Telescopes Telescope History u Galileo Galilei built first

Telescopes

Telescope History u Galileo Galilei built first refractive telescope in 1609 u Isaac Newton built the first reflective telescope in 1668

1 st Reflecting Telescope by Isaac Newton

Optical Telescopes that contain mirrors, lenses, or both u Three properties: u • Light-gathering power • Resolving power • Magnifying power

Optical Telescopes u Telescopes with larger mirrors/lenses: • Can“see”farther into space • Have greater resolution u Magnification can be changed by using different eyepieces u Usually placed on mountain tops to reduce city lights

Refracting Telescopes Telescope uses two lens to bend or refract light u Simplest of all telescopes u First refracting telescope capable of magnifying objects 30 times. u

Objective Lens u Most important lens is the objective lens • Bends the light from a distant object and focuses the light at the focus to produce an image • The objective lens produces a very small, bright image of an object u u Focus= central point Focal length= distance between the focus and the objective lens

Eyepiece Lens The second lens used in a refractive telescope u Eyepiece magnifies image produced by the objective lens u

Simple Refracting Telescope

Disadvantages Shorter wavelengths of light are bent more than the longer ones u Chromatic aberration: u • Weakens image and creates a halo of color around it • When red light is in focus, a bluish halo appears. u Very hard to produce a large piece of high-quality, bubble-free glass

Yerkes Observatory Largest Refracting Telescope

Yerkes Observatory Williams Bay, Wisconsin

Refracting Telescope at Lick Observatory Southern California

Lick Observatory

Reflecting Telescopes Uses a concave (curved) mirror that focuses the light in front of it u Mirror is coated in a highly reflective material, an aluminum compound u Two mirrors- one large & concave and one small & flat u

Reflecting Telescope

Advantages No Chromatic aberration because reflected light is not dispersed into its component colors. u Glass does not need to be highquality because light does not pass through it. u Disadvantage–secondary mirror blocks some light entering the telescope. u

Mount Palomar Observatory California

Mirror for Hale Telescope at Mount Palomar Observatory

Hale Telescope

Keck Telescopes World’s Largest Reflecting Telescopes Hawaii

Schematic of Keck Multiple Mirros Telescope (MMT)

Kitt Peak Observatory Arizona

La Palma Observatory Canary Islands, Spain

Mc. Donald Observatory Texas

Cerro Tololo Observatory Chile

Invisible Light u Stars produce light wavelengths that are not visible to our eyes • Gamma rays, X-rays, ultraviolet radiation, infrared radiation, and radio waves • Most of these can not get past our atmosphere… so we must get our cameras above it!

Radio Telescopes These big dishes are used to detect radio waves u Focuses incoming radio waves on an antenna and transmits these to an amplifier. u

Radio Signals Radio signals are weak so it requires a very large dish u These telescopes have poor resolution u • Radio Interferometer= Wire several telescopes together

Advantages Less affected by turbulence in the atmosphere, clouds, and weather u No protective dome is required = cheaper u Can be used and “viewed” 24 hours a day u Radio signals can pass through intersteller dust clouds u

Disadvantages u Can be affected by human-made radio interference • Usually placed in valleys to block interference

Largest Radio Telescope in World Arecibo, Puerto Rico

VLA Radio Telescope Socorro, New Mexico

VLA

Space Telescopes u Orbit above Earth’s atmosphere and produce clearer images

Hubble Space Telescope Built by NASA and sent in April 1990 u 10 billion times more light-gathering power than the human eye u Given us amazing images of space u

www. hubblesite. org

Other Space Telescopes u Chandra X-Ray Observatory • NASA uses to study X-rays • Launched in 1999 • Gather data about black holes u Compton Gamma-Ray Observatory • Used to study visible light and gamma rays u In 2018, NASA will launch James Webb Space Telescope to study infrared radiation • Run into many obstacles and budget problems