getting the measure of the universe dr. martin hendry glasgow university
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Getting the Measure ofGetting the Measure ofthe Universethe Universe
Dr. Martin Hendry
Glasgow University
Ptolemy: 90 – 168 AD
Nicolaus Copernicus1473 – 1543 AD
Retrograde motion of Mars
Earth
Sun
Venus
We can use Pythagoras’ theorem!!
Solar Eclipses 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:Nowadays we can use radar:
Distance = Speed x TimeDistance = Speed x Time
Nowadays we can use radar:Nowadays we can use radar:
Distance = Speed x TimeDistance = Speed x Time
But what is the speed of light?…
The ElectromagneticSpectrum
Light wavesLight waves
Wavelength
Frequency = No of waves producedper second
Light wavesLight waves
Wavelength
Frequency = 2450 MHz = 2450 Million waves
per second
Light wavesLight waves
Wavelength
Speed = 2450 million wavelength
Light wavesLight waves
Light travels 300,000 km everyLight travels 300,000 km everySecond……Second……
…………That’s about 10 million, That’s about 10 million, million kilometres every year!!!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
SpectroscopySpectroscopy
What can we learn from spectra?
Absorption
e -
e -
Emission
e - 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 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!
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