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Astronomy and the Electromagnetic Spectrum Keith Grainge.

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Presentation on theme: "Astronomy and the Electromagnetic Spectrum Keith Grainge."— Presentation transcript:

1 Astronomy and the Electromagnetic Spectrum Keith Grainge

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

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

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

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

6 EM radiation and Astronomy EM radiation and Astronomy The vast majority of astronomical data comes from observations of EM radiation. The vast majority of astronomical data comes from observations of EM radiation. Until 1950s all astronomy was done in the optical band. Until 1950s all astronomy was done in the optical band. Astronomy now done all the way from gamma rays to radio. 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. 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. Dust obscures regions of star formation. Infrared radiation can be used to see through the dust. Hubble Space Telescope – Optical image of the Orion Nebula Anglo-Australian Telescope – Infrared image

8 Active Galaxies Centaurus A

9 Gamma rays ( m) The Sky at different wavelengths

10 X-rays ( m)

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

12 The Sky at different wavelengths Visible light (  m)

13 The Sky at different wavelengths Infrared (100  m)

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

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

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

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

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

19 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 larger the telescope the better the resolution. The longer the wavelength the larger the telescope we need to use to achieve a given resolution.The longer the wavelength the larger the telescope we need to use to achieve a given resolution. Angular Resolution

20 Improving Resolution with Interferometry The Ryle Telescope

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

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

23 Spectral Resolution Atoms and molecules absorb and emit at particular frequencies  line spectra. Atoms and molecules absorb and emit at particular frequencies  line spectra. Can learn temperature, density, and chemical composition. Can learn temperature, density, and chemical composition. Also velocity and distance … 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 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) Today the universe contains structure and is very cold (2.73K) In the beginning the universe was very hot and very, very smooth. In the beginning the universe was very hot and very, very smooth. Over 13 billion years the universe has expanded and cooled. 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. During this time the structure we see around us today has formed under the influence of gravity.

34 The formation of Structure

35 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 Optical + infrared image Molecular Cloud Barnard 68 Optical image

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

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

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

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

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


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