ASTRO 7N Unit 3 P1 and P2
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ASTRO 7N
Unit 3 Part 1
What is the sun?
o
The sun is a star like any other star in the nighttime sky. It is the nearest star to us and provides light to our solar system
Spots on the sun
o
Sunspots, occur when strong magnetic activity in the suns outer layers causes some relative cooling in small regions. Cooler regions on the suns surface look darker than the rest
Like how we humans and animals, etc., all glow in
o
Infrared light
The sun is 109 time the earths radius. That would mean you could fit about ____ earths inside the suns volume.
o
A million
What about the mass, about 333,000 earths. About how much of the total mass of all the objects in the solar system is contained in the sun alone?
o
99% of all the mass in the entire solar system in in the sun.
Remaining 1%, about 70% in Jupiter, 20%ish is in Saturn, and the last 10% is in Earth, Neptune, all the other planets, and all of the asteroids and comets
The sun is mostly made of Hydrogen (H) and Helium (He). 73% H and 25% He by mass and about 92% H and 8% He by atom count. With the remaining percent, it is made up of
chemical elements. Dominated by carbon and oxygen, some iron an trace amounts of everything else.
Most obvious layer of the sun is the photosphere
. It is the outermost layer of the sun, but is the region of the sun from which the most visible light is emitted. About 5780 Kelvin
Outside the photosphere is the chromosphere
which is thinner. In this region neartest to the photosphere it is made up of cooler thinner gas.
Toward the upper regions of the chromosphere, towards the outer region called the corona
the solar atmosphere becomes much less dense. Typically not seen unless a total solar eclipse comes
Granules the grainy texture of the sun, bubbly hot material
The bubbly hot material comes up through the convective zone
, a large region beginning below the photosphere
A powerful burst of material, influenced by local magnetic activity will creates a solar flare
(volcano looking) or a prominence
(the “hoop”). This depends on the strengths, flares or prominences can result in material being expel from the sun into deep space, other times the material falls back onto the sun
Below the convective zone is the radiative zone
. Through this region there aren’t any convective cells to transfer material energy outward. Energy travels outward instead through absorption and re-emission of photon from one atom to another.
Sun gets hotter the deeper in you go
The core
has an energy output of about 4 x 10^26 watts
We’ve been peeling this sucker apart to see what makes it tick but what physical process would generate this kind of energy?
o
Nuclear fusion
Atoms in the suns core region are incredibly energetic
In the interior of the sun, temps are so high that atoms of hydrogen and helium have lost their electrons
E= mc^2
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E= Energy, m= mass, c= speed of light (squared)
Can you tell how many protons a hydrogen atom (H) has, and how many protons a helium atom (He) has?
o
Hydrogen has 1 proton and helium has 2 protons
In the sun, the proton-proton chain makes “4He” (helium-4) the dominant form of helium. 4He has…
o
Two protons, because it is helium, and two neutrons to make 4 total particles in the nucleus
What is the first step in the p-p chain?
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A proton combines with a proton to make Hydrogen-2 (Deuterium)
What happened to the protons during the first step of the chain?
o
One of the protons converted into a neutron, still contained with the Hydrogen- 2
Why was there a big burst of energy?
o
Because the mass of the particles starting the reaction is more than that of the products. Mass is converted to the energy via E=mc^2
What is the second step in the reaction?
o
Hydrogen-2 combined with an additional proton, to make Helium-3
What happened?
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Again there is some energy released (a gamma-ray photon) and we end up with Helium-3
What is the final step in the p-p chain?
o
Helium-3 combines with another Helium-3, to make Helium-4 (and two protons are left over)
What else do you see?
