Transcript measure
Getting the Measure of the Universe Dr. Martin Hendry Glasgow University Ptolemy: 90 – 168 AD Nicolaus Copernicus 1473 – 1543 AD Retrograde motion of Mars Sun Earth Venus We can use Pythagoras’ theorem!! Solar Eclipses Total Eclipse Zone only about 20km across, but sweeps over many countries as the Earth spins Tycho Brahe: 1546 – 1601 AD Kepler’s laws, published 1609, 1619 Galileo Galilei: 1564 – 1642 AD Galilean Moons: 1610 Isaac Newton: 1642 – 1727 AD The Principia: 1684 - 1686 Nowadays we can use radar: Distance = Speed x Time Nowadays we can use radar: Distance = Speed x Time But what is the speed of light?… The Electromagnetic Spectrum Light waves Light waves Wavelength Frequency = No of waves produced per second Light waves Wavelength Frequency = 2450 MHz = 2450 Million waves per second Light waves Wavelength Speed = 2450 million wavelength Light travels 300,000 km every Second…… ……That’s about 10 million, million kilometres every year!!! The stars are VERY far away. The nearest star (after the Sun) is about 40 million million km from the Earth. It takes light more than 4 years to travel this distance. If the distance from the Earth to the Sun were the width of this screen, the next nearest star would be in Rome. Measuring Astronomical Distances: Parallax Measuring Astronomical Distances: Parallax Even the nearest star shows a parallax shift of only 1/2000th the width of the full Moon Spectroscopy What can we learn from spectra? Absorption ee- Emission ee- Wobbly stars: the key to finding extra-solar planets Planets are too faint to see directly but Planets and stars orbit their centre of mass - so stars wobble The Sun’s “wobble”, due to Jupiter, seen from 30 light years away = width of a 10p coin in Madrid Doppler Shift Star Laboratory 51 Peg – the first new planet So we can use spectra to tell what stars are made of….. ……If those stars have planets, we can also use spectra to find them, and tell what gases are in their atmospheres!