Transcript Linking Asteroids and Meteorites through Reflectance

Astronomy 101
The Solar System
Tuesday, Thursday
Tom Burbine
[email protected]
Course
• Course Website:
– http://blogs.umass.edu/astron101-tburbine/
• Textbook:
– Pathways to Astronomy (2nd Edition) by Stephen Schneider
and Thomas Arny.
• You also will need a calculator.
• There is an Astronomy Help Desk that is open
Monday-Thursday evenings from 7-9 pm in Hasbrouck
205.
• There is an open house at the Observatory every
Thursday when it’s clear. Students should check the
observatory website before going since the times may
change as the semester progresses and the telescope
may be down for repairs at times. The website is
http://www.astro.umass.edu/~orchardhill/index.html.
HWs #6, #7, and #8
• Due by Feb. 23rd at 1 pm
News: Water on Enceladus (moon of Saturn)
• The Cassini spacecraft found negatively
charged water ions in the atmosphere
• On Earth, such ions are often seen where liquid
water is in motion, such as waterfalls or
crashing ocean waves.
/
http://www.msnbc.msn.com/id/35313176/ns/technology_and_science-space
Atoms make up molecules
• H2O - water
• CO2 – carbon dioxide
• CH4 - methane
Spectroscopy
• Spectroscopy is the study of the interaction
between radiation and matter as a function of
wavelength (λ).
• You can use spectroscopy to determine what is in
a body (planet, star, etc.) or atmosphere
http://upload.wikimedia.org/wikipedia/commons/f/f5/Light_dispersion_conceptual_waves.gif
• How did scientists determined that there was
water on the Moon?
Water on the Moon
Grey - H2O and OH absorptions
White line - NASA' Cassini spacecraft
Blue line - NASA's Moon Mineralogy Mapper instrument on the Indian Chandrayaan-1 spacecraft
http://www.nasa.gov/images/content/388950main_ROGER_2-516.jpg
Definitions
• Reflectance – How much light an object reflects
• Absorption – Light is absorbed and not reflected
Light cause water molecules to vibrate
• http://www.btinternet.com/~martin.chaplin/vibrat.
html
How much water?
• If you had a cubic meter of lunar soil, you could
squeeze it and get out a liter of water
• Water has to be near the surface
How do you use light to determine
what is in an astronomical body
like a star?
What happens when
electrons absorb energy?
http://www.meditech.cn/images/pic9.jpg
http://library.thinkquest.org/C006669/media/Chem/img/bohr.gif
Energy levels where an electron can reside
To go to a higher energy level, an electron needs to gain energy
To go to a lower energy level, an electron needs to lose energy
eV
• 1 eV = 1.6 x 10-19 Joules
Rules
• An electron can not jump to a higher energy level
unless it gains energy from somewhere else
– Absorbs a photon
– Gains kinetic energy from an impacting particle
• To go to a lower energy level, the electron must
lose energy
– Emits a photon
• Electron jumps can occur only with the particular
amounts of energy representing differences
between possible energy levels
Heated hydrogen gas
Emission line spectrum
White light through cool hydrogen gas
Absorption line spectrum
Types of spectra
• Emission – radiation is emitted at characteristic
wavelengths
– Material is “hot” so electrons keep on bumping into
each other and transferring kinetic energy to each
other so they jump between particular energy levels
• Absorption – radiation is absorbed at
characteristic wavelengths
– Radiation passes through the material
http://www.astro.bas.bg/~petrov/herter00_files/lec07_04.jpg
So why is this important
• Different elements have different number of
electrons
• Different elements have different energy levels
for their electrons
So
• Different elements can absorb light at specific
energies
• Different elements can emit light at specific
energies
• So if you can measure the wavelength of the light
from an astronomical body, you can determine
whats in it
Emission line spectra
How can you
determine velocities of objects?
• Doppler Shift – The wavelength of light changes
as the source moves towards or away from you
• Since you know the wavelength position of
emission or absorption features
• If the positions of the features move in
wavelength position, you know the source is
moving
So
• Source moving towards you, wavelength decreases
– blueshift
• Source moving away from you, wavelength increases
– redshift
• http://www.youtube.com/watch?v=-t63xYSgmKE
• http://www.youtube.com/watch?v=a3RfULw7aAY
nanometer
• 1 nanometer = 1 x 10-9 meters
Blackbody
• A black body is an object that absorbs all
electromagnetic radiation that falls onto it.
