Download and Concept Self-test (1,2,3,5,6,7,8,9)

Homework: Pages 442-3
and
ALL USING COMPLETE SENTENCES
Due Tuesday 11 April 2017
BRING TEXTBOOK TO CLASS TOMORROW
20 points assignment – don’t forget!
Sun Test 2017 April 04 Results.
I. Measuring the Stars
A. PARSEC – PARallax arc SECond
The distance an object is from Earth if
it appears to move only 1 arc second
(angle) as Earth orbits to the opposite
side of the Sun.
B. Closest star to our Sun is
Centauri, which is part of
Proxima
the Alpha
Centauri complex of 3 stars orbiting each
other in the Southern sky – we
cannot see it from our hemisphere.
1. It is 1.3 Parsecs (1.3 pc) from Earth to
Proxima Centauri (4.3 ly) yet we see it fine.
What is there between us and it, 4.3 ly away?
Not much, otherwise the light would be
blocked out – so space is “space.”
- The 2nd closest star from our Sun, at
only 1.8 pc (6.0 ly) away
Moves 10 arc seconds per year! Only a few stars
move even 1 arc second per year; yet, over the
course of your lifetime, it will barely move one
degree.
Alpha Centauri will move 3 ½ arc seconds
per year.
II. Stellar Motion – Stars move in two directions that
we observe from Earth:
 Transverse component is the star’s motion across
(V) the sky.
 Radial component is the star’s motion along our
sight – directly towards or away, from us.
Proper Motion – Annual movement of a star across
the sky (transverse) compared to it’s relative
position to the Sun.
Magnitude scale originally
created by 2nd Century Greek
Astronomer Hipparchus.
Ranked naked eye brightness
into 6 group, with “1” being
the brightest and “6” the
dimmest.
Modified today as:
 No longer limited to whole
numbers.
 It is “apparent” magnitude only.
 Goes beyond “1-6” range.
 5 magnitude change is
exactly a factor of
100 apparent brightness difference.
ABSOLUTE MAGNITUDE – The apparent magnitude of
all objects if they were all viewed at a distance of 10
parsecs (pc) from the observer. Absolute magnitude is
equivalent to luminosity.
Temperatures of Stars – Remember, using color (EM
wavelength) we can determine temperature using
Wiens law. l = 0.29 cm/K
Blackbody curve is so
constant, Astronomers only
need to measure apparent
brightness using at few as
two frequency measurements.
Table at right “V” is
measured using “visible” light
range (490-590 nm) and “B”
blue line sees only “blue”
light from 380-480 nm.
Star “A”is Rigel, where it is
very hot, (30,000 K) so more blue light than yellow.
Star (c) is like Betelguese, having more red than blue,
being a cooler star at 3000 Kelvin.
Originally based upon Hydrogen spectral line
intensities, thinking that some stars had more
hydrogen than others, with “A” type stars having
the most, “B” the second most all the way to “P”
having the least. More recent understanding of Hspectra revealed the concentration
misunderstanding; yet, the Letter classification
remains, with only OBAFGKM letters remaining as
stars were slightly reclassified.
Classification is based upon STELLAR
SURFACE TEMPERATURE.
TABLE 17.2 Stellar Spectral Classes
SPECTRAL
CLASS
SURFACE
TEMPERATURE
(K)
PROMINENT
ABSORPTION
LINES
FAMILIAR
EXAMPLES
O
30,000
Ionized helium
strong; multiply
ionized heavy
elements; hydrogen
faint
B
20,000
Neutral helium
moderate; singly
ionized heavy
elements; hydrogen
moderate
Rigel (B8)
A
10,000
Neutral helium very
faint; singly ionized
heavy elements;
hydrogen strong
Vega (A0),
Sirius (A1)
F
7,000
Singly ionized heavy
elements; neutral
metals; hydrogen
moderate
Canopus (F0)
G
6,000
Singly ionized heavy
elements; neutral
metals; hydrogen
relatively faint
Sun (G2),
Alpha Centauri
(G2)
K
4,000
Singly ionized heavy
elements; neutral
metals strong;
hydrogen faint
Arcturus (K2),
Aldebaran (K5)
M
3,000
Neutral atoms strong;
molecules moderate;
hydrogen very faint
Betelgeuse
(M2), Barnard's
Star (M5)
Stellar Sizes
http://www.youtube.com/watch?v=wHiHFXtE0js
Hydrostatic (Main-Sequence) Equilibrium:
The simple model of any main sequence star is
of a dense gas/fluid in a state of hydrostatic
equilibrium. The inward acting force, gravity,
is balanced by outward acting forces of gas
pressure and the radiation pressure.
BINARY STARS: Two stars the orbit each
other. Detected by observing both
transverse motion and radial motion (via
red/blue shift of spectra) as they orbit each
other.
STELLAR LIFETIMES
The rapid rate of nuclear burning deep inside a
star releases vast amounts of energy per unit time.
How long can the fire continue to burn? We can
estimate a star's lifetime simply by dividing the
amount of fuel available (the mass of the star) by
the rate at which the fuel is being consumed (the
star's luminosity):
Star lifetime is proportional to:
mass
luminosity
Luminosity = 4psR2T4
or, if you use Solar units where L is
measured in solar luminosities, then we can
say:
Luminosity = R2T4 where the average
temperature of the photosphere is 5800 K, so
we adjust temperatures accordingly.
What is the luminosity of a star having 3 times the radius of
the Sun and a temperature of 10,000 K?
