Chapter 3 Stars

3A-1  Gnomon – a pole, column of stones, pillar, or pyramid (like a crude clock or calendar)  Uses: -Tell time of day (movement of shadow) -Tell time of year (by length of shadow) -Show motion of heavenly bodies

3A-2 Refractor Telescopes Use lenses Objective lens refracts (bends) light Ocular or eye piece lens focuses & magnifies image

3A-2 Refractor Telescopes  Functions of a Telescope 1.Light gathering 2.Magnification: make it bigger 3.Resolution: make it clearer *many stars seen with naked eye are actually 2 or more stars

Chromatic Aberration  Color distortion due to using lenses to refract light  Happens because different wavelengths of light bend different amounts and focus on different points

Chromatic Aberration Solutions  Use very thin lenses that don’t bend light much (makes telescope very long)  Use a compound lens (one convex & one concave) cemented together

Chromatic Aberration  Sir Isaac Newton discovered white light is made of many colors (each with a different wavelength)  His solutions was to use mirrors instead of lenses

Homework: SRQ 3A-1

BELL WORK What is a gnomer? * Please answer this question in your own words (Don’t just copy a definition from your notes.)

3A-3 Reflecting Telescopes Developed by Newton Use mirrors Ex: Newtonian Reflector & Cassegranian Reflector

3A-3 Newtonian Reflector Has concave mirror, flat mirror, & eye piece Image is viewed from the side

3A-3 Cassegranian Reflector  Light enters, reflects off large concave mirror with hole in center  Reflects to a convex mirror, which reflects through the hole to the ocular Advantage: compact design

Mirrors & Telescopes  Telescopes with mirrors can be built much larger than lens- telescopes -Some 10 m in diameter! -No aberration if shaped in parabolic curve

Mirrors & Telescopes 3 Advances in Mirror Design (made mirrors larger than 5 m possible) 1.Honeycomb mirror – reduces mirror weight by spincasting 2.Segmented mirrors – smaller pieces fit together to make large mirror 3.Meniscus mirror – very thin & controlled shape by computerized actuators

Composite Telescope  Uses mirrors & correcting lens objective  Gives fine detail over a wide field - Ex: Schmidt telescope *Be able to diagram all 4 types of telescopes in 3A-2 & 3A-3

3A-4 Non optical telescopes Do not use visible light Study other waves given off by stars (Radiowaves, infra red, ultra violet, gamma & x rays) Atmosphere blocks most of these, but does not block radio waves

Non optical telescopes Radio telescope: -Has large, dish shaped antenna -focuses amplifies & analyzes radio waves from space -Can send radio waves (as radar) -Separate radio telescopes can work together

Non optical telescopes  Other telescopes  Chandra x-ray telescope  Hubble Space Telescope (HTS)  Placed in orbit in 1990, has optical & non optical equipment  Can “see” things hidden behind dust, takes pictures, transmits them to earth *placed above earth & can see things filtered out by atmosphere

Telescope Mounts Must be able to move vertically & horizontally to point in any direction Altazimuth mount: has separate vertical & horizontal controls Equatorial (German) mount: Telescope tube rotates around attached pole, pole points to celestial pole Dobsonian mount: useful for amateurs, has a turn table on the ground and is a modified Altazimuth

Recording telescope images Optical telescope: Image recorded by camera & photographs Non-optical telescope: Computer turns strip chart/digital data into picture Main star charts & catalogs 1. hipparchus catalog 2. Tycho-2 catalog (2.5 mil. stars)

Keeping track of star data Main star charts & catalogs 1. Hipparchus catalog 2. Tycho-2 catalog (2.5 mil. stars)

Homework: SRQ 3A-2 (all) SRQ 3A-3 (1-6) Study for Quiz 3A