Astronomy 101
The Solar System
Tuesday, Thursday
2:30-3:45 pm
Hasbrouck 20
Tom Burbine
tomburbine@astro.umass.edu
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.
Office Hours
• Mine
• Tuesday, Thursday - 1:15-2:15pm
• Lederle Graduate Research Tower C 632
• Neil
• Tuesday, Thursday - 11 am-noon
• Lederle Graduate Research Tower B 619-O
Homework
• We will use Spark
• https://spark.oit.umass.edu/webct/logonDisplay.d
owebct
• Homework will be due approximately twice a
week
HW #5
• Due today
HW #6
• Due Tuesday
http://www.post-gazette.com/pg/09271/1000779-369.stm
Messenger just flew by Mercury
http://www.msnbc.msn.com/id/33092470/ns/technology_and_science-space/
Energy
• Energy is the ability to generate motion
Conservation of Energy
• Energy is neither created or destroyed – it just
changes forms
• Conservation of Energy
– The energy in a closed system may change form, but
the total amount of energy does not change as a result
of any process.
Energy units
• In English Units, we use calories to measure
energy
• In science (and in this class), we will use joules to
measure energy
• 1 Joule = 1 kg*m2/s2
3 basic categories of energy
• Kinetic energy – energy of motion
• Potential energy – energy being stored for
possible conversion into kinetic energy
• Radiative energy – energy carried by light
Kinetic energy
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Kinetic energy = ½ mv2
m is mass in kg
v is velocity in meters/s
Remember: a joule has units of kg*m2/s2
• How much kinetic energy does a 2 kg rock have if
it is thrown at 20 m/s?
• Kinetic energy = ½ mv2
• A) 200 J
• B) 400 J
• C) 40 J
• D) 800 J
Answer
• KE = ½ * 2 * (20) *(20) = 400 joules
Thermal energy
(kind of kinetic energy)
• Temperature is a measure of the average kinetic
energy of the particles
• Higher temperature – more kinetic energy,
particles moving faster
• For examples, air molecules around you are
moving at ~600 m/s
http://eo.ucar.edu/webweather/molecules.html
Temperature scales
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In America, we use Fahrenheit
Water freezes at 32 degrees F
Water boils at 212 degrees F
Everywhere else, they use Celsius
Water freezes at 0 degrees C
Water boils at 100 degrees C
In Science
• Temperature is measured in Kelvin
• Zero Kelvin is absolute zero – nothing moves
• Add 273.15 to the Celsius temperature to get the
Kelvin temperature
• 273.15 Kelvin = 0 degrees Celsius
Gravitational Potential Energy
• Gravitational Potential Energy released as an
object falls depends on its mass, the strength of
gravity, and the distance it falls
• For example, your gravitational potential energy
increases as you go farther up in the air
• This is because you hit the ground at a faster
speed if you jump from a higher distance
Gravitational Potential Energy
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PE = -G m*M/r
G is the Gravitational constant
m is mass of one body
M is mass of second body
r is distance (people also use variable d)
• KE + PE = 0
• As kinetic energy increases, potential energy
decreases
Converting Mass to Energy
• What is the most famous formula in the world?
E = mc2
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m is mass in kilograms
c is speed of light in meters/s (3 x 108 m/s)
So E is in joules
very small amounts of mass may be converted
into a very large amount of energy and
Who came up with it?
• How much energy can be produced if you can
convert 10 kg of material totally into energy?
• E = mc2
• A) 3.0 x 108 J
• B) 3.0 x 1016 J
• C) 9.0 x 1017 J
• D) 9.0 x 1010 J
Answer
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E = 10 kg * (3 x 108 m/s) * (3 x 108 m/s)
E = 10* (9 x 1016) J
E = 90 x 1016 J
E = 9.0 x 1017 J
Mass-Energy
• E=mc2
• So Mass is a form of potential energy
• Where is one place where you see mass converted
into energy?
Light
• Light is a form of energy
Light
• These are all forms of light
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Gamma rays
X-rays
Ultraviolet light
Visible light
Infrared light
Radio waves
Light
• Can act as a particle
• Can also act as a wave
Particle aspect
• Particles called photons stream from the Sun and
can be blocked by your body
Photons
• Light is quantized
• Comes in discrete packets called photons
Wave aspect
Thomas Young Experiment
• http://micro.magnet.fsu.edu/primer/java/interference/dou
bleslit/
Characteristics of waves
• velocity = wavelength x frequency
• Wavelength = distance
• Frequency = cycles per second = hertz
For light
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c = wavelength x frequency
In vacuum, speed of light stays the same
So if wavelength goes up
Frequency does down
f = frequency
λ = wavelength
c=λxf
Calculations
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c=λxf
So if the wavelength is 1 x 10-12 m
3 x 108 m/s = 1 x 10-12 m * f
f = 3 x 108 m/s/1 x 10-12 m
f = 3 x 1020 s-1 = 3 x 1020 Hz
Calculations
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c=λxf
So if the frequency is 1 x 1015 Hz
3 x 108 m/s = λ * 1 x 1015 Hz
λ = 3 x 108 m/s/1 x 1015 Hz
λ = 3 x 10-7 m
Energy of light
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Energy is directly proportional to the frequency
E=h*f
h = Planck’s constant = 6.626 x 10-34 J*s
since f = c/λ
Energy is inversely proportional to the wavelength
E = hc/λ
VIBGYOR
violet
red
Higher the frequency, Higher the energy of the photon
Higher the wavelength, Lower the energy of the photon
ROYGBIV
• ROYGBIV
• Red – long wavelength
• Violet – short wavelength
http://www.arpansa.gov.au/images/basics/emr.jpg
Calculations
• What is the energy of a radio wave with a
frequency of 1 x 107 Hz?
• E=h*f
• h = Planck’s constant = 6.626 x 10-34 J/s
• E = 6.626 x 10-34 J/s * 1 x 107
• E = 6.626 x 10-27 J
Calculations
• What is the energy of a gamma ray photon with
wavelength of 1 x 10-15 m
• E = hc/λ
• h = Planck’s constant = 6.626 x 10-34 J/s
• E = 6.626 x 10-34 J/s * 3 x 108 m/s / 1 x 10-15 m
• E = 1.99 x 10-10 J
So why are some types of radiation
dangerous?
• Higher the energy, the farther the photons can
penetrate
• So gamma and X-rays can pass much more easily
into your the body
• These high-energy photons can ionize atoms in
cells
• Ionization means removes electrons from an atom
More dangerous
When you measure an astronomical body
• You measure intensity
• Intensity – amount of radiation
Matter
• Matter is material
Atoms
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Atoms are made up of 3 types of particles
Protons – positive charge (+1)
Electrons – negative charge (-1)
Neutrons – neutral charge (no charge)
Protons and Neutrons are found in the nucleus
Elements
• Different elements have different numbers of
protons
• The properties of an atom are a function of the
electrical charge of its nucleus
Charge
• If an atom has the same number of electrons and
protons, it has a neutral charge
• More electrons than protons, negatively charged
• More protons than electrons, positive charged
• Neutrons have neutral charge so don’t affect the
charge of an atom
Definitions
• Atomic Number – Number of protons
• Atomic Mass – Number of protons and neutrons
• U235 – atomic mass
92- atomic number
• Isotopes – Same number of protons but different
numbers of neutrons
Any Questions?