Seeing into the Universe
Telescopes are our window into the workings of the universe. In this extract from The Cosmic Mystery Tour, Nicholas Mee takes us from Galileo’s moons of Jupiter to the discovery of Sirius B (the ‘Pup Star’), our nearest white dwarf.
Galileo first pointed his telescope at the night sky just five lifetimes ago. His enhanced view of the heavens would revolutionize our understanding of the universe.
Wherever Galileo looked he made sensational discoveries. He could see mountains and craters on the Moon. Venus appeared as a crescent and showed phases like the Moon. There were dark spots on the face of the Sun and the Milky Way was composed of innumerable stars invisible to the unaided eye. Most spectacular of all were four moons that he watched dancing around Jupiter from night to night. Galileo raced to tell the world in a booklet called Starry Messenger, which was rushed into print early in 1610. This new vision of the cosmos transformed astronomy and shattered traditional ideas of the universe and our place within it.
In the centuries since Galileo each technological advance in observing the heavens has produced further dramatic discoveries.
The first telescope factory in the United States was established in the 1840s by Alvan Clark, a portrait painter and engraver from a family of Cape Cod whalers. He was joined in the business by his sons Alvan Graham Clark and George Bassett Clark. Over the next half century, the company would grind lenses for some of the largest refracting telescopes ever made, five times setting new world records for their size. The biggest undertaking of all was a 40-inch lens for the Yerkes Observatory in Williams Bay, Wisconsin, which remains the largest refracting telescope in the world.
In 1861, Alvan Clark & Sons was commissioned to make an 18.5-inch telescope for the University of Mississippi. Due to the outbreak of the Civil War the telescope never reached its intended destination and in 1866 it was installed at the Dearborn Observatory of the University of Chicago. While testing the instrument on 31 January 1862, Alvan Graham Clark looked at Sirius, the brightest star in the night sky. Twenty years earlier Friedrich Bessel had noticed a slight wobble in the position of Sirius and concluded this must be due to the gravitational attraction of an unseen companion. Clark became the first person to glimpse the companion star and confirm Bessel’s prediction. Sirius is in the constellation Canis Major, one of the dogs accompanying Orion the Hunter. Since ancient times Sirius has been called the Dog Star, so its companion, Sirius B, is sometimes known affectionately as the Pup. There is something rather odd about the Pup. The masses of the two components of Sirius can be determined from their orbit. Sirius A is twice the mass of the Sun, while Sirius B is almost the same mass as the Sun, so the brilliant Dog Star has just twice the mass of the faint Pup, yet it is incomparably brighter. The Hubble Space Telescope image shows just how great the difference in luminosity is. The main star is Sirius A and its companion — the Pup — is the tiny dot close to the bottom left spike. In 1915, the Pup was recognized as a white dwarf.
These stars are remarkable because they are extremely hot — the temperature of the Pup is around 25,000 K — but very faint compared to other stars of the same mass. At a distance of 8.6 light years, the Pup is the closest white dwarf to us.
Although the Pup is very difficult to spot, even with a good telescope, Sirius is a magnificent sight on a winter’s night in the northern hemisphere. Sirius can be found by following the line of Orion’s belt. It takes 50 years for Sirius A and B to complete one orbit. Their average separation is comparable to the distance between the Sun and Uranus. At the moment they are approaching their widest separation, which will occur in 2019, so if you do fancy tracking down the Pup with a telescope the next few years will offer the best opportunity.
Nicholas Mee studied theoretical physics and mathematics at the University of Cambridge. He gained his PhD there in theoretical particle physics, with the thesis Supersymmetric Quantum Mechanics and Geometry. He is also author of the award-winning popular science book Higgs Force: Cosmic Symmetry Shattered, and co-author of The Physical World: An Inspirational Tour of Fundamental Physics.
