Exploring the Sun: Our Local Star

Don’t forget your sunblock!(2.2)

The Sun• Most important celestial object for life

on Earth– Contributes heat moderate temperatures

– Contributes light visibility

– Photosynthesis provides autotrophs with energy to make food, provides consumers with food

Where Did it Come From?• Current theory: Solar Nebula Theory

– Stars and planets formed together• A Star is a celestial body of hot gasses (H

and He)• When a star forms, its hot core remains

surrounded by gas and dust that hasn’t been pulled into the center– Gas and dust = nebula– Sometimes, this leftover material drifts into

space– Sometimes, it remains in the nebula, bound by

gravity

How the Solar System Formed

How the Solar System Formed• Gravity sets gas and

dust particles into motion– No resistance in

space!– The closer the

particles get to each other, the stronger the force of gravity

• Particles aren’t perfectly aligned so they end up spinning around in a nebula

How the Solar System Formed• Spinning nebula

contracts and flattens into a disc– Accretion disc

• Particles begin to gather in the centre of the nebula– Forming a protostar

(hot, condensed object)

How the Solar System Formed• Tiny grains or small lumps collect in

nebula attract others and build up to bigger, rocky lumps called planetismals

• If planetismals survive collisions, they may build up to full planets like those in our solar system

• If their mass is >10x that of Jupiter, fusion begins and a star is formed

How the Solar System Formed

How the Solar System Formed

How the Solar System Formed

Extrasolar planets• Many planets have

been discovered in orbit about stars other than the Sun– “extrasolar planets”

• They can be detected by – A) the dimming of

their star’s light as they pass in front of it

– B) direct photos

How the Sun Formed• Nebula collapses, contracts, and gas

compresses– Friction of all that material in nebula

causes a temperature increase

• At 10 000 000°C, nuclear fusion begins– The combining of 2 atomic nuclei to form

1 large nucleus– H + H He + energy

Sun’s Nuclear Fusion

H

H

HeSmall atoms

Large atom

+ Energy!

• 1 g of Hydrogen provides enough energy for a home in Canada for about 40 years

Sun’s Nuclear Fusion• H nuclei combine to form Helium

– Requires massive pressure and temp– Now called “protostar”

• He is more dense that H– :. He settles in Sun’s core

• Pressure in the core is very high. When is balances with force of gravity pulling in matter toward core = stable star

Sun’s Nuclear Fusion

Sun’s Nuclear Fusion• When the sun converts ~ 10% of H

to He, He core accumulates and undergoes fusion itself– Sun changes physically

• He core grows• H fusion (ring around core) also grows• :. The sun is growing… yowsa!• ~ 30% larger than its protostar phase

Sun’s Nuclear Fusion

Structure of the Sun

• He core (where solar energy is produced)• Radiative zone: 86% of sun’s energy radiates outward

from core• Convective zone: outer layer transfers energy in

convection currents back in towards sun• Photosphere: “surface” layer of sun

2 Important processes: Convection and Radiation

Features of the Sun

Sunspots• Def: An area of strong

magnetic force on the photosphere

• Sunspots are not dark, they are bright– Appear dark due to contrasting

temperature to photosphere• Photosphere: 6000˚C• Sunspot: 4500˚C

Sunspots• By observing sunspots, astronomers

learned the sun rotates in 27-35 days

• Gradually grow, may fade and disappear altogether

• Occur in 22-year cycles

Solar Flare

Solar flare: Magnetic fields explosively eject intense streams (solar wind) of charged particles into space

Solar Flare• If one of the streams hits Earth, it

can:– Disrupt telecommunication and

electrical equipment– Usually beautiful auroras

• Shimmery curtains of high energy, charged particles

• Electric currents charging gasses in Earth’s atmosphere