Download HW #3: Available online now. Due in 1 week, Nov 3rd, 11pm. Buy

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HW #3: Available online now.
Due in 1 week, Nov 3rd, 11pm.
Buy-back points tallied and added: 750
points “bought-back”.
Last Withdrawal date: this friday, Oct 31st.
Evening Observing: next four nights, 8:30–
9:45pm. WEATHER PERMITTING.
Of Sunspots and the Earth
Question #1 on Exam 2: many of your secondguessed yourselves.
Sunspots are about the same size as earth,
some smaller, some bigger.
But, figure 6.2 says a sunspot could “swallow
several earths”. The biggest could.
Since this was confusing, if you changed your
correct answer in the buy-back extra-credit,
you got full points (+2).
The image at right shows a
picture of the Sun. The dark
spots located on this image
are sunspots. How does the
size of Earth compare
(approximately) to the
size of the sunspot that is
identified on the image of the
Sun?
A) Earth and the sunspot
are about the same size.
B) The sunspot is much
larger than Earth.
C) The sunspot is much
smaller than Earth.
Sunspot
The image at right shows a
picture of the Sun. The dark
spots located on this image
are sunspots. How does the
size of Earth compare
(approximately) to the
size of the sunspot that is
identified on the image of the
Sun?
✪
A) Earth and the sunspot
are about the same size.
B) The sunspot is much
larger than Earth.
C) The sunspot is much
smaller than Earth.
Sunspot
Last Time
Light: carrier of information from the
universe.
Visible light just a tiny portion of all the
“electromagnetic spectrum”. Even radio is a
form of light.
Light has a “wavelength” and “frequency”.
High frequency=high energy=show
wavelength, and visa versa.
Last Time
Matter, composed of atoms, identified by
atomic number (number of protons). This
sets their properties.
Isotopes have same number of protons, but
different number of neutrons (e.g. Carbon
13).
Light and matter interact by emission/
absorption/reflection/transmission.
Last Time
The “Spectrum” of a source describes its
intensity at each wavelength of light.
There is a special spectrum of “perfectly
black” emission, called “blackbody”. Most
objects, including stars, emit a spectrum
close to blackbody radiation.
Hotter blackbody = shorter wavelength of
peak emission.
The filter experiment
(take 2)
A red object absorbs all but red light.
A red filter transmits all but red light.
High energy, short wavelength, high frequency
Electromagnetic
Spectrum
Visible light:
red, orange, yellow, green,
blue, indigo, violet
(ROY G BIV)
Invisible Light:
Ultraviolet = bluer than blue
Infrared = redder than red
(heat!)
Other wavelengths:
Short: X-rays, gamma-rays
Long: microwave, radio
Low energy, long wavelength, low frequency
Spectroscopy
Prism separates light
into different colors
– Continuous spectrum
contains all colors
Example: blackbody spectrum
Spectroscopy
– Absorption Line
spectrum
Some colors are missing (discrete
lines)
The Solar Spectrum
The Solar Spectrum
Na
H
Mg
Spectroscopy
Emission Line spectrum
Only certain colors are
present (discrete lines)
Spectrum for each element unique (like
fingerprints)
How it Works
Thought question
Which letter(s) mark absorption lines?
A
B
C
D E
Thought question
Which letter(s) mark absorption lines?
A
B
C
✪
D E
✪
Thought question
Which letter(s) mark Emission lines?
A
B
C
D E
Thought question
Which letter(s) mark Emission lines?
A
✪
B
C
D E
Doppler Shift (again)
Just like a train, the pitch (frequency) of
light changes if the light source is moving.
Moving away: redshifted.
Moving towards: blueshifted.
