Optics and Telescopes Kathy Cooksey Acknowledgements Tyler Nordgren & Julie Rathbun University of Redlands Johnny B. Holmes Christian Brothers University

Outline Optics and telescopes Understand different types Why does size matter? Why put them in space?

Refraction & Lens-users Eq. f f o i as o approaches infinity i approaches f

Refraction & Lens-users Eq. f f o i o > 0 AND o > f i > 0 AND i > f f > 0

Refraction & Lens-users Eq. f f o i as o gets smaller, i gets larger

Refraction & Lens-users Eq. f f oi as o approaches f, i approaches infinity

Refracting Telescope objective lens eyepiece fofo fefe Two lenses: How does it work?

Refracting Telescope objective lens eyepiece fofo fefe Two lenses:

Model Optical Rail champions.com/science/experiments/simo pticsmirror.htmhttp:// champions.com/science/experiments/simo pticsmirror.htm Magnification Image Inversion Multiple optics –Image re-inversion ;)

Purpose of Telescope 1. Increases amount of light we see: Sensitivity is proportional to collecting area. If one telescope is 3 times bigger than another, then it can see 3 2 = 9 times fainter objects. 2. Increases detail (resolution) we see: Resolution is inversely proportional to telescope diameter. If one telescope is 3 times bigger than another, then it can see 3 times smaller angles (3 times smaller objects or detail).

Andromeda Galaxy Copyright by AURA Sensitivity Telescope size doubled from left to right

Resolution Andromeda Galaxy Copyright by AURA (a) 10’ (b) 1’ (10 times bigger than a) (c) 5” (12 times bigger than b) (d) 1” (5 times bigger than c) Human eye: 0.5’ in visual range

Side Note: Exposure Time Point telescope, open shutter, and expose for a long time (integration) Gather more photons and improve image Human eye has limited integration time

Telescopes & Light Collect “light” –Visible light is just part of whole spectrum of “light” Light is all astronomers have!!! Electromagnetic spectrum (EM): whole range of varieties of “light”: –Example: visible light comes from lamp in your house –Example: radio waves come from radio station –Other types of radiation: microwaves, infrared and ultraviolet light, X-rays, and gamma-rays

EM Radiation

Radio Optical and infrared X-ray UV γ-ray

Types of Telescopes

Refracting Telescope objective lens eyepiece fofo fefe Two lenses (as we made)

Optical Yerkes 40-in Refractor

All modern astronomy telescopes are reflectors Use mirrors for primary optic

Reflecting Telescope Light from far away mirror focuses light Problem: how do we get to focused light without blocking incoming light?

Reflecting Telescope Light from far away mirror focuses eyepiece light Solution #1: If mirror is big enough (say100 to 200 inches in diameter), we can sit right in middle and won’t block much light - this is called prime focus.

Radio Arecibo 300-ft Reflector

Reflecting Telescope Light from far away eyepiece mirror focuses light Solution #2: Use secondary mirror to reflect light off to side of telescope - this is called Newtonian focus.

Reflecting Telescope Light from far away primary mirror focuses light eyepiece Solution #3: Use secondary mirror to reflect light out back of telescope - this is called Cassegrain focus.

Optical Hooker 100-in Reflector

Some Large Optical Telescopes Location, location, location

Optical & IR Keck Twin 10-m Reflector

Keck Primary Mirrors Large! –Formed by 36 individual hexagonal segments All must be kept positioned relative to their neighbors –To accuracy of four nanometers, or 1,000 times thinner than human hair

Lick Observatory Shane 120-in Nickel 40-in

Lick Observatory Adaptive Optics Teaser

Atmospheric Seeing

Ground - KPNO 4.0m Copyright NOAO /AURA/NSF Space - HST – 1.0m Hubble Space Telescope

Summary Refracting telescope: primary lens Reflecting telescope: primary mirror –All modern telescopes Sensitivity: amount of light –Proportional to collecting area Resolution: detail –Inversely proportional to telescope diameter Bigger is better Space is atmosphere free