1. Astronomy and the Electromagnetic Spectrum
Where you see QQQ this means ask the audience and try and involve them in answering the question.
Keith Grainge

2. Outline Introduction to the Electromagnetic spectrum.
The Universe at different wavelengths.
Observing EM radiation.
Cosmology.

3. White light spectrum
A prism will split white light into it component colours
This is only part of the story….

4. Electromagnetic Radiation
Maxwell was the first to propose that light was a travelling electromagnetic wave.
Predicted that the spectrum should continue beyond the visible.
All these waves travel at the same speed.
wavelength
Characterised by different frequency or wavelength (c=f)
Quantum mechanics  can think about light being carried by photons.
Photon energy  frequency.

5. The Electromagnetic Spectrum
microwave
visible
X-ray
radio
infrared
ultraviolet
Gamma ray
Radio waves  centimetres or metres
Gamma rays
 100 femtometres
Visible light
 100 nanometres

6. EM radiation and Astronomy
The vast majority of astronomical data comes from observations of EM radiation.
Until 1950s all astronomy was done in the optical band.
Astronomy now done all the way from gamma rays to radio.
Observations in other wavebands open different windows on the Universe - very different phenomena visible.

7. Infrared Radiation
Dust obscures regions of star formation. Infrared radiation can be used to see through the dust.
Anglo-Australian Telescope – Infrared image
Hubble Space Telescope – Optical image of the Orion Nebula

8. Active Galaxies
Centaurus A

9. The Sky at different wavelengths
Gamma rays (10-14 m)

10. The Sky at different wavelengths
X-rays (10-10 m)

11. The Sky at different wavelengths
Ultraviolet (10-5010-9 m)

12. The Sky at different wavelengths
Visible light ( 10-9 m)

13. The Sky at different wavelengths
Infrared (10010-6 m)

14. The Sky at different wavelengths
Microwaves ( 1 cm)

15. The Sky at different wavelengths
Radiowaves ( 1 m)

16. Observing EM radiation
(Telescope design)
Site.
Angular resolution.
Sensitivity.
Frequency resolution.

17. Atmospheric Transmission
radio
infrared
visible
ultraviolet
X-ray
gamma ray

18. Angular Resolution
Any telescope has a limited ability to see fine detail, known as its angular resolution.
Angular resolution of observer
observer

19. Angular Resolution
The resolution of a telescope depends on the size of the telescope relative to the wavelength being observed.
The larger the telescope the better the resolution.
The longer the wavelength the larger the telescope we need to use to achieve a given resolution.

20. Improving Resolution with Interferometry
The Ryle Telescope

21. Very Long Baseline Interferometry
Milli-arcsecond resolution
Equivalent to imaging a penny at 2000km!

22. Sensitivity
A telescope’s sensitivity determines its ability to detect faint (as opposed to small) objects.
Depends upon collecting area.

23. Spectral Resolution
Atoms and molecules absorb and emit at particular frequencies  line spectra.
Can learn temperature, density, and chemical composition.
Also velocity and distance …

24. The Doppler Effect

25. The Doppler Effect for EM radiation

26. Cosmological Redshift
Distant objects are redshifted i.e. receding  Universe is expanding

27. The Cosmic Microwave Background
The background is the left over radiation from the Big Bang. It has now cooled to a temperature of 2.7 K

28. The Cosmic Microwave Background
Imprint in the background due to the motion of the Earth, about 1 part in 1,000 of the total intensity

29. The Cosmic Microwave Background
The ripples in the background correspond to only about one part in 100,000 of the total intensity

30. The local Universe - The Sun
A photograph of the Sun
Ultraviolet image of erupting prominence

31. The local Universe - Galaxies
Spiral Galaxy M63
If this were our Galaxy, our
Sun would be located about here

32. The Universe on the Largest Scale - the Cambridge APM survey
Over 2 million galaxies in direction of the South Galactic pole. The map covers about one tenth of the sky

33. Structure Formation
Today the universe contains structure and is very cold (2.73K)
In the beginning the universe was very hot and very, very smooth.
Over 13 billion years the universe has expanded and cooled.
During this time the structure we see around us today has formed under the influence of gravity.
So we know what the universe looks like today. But in the beginning it was hot and smooth. Elaborate.
Explain universe has expanded and cooled and is filled with radiation left over from Big Bang.
We can observe universe when it was only 300,000 years old.

34. The formation of Structure

35. HST image of colliding galaxies NGC 4038 and NGC 4039
Interacting Galaxies
HST image of colliding galaxies NGC 4038 and NGC 4039

36. Interacting Galaxies (2)

37. Summary
We can learn about the history of the universe by observing at different wavelengths.
In the beginning the universe was hot and smooth. Now it is cold and structured.
Gravity is dominant on large scales and has shaped the universe.

38. Star formation

39. A hole in the stars? Optical + infrared image
Molecular Cloud Barnard 68
Optical image

40. The Sky at different wavelengths
Radiowaves (More than 1 cm)
Microwaves ( 1 cm)
Infrared (10010-6 m)
Visible light ( 10-9 m)
X-rays (10-10 m)
Ultraviolet (10-5010-9 m)
Gamma rays (10-14 m)

41. Clusters of galaxies
Abell2218
HST
The size of a cluster of galaxies is about 50 times the size of our Galaxy.

42. Atmospheric Transmission
The atmosphere is opaque over much of the EM spectrum.
Ground based astronomy is only possible in the optical, the radio and the IR.
Satellites needed otherwise.

43. The Electromagnetic Spectrum
Visible light is just a small part of the EM spectrum.
Runs from gamma rays to radio waves.

44. The Electromagnetic Spectrum
Visible light is just a small part of the EM spectrum.
Many examples in everyday life.