For an explanation, see the main splats page
SPLATS about observational astronomy
The principles of observational astronomy
- In 1572, Tycho Brahe saw a new star in the sky, a 'nova' as we say now. This was the first evidence against the ancient view that the heavens were unchangeable.
- In 1610, Galileo Galilei saw four 'new stars', actually moons of Jupiter, further evidence that the skies were not, as orthodox rulers claimed, unchangeable.
- Stars have an absolute magnitude that is always the same, no matter where they are. They also have a relative magnitude depending on where they are seen from.
- Stars have an apparent brightness from a particular viewpoint, with distant objects appearing dimmer than similar objects that are nearer to us.
- Relative magnitude follows the inverse square law. Of two stars of identical absolute magnitude, the one twice as far off has a quarter the relative magnitude.
- In 1826, Heinrich Olbers posed his paradox: if the universe is infinite, he asked, why is the sky so dark at night? The answer involves the red-shift.
- Armand Fizeau was the first to point out that a star, moving away from us, should show an observable Doppler effect red-shift in the spectral absorption lines.
- Distant objects have a larger redshift, which is taken by astronomers to indicate that they are travelling away from us faster than nearby objects.
- The Hubble constant relates distance to redshift, and tells us how fast the universe is expanding, from which we can deduce that the universe will not collapse.
- In 1869, William Huggins used red-shift data to estimate that the star Sirius is moving away from the Earth at about 30 kilometres (20 miles) a second.
- Barnard's star is the fastest moving star as it shifts position in the star field: it takes 180 years to move across half a degree of sky, the moon's width.
- Cepheid variables are stars that have a frequency of variation which relates to their absolute magnitude, which means we can use them as 'standard candles'.
- In 1912, Henrietta Leavitt discovered the period to luminosity relationship for Cepheid variable stars from studies of the Large and Small Magellanic Clouds.
- In 1914, Ejnar Hertzsprung estimated distance to the Small Magellanic Cloud using Cepheid variables, as 3000 light years, a lot lower than the current 210,000.
- In 1918, Harlow Shapley set out to use Cepheid variables and offered a model for the shape of the Milky Way. He was unaware there are two types of Cepheids.
- In 1924, Edwin Hubble used Cepheid variables in a nebula, Messier 31 in Andromeda to show the nebula was some 750,000 light years away, outside our own galaxy.
- Spectrum analysis of the absorption and transmission in light from distant objects can reveal a great deal about them and the elements that they are made of.
- Astronomy includes the study of cosmology, the branch of science that tries to explain how the universe and everything in it began, using the laws of physics.
- In 1782, John Goodricke noticed that the variations in brightness of Algol are periodic and proposes that it is partially eclipsed by a body moving around it.
- In 1803, William Herschel found, as John Michell had suggested, that binary stars existed. Michell felt this was more likely than stars being near each other.
- In 1863, Richard Carrington discovered that sunspots rotate at different speeds at different latitudes on the sun, revealing that the Sun was in some way fluid.
- In 1975, Gerald Smith, Frederick Landauer, and James Janesick use a charge-coupled device to observe Uranus, the first astronomical CCD observation.
- Quasars got their name from being quasi-stellar objects. Each is believed to be powered by a black hole, a very dense object, from which light cannot escape.
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