1. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Welcome!
Sun and Seasons
Revised for Harris County Dept of Education Workshop, Feb. 3., 2009, by
Christine Shupla,
Photo from
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Created by the Lunar and Planetary Institute
For Educational Use Only
LPI is not responsible for the ways in which this powerpoint may be used or altered.
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2. What are we going to cover
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
What are we going to cover
Properties of the Sun
Influence on Earth:
Gravity
Light
Solar wind
Life cycle of the Sun
Seasons
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Photo from
Lunar and Planetary Institute

3. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
The Sun
Is a star
Made of gases
Is our primary source of energy
70% hydrogen and 28% helium
Light (radiation)
The Nine Planets website has all of this excellent information:
The Sun contains 99.8% of all of the mass in our Solar System.
It is a yellow, medium-temperature star– 9,981°F (5527°C) on the outside and 28 million°F (15 million°C) in the center.
Image at
Lunar and Planetary Institute

4. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
How Big is the Sun?
Activity: Let’s measure the Sun
Our Sun is 865 thousand miles (1,390,000 km) wide. Even a medium-sized sunspot is as big at the Earth!
Photo from
Lunar and Planetary Institute

5. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
How Big is the Sun?
About 110 times wider than Earth Or
1.3 million times bigger than Earth
Our Sun is 865 thousand miles (1,390,000 km) wide. Even a medium-sized sunspot is as big at the Earth!
Photo from
Photo from
Lunar and Planetary Institute

6. How does our Sun compare to other Stars?
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
How does our Sun compare to other Stars?
Active stars range in size from supergiants to dwarfs
Stars range from very bright (supergiants) to very dim (dwarfs)
Stars range from very hot blue on the outside (O class) to cool red on the outside (M class)
Our Sun is a dwarf—medium mass
Our Sun is a medium-bright dwarf
Our Sun is in-between--yellow
Supergiants can be hundreds to thousands of times bigger than our Sun, and possibly up to 100 times more massive than our Sun. The smallest stars are about 1/100 of the Sun’s mass.
Temperature ranges for the outside of a star (spectral classification): O (blue), B (blue-white), A (white), F (white-yellow), G (yellow), K (orange), M (red)
Very large stars can be very hot on the outside (O class) or cool on the outside (all the way down to M class)—all large stars are extremely hot in their cores.
All small active stars (excludes remaining cores of old stars) are cooler on the outside and in their cores, compared to the most massive stars.
Lunar and Planetary Institute

7. So is our Sun an average star?
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
So is our Sun an average star?
No—most stars are smaller and cooler than our Sun BUT
Most of the bright stars we see are bigger and hotter
For more details and a graph, go to Nick Strobel’s Astronomy Notes:
Lunar and Planetary Institute

8. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Sun’s Magnetic Field
Winds up due to differential rotation
Eventually forms loops and becomes tangled
Animation of how the Sun's magnetic field winds up and loops out.
Movie at
Animation of how the Sun's magnetic field winds up and loops out.
Movie at
Lunar and Planetary Institute

9. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Inside the Sun
Core
Radiative Zone
Convection zone
Image at
Core
.25 of the Sun’s radius
H fusing to form He
Radiative Zone
.25 to .85 of Sun’s radius
Energy radiated from one particle to the next
Interface Layer
Change in fluid flow
generates Magnetic field
Convection zone
.85 to 1.0 of Sun’s radius
Gases rising in circulation cells
Radiation is formed in the core from nuclear fusion—hydrogen atoms fusing to form helium
The radiation escapes from the core and bounces around in the radiative layer, with atoms absorbing the radiation then re-releasing it in random directions.
The radiation moves more quickly through the convection layer, as the atoms are being circulated up to the surface in circulation cells.
Finally, when the radiation reaches the bottom of the atmosphere (the photosphere) it is emitted into space, primarily as visible light. The radiation takes thousands to millions of years to travel from the core to the Sun’s atmosphere. It only takes 8 minutes to reach us on Earth.
Image at
Lunar and Planetary Institute

10. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
The Sun’s Atmosphere
Photosphere
Chromosphere
Corona
Photosphere image and information:
Chromosphere image and information:
Corona information:
Corona image from
Go to for additional information
Photosphere image:
Chromosphere image:
Corona image:
Lunar and Planetary Institute

11. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Energy from the Sun
Nuclear chain reaction (hydrogen forming helium)
Releases radiation (gamma rays)
The gamma ray loses energy as it bounces around inside the Sun
It is finally released at the photosphere, primarily as visible light
Information and images at .
Image at
Lunar and Planetary Institute

12. Features in the Photosphere
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Features in the Photosphere
Sunspots
Dark and small (but brighter than Full Moon and big as Earth)
Cool-- temperatures only 6,200 F (Sun’s surface is 10,000 F)
Associated with magnetic fields: one set of spots is positive, other is negative
Image at
Information at
Image at
Lunar and Planetary Institute

13. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
More on Sunspots
Our Sun has an activity cycle of 11 years
Sunspots appear at specific latitudes on Sun
Bands of latitude move towards equator during cycle
Basic information and image at
Sunspot cycle and detailed data for activities at
Images at and
Lunar and Planetary Institute

14. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Solar Events
Flares (Explosions of energy on the surface of the Sun)
Prominences
Coronal Mass Ejections (massive clouds of plasma ejected from the Sun)
Movie: Six months with EIT 171 (Aug. 12, Feb. 9, 2004)
Information on flares at
Movie: Six months with EIT 171 (Aug. 12, Feb. 9, 2004)
Lunar and Planetary Institute

15. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Solar Wind
Blows charged particles and magnetic fields away from the Sun
Charged particles captured by Earth’s magnetic field
Create Auroras or Northern and Southern Lights
Image and information at
Image at
Lunar and Planetary Institute

16. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Auroras
Electrons from solar wind are captured by the Earth’s magnetic field
Interact with atoms in our atmosphere: oxygen and nitrogen make red and green; nitrogen can also make violet
Northern lights are Aurora Borealis, while southern are Aurora Australis
Animation of solar wind impacting the magnetosphere and creating aurora
Animation of solar wind impacting the magnetosphere and creating aurora
A booklet is available at
Lunar and Planetary Institute

17. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Coronal Mass Ejection
This series of images of coronal mass ejections taken with LASCO C3 (May 1-31, 1997) at
Information at
This series of images of coronal mass ejections taken with LASCO C3 (May 1-31, 1997) is available at
The eruption of a huge bubble of hot gas from the Sun
Lunar and Planetary Institute

18. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
CME’s effects on Earth
Can damage satellites
Very dangerous to astronauts
Power problems
Animation of a CME leaving the Sun, slamming into our magnetosphere.
Animation of a CME leaving the Sun, slamming into our magnetosphere.
Lunar and Planetary Institute

19. Influences on Earth Gravity Light (Radiation)
Solar Wind (already discussed)

20. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Gravity
Orbits
The Sun’s powerful gravity keeps the planets in orbit
From
Lunar and Planetary Institute

21. Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Radiation
Our Sun (and all active stars) emits radiation
Radio, infrared, visible, ultraviolet, x-ray and even some gamma rays
Most of the sunlight is yellow-green visible light or close to it
Some information at
Image and info at or
The Sun at X-ray wavelengths
Image and info at and .
Lunar and Planetary Institute

22. Sun’s Radiation at Earth
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Sun’s Radiation at Earth
The Earth’s atmosphere filters out some frequencies
Ozone layer protects us from some ultra-violet, and most x-rays and gamma rays
Water and oxygen absorb some radio waves
Water vapor, carbon dioxide, and ozone absorbs some infrared
Electromagnetic spectrum .
Lunar and Planetary Institute

23. Sunlight is absorbed by Earth
The Sun does NOT send “heat rays” into space. Some of its light is infrared, but that is not the same thing as heat.
The Sun’s light is absorbed by Earth (clouds, plants, oceans, rock…)
By absorbing the light, we are transforming it into heat energy

24. Sun as a Source of Energy
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Sun as a Source of Energy
Light from the Sun is absorbed by the Earth, unevenly to:
drive wind bands – which drive surface currents
drive deep ocean currents
drive water cycle
drive weather
Left image caption Every day the Moderate-resolution Imaging Spectroradiometer (MODIS) measures sea surface temperature over the entire globe with high accuracy. This false-color image shows a one-month composite for May Red and yellow indicates warmer temperatures, green is an intermediate value, while blues and then purples are progressively colder values.
Information about the water cycle at
NASA image at
Credit: NASA GSFC Water and Energy Cycle
Lunar and Planetary Institute

25. Sun as a Source of Energy
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Sun as a Source of Energy
Plants need light for photosynthesis
Without its heat, the only inhabitable areas on Earth would be near volcanic vents
Images from and
Lunar and Planetary Institute

26. In a few Billion years… Red Giant
Image at

27. Our Sun’s Habitable Zone
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
Our Sun’s Habitable Zone
Billions of years ago, things may have been different
The Sun was cooler (by up to 30%!)
Earth’s atmosphere was different (thicker, carbon dioxide)
Conditions will be different in the future
By many accounts, increases in the Sun’s temperature will make Earth uninhabitable in 1 billion years or less
These changes will also affect other planets… Mars?
Animation at
Information on Venus’ history at
Information on Mars’ history at
Details and animations at
A sun-like star grows into its red giant phase, increasing in size and luminosity. Energy in the form of heat can now reach a once-frozen and dead moon. The icy surface quickly melts into liquid water, filling in old craters with warmer seas. The stage is now set for the possible formation of new life.
Details on solar constant at
Lunar and Planetary Institute

28. By 5 billion years… White Dwarf
Notes for HCDE Workshop on Sun and Seasons Feb. 4, 2009
By 5 billion years… White Dwarf
NOVEMBER 5, 1998: NGC 3132 is a striking example of a planetary nebula. This expanding cloud of gas surrounding a dying star is known to amateur astronomers in the Southern Hemisphere as the "Eight-Burst" or the "Southern Ring" Nebula.
The name "planetary nebula" refers only to the round shape that many of these objects show when examined through a small telescope. In reality, these nebulae have little or nothing to do with planets, but are instead huge shells of gas ejected by stars as they near the ends of their lifetimes. NGC 3132 is nearly half a light year in diameter, and at a distance of about 2,000 light-years is one of the nearest known planetary nebulae. The gases are expanding away from the central star at a speed of 9 miles per second.
Image at
Lunar and Planetary Institute