2.2 Origin of the Universe

Earth is a small rocky planet that circles the sun, one of the hundreds of billions of stars making up the milky way.

Size of the Universe: Luminosity

The brightness of pulsating stars, called cepheid variables, was used to determine distance from Earth Brighter stars mean they are closer to Earth, and Dimmer stars mean they are farther from Earth.

Repeated measurements determined cepheid variables were moving away from Earth, interpreting the universe is expanding.

Size of the Universe: Doppler Effect

Doppler effect is the apparent change in the frequency of sound waves or light waves due to the motion of a source relative to an observer; for example, the change in frequency (pitch) of a siren from a passing police car.

Light on Earth is a form of solar radiation and occurs at specific wavelengths from 380-750 nanometers.

Astronomers use the degree of “red shift” to determine the distance to far away galaxies • more than 13 billion light-years (distance) from Earth.

Size and age of the Universe

If the color of light from other stars is “shifted” toward the red end of the spectrum

• Other objects in the universe are moving away from Earth and from each other ,

• The farther away the star, the greater the redshift and the faster the star is moving away from us ,

• The universe must be expanding,

• Light from the most distant stars has traveled more than 13 billion light-years (distance) in 13 billion years (time).

The Big Bang Theory

Reversing the expansion of the universe suggests the universe began with an episode of rapid expansion from a much more compact form.

The almost instantaneous period of rapid expansion is known as the Big Bang.

Within hours of the Big Bang, simple elements (hydrogen, helium) formed as subatomic particles combined − Hydrogen – 1 proton + 1 electron − Helium – 2 protons + 2 neutrons + 2 electrons

Stars and Planets:

• Hydrogen formed soon after the Big Bang.

• Other elements and complex compounds formed during the life cycle of stars.

• Gravity pulled together irregular clouds of gas and dust generated from the Big Bang to form galaxies (systems of stars).

• Gas and dust material clumped together to form millions of stars (an ongoing process).− Very high temperatures and pressures in the interiors of stars fuse hydrogen atoms together – nuclear fusion – to form helium − Stars burn out when hydrogen is used up.

• The predominant element in the Sun is hydrogen, and then helium: by mass, it is 70% hydrogen, 28% helium, 1.5% carbon, nitrogen, and oxygen, and 0.5% all other elements.

• The sun will collapse when hydrogen is used up − resulting in a temporary temperature rise and expansion (to form a red giant star) − higher temperatures would fuel more fusion converting helium  carbon.

• Fusion would end when helium is used up • The loss of the heat of fusion would form a smaller white dwarf star that will cool to a black dwarf star.

• Giant stars collapse over multiple stages, initially forming red supergiant stars − Collapse forms increasingly complex elements (e.g., carbon-oxygen)

• The final stage is a massive explosion – a supernova – that fuses heavier elements together and blasts them through the universe.

• When stars form, they are surrounded by a rotating disk of cosmic debris

• Gravity pulls debris together to form planets that revolve in a consistent direction around the star − Heavier, rocky planets closer to the star − Lighter, gas-rich planets farther from the star.

• Potentially thousands or millions of extra-solar planets revolve around other stars

Our solar system

• Solar system - sun and surrounding planets.

• Sun = 99.8% of the total mass of the solar system − Sun 150,000,000 km from Earth

• Sun undergoes differential rotation − Sun’s equatorial region rotates faster (25 days) than polar regions (36 days) − Resulting in disruption of the sun’s magnetic field to produce sunspots and solar flares.

• The solar wind is a stream of charged particles emitted from the sun’s magnetic field (1,600,000 km/hr)

• Earth’s magnetic field deflects the solar wind.

• Interactions of the solar wind with Earth’s magnetic field generate aurora in the upper atmosphere of polar regions.

• Occasional solar eruptions can disrupt Earth’s magnetic field to produce electrical blackouts − Satellites in greater danger from solar flares than features on the surface.

There are Eight Planets in our solar system 4 terrestrial planets (Mercury, Venus, Earth, Mars), and 4 Jovian planets (Jupiter, Saturn, Uranus, Neptune).

What about Pluto? Improved technology resulted in recent discoveries of several distant objects that were similar in size or larger than Pluto.

International Astronomical Union (IAU) could either

1. Consider the new objects as new planets OR

2. Classify the new objects – and Pluto – as a new group of objects • IAU chose option #2

IAU adopted a new definition of the term planet: A planet is an object that orbits a star and is massive enough (~400 km radius) for gravity to pull its material into an approximately spherical shape. A planet would have cleared the neighborhood around its orbit. • Pluto does not meet the last part of the definition and was considered a founding member of a new class of objects - dwarf planets.

Terrestrial Planets are Composed of rocks and divided into compositional layers.

Earth’s Crust is composed of lighter elements (e.g., silicon, oxygen).

Earth’s Mantle/Core is composed of heavier elements (e.g., iron, nickel) found in metallic meteorites.

Jovian Planets are Large gas giants, much of the volume of the Jovian planets is a thick atmosphere overlying oceans of liquid gases and is characterized by many moons and ring systems.

