Download Light

Sally Seebode
Teacher San Mateo High School
CSTA San Jose, October 2012
How do we Experiment?
We interact with objects and make
observations.
How do you
interact with a
star?
All we can do is
collect the light
stars send us.
We learn about stars by collecting and
interpreting the light they send us.
Artists concept of Giant Magellan Telescope
Understanding information from light
• What is light?
• What creates light?
• What information can we get from light?
What is light?
• Light is a common term used to refer to
Electromagnetic Radiation
• Types of electro magnetic radiation:
Visible light, radio wave, X-rays, infra red waves
(heat), ultra violet waves, gamma rays,
microwaves
Teaching Light Spectrum
White light is composed of many different wavelengths
Demonstration: make a rainbow
Equipment: Overhead projector, 2 sheets of paper to make
a slit, a diffraction grating (Edmund Scientific 2 12” x 6”
sheets $8.95 or 15 gratings $7.95)
With sheets of paper, make a thin slit on overhead. Place
diffraction grating over projector lens.
Show students that white light splits into rainbow of colors.
Discuss colors and order/energy if appropriate.
Students record colors as they see them and label them
appropriately.
Making the Invisible, Visible
Introducing Infra-red
The Herschel
Experiment:
Many online
sources.
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/h
erschel_experiment.html
Making the Invisible, Visible
Introducing Infra-red
The Herschel
Experiment:
Students find that the thermometer just outside
the light gets the hottest.
Use this to instruct that there is light that our
eyes cannot detect.
Be careful not to interpret that it is the most
energetic light.
Making the Invisible, Visible
Introducing Infra-red
Get the fire department to bring
their thermal camera to class for
the day.
Or
Have students look through
following website
IR images
Understanding information from light
•• What is light?
•• What creates light?
•• What information can we get from light?
How light is created?
• Light originates from a vibration of a charged
particle (typically an electron)
• This vibration causes a pattern of electric and
magnetic fields that spread away from the
source in all directions.
Electron
What type of things emit light?
To emit light, an object must have thermal
energy: moving particles.
What types of things have these?
Anything with temperature
All matter emits light
All bodies in the Universe have some temperature.
• All bodies are composed of molecules/atoms
• When molecules “jiggle” = thermal motion
• Temperature is a measure of thermal motion
• Temperature of the Universe > 0 Kelvin
So,….
All matter emits light: black body radiation
Type of Light links to Temperature
• Background Cosmic Radiation
– radio waves, no visible light
• People (300 K)
– Infrared, no visible light
• Hot Stove (700 K)
– Red, orange
• Hot Iron (1000 K)
– Red, yellow, blue-white
• Star (3000 – 15000 K)
– “cool” = reddish white
Betelgeuse
– “hot” = bluish white
Sirius
Understanding information from light
•• What is light?
•• What creates light?
•• What information can we get from light?
Interpreting Light
• Objects do not emit just one wavelength of
light. They emit ranges. Their peak λ
corresponds to their temperature
Spectral Energy Distributions
A spectral energy distribution (SED) is a plot of
brightness (flux) versus wavelength of light
from a given star or stellar system.
Objects at different temperatures have
distinguishable SEDs.
Example: Star Spectral Types:
O,B,A,F,G,K,M
SED Tool
SED Tool
Students identify a main sequence star’s:
• spectral type
• temperature
• radius
• Distance from us
SED 1
Focuses on spectral type and temperature
SED Tool
Students determine distance and spectral type
of a star.
SED II
You can use given data or get archival data from
SIMBAD, or make photometric measurements
from a telescope.
Planetary Nebula
White Dwarf
Active Galactic Nuclei
A team of students worked
identifying stellar objects from
photometric data from the
Kepler survey (KIC).
Planetary nebula, white dwarfs,
X-ray binaries, cataclysmic
variables,
Using SEDs, able to identify with
about 80% accuracy
Further ways to interpret light
Noticing light that is missing also informs us
about objects and helps us describe them.
Analogy: cloud passes over head, you may not
have to see it to know it is there.
Teaching Spectroscopy
When light passes through a medium, some light is removed
Demonstration: spectroscopy with filters
Equipment: Overhead projector, 2 sheets of paper to make
a slit, diffraction grating, Arbor Scientific Color Filter Set (6
pack) ($12)
Place filters over half of slit on overhead so diffraction
grating is splitting white light and filtered light.
Students record colors from filtered light as they see them.
They make statements next to each spectrum stating filter
used and color(s) missing (absorbed).
Teaching Spectroscopy
Knowing what light is removed, tells us about the
substance the light passed through.
Spectrum of Sun
Describe what you see?
What did the sunlight pass through to create these
black lines (absorption lines)?
Photo from the Canadian Space Agency
Teaching Spectroscopy
Connect rainbow type spectra to 2 D graphical
representation.
Indicates
Calcium
H delta
Indicates
4101 Å
Hydrogen
H gamma
4340 Å
Epsilon Aurigae
April 19, 2009
Spectroscopy Resources
CSM Catalog
website:http://collegeofsanmateo.edu/astronomy/i
mages/SpectraCatalog.pdf
ARBSE NOAO
Astronomy Research Based Science Education website
Kepler Transit Resources
website
Thank You
Please email me if you would like a copy of this
presentation or particular links/websites or if
you have questions about what was presented
here.
[email protected]