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Starts With A Bang

NASA’s New Horizons Sees A Different Night Sky From 4 Billion Miles Away

Proxima Centauri and Wolf 359, two of the closest stars to our Solar System, were measured on April 22/23 from Earth and New Horizons simultaneously. The closest stars appear to shift relative to the more distant background stars: a geometric phenomenon known as parallax with enormous importance for astronomy. (NASA/JOHNS HOPKINS APPLIED PHYSICS LABORATORY/SOUTHWEST RESEARCH INSTITUTE/LAS CUMBRES OBSERVATORY/SIDING SPRING OBSERVATORY/UNIVERSITY OF LOUISVILLE/HARVARD AND SMITHSONIAN CENTER FOR ASTROPHYSICS/MT. LEMMON OBSERVATORY; EDITS BY E. SIEGEL)

The view from beyond Pluto is far enough from Earth that we can see the stars shift.

NASA’s New Horizons, humanity’s first spacecraft to encounter Pluto, is more than 4.3 billion miles (7 billion km) from Earth.

A computer simulation of the New Horizons flyby of Pluto, based on the full suite of data obtained by the spacecraft and reconstructed based on its trajectory past this distant world. (NASA)

At these incredible distances, the closest stars shift configurations relative to more distant background objects.

By viewing stars from two locations separated by more than 7 billion kilometers (4.3 billion miles), humanity has now been able to measure the largest parallax of a star of all-time. The New Horizons spacecraft, most famous for imaging Pluto and its moons up close, has set yet another record. (PETE MARENFELD, NSF’S NATIONAL OPTICAL-INFRARED ASTRONOMY RESEARCH LABORATORY)

The same effect occurs when you alternate which eye views your thumb: parallax.

An application of parallax, where a foreground (finger) object appears to shift relative to the background (trees) as you move from your left eye to your right. The larger the spacing between your eyes is (your baseline) the larger the apparent shift (and the associated parallax angle) will be. (E. SIEGEL, 2010)

With enough distance between your proverbial “eyes,” the closest stars to Earth appear to move.

The parallax method, employed since telescopes became good enough to measure it in the 1800s, involves noting the apparent change in position of a nearby star relative to the more distant, background ones. Knowing the distance between your two observing points and measuring the angular shift allows you to calculate the distance to the object in question. (ESA/ATG MEDIALAB)

The parallax method is the most reliable way to calculate the distance to the stars.

61 Cygni was the first star to have its parallax measured, but also is a difficult case due to its large proper motion. These two images, stacked in red and blue and taken almost exactly one year apart, show this binary star system’s fantastic speed. If you want to measure the parallax of an object to extreme accuracy, you’ll make your two ‘binocular’ measurements simultaneously, to avoid the effect of the star’s motion through the galaxy. (LORENZO2 OF THE FORUMS AT HTTP://FORUM.ASTROFILI.ORG/VIEWTOPIC.PHP?F=4&T=27548)

No spacecraft equipped with a functioning, high-resolution camera has ever been as distant as New Horizons presently is.

By illustrating the Solar System to scale (but the stars not to scale), we can see how New Horizons gives us a perspective that we could never achieve by staying in (or close to) Earth’s orbit alone. (BRIAN MAY)

On April 22/23, Earth and New Horizons simultaneously observed two relatively close stars.


The first was Proxima Centauri, the closest star beyond the Sun: 4.24 light-years away.

A portion of the digitized sky survey with the nearest star to our Sun, Proxima Centauri, shown in red in the center. This is the nearest star to Earth, located just over 4.2 light-years away. From the vantage point of New Horizons, Proxima Centauri will appear to shift relative to these more-distant background stars. (DAVID MALIN, UK SCHMIDT TELESCOPE, DSS, AAO)

Its observed shift of 32 arc-seconds is the greatest stellar parallax ever measured.

Proxima Centauri, the closest star to Earth at just 4.24 light-years away, shows the largest parallax ever recorded of a star beyond our Solar System. Measuring the sky from Earth and New Horizons simultaneously has set a new all-time parallax record. (NASA/JOHNS HOPKINS APPLIED PHYSICS LABORATORY/SOUTHWEST RESEARCH INSTITUTE/LAS CUMBRES OBSERVATORY/SIDING SPRING OBSERVATORY)

For comparison, Proxima Centauri appeared to move by more than the angular size of Mars or Saturn from Earth’s perspective.

The seven extraterrestrial planets of the solar system: Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune. Photographed in 2019 with a Maksutov telescope from Mannheim and Stockach in Germany. The angular sizes and colors shown are accurate, but the brightnesses have been adjusted: Venus is some 63,000 times brighter than Neptune, or 12 astronomical magnitudes; the same difference as between the full Moon and a typical bright star like Vega or Capella. (GETTY IMAGES)

The second target, Wolf 359, is nearly twice as distant: 7.86 light-years away.

This color image of the nearby star Wolf 359 (bright star) shows its current position as seen from Earth, as of late 2019. The green circle, significantly well-separated from the location of Wolf 359 as seen terrestrially, is what New Horizons is predicted to see from its distant position in the Solar System. (WILLIAM KEEL/UNIVERSITY OF ALABAMA/SARA OBSERVATORY)

Its shift is barely half of Proxima Centauri’s, but still measurable.

This two-frame animation blinks back and forth between New Horizons and Earth images of Wolf 359, clearly illustrating the different view of the sky New Horizons has from its deep-space perch, some 7 billion km (4.3 billion miles) from Earth. (NASA/JOHNS HOPKINS APPLIED PHYSICS LABORATORY/SOUTHWEST RESEARCH INSTITUTE/UNIVERSITY OF LOUISVILLE/HARVARD AND SMITHSONIAN CENTER FOR ASTROPHYSICS/MT. LEMMON OBSERVATORY)

ESA’s Gaia mission significantly surpasses this precision.

This image is a single projection of Gaia’s all-sky view of our Milky Way Galaxy and neighboring galaxies, based on measurements of nearly 1.7 billion stars. By studying the stars in our galaxy and measuring properties of our own Solar System, we can infer properties about the galaxy as a whole. (ESA/GAIA/DPAC)

Despite shorter baselines, it’s identified parallaxes for over 1 billion stars.

The Gaia Deployable Sunshield Assembly (DSA) during deployment testing in the S1B integration building at Europe’s spaceport in Kourou, French Guiana, two months before launch. Despite significantly shorter baselines, superior instruments make Gaia a superior parallax-measuring machine to New Horizons. (ESA-M. PEDOUSSAUT)

Mostly Mute Monday tells an astronomical story in images, visuals and no more than 200 words. Talk less; smile more.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.


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