Astronomy 2. Most of human history, people thought sun burned some type of fuel to make energy Not until the 21 st century did scientists figure out.

Astronomy 2

Most of human history, people thought sun burned some type of fuel to make energy

Not until the 21st century did scientists figure out where sun’s energy comes from

Electromagnetic energy is a type of energy that can travel through space an example is visible light

Light travels in wavelengths There are many things

that travel in wavelengths (radio waves, microwaves, ultraviolet rays, x-rays)

The electromagnetic spectrum breaks visible light down into the colors that make it up When you shine light

through a prism you can see the different colors of visible light

Visible light is composed of red, orange, yellow, green, blue and violet – like a rainbow

1. Core2. Inner zones3. Atmosphere

Inner zones and atmosphere divided into more layers

Continuous – gradual change between layers

Makes up 10% of sun’s diameter

Diameter = 1,300,000 km

Temp at core is 15,000,000 ℃

No liquid or solid can exist – entirely plasma

Sun’s mass 300,000 times bigger than Earth’s mass

So, gravity is greater Center of sun – 10 times

more dense than iron

Pressure and heat of sun change structure of atoms in core

Most atoms are nucleus surrounded by electrons

Heat and pressure of sun strips electrons from nuclei plasma

Nuclei can be changed by nuclear reactions

Hydrogen fused into helium

Nuclei of hydrogen atoms are primary elements in fusion of sun

Hydrogen made of 1 proton, 1 electron

Electron ripped off, so only protons remain

1. Two hydrogen nuclei (protons) collide and fuse

2. One of the protons changes to neutron

3. Another proton combines with proton-neutron pair making a nucleus of 2 protons

4. Two of these nuclei collide and fuse

5. Resulting group throws off two protons

Remaining combination of 2 protons and 2 neutrons is nucleus of helium atom

During each step, energy given off

Helium nucleus has about 0.7% less mass than hydrogen nuclei that combined to form it

Loss in mass converted to energy

Hoover Dam provides energy to most of Western US

2,080 megawatts

380 billion billion megawatts EVERY SECOND

380,000,000,000,000,000,000

Before reaching sun’s atmosphere, energy made in core moves through two inner zones

Radiative zone surrounds core

Temp is about 2,500,000℃

Energy moves from atom to atom as radiation

Electromagnetic radiation transfers energy through space

Convective zone around radiative zone

Temp about 1,000,000℃

Energy made in core moves by convection transfer of energy by moving liquids or gases

Hot gases carry heat energy to sun’s surface

As atoms of hot gases move out and expand, they radiate and lose heat

Cooling gases become denser than other gases Sink to bottom of convection zone There, cooled gases heated by radiative zone

and rise again Heat transferred to surface as gases rise and

sink

Surrounds convective zone Atmosphere uppermost area of solar

gases Has 3 layers1. Photosphere2. Chromosphere3. Corona

Photosphere innermost layer of solar atmosphere

Made of gases bubbling up from convective zone

Temp about 6,000℃ Layer has grainy

appearance called granulation

Results from gases rising and sinking

Much of energy given off is as visible light

It’s what we see from earth

So, photosphere is considered “surface” of the sun

Chromosphere “color sphere” above photosphere

Thin layer of gases that glows with reddish light

Temp ranges from 4,000-50,000℃

Gases of chromosphere move away from and toward photosphere

In upward movement, they sometimes form narrow jets of hot gas that shoot out from chromosphere then fade

Sometimes these jets reach 16,000 km high

Corona “crown” outermost layer of sun’s atmosphere

Huge cloud of gas heated by sun’s magnetic field to temp of about 2,000,000℃

Relatively thin Prevents most atomic particles from sun’s

surface from escaping into space

Some electrically charged particles (ions) leak into space through holes in corona

Particles are called solar wind

Chromosphere and corona not seen from earth b/c of brightness of blue sky during the day

During solar eclipse – moon blocks sun – can see corona

Solar Activity

Gases of inner zones and atmosphere are in constant motion

Energy made in sun’s core and force of gravity combine to cause rising and falling of gases

Gases also move because sun rotates on its axis

Because the sun is plasma/gas, not solid, different parts rotate at different speeds

Closest to sun’s equator take only 25.3 earth days to make one rotation

Points near poles take 33 earth days

Average = 27 earth days

Combination of up-and-down movement of gases in convective zone and movement of sun’s rotation produces magnetic fields

These fields slow down activity in convective zone

Slower convection means less gas is transferring heat from core to photosphere

So, regions of photosphere near strong magnetic fields are up to 3,000℃ cooler than surrounding areas

Cooler areas appear darker than areas around them

Sunspots cool, dark areas of gas within photosphere that are caused by magnetic fields

Large sunspots can be more than 100,000 km in diameter (several times the size of earth)

Astronomers found that sunspots first appear in groups midway between sun’s equator and poles

As they disappear, new ones seems to appear near sun’s equator

Shift of sunspots was one of first indications that sun rotates

Number of sunspots also changes according to average 11-year cycle called the sunspot cycle

