Introduction+to+Astronomy+(chapters+21-24)

=**Unit 9: Introduction to Astronomy (chapters 21-24)**=

Golden Age of Astronomy

 * Mainly focused around Greece dating mainly before Christ. (384 BC to 168 AD)
 * Early astronomer used philosophical arguments to explain the natural phenomena because they had limited observational data.
 * Most early astronomers held the "Geocentric" view of the universe, in which the Earth was the center of the universe and all heavenly bodies revolved around the earth.
 * The seven heavenly bodies recognized by the early astronomers were: Sun, Moon, Mars, Venus, Mercury, Saturn, and Jupiter.
 * Major contributions by some famous Greek Astronomers
 * Aristotle- first to state the **Geocentric view**. Also stated that the earth was a sphere along with the heavenly bodies.
 * Aristarchus- first to state the **Heliocentric view**, that the sun was the center of the universe. Determined the distance from Earth to the sun and to the moon.
 * Eratosthenes-determined the diameter of the earth based upon the angle of the sun producing shadows in two different cities in Egypt.
 * Hipparchus-composed a star chart and developed a way to predict solar eclipses and figured out the precession of the equinoxes.
 * Ptolemy-held the **geocentric view** around 141 AD and explained that orbits were circular(known as the Ptolemaic model). Also explained retrograde motion.
 * [[image:TGA377t.jpg width="576" height="432"]]
 * Most work from the early Greek Astronomers were lost

Birth of Modern Astronomy

 * Increase in exploration and questioning of the natural phenomena lead to advances in astronomy that eventually disproved/discounted the Ptolemaic model.
 * Major contributors to the Modern Age
 * Copernicus-discovered works by Aristarchus and realized that the Earth was a planet and used this information to reason the daily motions of the heavens. Developed the **heliocentric view** in which the sun was the center of the universe and not the earth. He still stated that orbits of planets were circular around the sun.
 * Tycho Brahe-compiled 20 years of astronomical data and developed a way to measure distances to nearby stars (**Stellar Parallax)**. Data from measurements never showed an apparent shift in stars so Brahe didn't agree with Copernicus in that the sun was the center of the universe. His problem with the data was that the stars he used to measure distances where so far apart that the angle was so insignificant that it appeared as no shift happened.
 * Kepler-used data from Brahe to prove Copernicus right. Developed **Laws of Planetary Motion** (orbits around the sun are **elliptical**, varied orbital speeds based upon law of equal areas, orbit periods of planets are proportional to the distance from the sun.) **AU** (astronomical units is a way to measure distances from the sun to objects. 1 AU is 93 million miles.
 * [[image:TGA380t.jpg width="448" height="336" caption="Law of Equal areas; varied speeds"]]
 * [[image:TGA382t.jpg width="448" height="336"]]
 * Galileo-built a telescope without ever seeing the plans for one or one itself. Was able to view distance objects like the moon, jupiter, venus, and the sun. Discovered that there were features on the moon, that Venus underwent phases, that the sun has sunspots and determined the sun's rotational period, that the planets were circular disks, and found Jupiter's 4 largest satellites (moons).
 * Newton-developed the Law of Universal Gravitation, 3 Laws of Motion (inertia, f=ma, action/reaction). Proved that both the force of gravity from the sun AND inertia keeps the planets revolving around the sun in elliptical orbits. Law of Universal Gravitation states that there is a force that acts on bodies and that force is directly proportional to the masses of the object and inversely proportional to the squared distance between them. So if the masses increase between objects, then the force of gravitational pull also increases. If the distance increases between objects, then the force of gravitational pull decreases.

