1929 – USA
‘Galaxies are moving away from each other and us at an ever-increasing rate. The more distant the galaxy, the faster it is moving away’
This means that the universe is expanding like a balloon. The principle of an expanding cosmos is at the heart of astronomical theory.
Before 1930, astronomers believed that the Milky Way was the only galaxy in the universe. The discovery of Cepheid variables, which brightened and dimmed in a regular rhythm gave a clue as to the true size of the universe.
In 1923, Hubble spotted a Cepheid variable in the Andromeda Nebula, previously supposed to be clouds of gas. This led to the conclusion that Andromeda was nearly a million light years away, far beyond the limits of the Milky Way and clearly a galaxy in its own right. Hubble went on to discover Cepheids in other nebula and proved that galaxies existed beyond our own.
He began to develop a classification system, sorting galaxies by size, content, distance, shape and brightness. He divided galaxies into elliptical, spiral, barred spiral and irregular. These are subdivided into categories, a, b and c according to the size of the central mass of stars within the galaxy and the tightness of any spiraling arms.
The Earth’s atmosphere alters light rays from outer space; the Hubble Space Telescope, being above the atmosphere, receives images with far greater clarity and detail than any Earth-based optical instrument and its camera can achieve a resolution ten times greater than the largest Earth based telescope.
Construction began on the HST in 1977 and it was launched by the space shuttle Discovery on 25 April 1990. The instruments can detect not only visible light but also infra-red and ultra-violet.
Hubble noticed that the galaxies appeared to be moving away from the region of space in which the Earth is located. It appeared that the further away a galaxy was, the faster it was receding. The conclusion was that the universe, which had previously been considered static is in fact expanding.
In 1915, EINSTEIN’s theory of relativity had suggested that owing to the effects of gravity, the universe was either expanding or contracting. Einstein knew little about astronomy and had introduced an anti-gravity force into his equations, the cosmological constant. Hubble’s discoveries proved Einstein had been right after all and Einstein later described the introduction of the gravitational constant as ‘the biggest blunder of my life’.
Hubble’s discovery that the universe is expanding led to the development of the ‘big-bang’ model of the universe.
- Scientific Cosmology (aip.org)