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Cosmic Challenge: Barnard's Star

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Cosmic Challenge:
Barnard's Star


August 2023


Phil Harrington



This month's suggested aperture range:


Giant binoculars


3 to 5-inch
(7.6-12.7 cm) telescopes










Star with high
proper motion

17h 57.6m

+04° 41.6






The curtain opened on this challenge in September 1916, when a pair of articles written by Edward Emerson Barnard appeared in the journals Nature and The Astronomical Journal. Both recounted Barnard's discovery of a faint star in the constellation Ophiuchus that appeared completely unremarkable except for the fact that its proper motion was faster than any other star ever found. Proper motion is the apparent angular distance that an object shifts against the background celestial sphere over a specified period of time.



Above: Summer star map showing the location of this month's Cosmic Challenge.


Credit: Map adapted from Star Watch by Phil Harrington.


Above: Finder chart for this month's Cosmic Challenge.


Credit: Chart adapted from Cosmic Challenge by Phil Harrington.
Click on the chart to open a printable PDF version in a new window.


All stars exhibit proper motion to a degree because of their motion caused by the Milky Way's slow rotation as well as their own gravitational interaction with nearby stars. As a rule, a star's annual proper motion is limited to fractions of an arc-second. That's why the constellations we see and enjoy today appear as they did when they were first created by the first civilizations thousands of years ago.


There are, however, exceptions to this rule. Barnard's initial computations found that "his" star had a proper motion of 10.3 arc-seconds per year, far exceeding any other star discovered up to that point. No doubt it was this curious behavior that led stellar astronomers to investigate this star's other characteristics and see if any contributed to Barnard's Star's rapid transit. Their studies showed it to be a rather ordinary red dwarf sun, spectral class M4V to be exact, lying just 6 light years from us and closing. Right now, it shines weakly at magnitude 9.5, but as the millennia pass, it will be growing brighter steadily, if only subtly, as it draws closer to our solar system. According to Burnham's Celestial Handbook, in about 8,000 years Barnard's Star will have closed to less than 4 light years. In the process, its annual proper motion will have accelerated to 25 arc-seconds and it will have grown in brightness to about magnitude 8.6.


That's magnitude +8.6, incidentally. Even though Barnard's Star will be our solar system's closest neighbor in that distant era, its small size and low luminosity will keep it well below naked-eye limit. With a mass only 16% of the Sun and an estimated diameter of 140,000 miles ( 224,000 km ), Barnard's Star radiates only 0.04% as much energy as our star. As a result, it will never outshine some of our other neighbors like Sirius or Alpha Centauri.


Above: Animation showing the motion of Barnard's Star from 2018 to 2022.

Images and animation created by CN'er John Rehling (rehling)



Red dwarf stars are by far the most common type of star in our universe, accounting for approximately 75% of the population. Although their low masses keep them below naked-eye visibility, their typical life spans extend well beyond that of more massive stars like the Sun. While our star is expected to exist for a total of 10 to 11 billion years, red dwarfs like Barnard's Star may go on for a trillion years or more.


Barnard's Star received a great deal of attention in the 1960s when Dutch astronomer Peter van de Kamp claimed to have discovered a giant planet (or planets) in orbit. Van de Kamp's claim was accepted for years, but was ultimately proven wrong by later studies. Still, the prospect of a nearby solar system caused wide speculation back then. What would the planets look like? Were they inhabited? Could we visit them?  The latter question was studied closely by the British Interplanetary Society from 1973 to 1978 as part of their Project Daedalus program. Project Daedalus was to be an unmanned scientific research mission propelled by a two-stage nuclear fusion engine. Designed to accelerate to 10% the speed of light, the spacecraft would take an estimated 50 years to reach its destination.


But then, an international group of astronomers revealed in November 2018 that by using radial velocity measurements, they had detected a potential super-Earth planet in a relatively close orbit around Barnard's Star. Was van de Kamp right after all? Excitement grew again. That is, until 2021, when the existence of the planet was disproven. It turns out that the 2018 radial velocity data was caused by a stellar activity cycle, rather than the presence of a planet.


Use the chart above to find Barnard's Star. With your widest field eyepiece in place, position 5th-magnitude 66 Ophiuchi along the eastern edge of the view and look toward the opposite side for an arrowhead-shaped asterism of faint stars that points eastward. Barnard's Star lies less than 10 arc-minutes to the arrow's northeast, near an 11th-magnitude sun.


Have a favorite challenge object of your own?  I'd love to hear about it, as well as how you did with this month's test.  Contact me through my website or post to this month's discussion forum.


Until next month, remember that half of the fun is the thrill of the chase.  Game on!

About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2023 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.


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