Transcript Photon

Astronomy 1020
Stellar Astronomy
Spring_2016
Day-13
Course Announcements
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1st “Hot Topics in Science”: Tues. 2/23 6-8pm E106B
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Topics this semester are: Human Cloning, Environmental
Toxicology, & Fracking … includes pizza.
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Dark Night Observing: Mon. 2/29 & Wed. 3/2 –
7:30pm at the APSU Observatory
Exam-2 – Fri. 3/4 Chapters 5 & 6
Smartworks Chapters 5 & 6: Due Fri. 3/4
Spring Break Mar. 5-13 (Sat.-Sun.)
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APSU Research and Creativity Forum April 15, 2016
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Abstracts are due: 4:00pm Fri., March 18
Feb. 29 – Last day to drop with an automatic “W”
Apr. 1 – Last day to drop a class with W, F, FA
Course Announcements
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Colloquium on Friday, Feb. 19. @3:00pm B310
Dr. David James, Cerro-Tololo InterAmerican Obs.
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Open Clusters, Stellar Evolution and Calibrating the Ages
of Stars: Blanco 1
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Galactic open clusters are laboratories, provided by nature, for
us to study stellar evolution. Using 1m-, 4m- and 8m-class
telescopes, I will show how spectroscopic and photometric
observations of solar-type stars in open clusters allow us to
establish a stellar chronometer, and create an age-ranking
system for an ensemble of nearby, well-studied clusters. With
the aid of new observations of Blanco 1, an high-Galactic
latitude, Pleiades-age cluster, I will show how deriving stellar
age must be based upon very high quality observational data
and a diverse range of stellar models.
But, where does light actually
come from?
Accelerating charges (think electrons
and protons) produce light –
electromagnetic radiation!
Photons
 Light also behaves as a particle.
 Photon: particle of light.
 Photons carry energy and can have
different amounts of energy.
 Photons with high energy = light with high
frequency.
 Photons with low energy = light with low
frequency.
 Atoms can absorb or emit photons.
Einstein (Nobel Prize)
In 1905 Einstein
calculated the energy of
a particle of light
(photon) and proposed
the photoelectric effect.
photon
Ephoton = hc/ = hn
e-
 Light moves at 300,000 km/s in a vacuum.
 First measured by Rømer when observing
Jupiter’s moons.
 Speed is slower in other materials, e.g.,
glass.
 Wavelength ():
length between
crests.
 Amplitude: height.
 Frequency (f):
number of waves
that pass by each
second.
 Period (P): time to
complete one cycle.
 A long wavelength
means low
frequency.
 A short wavelength
means high
frequency.
 The speed of light, c,
is constant.

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 Light is a wave of combined electricity and
magnetism, called an electromagnetic wave.
 Changing electric and magnetic fields create a
self-sustaining electromagnetic wave.
Maxwell – EM Field Theory
Scottish physicist James Clerk
Maxwell showed mathematically
in the 1860s that light must be a
combination of electric and
magnetic fields.
MATH TOOLS 5.1
 Knowing the speed of light and one other
variable, either the wavelength or frequency
of the light in question, you can find the
remaining quantity.
 Example: Find the wavelength of the light
wave coming from a radio station
broadcasting on 770 AM:
EM Spectrum
Like the flavors
of Ice cream –
they each
provide us with
different
information.
But what do
you get when
you put all the
flavors (light)
together?
Lecture Tutorial
EM Spectrum: (pg. 47)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
one another. Take time to understand it
now!!!!
• Come to a consensus answer you both agree
on.
• If you get stuck or are not sure of your answer,
ask another group.