Chapter 3 Telescopes

Gemini North Telescope, Mauna Kea, Hawaii

Optical telescopes Light buckets Reflectors and refractors Advantages of reflectors Reflecting telescope designs

Reflection and Refraction Reflection - the bouncing of light (or EM radiation) off of a shiny surface Refraction - the bending of light as it travels from one transparent substance to another

Figure Reflecting Mirror

Figure 3.1 Analogy - Light Bucket

Figure Refracting Lens

Figure Image Formation

Figure Reflectors and Refractors

Reflecting Telescope Advantages No chromatic aberration No UV or IR absorption Supported at back (lenses supported at edges) Only has one optical surface

Figure Reflecting Telescopes

Figure 3.6 Keck Telescope

Discovery 3-1 The Hubble Space Telescope

Detectors Photographic film Charge-coupled devices or CCDs CCDs more efficient (75% vs. 5%) CCDs collect data in digital format

Figure 3.7acd CCD Chip

Figure 3.7b CCD Chip

Figure Image Processing a) ground based, b) HST flawed, c) image processed, d) HST fixed

Light-gathering power Depends on collecting area of mirror Area  diameter 2

Figure 3.9 Sensitivity Same Exposure time, but (b) taken with twice the size telescope as (a)

Figure Mauna Kea Observatory a) Aerial view, b) Subaru telescope one piece mirror

Figure VLT Observatory - Paranal Observatory, Atacama, Chile

Resolving power Ability to see fine detail Larger diameter mirror resolves finer detail More detail at shorter wavelengths Limited by diffraction

Figure Resolution (a) 10’ (b) 1’ (c) 5” (d) 1”

Figure Diffraction

Seeing Atmospheric blurring Seeing disk - circle over which star’s light is spread Stars twinkle Planets don’t

Figure Atmospheric Turbulence

New telescope designs Active optics - control environment and mechanics of telescope Adaptive optics - control mirror shape in real time to remove effects of atmosphere

Figure Active Optics (a) without (b) with active optics

Figure Adaptive Optics

Figure Radio Telescope

DirecTV dish at far southern latitudes Large size Low angle El Chalten, Argentina

Figure Arecibo Observatory

Figure Radio Galaxy

Interferometer Telescopes in an array Combine signals Increases resolving power Resolving power determined by array size Photon-gathering power determined by total area of reflectors

Figure VLA Interferometer

Figure Interferometry

Figure Radio-optical Comparison

Figure Optical Interferometry

Figure 3.24 Infrared Telescope

Figure Infrared Images

Figure 3.26 Ultraviolet Images

Figure X-ray Telescope Reflection at grazing angles

Figure 3.28 Chandra (X-ray) Observatory

Figure 3.29 X-Ray Image of Supernova Remnant

Figure Gamma-ray Image Gamma-ray blazar in 3C279

Table 3-1 Astronomy at Many Wavelengths Table 3.1

Figure 3.31 Milky Way Galaxy at Multiple Wavelengths