Presentation on theme: "Astronomy and the Electromagnetic Spectrum"— Presentation transcript:
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 spectrumA prism will split white light into it component coloursThis 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.wavelengthCharacterised by different frequency or wavelength (c=f)Quantum mechanics can think about light being carried by photons.Photon energy frequency.
5 The Electromagnetic Spectrum microwavevisibleX-rayradioinfraredultravioletGamma rayRadio waves centimetres or metresGamma rays 100 femtometresVisible 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 RadiationDust obscures regions of star formation. Infrared radiation can be used to see through the dust.Anglo-Australian Telescope – Infrared imageHubble Space Telescope – Optical image of the Orion Nebula
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 (10-5010-9 m)
12 The Sky at different wavelengths Visible light ( 10-9 m)
13 The Sky at different wavelengths Infrared (10010-6 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 radioinfraredvisibleultravioletX-raygamma ray
18 Angular ResolutionAny telescope has a limited ability to see fine detail, known as its angular resolution.Angular resolution of observerobserver
19 Angular ResolutionThe 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 resolutionEquivalent to imaging a penny at 2000km!
22 SensitivityA telescope’s sensitivity determines its ability to detect faint (as opposed to small) objects.Depends upon collecting area.
23 Spectral ResolutionAtoms and molecules absorb and emit at particular frequencies line spectra.Can learn temperature, density, and chemical composition.Also velocity and distance …
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 SunUltraviolet image of erupting prominence
31 The local Universe - Galaxies Spiral Galaxy M63If this were our Galaxy, ourSun 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 FormationToday 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.
37 SummaryWe 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.