Astronomers have long used a so-called parallax effect — how a star appears to shift against its background when seen from different locations — to measure distances to stars. In April 2020, NASA’s New Horizons spacecraft turned its Long-Range Reconnaissance Imager (LORRI) instrument to two nearby red dwarfs, Proxima Centauri and Wolf 359, showing just how they appear in different places than ground-based telescopes see from Earth.
These images show Proxima Centauri, a red dwarf located 4.244 light-years away from the Sun in the southern constellation of Centaurus. The ground-based image of the star was obtained on April 22 at 12:51 UT (8:51 a.m. ET) by a remotely operated 0.4- telescope at the Siding Spring node of the Las Cumbres Observatory in Australia. This is 9 minutes earlier than the New Horizons image, relative to Proxima Centauri time. The timing accounts for New Horizons being nearly 3 light hours closer to Proxima Centauri than Earth when the images were taken. Image credit: Siding Spring node, Las Cumbres Observatory / NASA / Johns Hopkins Applied Physics Laboratory / Southwest Research Institute.
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.
Similarly, as Earth makes it way around the Sun, the stars shift their positions.
But because 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.
“No human eye can detect these shifts,” said New Horizons principal investigator Dr. Alan Stern, a researcher at Southwest Research Institute.
“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 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,” added New Horizons science team member Dr. Tod Lauer, a scientist at NSF’s National Optical-Infrared Astronomy Research Laboratory.
These images show Wolf 359, a red dwarf located approximately 7.9 light-years away in the constellation of Leo. The ground-based image of the star was obtained on April 23 at 04:37 UT (12:37 a.m. ET) with the University of Louisville 0.6-m telescope located at Mt. Lemmon Observatory. This is 37 minutes later than the New Horizons image, relative to Wolf 359 time. The timing accounts for New Horizons being nearly 4 light hours farther from Wolf 359 than Earth when the images were taken. Image credit: Mt. Lemmon Observatory / John F. Kielkopf, University of Louisville / Karen A. Collins, Harvard and Smithsonian Center for Astrophysics / NASA / Johns Hopkins Applied Physics Laboratory / Southwest Research Institute.
“New Horizons is truly a mission of firsts, and this demonstration of stellar parallax is no different,” said New Horizons program scientist Dr. Kenneth Hansen, a researcher at NASA Headquarters in Washington.
“The spacecraft continues to speed away from Earth toward interstellar space and is continuing to return exciting new data for planetary science.”
“It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth,” Dr. Stern said.
“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.”
“The professional and amateur astronomy communities had been waiting to try this, and were very excited to make a little space exploration history,” Dr. Lauer said.
“The images collected on Earth when New Horizons was observing Proxima Centauri and Wolf 359 really exceeded my expectations.”
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This article is based on text provided by the National Aeronautics and Space Administration.
