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Lecture 1: opacity of atmosphere Optical and radio telescopes

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Presentation on theme: "Lecture 1: opacity of atmosphere Optical and radio telescopes"— Presentation transcript:

1 Lecture 1: opacity of atmosphere Optical and radio telescopes Angular resolution Adaptive optics and interferometry

2 Atmospheric absorption

3 Telescopio Nazionale Galileo (3.5m) Hubble Space Telescope (2.4m) 2.5m Mount Wilson telescope

4 Airy disk ϑ ≈ sinϑ = 1.22 λ/D

5 Angular Resolution Resolution or minimum resolvable distance is the minimum angular distance between distinguishable objects in an image Sources with angular size larger than the resolution are called Extended, otherwise their are point-like, i.e., their angular Extent does not exceed the point spread function The resolution of ground-based optical images is limited by the Atmospheric seeing (about 1-2 arcseconds on average). How can one overcome the atmospheric limitation in optical? By using adaptive optics By using interferometry By putting a telescope in space (HST)

6

7 Adaptive optics use wavefront sensors to adapt a deformable mirror to variations of the local seeing
2” Adaptive optics at Gemini telescope

8 Radiotelescopes Resolution: ~10 arcmin Parabola in Medicina, Bologna
Natural concavities favour Screening from human-related Radio-interference Resolution: ~10 arcmin Parabola in Medicina, Bologna (32m) Arecibo (300m)

9 Radio-interferometry: Aperture synthesis
Croce del Nord (Medicina) Radio-interferometry: Aperture synthesis Angular resolution: ~1 arcsec Very Large Array (New Mexico)

10 Very Long Baseline Interferometry (ang. Res.: milliarcsecond)
European VLBI Network (EVN) Very Long Baseline Array (VLBA)

11 The VLBI Space Observatory Program (VSOP) HALCA: Japanese 8m
Antenna orbiting the Earth Ang. Res: milli-to-microarcsec 30000 km Halca Relativistic jet Of the active galaxy Mkn501 (z = 0.033)

12 Suggestion for an excellent textbook:
Malcolm Longair High Energy Astrophysics Cambridge University Press, 1981 [my edition dates to 1981, but there are more recent ones]

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