TelescopesRefractors and ReflectorsVarious DesignsImportant PropertiesModern AdvancesBeyond Visible Light

Basic Optics - RefractionLight is bent or refracted when it changes speed going through a lens or prism.Where the refracted rays meet is the focal point.Distance from the lens to the focal point is the focal length.

Basic Optics - ReflectionWhen light strikes a mirror it is reflected at an angle equal to its incident angle.Rays of light striking a curved mirror will meet at a focal point.The distance from the vertex of the mirror to the focal point is the focal length.

Reflectors and RefractorsA reflector telescope has a mirror as its objective.A refractor telescope has a lens as its objective.The main function of a telescope is to gather light.

Chromatic AberrationDifferent wavelengths focus at different distancesWorlds Largest Refractor - Yerkes Observatory

Reflectors

Why Mirrors?Light gathering power - size matters!lgp increases with the square of the radiusMore lgp, more resolution!Magnification is third!

200 Hale Telescope Mt. Palomar

Comparing lgp lgp depends upon the area of the lens or mirror; A = r2

lgp = (Dbig/Dsmall)2

Calculating Magnificationfobjfeye

M =Mmax = 20 x Dcm

Practical Limit of MagnificationSmaller focal length eyepieces give greater magnification.They also limit light & increase diffraction.At some point the image is too poor to be useful.

Mmax = 20X____cmx D

Resolving PowerThe ability of a telescope to distinguish two objects.Measured in arcseconds ( 1 arcsecond is 1/3600)a =11.58_______D (in cm)

Modern AdvancesBinocular TelescopesLBT - two 8.4 m mirrors with adaptive opticsLGP of an 11.8 m mirrorDetail of a 22.4 m mirrorSurpasses HST in clarity

Adaptive OpticsCorrect for atmospheric turbulenceUse the light from a guide star or laser to determine what the atmosphere is doing to the light passing through it.Distortable mirror will change shape to correct the image.

Beyond Visible LightRadio Telescopes

VLA Telescope

UV and X-Ray TelescopesSOHOChandra

HST and James Webb

/