The Doppler Effect ONLY tells us
the about an objects motion
towards or away from us
Thought Question:
You measure a line of hydrogen at 656.3 nm
in the lab. The same line has a wavelength
of 659 nm in a star. The star:
a) is moving away from you
b) is moving towards you
c) is not moving at all
Thought Question:
You measure a line of hydrogen at 656.3 nm
in the lab. The same line has a wavelength
of 659 nm in a star. The star:
✪ a) is moving away from you
b) is moving towards you
c) is not moving at all
Model Atom
Electrons orbit nucleus
Number of electrons = number of protons
• Ionization = removing electrons
Only certain orbits are allowed
hydrogen
helium
Atomic Energy Levels
In order to move between orbits (levels), the
electron need gain or lose a specific amount of
energy, and only that amount.
level 3
level 2
level 1
1H
not to scale
1 eV (electron Volt) = 1.6 x 10-19 J
Atomic Absorption
Atom absorbs photon
energy
electron “jumps” to
higher energy orbit
only certain
discrete orbits are
allowed
• Atom can absorb
only discrete
colors (energies)
Atomic Emission
Electron “jumps”
to a lower energy
orbit
Atom emits
photon
– can emit only
discrete colors
same colors
(wavelengths/
energies) as
absorption
Chemical Fingerprints
each element or molecule has:
a unique set of energy levels, and so
a unique emission/absorption line
spectrum
we can determine the composition of a gas by
looking at its spectrum!
Spectrum Demo
Get a grating.
Hold it up and look through it at the lamps.
Should see various “Rainbows” going off in
several directions.
Please return at the top of the table, at the
end of class.
Sun
Sun
Hydrogen
Helium
Carbon
Nitrogen
Oxygen
Neon
Sodium
Magnesium
Aluminum
Silicon
What can we learn
Light can tell us:
the temperature of an
object.
It’s chemical composition
(what it’s made of!).
Velocity of motion.
...much more (from
across the universe!).
Workbook Time
Analyzing Spectra, Page 69.
Consider the two spectral curves for Star V
and Star Y shown in the graph at right. What
can you determine about the relative
temperatures of the two stars?
A) Star V is at the higher
temperature.
B) Star Y is at the higher
temperature.
C) Both stars are the
same temperature.
D) The relative temperatures
of the stars cannot be
determined
Consider the two spectral curves for Star V
and Star Y shown in the graph at right. What
can you determine about the relative
temperatures of the two stars?
A) Star V is at the higher
temperature.
B) Star Y is at the higher
temperature.
✪
C) Both stars are the
same temperature.
D) The relative temperatures
of the stars cannot be
determined
Red Hydrogen Line
Yellow Sodium Lines
Telescopes
Eyes on the Heavens
What good are
telescopes?
Like giant “light buckets”, they collect
more light than our eyes can (larger
collecting area).
They can see more detail than our eyes can
(better resolution).
They can detect other forms of light, like xrays, infrared, radio (better wavelength
coverage).
Bigger is better!
Collects more light
Bigger is better!
Better angular
resolution
0.15 m
0.50 m
2.4 m
5.0 m
Ability to
separate two
nearby objects.
Basic Telescope Design
Refracting: lenses
Refracting
Telescope
Yerkes 1-m refractor
Basic Telescope Design
Reflecting: mirrors
Reflecting
Telescope
Gemini 8 meter
Tom Jarrett
Mauna Kea, HI
Twin 10-m Keck Telescopes
Using telecopes
Astronomers almost never
“look through” a telescope
with their eyes.
Instead instruments are
used which are more
sensitive, can see other
wavelengths of light, and
can record their data
directly are used.
Radio Telescopes
Why do we put telescopes
in space?
We can over
come problems
with the Earth’s
atmosphere
1.) Light Pollution
1.) Light Pollution
Bright Sky
Dark Sky
2) Atmospheric Turbulence
Atmospheric
turbulence causes
“twinkling” which
blurs the image
Limits the angular
resolution of all
big telescopes to
about 0.5
arcseconds
2) Atmospheric Turbulence
Image 1: From sea
level
(3 arcseconds)
Image 2: From a
mountain (0.5
arcseconds)
Image 3: Hubble
Space Telescope
(0.1 arcseconds)
3) Atmospheric Absorption
Most radiation is absorbed by the
atmosphere
(which is a good thing!)
Technology & Astronomy
Adaptive optics: A fast computer figures how
the atmosphere is distorting the light and
moves a deformable mirror to compensate.
Technology & Astronomy
Interferometry:
allows individual
telescopes to
work together to
achieve the
angular
resolution of a
larger telescope.
Very Large Array (New Mexico)
Reminders
Hand in Gratings before you go!
HW #3 due in 1 week.
Observing this week. Check website for
weather updates.
Read Chapter 10 for next time!