New Improved Eyes Telescopes and “Invisible” Astronomy

Galileo Redux  Galileo first used the telescope to make important observations  An optical telescope since it used visible portion of spectrum  All telescopes are “light buckets”  Stellar Parallax is finally seen (1830’s)  Cosmological Models were refined

Optics  When light passes from one transparent material (medium) to another its speed changes (Water, glass)  This causes REFRACTION (bending) of the light rays  Rainbows, “broken” pencils  Does depend on Wavelength of light

Refraction Air Water

Optics  When light hits a polished opaque surface, it is REFLECTED with no change in speed  Mirrors, shiny metallic objects  Light will bounce off at the same angle that it came in  Doesn’t depend on wavelength of light

Reflection Mirror 40º

Image Formation  Light is reflected or given off by objects  Lens and Mirrors can be used to direct and focus this light  Lenses use refraction  Mirrors use reflection  When light rays return to same relative positions they started at from the object, an image is formed

Image Formation  For very distant objects (stars, galaxies, planets) this light is focused at the focal point of the lens or mirror  This image is then transferred to the detector (eye, photographic plate, CCD)  The image forms at the distance of the focal length from the lens or mirror

Telescopes  3 parts  Objective  Instrument  Mount

The Jobs of a Telescope  Light Gathering Power –Most important  Determined by Area of the Objective Lens  Resolution-  Determined by Diameter of the Objective Lens  Magnification-Least Important  Determined by Focal Length of Eyepiece

Telescopes  Use lenses and/or mirrors  Objective (Lens or Mirror) –focuses light  Prime Focus-focal point of objective  Eyepiece (Lens) or other Instruments capture image  Doesn’t have to be an “optical” image

Telescopes  Refractor  Lens objective  Think long and skinny  How do they work? How do they work?  Reflector  Mirror Objective  Think short and stout  How do they work? How do they work?  Both can have lens eyepiece

Refractor Problems  Big Glass costs Big $$$  Must be large to focus light  Unstable and Difficult to move  Chromatic Aberration  Spherical Aberration  Absorption of light  Big Glass is heavy leading to saggy lenses  Imperfections in Glass, bubbles, cracks etc.

Reflector Problems  Do not have Chromatic Aberration, absorptions, size or imperfection problems  Still have spherical aberration but this can be corrected with an extra attachment (Schmidt Corrector Plate)  All big telescopes are reflectors, some containing “fish-eye” mirrors

Reflectors Keck 1 Fish eye mirror

Reflector Hobby-Eberly Telescope helped pioneer the fisheye technology Telescope still works after one of the mirrors was shot!

Solar Telescope

Telescope’s Job Description  All telescopes perform same jobs  Gather Light  Light Gathering Power-Area of Objective  Resolve Detail  Resolution-Diameter of Objective  Magnify Image  Focal Length of Eyepiece

Invisible Astronomy  Many wavelengths we can’t see  Special telescopes can “see” them  Optical Telescopes (Keck)  Radio Telescopes (VLA)  X-ray Telescopes (Chandra)  UV (Fuse)  Infrared (IRTF)

Chandra X-ray Observatory Orbiting X-ray telescope searching for high energy objects such as Black Holes

Invisible Astronomy  Much more information  Different types of situations make different wavelengths of light  One object, observed at different wavelengths can provide new insights  It may look quite different at the different wavelengths

Sun at Several Wavelengths X-ray EUV UV Visible

Radio Telescopes  Can be used singly or in groups  Bigger “eye” – more sensitive  Can observe night and day, rain or shine  Grouping-Interferometry  Improves resolution

Very Large Telescope Arecibo Radio Telescope is the largest on Earth at 1000 ft wide Astronomy Picture of the Day

Very Large Array 27 “house sized” radio antennae that can be move on railroad tracks They span an area equal to a small city in land area Astronomy Picture of the Day

Invisible Astronomy  Earth’s Atmosphere absorbs much of EM spectrum  Visible, some Infrared, Radio make it through  Get above atmosphere

Summary  Telescopes are “light buckets”  3 important jobs  2 basic types  Invisible Astronomy provides much more information