Telescopes

Telescope History

Galileo Galilei built first refractive telescope in 1609

Isaac Newton built the first reflective telescope in 1668

1st Reflecting Telescope by Isaac Newton

Optical Telescopes

Telescopes that contain mirrors, lenses, or both

Three properties:• Light-gathering power• Resolving power• Magnifying power

Optical Telescopes

Telescopes with larger mirrors/lenses:• Can“see”farther into space• Have greater resolution

Magnification can be changed by using different eyepieces

Usually placed on mountain tops to reduce city lights

Refracting Telescopes

Telescope uses two lens to bend or refract light

Simplest of all telescopes First refracting telescope capable of

magnifying objects 30 times.

Objective Lens

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

Focus= central point Focal length= distance between the focus

and the objective lens

Eyepiece Lens

The second lens used in a refractive telescope

Eyepiece magnifies image produced by the objective lens

Simple Refracting Telescope

Disadvantages

Shorter wavelengths of light are bent more than the longer ones

Chromatic aberration: • Weakens image and creates a halo of

color around it• When red light is in focus, a bluish halo

appears. Very hard to produce a large piece of

high-quality, bubble-free glass

Yerkes ObservatoryLargest Refracting Telescope

Yerkes ObservatoryWilliams Bay, Wisconsin

Refracting Telescope at Lick ObservatorySouthern California

Lick Observatory

Reflecting Telescopes

Uses a concave (curved) mirror that focuses the light in front of it

Mirror is coated in a highly reflective material, an aluminum compound

Two mirrors- one large & concave and one small & flat

Reflecting Telescope

Advantages

No Chromatic aberration because reflected light is not dispersed into its component colors.

Glass does not need to be high-quality because light does not pass through it.

Disadvantage–secondary mirror blocks some light entering the telescope.

Mount Palomar ObservatoryCalifornia

Mirror for Hale Telescope at Mount Palomar Observatory

Hale Telescope

Keck TelescopesWorld’s Largest Reflecting Telescopes

Hawaii

Schematic of KeckMultiple Mirros Telescope (MMT)

Kitt Peak ObservatoryArizona

La Palma ObservatoryCanary Islands, Spain

McDonald ObservatoryTexas

Cerro Tololo ObservatoryChile

Invisible Light

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

Focuses incoming radio waves on an antenna and transmits these to an amplifier.

Radio Signals

Radio signals are weak so it requires a very large dish

These telescopes have poor resolution• Radio Interferometer= Wire several

telescopes together

Advantages

Less affected by turbulence in the atmosphere, clouds, and weather

No protective dome is required = cheaper

Can be used and “viewed” 24 hours a day

Radio signals can pass through intersteller dust clouds

Disadvantages

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

interference

Largest Radio Telescope in WorldArecibo, Puerto Rico

VLA Radio TelescopeSocorro, New Mexico

VLA

Space Telescopes

Orbit above Earth’s atmosphere and produce clearer images

Hubble Space Telescope

Built by NASA and sent in April 1990 10 billion times more light-gathering

power than the human eye Given us amazing images of space

www.hubblesite.org

Other Space Telescopes

Chandra X-Ray Observatory• NASA uses to study X-rays• Launched in 1999• Gather data about black holes

Compton Gamma-Ray Observatory• Used to study visible light and gamma rays

In 2018, NASA will launch James Webb Space Telescope to study infrared radiation• Run into many obstacles and budget problems