Astronomy Notes

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Big Bang Theory: It explains how the universe formed 14 billion years ago. It states that all matter and energy started out densely concentrated in a small area. After a huge explosion, matter formed as it moved away from the explosion area. Universe is still expanding in all directions. Some Evidence for Big Bang Theory: Presence of background radiation all over universe supports explosion theory. Red shift of galaxies supports idea that everything is expanding and moving away

What do Astronomers look for to prove an expanding universe and red shift? Electromagnetic Spectrum = full range of frequencies that make up all light and energy in space.

All energy in the spectrum and space has a wavelength. = distance between consecutive crests

All energy in the spectrum and space also has a frequency. = number of crests that pass one point in one second

How are these two things related? Inverse relationship When wavelength increases, frequency decreases.

Energy Frequency is proportional to energy and temperature. High frequency = hot = high energy

Visible Light = Roy G. Biv Red, Orange, Yellow, Green, Blue, Indigo, Violet Low freq. High freq. Long wl Short wl Low energy High energy

On ESRT p.14

Doppler Effect = apparent change in wavelength caused by relative motion between source of radiation and receiver. This causes the lines in spectra to move right or left.

Video Doppler Effect Video

Red Shift Object is moving away Wavelength increases (red = longer) Spectral lines move toward red side Evidence of expanding universe

Blue Shift Object is moving toward us Wavelength decreases (blue = shorter) Spectral lines shift toward blue side

Video Doppler Effect Video Sheldon's Doppler Effect

Hubble’s Law Based on red shift of distant galaxies Galaxies farther away have more red shift so they are moving faster away from us. Faster moving galaxies are farther away from us. Shows that universe is expanding

Galaxies: A galaxy is a collection of billions of stars plus gas and dust held together by gravity.

3 types of galaxies are: Elliptical (ball or oval) Spiral (center bulge with disk, spiral arms in disk) Irregular (no pattern)

Our galaxy is the Milky Way. Spiral Over 200 billion stars Our Sun is located more than half way out from the center (28,000 ly) on the edge of a spiral arm Diameter is 100,000 light-years across

Distances: Size and Ages: Astronomical Unit (AU) = average distance between Earth and Sun = 150 million km Light-year (ly) = distance light travels in one year = 9.5 x 1012 km Size and Ages: Universe: biggest and oldest Galaxy: inside the universe Solar System: inside a galaxy, our solar system has only ONE star (Sun) and is 4.6 billion years old

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Stars: Star = a ball of gas that is undergoing nuclear fusion Nuclear fusion = combining (or fusing) of nuclei of smaller elements to form larger elements plus energy In order for nuclear fusion to begin, the star must acquire enough mass from the surrounding dust and gas. Must have high temperature and pressure for fusion Hydrogen (the “fuel”) fuses into helium (the “product”) plus energy

Surface temperature determines color (red = cool, blue = hot) Luminosity = actual brightness. Measures how bright a star would be compared to the sun if at the same distance. Apparent Magnitude = how bright a star appears from Earth

HR Diagram (Hertzsprung-Russell). ESRT p.15 Chart of temperature versus luminosity (not a map) Star groups/families shown Most stars are main sequence (like the Sun)

Luminosity and Mass Big, Bright Small, Dim Hot Cold Temperature and Color

Our Sun: Compared to other stars, our Sun is just average. Sun’s atmosphere has 3 regions: Photosphere (“surface” bottom layer of atmosphere) Chromosphere Corona (huge outer region that is visible during eclipse) Sunspots are areas of sun that are darker and cooler than the normal surrounding surface.

Solar wind is a constant stream of electrically charged particles moving away from the Sun. Sun’s energy is produced by fusion in the core. Sun is mostly composed of hydrogen. Over time, there will be less hydrogen and more helium. Sun and solar system are 4.6 billion years old. Our sun is roughly half-way through its life cycle.

Solar Winds Create Aurora Borealis

Evolution of Stars Stars form inside a nebula (cloud of dust and gas). When mass of nebula is large enough, the temperature and pressure at the center become high enough for fusion to start. When fusion starts it is officially a star. A star spends most of its life as a main sequence star, fusing hydrogen into helium. Currently, 90% of all stars are in this stage.

