“It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth.” Those are the words of Alan Stern (Southwest Research Institute), who is principal investigator for New Horizons. A breathtaking 7 billion kilometers from Earth, the spacecraft has just returned images showing the parallax effect for two nearby stars.
That ‘alien sky’ would look pretty much the same to the human eye except in the case of the closest stars, but the displacement of both Proxima Centauri and Wolf 359 against the deep space background is apparent in the images below. Proxima Centauri, the nearest star to our own, is shown in the top image, with Wolf 359 in the following one.
Image: This two-frame animation blinks back and forth between New Horizons and Earth images of each star, clearly illustrating the different view of the sky New Horizons has from its deep-space perch. Credit: NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute/Las Cumbres Observatory/Siding Spring Observatory.
This is stirring stuff. Taking parallax measurements of objects relatively nearby shows the kind of shift that first allowed astronomers to measure the distance to particular stars, beginning with 61 Cygni in 1838. That measurement was the work of Friedrich Bessel, whose attention had been drawn to the star by astronomer Giuseppe Piazzi, who had discovered its large proper motion compared to other stars. We now know that 61 Cygni has the 7th largest proper motion listed in the Hipparcos catalog, with Barnard’s Star and Kapteyn’s Star as numbers one and two.
Parallax studies like these have always involved looking at where a star is at one side of the Earth’s orbit and then at the other, but with the baseline given to us by New Horizons, we can detect the tiny shift not only with precise instrumentation but with the human eye as well. This is the largest parallax baseline ever, notes New Horizons science team member Tod Lauer (National Science Foundation), who coordinated the parallax demonstration, and who goes on to describe the images as “the first demonstration of an easily observable stellar parallax.”
But let me also quote Brian May, who often raises eyebrows when people realize that the rock guitar legend doubles as an astrophysicist and, I suspect, a science fiction fan. May worked with New Horizons deputy project scientist John Spencer (SwRI) to produce the striking images. Says May:
“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. 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!”
I’m a great enthusiast for robotic telescope installations like the one at Las Cumbres Observatory at Siding Spring Observatory in Australia and Mt. Lemmon Observatory in Arizona, both of which were used to acquire Earth-based images of Proxima Centauri and Wolf 359, but to have the concept extended to a spacecraft at this distance from Earth is a bit mind-boggling. New Horizons needed, at the time of these observations, almost six hours and thirty minutes to get a signal home, and it will eventually exit the Solar System entirely, like both our Voyagers. An indication of the distances involved is provided by the fact that in the Proxima Centauri image, the second closest star is 120 times more distant than Proxima itself.
You’ll recall that the New Horizons team put out a call for amateur astronomers to send matching images of the two stars taken on April 22 and 23rd, with timing adjusted to the fact that New Horizons was almost three light hours closer to Proxima Centauri than Earth (and almost four light hours farther from Wolf 359) when the images were taken. You can use the hashtag #NHparallax for more, or visit this New Horizons page, where images can be downloaded in FITS format, commonly used by astronomers to preserve image fidelity while including technical data about the image, as well as readily readable 16-bit PNG format.