Io and Jupiter as seen by New Horizons during its 2008 flyby.
(Credit: NASA/Johns Hopkins University APL/SWRI).

Light-travel-time Effect Finds New Astronomical Applications

by DAVID DICKINSON on FEBRUARY 25, 2013

Sometimes the tried and true methods are still the best, even in observational astronomy. Researchers at the University of Prague demonstrated this recently in a study of the eclipsing binary system V994 Herculis (V994 Her).

Researchers P. Zasche and R. Uhla used a method known as the Light-travel-time Effect to verify that V994 Her is actually a double binary. If that method sounds familiar to any astronomy historians out there, that’s because it was first used by 17th century astronomers to gauge the speed of light.

V994 Her is a rarity in the skies. While many eclipsing binaries are known, V994 Her is one of only six quadruple eclipsing binary stars discovered. An eclipsing binary star is a system where the two stars pass one in front of the other from our line of sight. Although too close to be split visually, eclipsing binaries rise and fall in brightness periodically. One famous example is the star Algol (Beta Persei) in the constellation Perseus. Algol means the “Demon Star” in Arabic, which suggests that its curious nature was known to Arab astronomers in pre-telescopic times.

Of course, for this to occur, the two stars need to be in a fairly tight orbit which is nearly edge-on to our Earthly vantage point. Researchers looking for exoplanet transits face the same dilemma. Thus, a system with two eclipsing binary pairs is very rare indeed. Although observed by the Hipparcos satellite during its survey in 1997, the true nature of the V994 Her system wasn’t realized until 2008.

Author Douglas Adams once said that “Light travels so fast that it takes most races thousands of years to realize that it travels at all.” It’s strange to think of in the modern Space Age, but there was no reason for early astronomers to suppose that light transmission wasn’t instantaneous. There were simply no everyday situations that could suggest otherwise.

Read more: Light-travel-time Effect Finds New Astronomical Applications — Universe Today.

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