Again a burst of energy and Helium-4 is produced, with two protons moving off to the side
So “luminosity” refers to ____ whereas “brightness” must mean ____
o
Absolute power output at the source / apparent output as observed at some distance
After doubling the distance from the light source, the bottom telescope’s brightness readout ____, to about ____ the top detector's value.
o
Decreased / one quarter
On tripling the distance from the light source, the bottom detector’s readout_____, to about _____ the top detectors vaule. o
Decreased / one ninth
2 x distance… ¼ the flux
3 x distance… 1/9 the flux
How far out would you need to move the bottom detector, next to a star set to luminosity 100, to read the same as the top one at distance = 1 by the 25 stars?
o
Out to twice the distance (R=2)
Brightness = luminosity / (4 x pi x distance^2)
Like some of the other mathematical relations we have discovered already, does this mean that the parallax angle vary directly with distance, or is it inverse relation.?
o
The size of the parallax angle is inversely proportional to the distance to the star
1 parsec = about 3.26 light-years, or 1 parsec = 206,265 AU \
Alpha Centauri is one of the nearest stars to the sun, parallax angle of about 747 milliarcseconds
Copper Quiz 1
o
What is the general result of the proton-proton chain?
4H
He + energy + other products
o
The corona of the sun…
Is visible during a solar eclipse
o
In the convective zone of the sun…
Columns of hot gas rise, cool, and descend o
What part of the sun do we typically see?
Photosphere
o
In nuclear fusion, energy is produced because…
The mass of the reacting chemicals is larger than that of the products.
Copper Quiz 2
o
When using different points in the earths orbit as a baseline for a parallax experiment it is best to the observation…
6 months apart
o
One star is four times farther away than another. The parallax angle of the more distant star is…
4 times smaller than that of the nearest star
o
The parallax angle for the star Hadar is 0.010 arcseconds (0.010”). How far away is Hadar?
100 pc
o
Put one of your thumbs at arm’s length in front of your face. Now focus on something in the background and look through one eye at a time. What do you notice about your thumbs?
It appears to move more when it is closer
o
Star A is 4 times more luminous as Star B. Star A is 2 times as far away as star B. Which star appears brighter and by how much?
The stars appear the same brightness Unit 3 Part 2
1974 there was the great Arecibo radio telescope that sent a message out to a cluster of stars in order to try and communicate.
Absorption lines are: Produced when photons of specific wavelengths are absorbed in a stars outer layers by the electrons of specific chemical elements.
Sun has a temperature of 6000 kelvin as well as the G0 star
Luminosity: the absolute amount of energy a star produces in a second, like the wattage of a lightbulb
Radius of the sun, solar radius, 110 times the earths radius
The parallax angle for Alpha Centaur is 0.74 arc seconds
Distance in parcsecs = 1 over the parallax angle in arc seconds
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1/0.74 arcseconds = 1.35 parsecs
o
1 parsec is about 3.26 light years
o
At 1.35 parsecs away at the speed of light it would take over 4 years to get to Alpha Centauri
Proxima Centauri spectral type is closest to…
o
M5, it is much less luminous than the sun, 0.00006 times the suns luminosity.
o
The radius is 0.145 Solar Radii, that is 14.5% the radius of the sun
So Proxima Centaur is in the lower right of the diagram, which seems to correspond to _____ temperatures and ______ luminosities.
