Goals of the Parallax Program

The New Horizons parallax program will:

• Demonstrate vividly the immense distance NASA's New Horizons spacecraft has traveled by showing the parallactic shift of two nearby stars with respect to the more distance background stars seen in the fields around them.
• Provide a first-ever demonstration of large and "pure" stellar parallaxes. With simultaneous Earth and spacecraft observations of the same stars, the stars' drifts are unimportant. Parallaxes are recovered instantly, not requiring years of observations to isolate the parallaxes as Earth goes around in its orbit, during which the closer stars also drift against distance background stars. Given the large baseline distance provided by New Horizons' location at the outer edge of the Kuiper Belt, the parallaxes will be instantly obvious when comparing Earth-based and New Horizons images.
• Provide a first-ever demonstration of using stars for interstellar navigation of a spacecraft. With parallax observations of two widely separated stars, the distance and location of the New Horizons spacecraft can be roughly determined. While in practice navigation of New Horizons is done to high accuracy with tracking provided by NASA's Deep Space Network, the parallax images can provide less-accurate, but autonomous of navigation that, in principle, could be done by the spacecraft independently of Earth-based tracking. Optical imagery by robotic planetary missions is used for navigation to bodies within the solar system, but has not been used to establish the interstellar trajectory of a spacecraft heading into the galaxy.
• Engage interested amateur astronomers around the world in the parallax observations. The stars targeted by New Horizons can also be observed by amateur astronomers with 6-inch or larger telescopes equipped with electronic cameras. New Horizons will provide publicly available images obtained in its parallax program, for comparison to images obtained with amateur telescopes. The New Horizons project will also provide its own demonstration of parallaxes to the public using images obtained by professional observatories involved in the demonstration.

This figure illustrates the phenomenon of stellar parallax. When New Horizons and observers on Earth observe a nearby star at the same time, it appears to be in different places compared to more distant background stars -- this is because New Horizons has traveled so far out in space (nearly 5 billion miles) that it has to look in a different direction to see that star. The small images below Earth and New Horizons show each unique view. Note that the farther-away background stars stay in the same place, but the nearby star appears to move between the two vantage points. (Credit: Pete Marenfeld, NSF's National Optical-Infrared Astronomy Research Laboratory)

This figure, by New Horizons contributing scientist Brian May, shows the parallax as an effect of New Horizons' travels deeper into the Kuiper Belt. Traditionally, parallax is measured as the Earth orbits around the sun. The two lines at left show the lines of sight from Earth to the star on either side of Earth's orbit. This causes a small shift in the position of the nearby star compared to more distant stars. New Horizons is so far away that a much larger shift in the line of sight to the star occurs. (Credit: Brian May)

The Target Stars

Simultaneous Observations

While simultaneous Earth and spacecraft observations provide the aesthetically purest demonstrations of the parallactic shifts of stars provided by New Horizons' great distance, images can be obtained by any Earth-based observer at any time close enough to the specified epochs. In fact, for both stars, Earth observations obtained within a week of the nominal times above will have negligible drift corrections.

A timeline showing the Earth and spacecraft observation epochs is below. New Horizons will be 4.36 billion miles (7.01 billion kilometers) from Earth, with a one-way light travel time of 6 hours and 30 minutes. At the time, Earth's orbital motion will be faster than New Horizons' cruise velocity, so the spacecraft actually gets closer to Earth during the observation period.

Finding the Star Fields

Where to find Wolf 359 and Proxima Centauri in the sky? Claudio Martinez, of the AZARA Natural History Foundation, Argentina, created this set of star charts. Martinez leads a team of small telescope observers that hopes to obtain images for the New Horizons parallax program.

Both Wolf 359 and Proxima Centauri are too faint to be seen by the naked eye or even with small telescopes, but can be located by skilled amateur astronomers equipped with electronic cameras and telescopes of 6-inch aperture or larger.

The epoch 2000 RA and Dec coordinates of the stars with proper motion (drift) corrections to Jan. 1, 2020, are:

• Wolf 359: 10 56 23.665 + 06 59 58.48
• Proxima Centauri: 14 29 31.962 - 62 40 30.77

Star charts of the Wolf 359 and Proxima Centauri fields are below. The fields of view correspond to that of New Horizons' Long Range Reconnaissance Imager (LORRI), which will be used to obtain the spacecraft images. The target stars are at the center of the field. Note that Wolf 359 has a high galactic latitude and thus has a sparse background, while Proxima Centauri is close to the central plane of the Milky Way and is rich with background stars. The charts are prepared for V-band observations.

William Keel (University of Alabama, SARA Observatory) has provided color images of the Wolf 359 and Proxima Centauri fields. These were obtained in late 2019, and the large proper motions of both stars (at the center of each image) will cause them to shift by over an arcsecond by April 2020. A green circle provides a rough estimate of where both stars will appear in the New Horizons images. Note that both images cover roughly a quarter of the field shown in the charts. Thanks to image depth and the use of redder filters, the images depict several relatively bright stars that are not visible in the charts.