Next stage depends on the original mass of the star at its birth. Path for Low and medium mass stars (like Sun): Main sequence star (Sun will be this for 10 billion years total) Red giant star (larger, cooler surface) White dwarf (small, dim, hot), then called a black dwarf when it is small, dark, and cold)

High mass stars will have shorter lifetimes because burn through hydrogen gas and pass through stages faster. Main sequence star Supergiant Supernova (explosion) Neutron star OR Black Hole, depending on mass

Sizes of other stars

Solar System Models Geocentric (not correct): old theory that Earth was in the center of everything / solar system Heliocentric (correct): theory made by Copernicus in 1600s that states the Sun is the center of our solar system

Geo: Earth-centered Helio: Sun-centered

Proof of helio-centric: Retrograde motion (appears that a planet moves backward compared to background stars) Happens when Earth passes another more distant planet (like Mars)

Proof cont… Galileo used telescope to study sky and helped support heliocentric theory. He observed moons orbiting Jupiter, showing that objects do not have to orbit only Earth.

Motions of all planets…. Rotation: the spinning of a planet on its own axis. Creates day and night Causes motion of Sun across daytime sky. Sun rises in east and sets in west Causes movement of stars around Polaris in night time sky Earth spins at a rate of 15 degrees/hour Earth rotates counter-clockwise as viewed from above north pole. Retrograde rotation means to spin opposite Earth’s rotation direction.

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Proof cont… Foucault pendulum: helps prove Earth is spinning, which helps explain why objects appear to move around us. you tube video from museum

Motions of All Planets…. Revolution: The movement of a planet around a central object such as a star. All planets in Solar System revolve around the Sun. Speed of revolution creates length of year. Direction of Earth orbit is Counter-clockwise

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Forces causing orbits: 1) Gravity (Isaac Newton): attractive force between objects If mass increases, then gravity increases. If distance increases, then gravity decreases.

2) Inertia: an object in motion will remain in motion unless acted upon by an outside force. Gravity pulls toward Center of Earth, Inertia keeps going Out into space

Kepler’s Laws of Planetary Motion 1st Law = planets travel in elliptical orbits with the Sun at one focus. Ellipse foci Length of major axis (longest diameter)

Aphelion = point in orbit farthest from Sun Perihelion = point in orbit closest to Sun

2nd Law Equal Area Law. Explains that planets move faster when closer to the Sun (and slower when farther away)

3rd Law Explains that planets will take longer to revolve around the Sun when they are farther away

Eccentricity Describes the shape of an orbit by stating how far “out of roundness” an ellipse is. Eccentricity = Distance between foci Length of major axis

Ecc = 0 means circle (least eccentric) Ecc = 1 means a line (most eccentric) Bigger ecc. means more oval; smaller ecc. means more circular. ESRT p.15 lists eccentricity for each planet.

Apparent Size of the Sun When the Earth is at Aphelion it is furthest away from the sun. This causes the apparent diameter of the sun to be smaller than normal. When the Earth is a Perihelion it is closest to the sun in its orbit. This causes the apparent diameter of the sun to be larger than normal.

Formation of Solar System

Step 1 4.6 billion years ago: a shockwave started a gravitational contraction of a nebula (gas/dust cloud)

Step 2 Most matter was pulled to center to form the Sun, where fusion started. Gas and dust started clumping in a disk around the Sun. Spinning from initial motion continues.

Step 3 Collisions (impact events) cause matter to collect into large masses. Denser materials are pulled closer to the Sun.

Step 4 Large masses become 8 planets with smaller masses as moons and asteroids. Planets orbit Sun in the same plane, counterclockwise. As Earth formed, gravity pulled denser materials to the center, creating layers based on density.

Step 2 Step 1 Step 3 Step 4

Solar System and Planets

Inner Planets Mercury, Venus, Earth, Mars

Inner (Terrestrial) Planets Rocky Dense Smaller size Close to Sun Close together

Earth’s Twin…. The planet closest in shape to Earth is Venus. Venus has an atmosphere rich in Carbon Dioxide which creates a very hot “greenhouse effect”.

Search for Life…. Missions onto other planets have been focused on the planet Mars. The search for liquid water on Mars continues with the “Curiosity Rover” mission.

Jupiter, Saturn, Uranus, Neptune The Outer Planets Jupiter, Saturn, Uranus, Neptune

Outer (Jovian) Planets Farther away from Sun Far apart from each other Larger sizes Larger masses Lower densities Made mostly of gas (gaseous)

Other Objects within our Solar System… Asteroid Belt A collection of asteroids located between the orbits of Mars and Jupiter The asteroid belt is thought to be the pieces of a planet that never formed. Comets A large solid rock-like collection of ice and dust that orbits the sun. Meteor A rock from outer space that is pulled into Earth’s gravitational field and enters out atmosphere. It burns up upon entry and is called a shooting star.

Comets