Transcript Telesopes

A105
Stars and Galaxies
Today’s APOD
Homework 4 due Sept. 21
Telescopes
Read units 26, 27
News Quiz Today
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 13
Quizzes – 100 pts, best 10 of 13
Exams – 600 pts
Project – 100 pts (100 only for outstanding
projects)
Observing – 100 pts, 4 activities required
DON’T GET FOOLED!
Three
types of
spectra
Continuous – Thermal Radiator
Emission – from hot gas
Absorption – 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
Stationary
Moving Away
Away Faster
Moving Toward
Toward Faster
Measuring the Shift
Doppler shift tells us ONLY about the part
of an object’s motion toward or away from us
The amount of blue or red shift tells us an
object’s speed toward or away from us:
This sketch of a telescope
was included in a letter
written by Giovanpattista
della Porta in August 1609
Beginnings…
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 collects
increases as the area of the primary mirror
(the square of the diameter)
Telescopes
and
how they work
to
mirrors
from
lenses…
Kirkwood
Observatory
• 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”
WIYN
New
technology
provides
better
performance
at lower
cost
WIYN TECHNOLOGY
in 6-8 meter telescopes
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
The Human Eye
Once used with a telescope to record
observations or make sketches
Not good at detecting faint light, even
with the 10-meter Keck telescopes
Detecting
the Light
•Photographic plates chemically
stores data to record fainter light
•Very inefficient: only 4% of the
light recorded on film
• 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)
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
Observatories 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. GroundBased
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
 Units 26, 27
 Homework #4
due (telescopes)
 Solar Lab 2 PM
Weds.
 Rooftop 8:30 PM
Weds.
 Read unit 30
 News Quiz on
Tuesday
 NovaSearch
homework (#5)
worksheet due
Thursday
 EXAM Sept 28