Post on 03-Jan-2016
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
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 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
The WIYN New Technology “Dome”
• Compact telescope chamber• Open for ventilation• Insulated to keep cool• Heated spaces kept separate
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
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