A105 Stars and Galaxies

Homework 4 due Sept. 21 Telescopes

Read units 26, 27News Quiz Today

Today’s APOD

ROOFTOP & SOLAR LAB Sept. 20

OBSERVING OPPORTUNITIES

• Rooftop session Sept. 20 at 8:30 PM–SWAIN WEST roof – take the

elevator to the 3rd floor and follow the signs

• Solar Lab Sept. 20 at 2:00 PM–Kirkwood Observatory, 2nd floor

Picking Up Homework

Pick up your homework from the bins by the elevator

We’ll put homework in the back of the lecture room the first day it’s returned

ELEVATOR BIN

GRADES!Homeworks – 100 pts, best 10 of 13Quizzes – 100 pts, best 10 of 13Exams – 600 ptsProject – 100 pts (100 only for outstanding

projects)Observing – 100 pts, 4 activities required

DON’T GET FOOLED!

Three types of spectra

Continuous – Thermal RadiatorEmission – from hot gasAbsorption – continuous spectrum passes through cooler gas

Continuous Spectrum

• The spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption

Emission Line Spectrum

• A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines

Absorption Line Spectrum

• A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum

Review:The Doppler Shift

for Light

• Astronomers us the Doppler effect to measure the “radial” velocities of astronomical objects

• Radial velocities are motions toward or away from us

Measuring the Shift

Stationary

Moving Away

Away Faster

Moving Toward

Toward Faster

Doppler shift tells us ONLY about the part of an object’s motion toward or away from usThe amount of blue or red shift tells us an object’s speed toward or away from us:

Beginnings…

This sketch of a telescope was included in a letter

written by Giovanpattista della Porta in August 1609

Thomas Harriet’s Drawings of the

Moon and Sun

Technology moves forward… Telescopes get BIGGER

Think about a square telescope…

Round ones work the same way

The amount of light a telescope collectsincreases as the area of the primary mirror(the square of the diameter)

Telescopes and

how they work

from lenses…

to mirrors

Kirkwood Observato

ry• 12” refracting

telescope (uses lenses to form an image)

• Built in 1901• Used for public

outreach and teaching

The 3.5-meter WIYN telescope Kitt Peak, Arizona

The WIYN Telescope

• Mirror: 3.5 meter diameter

• Located at Kitt Peak, Arizona

• Built in 1995• IU has a share

New Telescope

Technology• “Fast” mirror

• Lightweight mirror• Mirror shape

controlled• Mechanically simpler

mount• Temperature control

Casting the WIYN Mirror

Polishing the WIYN Mirror

The WIYN New Technology “Dome”

• Compact telescope chamber• Open for ventilation• Insulated to keep cool• Heated spaces kept separate

Breaking the “cost curve”

New technology provides better performance at lower cost

WIYN

in 6-8 meter telescopes

WIYN TECHNOLOGY

Going Observing• To observe at a major observatory, an

astronomer must:– Submit a proposal – Plan ahead– Work day and night

• Astronomers may also “observe” via the Internet– Space observatories– Data archives– Remote observing

Computers

• Operating a computer and being able to program are as important as knowing how to use a telescope

• Computers accomplish several tasks:– Solve equations– Move telescopes and feed information to

detectors– Convert data into useful form– Communicate and distribute data

Who are the Astronomers?

• Come from various backgrounds and countries• Studied physics and astronomy in college with

more specialized work in graduate school• Share deep passion for understanding the

Universe and how it works

Detecting the Light

• Electronic Detectors– Incoming light strikes an

array of semiconductor pixels that are coupled to a computer

– Efficiencies of 95% are possible

– CCD (Charged-coupled Device)

The Human EyeOnce used with a telescope to record observations or make sketchesNot good at detecting faint light, even with the 10-meter Keck telescopes

•Photographic plates chemically stores data to record fainter light

•Very inefficient: only 4% of the light recorded on film

Observing at Nonvisible

Wavelengths

• Astronomical objects radiate in wavelengths other than visible (thermal radiators)– Cold gas clouds – Dust clouds– Hot gases around black holes

• Telescopes for each wavelength region– Require their own unique design– All collect and focus radiation and resolve details– False-color pictures to show images– Some wavelengths must be observed from space

Is the Atmosphere Transparent or Opaque?

Applets\light_absorption.swf

Radio Telescopes

• Radio telescopes work the same way as optical telescopes• Large metal “mirror” reflects radio waves

Why Why Observatories Observatories

in Space?in Space?

• Even at wavelengths where the atmosphere is transparent, the atmosphere “blurrs” light– Why to stars “twinkle” (scintillation)?– The condition of the sky for viewing is

referred to as seeing– Distorted seeing can be improved by

adaptive optics

Space vs. Ground-Based Observatories

• Space-Based Advantages– Freedom from atmospheric blurring– Observe at wavelengths not transmitted by air

• Ground-Based Advantages– Larger collecting power– Equipment easily fixed

• Ground-Based Problems– Weather, humidity, and haze– Light pollution

Light Pollution

• artificial lighting threatens all observatories on the ground

• shield all outdoor lights

Exploring New

Wavelengths:

Gamma Rays• 1967 gamma-ray bursts from space discovered

by military satellites watching for Soviet nuclear bomb explosions

• Source of gamma-ray bursts is now (almost) understood

• Gamma rays from Milky Way center and remnants of exploded stars

Read unit 30 News Quiz on

Tuesday NovaSearch

homework (#5) worksheet due Thursday

EXAM Sept 28

Units 26, 27 Homework #4

due (telescopes) Solar Lab 2 PM

Weds. Rooftop 8:30 PM

Weds.