Welcome! Sun and Seasons 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. Photo from

What are we going to cover Properties of the Sun Influence on Earth: –Gravity –Light –Solar wind Life cycle of the Sun Seasons Photo from

The Sun Is a star Made of gases Is our primary source of energy 70% hydrogen and 28% helium Light (radiation) Image at

How Big is the Sun? About 110 times wider than Earth Or 1.3 million times bigger than Earth Photo from

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 in-between--yellow Our Sun is a dwarf—medium mass Our Sun is a medium-bright dwarf

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

Rotation At the equator, the Sun rotates once every 25.4 days Near its poles, the Sun rotates once every 36 days Known as “differential rotation” High cadence solar rotation, EIT 195Š(Dec , 1999) Movie at

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

Inside the Sun Core Radiative Zone Convection zone Image at

The Sun’s Atmosphere Photosphere Chromosphere Corona Photosphere image: Chromosphere image: Corona image:

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 Image at

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

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 Images at uestion17.html and uestion17.html

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) com/watch?v=TWjtY SRlOUI

1.What solar layer do you find Sunspots? A.Core B.Radiative Zone C.Convective Zone D.Photosphere E.Chromosphere

2. What solar layer does nuclear fusion occur? A.Core B.Radiative Zone C.Convective Zone D.Photosphere E.Chromosphere

3.Which solar event(like an explosion) travels at the speed of light? A.Flares B.Prominences C.Coronal Mass Ejections

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 at

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

4. Aurora Borealis can occur at which pole? A.North B.South

Coronal Mass Ejection The eruption of a huge bubble of hot gas from the Sun This series of images of coronal mass ejections taken with LASCO C3 (May 1-31, 1997) at

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.

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

Gravity Orbits –The Sun’s powerful gravity keeps the planets in orbit

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 The Sun at X-ray wavelengths Image and info at and

5. The sun produces most of it’s radiation in the visible spectrum. A.True B.False

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

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

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 NASA image at Credit: NASA GSFC Water and Energy Cycle

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

Young stars form in nebulae from Small Magellanic Cloud Image at

Star-forming region in the Large Magellanic Cloud:

Orion image at

Our Sun is a Regular/ Small Star Image at

In a few Billion years… Red Giant Image at

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

By 5 billion years… White Dwarf Image at

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5. The Sun will become a white dwarf when it dies……. A.True B.False

Massive Stars are different Image from

Betelgeuse Image from

Supernova—Massive Star Explodes Images at

Done with the Sun Time for Seasons!