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ASTRONOMY
SUN LECTURE
Name__________
Standards
• Understand the scale & contents of the universe
• Describe how stars are powered by nuclear fusion
• Know that some atomic nuclei can change, including fusion (e.g., the sun)
• Understand the concept of equilibrium
I. Our ________
A. Is unique to us in that it is the only nearby star.
1. ________ – glowing ball of _________ held together by its own ___________ and
powered by nuclear ____________ at its __________.
2. 300,000 times closer than our next nearest neighbor, Alpha ____________, which
is ____ light years away.
3. Our sun is ___ light minutes away from us.
B. It is the source of __________ and _________ for the maintenance of ________ on
Earth.
C. Our sun had a _____________ and it will have an _________.
1. Its age is just under 5 _____________ years.
2. It will last for another ___ billion years in its ______________ state.
D. Our sun is a typical star in that it is similar to other stars’ chemical and physical
properties.
1. It lays right in the ________________ of the observed range of stellar ________,
radius, brightness and _______________.
2. Therefore, we can apply knowledge of our sun to many other stars in the universe.
E. It is located ~___________ light years from the __________ of our galaxy.
1. It _____________ around the center of the galaxy once every _____ million years.
2. It moves at ________ mi/s or 148,000 mi/hr
II. Physical Properties
A. ______________  700,000 km (more than 100 Earth radii)
1. If Earth was the size of a _________, the sun would have a diameter of ___ m
and they would be __________ meters apart.
B. Astronomical unit (a.u.) = average distance from Earth to the sun
1. ______ million km or ____ million miles
C. _______  2.0 x 1030 kg (more than 300,000 Earth masses)
D. ____________ period  __ month
1. does not move as a solid body: moves faster at equator and slower at poles.
Rotation __________ from 25 – 34 days, with an average of _____ days
E. Surface temperature  _______ K (well above the melting point of any known material)
III. Luminosity
A. The sun radiates __________ into space, uniformly in _____ directions
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B. Solar ___________ – amount of solar energy reaching top of ____________ atmosphere
1. 50 – 70% of this energy reaches Earth’s surface
2. A typical sunbather receives solar energy equal to about 500 watts, roughly
equivalent to the output of a typical electric room heater or about ________ 100 W
light bulbs
C. The ________ amount of ____________ radiating in all directions from the sun (not just
what reaches Earth) is known as the _________________ of the sun, ~4 x 1026 watts.
D. Every second, the sun produces an amount of energy equivalent to the detonation of
about _______ billion 1-megaton nuclear bombs.
1. This is also equivalent to 4 trillion trillion 100 W light bulbs shining
simultaneously (about 1019 dollar’s worth of energy radiated every second.
IV. Sun’s __________________
A. ____ elements have been identified in the sun.
1. More elements probably exist, but our instruments can’t detect them because they
are in such small quantities.
B. Ten most common elements:
1. ______________: H2
2. Helium: ____
3. Oxygen: O2
4. _____________: C
5. Nitrogen: N
6. Silicon: ____
7. Magnesium: Mg
8. __________: Ne
9. Iron: Fe
10.Sulfur: ___
C. _______________ is by far the most abundant element at 71% of the sun’s total mass,
followed by ______________ at 27% of the sun’s mass.
1. This is the same for the universe as a whole.
V. Observing the Sun
A. ____________ (Solar and Heliospheric Observatory)
1. Spacecraft that studies the sun
2. Launched in _________
3. Operated primarily by the ______________ Space Agency (ESA)
4. Weighs two tons
5. Is located about 1.5 million km sunward of Earth (about 1% of the distance from
Earth to the sun)
a. This distance is known as the L1 _________________ point, where the
____________________ pull of the sun and Earth are __________
6. Is still in operation, well past its planned 3 year lifespan
7. Observes the sun 24 hours a day
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8. Uses dozens of instruments to study the solar _______________, surface and
________________
9. Allows astronomers to tell when the sun is preparing for mass ejections several
days before they occur
VI. Nuclear Fusion
A. The sun generates _____________ in its __________ by the process of ____________
1. During this process, the total _________ of the sun _______________ and
____________ is ____________
2. Einstein’s equation, _____________, tells us that ________ and ____________ are
__________________, and that a tiny bit of mass can produce a huge amount of
energy
B. During fusion, 4 ____________ atoms fuse to form 1 _____________ atom + ________,
or ______________________
1. 616,000,000 tons of hydrogen are converted to 612,000,000 tons of helium every
second
2. This means 4,000,000 tons of matter are converted into energy every second
C. In its current state, the sun is in __________________. This means the force of
_____________ pulling in exactly balances the force of _____________ pushing out
1. Our sun will remain in this state until it begins to use up its fuel supply and expand
into a red giant
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L. Brown
Modified from S. Wilson
November 2007
Updated February 2010
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