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PHY2083 ASTRONOMY Non-optical astronomy Signal-to-noise � σ(γ) = Nγ � Nγ S =� = Nγ N Nγ S Nγ (obj) = � 2 N Nγ (obj) + Nγ (sky) + Ndark + Nread Angular Resolution θmin θmin 1.22λ = radians D 1.22 × 206, 265λ = arcsec D The E/M spectrum • Black-body spectrum The E/M spectrum Radio Telescopes Radio waves are produced by a variety of physical mechanisms e.g. the interaction of charged particles with magnetic fields. Provides a window into processes not accessible at other wavelengths Radio waves interact differently with matter c.f. visible light => detector + telescope design different 76-m Lovell Telescope: Jodrell Bank Work out the resolution of this telescope at a wavelength of 10cm The parabolic dish reflects the radio energy of the source to an antenna. The signal is then amplified and processed to make a radio map. 305-m Arecibo Telescope:Puerto Rico Calculate the diameter a single-dish telescope would need to have to obtain a resolution of 1’’ at 21cm • An advantage of working at such long λ is that small deviations from an ideal parabolic shape are not crucial. • Can tolerate ~ λ/20 of perfect shape e.g. variations of 1cm ok when observing at 21cm Comparison between optical and radio telescopes • Remember: angular resolution of a telescope ∝ λ / D • Optical telescopes: ~25 milli-arcseconds (D = 5m, λ = 500nm • Radio telescopes: 1 arcmin (D = 100m λ = 2.8cm) • Distant radio sources have fine-scale structure < 1 milli-arcsec. 1 milli-arcsec @ λ = 2.8cm => D ~ 6000 km! Solution: Interferometry (c.f.Young’s doubleslit experiment) • Instead of building one huge dish: make several smaller telescopes and place them far away from each other • Combine the signal from these telescopes • In effect have 1 large telescope! Radio Interferometers P � = L sin θ L = nλ P θ P2 P1 Radio Interferometers Very Large Array, New Mexico Jupiter at radio wavelengths λ = 13 cm λ = 22 cm 8-m Gemini Telescope, Hawaii SOFIA (Stratospheric Observatory For Infrared Astronomy) Spitzer Space Telescope JWST (James Webb Space Telescope) Jupiter at mid-IR wavelengths λ = 5 µm Jupiter at near-IR wavelengths λ = 1 − 2 µm HST (Hubble Space Telescope) Jupiter at optical wavelengths λ = 400 − 600 nm Jupiter at UV wavelengths λ = 150 nm High energy astrophysics •Below ~ 300nm, the Earth’s atmosphere blocks all radiation => ultraviolet (uv) and xray astronomy not possible from the ground • Xray and gamma-ray photons cannot be easily reflected from any kind of surface (pass straight through / absorbed) Grazing incidence optics for high energy photons At grazing angles, some reflection is possible. Series of nested cylindrical mirrors to bring the photons (keV) to a focus XMM-Newton Gamma-rays • For gamma-rays, grazing incidence optics doesn’t work. => point in a direction, and count the number of gamma-ray photons received Note: traditional photographic plates / CCDs do not work for high-energy photons. Use other electronic detectors. Spatial resolution very low ~ 30” or worse. Gamma-ray observatories INTEGRAL (ESA) FERMI (NASA) MAGIC: Cosmic Ray Telescope These are high-energy protons, electrons, and atomic nuclei that reach the Earth. Highest energies ~ 1020 eV; source unknown Ice-Cube neutrino telescope Ice-cube Neutrino Telescope Gravitational Wave Observatories LISA (Laser Interferometer Space Antenna) 2020?