• Perfect emitter of radiation
• Radiates energy at every wavelength
http://www.daviddarling.info/images/blackbody.jpg
• Stars and
planets act can
be modeled as
blackbodies
http://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpg
• Stefan-Boltzman Law - The energy radiated by a
blackbody per second per unit area is proportional to
the fourth power of the temperature
Energy emitted  T4
s * m2
• Wien’s Law – There is an inverse relationship
between the wavelength of the peak of the emission
of a black body and its temperature
Peak position  1/T
• Stars and
planets act can
be modeled as
blackbodies
http://www.astro.ncu.edu.tw/contents/faculty/wp_chen/Ast101/blackbody_curves.jpg
Blackbody curves
• http://www.mhhe.com/physsci/astronomy/applets/
Blackbody/frame.html
http://www.rap.ucar.edu/general/asap-2005/Thur-AM2/Williams_DoD_Satellites_files/slide0005_image020.gif
http://csep10.phys.utk.edu/astr162/lect/light/radiation.html
Stefan Boltzman Law
• For the same size object (same surface area), energy
emitted per second is proportional to T4
• For example if a body goes from a temperature of
1,000 to 5,000 degrees Kelvin
• How many times more energy is emitted per second
from the hotter body?
– Energy emitted per second  (5000)4 = (5)4 = 625 times
(1000)4
Power
• Power is in Joules/second = Watts
Stefan-Boltzman Law
• Emitted power per square meter of surface = σT4
• Temperature in Kelvin
• σ = 5.7 x 10-8 Watt/(m2*K4)
•
•
•
•
For example, if the temperature of an object is 10,000 K
Emitted power per square meter = 5.7 x 10-8 x (10,000)4
Emitted power per square meter = 5.7 x 10-8 x (1 x 1016)
Emitted power per square meter = 5.7 x 108 W/m2
Wien’s Law
• Wavelength of Maximum intensity of the
blackbody curve peak = 2,900,000 nm
T (Kelvin)
• λmax = 2,900,000/10,000 nm
• λmax = 290 nm
• 1 nanometer = 1 x 10-9 meters
• λmax = 290 nm = 2.0 x 10-7 meters
New Rings around Saturn
•
•
•
•
•
•
Seen in the infrared by the Spitzer Telescope
Made of dust and ice; Dust is 80 Kelvin
Lies some 13 million km from the planet
Tilted 27 degrees from main ring plane
50 times more distant than the other rings and in a different plane.
Probably made up of debris kicked off Saturn's moon Phoebe by
small impacts.
Why infrared for dust?
• Cold things give off more light in infrared than
visible
When you observe an astronomical body
• You measure intensity
• Intensity – amount of radiation
When you see an object in the sky
• You measure its brightness
• Its brightness is a function of its
– Distance from Earth (can be calculated from orbit)
If star:
-Luminosity - is the amount of energy a body radiates
per unit time
If planet
– Albedo
– Size
Inverse Square Law
• The apparent brightness varies inversely by the
square of the distance (1/d2)
• If the Earth was moved to 10 Astronomical Units
away, the Sun would be 1/100 times dimmer
• If the Earth was moved to 100 Astronomical
Units away, the Sun would be 1/10000 times
dimmer
If the Earth was moved to 1 x 108 Astronomical
Units away, the Sun would be …
A) 1 x 10-12 times dimmer
B) 1 x 10-14 times dimmer
C) 1 x 10-16 times dimmer
D) 1 x 10-18 times dimmer
E) 1 x 10-20 times dimmer
If the Earth was moved to 1 x 108 Astronomical
Units away, the Sun would be …
A) 1 x 10-12 times dimmer
B) 1 x 10-14 times dimmer
C) 1 x 10-16 times dimmer
D) 1 x 10-18 times dimmer
E) 1 x 10-20 times dimmer
Luminosity-Distance Formula
• Apparent brightness = Luminosity
4 x (distance)2
Usually use units of Solar Luminosity
LSun = 3.8 x 1026 Watts
Magnitude System
brightest asteroid
4 Vesta
• Brighter –lower number
http://www.astronomynotes.com/starprop/appmag.gif
Magnitude difference Relative intensity
0
1
1
2
3
2.51
6.31
15.8
4
5
10
15
39.8
100
104
106
Initially
• Everybody observed with their eyes
Figure 7.1
Parallel light
Figure 7.2a
Lens
Figure 7.2b
Why are Telescopes better
than your eyes?
