WAVES MEDIUM VIBRATES PERPENDICULARLY TO THE WAVE DIRECTION IF f IS THE WAVE FREQUENCE AND λ IS THE WAVELEGTH THEN c, THE WAVE VELOCITY, IS GIVEN BY: c = λf EXAMPLES – ELECTROMAGNETIC WAVES – WAVES IN A STRING

ELECTROMAGNETIC WAVES FOR EVERY ELECTRIC WAVE THERE IS A CORRESPONDING MAGNETIC WAVE AT RIGHT ANGLES TO IT (AND VICE VERSA).

LONGITUDINAL WAVES PARTICLE MOTION IS PARALLEL TO THE WAVE DIRECTION EXAMPLE – SOUND WAVES

ELECTROMAGNETIC (E-M) SPECTRUM E-M WAVES IN NATURE RANGE FROM λ=.01 nm TO λ=1,000 m, A RANGE OF ANGSTROM = CM FROM SHORT TO LONG WAVELENGTH: – GAMMA (γ) RAYS – X-RAYS – ULTRA-VIOLET (UV) RAYS – VISIBLE RAYS (LIGHT) – INFRA-RED (IR) RAYS – RADIO WAVES TWO ATMOSPHERIC WINDOWS (LIGHT AND RADIO)

REFLECTION REACTION OF LIGHT WAVES WHEN THEY ENCOUNTER AN OPAQUE MEDIUM i=r WHERE: i IS THE ANGLE OF INCIDENCE r IS THE ANGLE OF REFLECTION

REFRACTION THE REACTION OF LIGHT WAVES WHEN THEY ENCOUNTER A TRANSPARENT INTERFACE θ 1 =θ 2 WHERE: θ 1 IS THE ANGLE OF INCIDENCE θ 2 IS THE ANGLE OF REFRACTION THE LIGHT RAY BENDS TOWARD THE NORMAL LINE IF IT GOES INTO AN OPTICALLY MORE DENSE MEDIUM (THE VELOCITY OF LIGHT IS SLOWER)

TOTAL INTERNAL REFLECTION WHEN LIGHT TRAVELS INTO AN OPTICALLY LESS DENSE MEDIUM IT WILL BEND AWAY FROM THE NORMAL LINE θ 1 = θ C (THE CRITICAL ANGLE) WHEN θ 2 = 90 o IF θ 1 >θ c THERE WILL BE NO REFRACTED WAVE THE TRANSPARENT INTERFACE WILL BEHAVE AS A PERFECT MIRROR

PRISM AS A MIRROR THE ADVANTAGE OF USING A PRISM AS A MIRROR IS THAT THE REFLECTING SURFACE CANNOT GET DIRTY

PRISMS IN BINOCULARS PRISMS ARE USED IN BINOCULARS TO – INVERT THE IMAGE – LENGTHEN THE “TELESCOPE” TO GET GREATER MAGNIFICATION

DIFFRACTION THE BENDING OF A WAVE WHEN IT ENCOUNTERS AN OBSTACLE

DISPERSION USING VARIABLE REFRACTION DISPERSION IS THE SPREADING OF LIGHT INTO ITS COMPONENT COLORS IN A PRISM BLUE LIGHT IS DISPERSED (BENT) MORE THAN RED LIGHT

PRISM SPECTROGRAPH THE ENTRANCE SLIT NARROWS THE LIGHT WAVES BEING CONSIDERED ALL THE LIGHT OF A GIVEN WAVELENGTH (COLOR) IS FOCUSED AT THE SAME SPOT ON THE FILM BLUE LIGHT IS BENT MORE THAN RED LIGHT THERE WILL BE AN IMAGE OF THE ENTRANCE SLIT FOR EACH COLOR THAT IS IN THE SOURCE. HENCE THE TERM “SPECTRAL LINE”

GRATING SPECTROGRAPH DISPERSION IS ACCOMPLISHED BY DIFFRACTION AND INTERFERENCE RED LIGHT IS BENT MORE THE ZERO ORDER IS CALLED THE “WHITE” FRINGE HIGHER ORDERS ARE DISPERSED MORE (THE SPECTRAL LINES ARE FARTHER APART)

RESOLUTION (RESOLVING POWER) RESOLUTION (α), THE MINIMUM ANGLE BETWEEN TWO OBJECTS SUCH THAT THEY CAN JUST BE DISTINGUISHED SINCE THE MINIMUM ANGLE IS SUBJECTIVE, LORD RAYLEIGH DEFINED IT TO BE WHERE THE AIRY DISKS OF ADJACENT STAR IMAGES OVERLAPPED AT “HALF POWER” THEN THE EXPRESSION FOR THE RESOLUTION BECAME: α(arcsec) = 250,000 λ/a NOTE: HIGH RESOLUTION CORRESPONDS TO SMALL α TO MAKE α SMALL EITHER λ MUST BE SMALL OR a MUST BE LARGE THAT’S WHY LARGER TELESCOPES HAVE HIGHER RESOLUTION

THE AIRY DISK

SPHERICAL LENS

CHROMATIC ABERRATION

SPHERICAL ABERRATION

COMPOUND LENSES ACHROMATIC DOUBLET – TWO LENSES MADE OF DIFFERENT TYPES OF GLASS (HAVING DIFFERENT INDICES OF REFRACTION) THE INDEX OF REFRACTION IS THE VELOCITY OF LIGHT IN FREE SPACE DIVIDED BY THE VELOCITY OF LIGHT IN THE MEDIUM. YOU CAN CHOOSE TWO WAVELENGTHS (COLORS) WHICH FOCUS AT THE SAME PLACE IF YOU USE THREE LENSES YOU CAN CHOOSE THREE WAVELENGTHS THAT FOCUS AT THE SAME PLACE IN ANY MULTIPLE LENSE ARRANGEMENT YOU CAN CHOOSE AS MANY WAVELENGTHS WHICH FOCUS AT THE SAME PLACE AS LENSES THAT YOU USE.

TELESCOPE PROPERTIES MAGNIFICATION (M): M = f 0 /f e, where f 0 is the objective focal length and f e is the eyepiece focal length SPEED (f #, f stop, focal ratio): f # = f 0 /a, where a is the aperture size RESOLUTION (α), the minimum angle between two objects such that they can just be distinguished: α(arcsec) = 250,000 λ/a

GALILEAN TELESCOPE VIRTUAL ERECT IMAGE – CURRENT DAY OPERA GLASSES

REFRACTING TELESCOPE INVERTED IMAGE

REFLECTING TELESCOPE PRIME FOCUSING SYSTEM

REFLECTING TELESCOPE NEWTONIAN FOCUSING SYSTEM

REFLECTING TELESCOPE CASSAGRAIN FOCUSING SYSTEM

REFLECTING TELESCOPE COUDE’ FOCUSING SYSTEM

REFLECTING TELESCOPES ADVANTAGES CAN BE TRULY PARABOLOIDAL CAN BE MADE LARGER ONLY ONE SURFACE TO GRIND EASIER TO SUPPORT FASTER (SHORTER FOCAL LENGTH) DISADVANTAGES SMALL FIELD OF VIEW

SCHMIDT CATADIOPTRIC TELESCOPE WIDE FIELD OF VIEW PRIMARY MIRROR IS SPHERICAL

MAKSUTOV CATADIOTRIC TELESCOPE WIDE FIELD OF VIEW PRIMARY MIRROR IS SPHERICAL

ABERRATION OF STARLIGHT THE APPARENT CHANGE IN A STAR’S LOCATION CAUSED BY THE EARTH’S MOTION DISCOVERED BY BRADLEY 1N 1729