o
Low/low
Alpha Centauri A, Brightest of the 3 stars (white). Dimmer- looking orange star nearby is Alpha Centauri B
Alpha Centauri A has a luminosity of 1.6 suns and a spectral type closest to G0
o
Bigger than the sun
Alpha Centauri B is closer to Alpha Centauri A than Neptune is to the sun
o
The luminosity of 0.5 suns and spectral type closest to k0, the radius is 0.6 times the radius of the sun
Barnard’s Star, small and red
o
Spectral class: M5
o
Luminosity: 0.00044 Solar Luminosities
o
Radius: 0.17 Solar Radii
Wolf 359
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Spectral type: M5
o
Luminosity: 0.000021 Solar Luminosities
o
Radius: 0.1 Solar Radii
Lalande 21185
o
Spectral type: M5
o
Luminosity: 0.006 Solar Luminosities
o
Radius: 0.1 Solar Radii
Sirius, binary star
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Spectral type: A0
o
Luminosity: 22.6 Solar Luminosities
o
Radius: 2.1 Solar Radii
Sirius B
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White dwarf star with an effective surface temp of 25,500 k
o
Luminosity: 0.003 Solar Luminosities
o
Radius: 0.0075 Solar Radii
BL Ceti, Binary Star
o
Spectral type: M5
o
Luminosity: 0.00006 Solar Luminosities
o
Radius: 0.17 Solar Radii
Bl Ceti B, second star of this binary o
Spectral type: M5
o
Luminosity: 0.00005 Solar Luminosities
o
Radius: 0.31 Solar Radii
Ross 154
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Spectral type: M5
o
Luminosity: 0.0003 Solar Luminosities
o
Radius: 0.15 Solar Radii
Ross 248
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Spectral type: M5
o
Luminosity: 0.0001 Solar Luminosities
o
Radius: 0.24 Solar Radii
Epsilon Eridani
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Spectral type: K0
o
Luminosity: 0.291 Solar Luminosities
o
Radius: 0.90 Solar Radii
Lacaille 9352
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Spectral type: M0
o
Luminosity: 0.011 Solar Luminosities
o
Radius: 0.63 Solar Radii
If they were hotter then they would be…
o
Bluer and on the left part of the HR diagram
Sirius B isn’t included in the list of the brightest stars because o
Sirius B, the white dwarf, isn’t very luminous and so it appears faint compared to the much more luminous Sirius A
How many times greater is the luminosity of Sirius A than Sirius B, the white dwarf?
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o
1000 times
Canopus
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Spectral type: F0
o
Luminosity: 1952 Solar Luminosities
o
Radius: 71.4 Solar Radii
o
More luminous than all the other stars so far. That must be why it looks so bright even at this large distance
Arcturus
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Spectral type: K0
o
Luminosity: 116 Solar Luminosities
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Radius: 25.1 Solar Radii
Vega
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Spectral type: A0
o
Luminosity: 51 Solar Luminosities
o
Radius: 2 Solar Radii
Capella
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Spectral type: G5
o
Luminosity: 76 Solar Luminosities
o
Radius: 13 Solar Radii
Rigel, brightest as seen from earth, large
o
Spectral type: A0
o
Luminosity: 38,700 Solar Luminosities
o
Radius: 63 Solar Radii
Procyon
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Spectral type: F5
o
Luminosity: 7 Solar Luminosities
o
Radius: 2 Solar Radii
o
Isn’t quite as luminous as any of the others, but it can still appear bright because it
is relatively closer to the sun
Achernar
o
Spectral type: B5
o
Luminosity: 116 Solar Luminosities
o
Radius: 5 Solar Radii
Betelgeuse
o
Spectral type: M0
o
Luminosity: 10000 Solar Luminosities
o
Radius: 1000 Solar Radii
As the temperature increases the star moves to the _____ on the HR diagram, and it gets _____ and ______
o
Right/larger/redder
The star moves up on the HR diagram, and it gets…
o
Bigger and the color doesn’t change, this is because your just changing the luminosity not the temperature
The nearest stars are:
o
Cooler and less luminous
Which of the following has the largest luminosity? o
Most massive main sequence star
Which of the following is the coldest at its surface?
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Type K main sequence star
Which star is the closest if all have the same apparent brightness?
o
A type M main sequence star
Which star is the furthest away if all have the same apparent brightness?
o
Type O main sequence star
Unit 3 Part 3
Main Sequence:
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The curve on the HR diagram where stars of different masses are located while they are converting hydrogen to helium in their cores.
The more massive stars don’t last as long, they produce huge amounts of energy, but for shorter times
Going up on the picture, stars go from red to yellow to blue. This means the mass of those stars is…
o
Increasing
For the horizontal axis, they all start on the left as “protostars,” meaning the horizontal axis is…
o
Time
The sequence of events for the Sun-like star is…
o
Prostar, Sun-like star on main sequence, red giant, planetary nebula, white dwarf
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Stars less massive than the sun will also end their lives as:
o
White Dwarfs
What is a brown dwarf?
o
It is an object with a mass less than 8% of the Sun, which cannot have enough nuclear reactions in its core to be a star.
Medium- Mass stars end as:
o
Type 2 supernovae then neutron stars
High-mass stars end as:
o
Black Holes