• They can observe light in different wavelength
regions (eyes can only see visible light)
• They can collect more light than eyes
• They can be built to compensate for the distorting
effects of the atmosphere
Refracting telescope
Figure 7.6
Reflecting Telescope
Reflecting Telescopes
Resulting image inverted
All large modern telescopes are reflectors
• Since light passes through the lens of a refracting
telescope,
• You need to make the lens from clear, highquality glass with precisely shaped surfaces
It is
• Its easier to make a high-quality mirror than a lens
Also,
• Large lenses are extremely heavy
Also
• Lens focuses red and blue light slightly differently
• Called chromatic aberration
http://en.wikipedia.org/wiki/File:Lens6a.svg
Also
• Light can be absorbed by the glass as it passes
through the glass
• Minor problem for visible, but severe for
ultraviolet and infrared light
Size of a telescope
• Diameter of its primary mirror or lens
• Light collecting area is proportional to the
diameter squared since
• Collecting area =  r2
• E.g., 8-meter telescope
a
b
• Telescope that took image b is twice as big as
telescope that took image a
• Larger the telescope, more detail can be seen
• Telescope on Mauna Kea (14,000 feet high)
• Telescope is Japanese Subaru 8-m telescope
Atmosphere
• Atmosphere can absorb light
• Atmosphere can scatter light
• Atmosphere can distort light (twinkling)
Twinkling
• Twinkling of stars is caused by moving air
currents in the atmosphere.
• The beam of light from a star passes through
many regions of moving air while on its way to an
observer’s eye or telescope.
• Each atmospheric region distorts the light slightly
for a fraction of a second.
Advantages of space-based telescopes
•
•
•
•
It can be open 24 hours, 7 days of week
Do not have to worry about distorting effects of
atmosphere
There is no extra background of light due to
scattering of light in the Earth’s atmosphere
Observe in more wavelength regions
Figure 7.20
http://www.scienzagiovane.unibo.it/English/radio-window/images/radiazioni-em.jpg
• Infrared light absorbed by molecules
http://www.ucar.edu/learn/1_3_1.htm
Not all light from a star reaches Earth
Light in space can be affected by dust
http://www.ipac.caltech.edu/2mass/outreach/survey.html
http://en.wikipedia.org/wiki/File:Rayleigh_sunlight_scattering.png
It does not help
• That you are closer to the stars
To measure light
•
•
•
•
In the past, they used photographic plates
Now they use CCDs (charge-coupled devices)
CCD are electronic detectors
CCDs are chips of silicons
Figure 7.5
CCDs
• CCDs convert light into electrons
Shared the 2009
Physics Nobel Prize
for their discovery
William Boyle
George Smith
How do they work?
• The CCD is made up of pixels.
• As the light falls on each pixel, the photons become electrons
due to the photoelectric effect. The photoelectric effect
happens when photons of light hit the silicon of the pixel and
knock electrons out of place.
• These electrons are then stored.
• Essentially, the charge in each row is moved from
one site to the next, a step at a time. This has been
likened to a “bucket row” or human chain,
passing buckets of water down a line.
• As these buckets of electrons reach the end of the line they
are dumped out and measured, and this analog measurement
is then turned into a digital value.
• Thus, a digital grid is made which describes the image.
Color separation for digital cameras
• Colored filters
CCDs
• CCDs can collect 90% of photons that strike them
• Photographic plates can only collect 10% of the
photons
• CCDs are split into squares called pixels
• Data is in electronic form
Hubble Telescope
• Can observe in visible, infrared, and ultraviolet
wavelength regions
• Named after Edwin Hubble, the father of modern
cosmology
Hubble (launched in 1990)
Telescope is the
size of a
school bus
2.4 m mirror
Initially
• Hubble’s primary mirror was polished to the
wrong shape
• Was too flat at the edges
• Was barely 2.3 micrometers out from the required
shape (1/50 the width of a human hair)
• Images were not focused as well as they could be
• Later shuttle mission fixed this problem by
installing a number of small mirrors
http://dayton.hq.nasa.gov/IMAGES/SMALL/GPN-2002-000064.jpg
Jupiter
• http://video.nationalgeographic.com/video/player/
science/space-sci/exploration/hubble-sci.html
Hubble replacement
• The first major components of the new James
Webb Space Telescope are now being assembled.
• While Hubble is the size of a bus, the new James
Webb will be the size of a jetliner.
• Will launch in 2014
• James Webb is a former NASA administrator
during the Apollo program
• http://www.youtube.com/watch?v=SpkrVw_E6N
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Any Questions?