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 Telescope1. Light gathering2. Magnification: make it bigger3. 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 lightHappens 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 telescopesChandra x-ray telescopeHubble 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