Getting the Measure of the Universe Dr. Martin Hendry Glasgow University
Ptolemy: 90 – 168 AD
Nicolaus Copernicus 1473 – 1543 AD
Retrograde motion of Mars
Earth Sun 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:
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?…
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 waves
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
Even the nearest star shows a parallax shift of only 1/2000 th the width of the full Moon
Spectroscopy
What can we learn from spectra?
Absorption e -
Emission e -
Wobbly stars: the key to finding extra-solar planets Planets and stars orbit their centre of mass Planets are too faint to see directly - so stars wobble but
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!