Nightfall by Asimov and BC 22 5866

In September 1941 Isaac Asimov published his short story Nightfall. (In 1990, two years before Asimov's death, he collaborated with author Robert Silverberg on a novel-length revision of the original story.)

The story was inspired by a quotation by Ralph Waldo Emerson:

If the stars should appear one night in a thousand years, how would men believe and adore and preserve for many generations the remembrance of the city of God!

The fictional planet Lagash (Kalgash in the novel adaptation) is located in a stellar system containing six stars (Onos, Dovim, Trey, Patru, Tano, and Sitha), which keep the whole planet continuously illuminated; total darkness is unknown, as are more distant stars.

A number of observations came together from academics in different departments of Soro University which lead to a startling conclusion:

• A psychologist is studying the effects of prolonged exposure to darkness


• An archaelogist discovers evidence that civilisation has suffered multiple cyclical collapses about every 200 years


• A journalist has learned some of the ideas of the group known as the Apostles of Flame, who believe the world would be destroyed in a darkness with the appearance of Stars that unleash a torrent of fire


• An astronomer calculates that once every 2049 years when there is only one star in the sky an eclipse (by a dark moon circling the planet) will plunge Kalgash into darkness

If you haven't read the novel and you have a penchant for Science Fiction get it out of your library and have a read. The book is a psychological thriller, but the reason for my posting on it is astronomical.

The six stars in Kalgash's system are obviously very close together. The primary sun of Kalgash is about the same difference from its star as the Earth is from the Sun. The other distance mentioned is a binary system (two stars revolving around each other) that is just further away than Saturn in the Solar System. A multiple star system this compact seemed something of a stretch.

Recently a real system that is even more compact has been discovered. This is called by the exciting name, BC 22 5866, and consists of four stars.

Universe Today describes the system as follows:

The stars are paired up together into binary groupings, and then these two pairs orbit a common centre of gravity. One pair orbits each other in less than 5 days - at a distance of a mere 0.06 astronomical units (1 AU is the distance from the Earth to the Sun). The second pair takes 55 days to complete an orbit, at a distance of 0.26 AU.

And finally, the two pairs take about 9 years to orbit one another at a distance of 5.8 AU - within the orbit of Jupiter in our own Solar System.

One AU is almost 150,000,000 kilometres, so 0.06 AU is 9,000,000 Km. Given that our sun is 1.4 million kilometres in diametre, a separation of two stars by 9 million Kms is very close. The second pair are closer than As Mercury's distance from to the Sun is 0.36 AU, the second pair of stars in BC 225866 are closer than our sun to its nearest planet.

The stars in the system are too close to be resolved in the largest telescopes available. The configuration of the BC 225866 was determined by spectroscopic methods. It will provide plenty of food for thought for theorists.