Telescopes Read Pages 68-88

Galileo’s Telescope

Spherical Aberration Spherical aberration in lenses

Perfect Lens “Thin”

Chromatic Aberration Chromatic aberration: A problem of lenses

Reducing Chromatic Aberration The Yerkes 40-inch Refractor

Purposes of Telescopes Gather and concentrate - Brighten Reveal greater detail – Resolution Make larger- Magnify

Brightness Gather and concentrate - Brighten – Light gathering power proportional to area – A= π r 2 – Double the radius 4x gathering power

What do telescopes do?

Angular Resolution Reveal greater detail – Resolution – Angular resolution- the angle between two adjacent objects that can be distinguished as two object. – Resolution varies with the diameter of the primary lens or mirror. – Double the size and halve the angle that can be distinguished.

Magnification We usually express this as 200X Magnification = focal length of primary focal length of eyepiece Magnification = 100 cm 0.5 cm = 200

Better Telescopes To make telescopes better you make them bigger. Brightness and Resolution- bigger diameter Magnification – longer focal length, longer telescope

Huygens’ 123-foot-long refractor Huygens 123 foot long telescope

Yerkes 40 inch (diameter) refractor The Yerkes 40-inch Refractor

Refracting vs Reflecting Refracting Large lenses are heavy to support only from the edge A lens must be flawless- bubbles block light Chromatic aberration in lenses Light is dimmed traveling through the glass Reflecting Mirrors can be supported from the back Only the surface of the mirror must be perfect No chromatic aberration in mirrors Light does not travel through the glass of a mirror Giant mirrors can be madeup of smaller segments.

Reflection vs Refraction Get to the root of it Refraction by lenses vs. reflection by mirrors

Newton to the Rescue (again) Newton used a metal primary mirror to capture light and a secondary mirror to direct the light out the side of the telescope.primary mirrorsecondary mirror Newton avoided the problem of chromatic aberration by using a mirror instead of a lens, but he could not clear up the blurry images caused by the spherical shape of the mirror. This problem, called spherical aberration, occurs in both spherical mirrors and lenses.chromatic aberrationspherical aberration

Parabolic shape eliminates spherical aberration

Parabolic Mirrors

Atmospheric Distortion

Hale Telescope Mount Palomar

Last Big Single Mirror Reflector Year completed:1948 Telescope type:Reflector Light collector: Aluminum-coated glass mirror Mirror diameter: 200 inches (5.0 m) Light observed:Visible Discovered visible evidence of quasars — very bright objects at very great distances that were later found to be supermassive black holes at the centers of distant galaxies.

Multi Mirror Telescopes

Keck I Year completed:1993 Telescope type:Reflector Light collector: 36 aluminum-coated glass mirror segments Mirror diameter: 400 inches (10 m) total Light observed:Visible Discovered the first visual evidence of a brown dwarf, a failed star. With its light-gathering power, found planets around other stars.

Atmospheric Windows (P 68)

Radio Telescopes Radio telescope design

Pictures from Radio Waves False Color

Hubble in Space

Hubble Highlights Year launched:1990 Telescope type:Reflector Light collector: Aluminum-coated glass mirror Mirror diameter: 94.5 inches (2.4 m) Light observed: Infrared, visible, ultraviolet Discovery Highlights: Helped determine the age of the universe and the way galaxies form. Revealed extraordinary details about the process by which Sun-like stars end their lives as planetary nebulae.

Chandra X-Ray Observatory

Chandra Highlights Year launched:1999 Telescope type:Reflector Light collector: 8 iridium-coated glass mirrors Mirror diameter: Each 32.8 inches (83.3 cm) Light observed:X-ray Discovery Highlights: Has allowed astronomers to study energetic events such as black holes, supernovae, and colliding galaxies. Has found new stars that may have planet-forming disks around them.

Spitzer (follows the earth)

Spitzer Highlights Year launched:2003 Telescope type:Reflector Light collector: Beryllium metal mirror Mirror diameter: 33.5 inches (85 cm) Light observed:Infrared Discovery Highlights: Has seen through dust clouds in our galaxy to better allow the study of star formation and black holes.

Webb 2013

Webb Highlights Year to be launched:2013 Telescope type:Reflector Light collector: Gold-coated beryllium mirror Mirror diameter: inches (6.5 m) Light observed:near- to mid-infrared Discovery Highlights: Telescope has not launched.

Human Eye as a Detector The human eye is a sophisticated, auto-focus, auto-exposure, electrical camera system. However, for all its versatility and importance in everyday life, it is a seriously limited astronomical detector:

Limitations of Human Eye eye is small, both brightness and resolution are improved with bigger diameter. maximum integration time only about 0.1 secs, eye has low sensitivity We cannot see in dim light, but cats can. Astronomers have long sought more capable detectors to use with telescopes.

Photographic Film or Plates Detects only 1-2% of incident photons but allows long integrations (hours) Requires chemical development of image after exposure Provides permanent storage of info, though not digital Large formats (up to 20" square for astronomy) Was the main astronomical detector used between 1900 and 1980.

Charged Coupled Devices Solid state electronics; widely used now in video cameras & TV The CCD surface is composed of thousands of independent, light-sensitive pixels. After exposure, pixel contents are shifted in 2 dimensions across the surface to an output amplifier and storage device.shifted Astronomical applications pioneered during development of Hubble Space Telescope ( ). Works well at both very short (TV) and very long (astronomy) exposure times x more sensitive than filmmore sensitive Digital image storage for immediate computer processing Small formats (2-in typical) but can "mosaic" CCDs to create large areas Small formats"mosaic" Now are the standard detectors used in astronomy