Sunspot cycle begins when number of sunspots is very low but is starting to increase

May not see any for several weeks

Gradually see more and more

Increases over next few years until it reaches a peak

At peak, 100 or more sunspots may be visible

After, they decrease Cycle begins when more

sunspots begin to appear

Magnetic fields also create other disturbances

Prominences great clouds of glowing gases

Form huge arches that reach above sun’s surface

Each solar prominence follows curved lines of magnetic force from one sunspot area to another

Some may last for several weeks or a year

One violent solar disturbance is solar flare sudden outward eruption of electrically charged atomic particles

May extend upward several thousand km within minutes

Few last more than 1 hour

Usually occur near sunspots

During peak in sunspot cycle, 5-10 solar flares can be seen each day

Some particles from solar flare flung out so forcefully they escape into space

These particles increase strength of solar wind

As they enter atmosphere of earth, they produce sudden disturbance in earth’s magnetic field magnetic storm

Interfere with communications on earth

Auroras effect of magnetic storm appears in sky as bands of light

When ions of solar wind approach earth, they are guided toward magnetic poles of earth by earth’s magnetosphere

Magnetosphere contains the magnetic field of earth

The ions hit the gas molecules in upper atmosphere, and produces green, red, blue or violet lights

Usually seen near poles

Also called northern lights or southern lights

Auroras usually happen 100 and 1,000 km above earth’s surface

Most frequent just after peak in sunspot cycle, especially after solar flares

Visible about 5 times a year

http://www.youtube.com/watch?v=982cTjWx_zc&feature=player_embedded

Formation of the Solar System

Includes sun and bodies revolving around the sun

1600-1700s scientists thought sun formed first, then threw off materials that later formed the planets 8 major bodies revolving around the sun

1796 – Marquis Pierre Simon de Laplace had a new idea

The sun and planets made from same spinning nebula

The entire solar system formed at about the same time

Nebular theory

From big bang, some matter gathered into clouds of dust and gas

Cloud of gas and dust that developed into our solar system is called the solar nebula

Larger than our solar system now

About 4-5 billion years ago, shock waves from nearby supernova or some other force caused cloud of gas and dust to contract, forming solar nebula

A star (the sun) started to form in center When temp high enough, fusion began About 99% of matter in solar nebula

became part of the sun

Planets formed in outer regions of solar nebula

Small bodies of matter in solar nebula called planetesimals joined together through collisions

Formed larger bodies called protoplanets

Gravity of protoplanets acted like magnets, pulling in other planetesimals from solar nebula

Eventually protoplanets condensed into existing planets and moons

Moons smaller bodies that orbit the planets

Both planets and moons are smaller and denser than protoplanets

Distance between protoplanet and developing sun influenced the composition of the planet that formed from the protoplanet

Four protoplanets closest to sun became Mercury, Venus, Earth and Mars

Contained large amounts of heavier elements like iron

Next four protoplanets became Jupiter, Saturn, Uranus, and Neptune

These formed in the cold areas of solar nebula

Icy material of outer protoplanets made of helium and hydrogen and frozen gases (water, methane, ammonia)

Inner planets probably could not build up gases b/c gravity is weak

Solar wind may have stripped away early atmosphere of lighter elements

b/c outer planets further away from sun and have HUGE gravity, they kept most of their original gases

Called the gas giants

When first formed, it was very hot 3 things contributed to heat1. Earth kept a lot of heat made when it

collided with planetesimals2. Increasing weight of outer layers pressed

on inner layers, making more heat3. Radioactive materials (radiate heat) were

plenty when earth first formed

Temp on young earth enough to melt iron Gravity pulled molten iron to center Denser materials flowed to center Less dense materials forced to outer

layers Earth eventually separated into 3 layers

Crust Mantle Core

The protoplanet that became earth could not hold gases b/c gravity was too weak

Collisions added more mass to protoplanet, gravity increased

Eventually it captured some hydrogen and helium that were in solar nebula

By the time earth was formed, the atmosphere was mostly hydrogen and helium

Today these two found mostly in upper atmosphere

Much of earth’s first atmosphere was probably lost as result of solar explosion or solar wind

Earth’s second atmosphere results from explosions within earth about 3 billion years ago

Heat in interior caused volcanoes to form

Volcanic eruptions released large amounts of gases

Mostly water and carbon dioxide

These formed new atmosphere

Sunlight probably caused ammonia and some water in atmosphere to form nitrogen, hydrogen and a little oxygen

Most of hydrogen escaped to outer space (too light to be held by gravity)

Early green plants – photosynthesis – increase levels of oxygen

Some oxygen formed ozone (in upper atmosphere)

Shielded earth from UV radiation from sun

As atmosphere was developing, earth was cooling enough for liquid water to form

Between 3-3.5 billion years ago water vapor started to condense

Fell as rain and formed oceans in lower surface areas

Ocean water absorbed carbon dioxide from atmosphere

By 1.5 billion years ago, atmosphere similar to what it is today