (Harvard and Smithsonian Center for Astrophysics). This is 37 minutes later than the New Horizons image, relative to Wolf 359 time. The timing accounts for New Horizons being nearly four light hours farther from Wolf 359 than Earth when the images were taken, says the research team.
"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," said Lauer.