Other Free Encyclopedias » Online Encyclopedia » Encyclopedia - Featured Articles » Contributed Topics from K-O

Olbers, Heinrich

night sky paradox universe

(1758–1840) German astronomer: discovered Pallas and Vesta, and presented the Olbers paradox.

Olbers, a physician and amateur astronomer, discovered two asteroids, Pallas and Vesta, and rediscovered the asteroid Ceres (discovered by , but lost again). He suggested that the asteroids originated in a small planet in the same orbit which had exploded. He also found five comets, one of which is named after him, and devised an accurate method of calculating their orbits.

He is now best known, however, for his phrasing in 1823 of a deceptively simple, but important question: ‘why is the sky dark at night?’ This quandary, noticed by in 1610 and discussed by , became known as the Olbers paradox. He assumed that the stars are evenly distributed and infinite in number (as proposed) and presented the thought that, in whatever direction we look in the night sky, it would be expected that the line of sight will end on the surface of a star. In which case, he argued, the entire night sky ought to have a brightness comparable to that of the Sun.

In modern cosmology the problem has been re-examined and the present answer seems to be that the expansion of the universe has the effect that, at a certain distance, objects are receding from Earth at the speed of light. This limits the seeable size of the universe, and within this limited radius there are not sufficient stars in all directions to yield a bright night sky. Alternatively, we can conclude that the universe is of finite size and contains a finite number of stars. These answers to the paradox were probably first given by the American poet and fiction writer Edgar Allan Poe (1809–49) in a lecture, and reprinted in his book Eurika in 1848.

Oldham, Richard Dixon [next] [back] Oilily

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or