If solar units are used: Luminosity = R2T4
1. Temperature is 10,000 K/5,800 K Sun = 1.724 times hotter
than Sun photosphere. So, we put 1.724 in place of “T”.
2. L = (R)2 (1.724)4 and since Radius is 3 times more, then:
3. L = (3)2(1.724)4 = 9(8.83) = 79.5 times more Luminous
than our Sun.
Review & Discussion:
1. Parallax is used to measure the distances in stars by
measuring the arc angle an object appears to move as the
Earth orbits the Sun. This angle can then be converted to
Parsecs.
2. A parsec (Pc) is the distance an object is if it appears to move
one arc second as the Earth moves 2 AU’s from one side of the
Sun to the other. A parsec is 3.26 light years long.
3. Two ways in which a star’s real motion translates into motion
observable from Earth are Transverse (sideways motion) and
Radial (toward or away) which allow us to determine actual
motion.
6. White dwarfs are much smaller than Red Giants,
but much hotter (8,500 K White – 4,000 Red).
Dwarfs are more dense than Red giants and white
dwarfs have a higher absolute magnitude than red
giants.
7. Absolute magnitude (brightness) is the inherent
brightness of an object, or how much light (photons) it
gives off per unit area; whereas, “Apparent”
magnitude is the brightness an object “appears” to be
when viewed at a certain distance.
8. Stellar temperature is measured by using Wien’s law
and preparing a blackbody curve using maximum
wavelengths from two filtered telescopes.
HOMEWORK: Read Chapter 18 and perform
pages 462-463:
Review (1-4, 7-9) complete sentences,
Concept. Mult. choice (1-4, 8-9) complete
sentences and
Problem #8 (Show work)
Use complete sentences and show work
Due Tuesday the 12th of April.
Problem #3 Pg. 463 Given the average density of interstellar
matter stated in Section 18.1 [10,000 atoms/cubic meter],
calculate how large a volume of space would have to be
compressed to make a cubic meter of gas equal in density to air
on Earth (1.2 kg/m3).
Each cubic meter will contain 1,000,000 atoms/m3,
so multiply that by 1.7 x10-27 kg/atom to get 1.7 x
10-21 kg/m3 to get the density of interstellar matter.
HOMEWORK: Pages 514-15
Review (1,3-6)
and
Concept M/C (1-5,7-9)
Due Friday 15 April 2016
EMISSION NEBULA
A cloud of high temperature gas
in which the atoms are energized
with the light and solar winds from
nearby stars or protostars , thus
emitting radiation . Act like
fluorescent light bulbs as the
gases fluoresce as electrons run
through the tube.
DARK NEBULA
Dark nebulae are immense clouds of gas
that are in front of a light source (star
cluster) that block out a zone of light.
Read chapters 17, 18 and 20.
Study your homework and class
assignments for the test.
Page 514 Review and Discussion
1. Stars don’t “live” forever due to the fact that they
eventually run out of Hydrogen (then Helium) to fuel
the nuclear fusion that makes a star a star. Cooler
stars live longer since they “burn” their fuel much
slower than hotter stars.
3. The Sun is predicted to burn Hydrogen in it’s core for
another 3-5 billion years.
4. When Hydrogen is depleted from the core, the
Helium will outweigh it and H fusion will continue in
the outer shell and the star will become a Red Giant.
5. What makes an ordinary star become a red giant is
when the mass of helium outweighs the mass of
hydrogen “burning” in the inner core, causing the
helium to collapse inward, which forces the
hydrogen to the outer core, where it continues
fusion. Since the H is now in the outer core, the
diameter is much bigger and, although the amount
of energy is still the same, it is spread over a
greater surface area, creating a cooler “Red Giant”
star.
6. The Sun will reach a diameter of about 0.6 AU
when it enters the red-giant branch.
Concept Self test: M/C page 515
1. A star will evolve “off the main sequence” when it uses up
C.) Most of the hydrogen in the core.
2. On the main sequence, massive stars b.) burn their
hydrogen fuel more rapidly than the Sun.
3. Compared to other stars on the H-R diagram, red-giant stars
are so named because they are a.) cooler.
4. When the Sun is on the red-giant branch, it will be found at
the b.) upper-right part of the H-R diagram.
5. After the core of a Sun-like star starts to fuse helium on the
horizontal branch, the core becomes a.) hotter.
7. A white dwarf is supported by the pressure of tightly packed
a.) electrons
8. When the Sun leaves the main sequence
“Red Giant on the H-R Diagram,” it will
become b.) brighter
9. A star like the Sun will end up as a b.) white
dwarf.
10. Compared to the Sun, stars plotted near the
bottom left of the H-R diagram are much
d.) denser.
http://lifeng.lamost.org/courses/astrotoday/CHAISS
ON/AT317/HTML/AT31707.HTM
HR Diagram – discussion and diagrams
1 Parsec
Neutron Stars
A neutron star is about 20 km in diameter and
has the mass of about 1.4 times that of our
Sun. On Earth one teaspoonful of a neutron
star would weigh a billion tons! Because of its
small size and high density, a neutron star
possesses a surface gravitational field about 2
x 1011 times that of Earth.
Neutron stars can also have magnetic fields a
million times stronger than the strongest magnetic
fields produced on Earth. Neutron stars are one of
the possible ends for a star. They result from
massive stars which have mass greater than 4 to
8 times that of our Sun. After these stars have
finished burning their nuclear fuel, they undergo a
supernova explosion. This explosion blows off
the outer layers of a star into a beautiful
supernova remnant. The central region of the star
collapses under gravity. It collapses so much that
protons and electrons combine to form neutrons.
Hence the name "neutron star"