Earth, the Sun, and The seasons.

Why is it colder in winter and warmer in summer?

• A common misconception is that Earth is closer to the sun during summer and farther away in winter, but Earth is actually closer to the sun in winter (in the northern hemisphere) and farther away in summer.

Why is it colder in winter and warmer in summer?

• Seasonal temperature contrasts are due to the tilt of the Earth’s axis and the angle of the Sun’s rays • Tilt = 23.5 degrees.

• The amount of solar energy (insolation) reaching Earth’s surface depends on the angle the Sun’s rays strike Earth •More heat is delivered by insolation where the Sun is directly overhead − As sunlight is distributed over a smaller area − Total annual insolation is the least at Poles, greatest at the Equator.

• Sun is directly overhead at different places (tropics, equator) during different seasons − During summer in the northern hemisphere, the sun is directly overhead at the Tropic of Cancer − During winter in the northern hemisphere, the Sun is directly overhead at the Tropic of Capricorn in the southern hemisphere.

• Sun is directly overhead at different places (tropics, equator) during different seasons − During spring and fall in the northern hemisphere; the sun is directly overhead at the Equator.

• Why day length changes- Hours of daylight change • With latitude – higher latitudes have more daylight than low latitudes in summer, less in winter • With a time of year – all locations have more daylight in summer and less in winter.

The unique composition of Earth

• Earth’s interior can be divided into three major compositional layers −

Crust – composed of lighter elements (e.g., silicon, oxygen) − Oceanic crust has an average composition that’s the same as basalt and is on average 4 miles thick. continental crust average composition similar to granate, and is thicker than oceanic crust 20/25 miles thick. continental crust and oceanic crust are not the same.

Mantle – composed of rocks made up of 3 key elements (oxygen, silicon, magnesium) , primarily made up of rocks, solid from top of outer core to base of crust.

Core – iron, and nickel − outer core is liquid

solid inner core − partially melted outer core is the source of Earth’s magnetic field.

seismic waves travel faster in stiff rock and slower in softer hotter rock.

compressional p waves can travel through any substance

shear s waves can only travel through solids, so the outer core of earth is liquid.

• Geothermal Gradient: temperature increases deep you go into earth. Temperature of the crust is 25c per kilometer / 72f per mile near surface. interior of the planet is hotter than exterior. volcanic activity gradient is higher surface hotter than elswerhe.

• Scientists recognize two layers with different properties near the surface − Lithosphere – a rigid outer layer composed of the crust and upper mantle − Asthenosphere – plastic, a slowly flowing layer in the uppermost part of the mantle.

• Lithosphere divided into large slabs known as tectonic plates − Plates move over Earth’s surface to produce earthquakes, volcanoes, mountain belts, and various features on the seafloor.

• Geothermal gradient • Earth’s temperature increases with depth • Average temperature rise is 25oC/kilometer • Heat generated by the: − Formation of the planet – all terrestrial planets cooled following formation  Only large planets still retain heat − Radioactive decay of elements in Earth’s interior.

• Earth shares many features with other planets, so what makes it so special? • Liquid water • Gravity and a protective atmosphere • Life-sustaining gases • A strong magnetic field.

• Liquid water is essential for life on Earth and is maintained by an appropriate temperature range (0-100oC) Venus − Too close to Sun, the original water evaporated to the atmosphere − Water vapor molecules (H2O)split by ultraviolet radiation and hydrogen lost to space Mars − Too cold today to have liquid water, some frozen.

• Earth’s size is sufficient to produce enough gravity to hold a thick atmosphere of gases in place Atmosphere protects us from: • Incoming asteroids/comets • Harmful solar radiation (x-rays, UV)

• Earth’s biosphere has altered the composition of the atmosphere to add oxygen and extract toxic carbon dioxide Atmosphere composition affects temperature: − Higher carbon dioxide content on Venus produces temperatures of 464oC.

• The composition of Earth’s atmosphere is just right to absorb enough heat to keep the average temperature of 15oC Greenhouse effect: − Water vapor and carbon dioxide (0.038%) gases absorb heat − Without the greenhouse effect, temperatures would be -18oC.

• Earth’s magnetic field protects Earth from the harmful solar wind that would strip away the atmosphere Magnetic field due to molten rocks in the outer core and relatively rapid planetary rotation: − Smaller planets or slowly rotating planets have lost heat and have weak magnetic fields.

From a Geocentric to Heliocentric System sun •

• Geocentric orbit hypothesis - Ancient civilizations interpreted the rising of the sun in the east and set in the west to indicate the sun (and other planets) revolved around Earth – This remained the dominant idea for more than 2,000 years.

• Heliocentric orbit hypothesis – a 16th-century idea suggested by Copernicus and Confirmed by Galileo’s early 17th-century observations of the phases of Venus – Changes in the size and shape of Venus as observed from Earth.

• Galileo used early telescopes to observe changes in the size and shape of Venus as it revolved around the sun.