Mapping Systems

 * 2 types of mapping systems that are used to explain the celestial sphere.
 * **Constellations**: sky divided into areas of constellations in which were named by the Greeks after heroes/mythology. 88 recognized constellation that divided the sky into units. Examples: Ursa Major, Ursa Minor, Orion, Taurus, Cancer.
 * **Equatorial system:** divides celestial sphere into coordinates like latitude and longitude on earth. **Declination** are distance above or below the celestial equator; expressed in degrees. **Right Ascension** is the distance eastward along with equator from the vernal equinox;expressed in hours (1 hour = 15 degrees)
 * [[image:TGA383t.jpg width="512" height="384"]]

Motion of Earth

 * 2 primary motions of earth
 * **Rotation**- spinning/turning around on an axis. One time around an axis is referred to as a day. **Mean solar day** is the time interval from one noon (where sun reaches its zenith) to the next noon. This averages 24 hours. **Sidreal day** is the time it takes Earth to make one complete rotation (360 degrees) in regards to a star that is NOT the sun. This is 23 hours, 56 minutes, 4 seconds. Mean solar day is used instead of Sidreal day because sidreal day has "noon" as 4 minutes earlier each day so after 6 months, "noon" would happen at "midnight".
 * [[image:TGA385t.jpg width="512" height="384"]]
 * **Revolution-**motion of an object around another object. One time around an object is referred to as a year. **Perihelion i**s when the sun is closest to the earth in its orbit. This happens in January. **Apihelion** is when the sun is furthest from the earth in its orbit. This happens in July. Apparent path of the sun across the celestial sphere is known as the **ecliptic**. Revolution of Earth is 365.26 days. Every 4 years leap year happens. This is because the revolution of the earth isn't exactly 365 days.
 * Precession is a third motion of the earth that is slow. Angle of the Earth on its axis is 23.5 degrees. This angle stays the same but the direction in which the axis points continually changes.
 * [[image:TGA388t.jpg width="448" height="336"]]

Earth-Moon System

 * Relative positions of the Sun, Moon, and Earth are constantly changing and creature features like moon phases and eclipses.
 * Lunar phases require 29.5 days to take place. This is known as Synodic Month. This was used for the first Roman calendars. This isn't accurate. The moon actually takes 27.3 days to revolve around the Earth and this is called the Sidereal moth. The difference between the Synodic Month and the Sidereal Month is due to the fact that the Moon hasn't reached its original location in regards to the Sun. This is where the 2 day difference comes from.
 * Rotational period and Revolution period are the same so there is only one side of the moon that faces the earth at all times.
 * Phases of the moon are systematic changes in the amount of light illuminated/reflected upon the Moon's surface. No light is a new moon. Sliver of light (1/4 of moon filled) is a **Crescent** moon. Half the moon filled with light is a Quarter moon. 3/4 of the moon light is a **Gibbous** moon. Fully lighted is a full moon.
 * As the moon increases in the amount of light reflected on the surface, this is known as **Waxing.** As the light decreases on the moon's surface, this is known as **Waning.** There are two quarter moons, the first quarter, which happens 1 week after the new moon phase and the last quarter, which happens 1 week after the full moon phase.
 * To go from new moon phase to new moon phase, takes roughly 4 weeks.
 * The four major phases of the moon are New Moon, 1st Quarter, Full Moon, and Last Quarter.
 * The four minor phases that happen are: Waxing Crescent, Waxing Gibbous, Waning Gibbous, and Waning Crescent. Where the Moon is in relation to the sun will determine the phase of the moon.
 * [[image:TGA389t.jpg width="512" height="384"]]
 * Eclipses happens when one object is blocked by another object. There are 2 types of eclipses that can occur.
 * Solar: happens when the moon is in a New Moon Phase and is directly between the Sun and the Earth. This cast a shadow onto the Earth.
 * Lunar: happens when the moon is in a Full Moon Phase and passes directly within the Earth's shadow.
 * Umbra is the inner shadow of an eclipse in which one can view a Total Eclipse of the Sun or Moon.
 * Penumbra is the outer shadows of an eclipse in which one can view a Partial Eclipse of the Sun or Moon.
 * Next Total Eclipse of the Sun to be seen in the US will happen in August of 2017.
 * [[image:TGA391t.jpg width="512" height="384"]]
 * [[image:TGA392t.jpg width="512" height="384"]]

Our Solar System

 * Theories for how our solar system formed
 * Big Bang Theory: Massive explosion in space that sent high energy particles racing through space. Some matter cooled and condensed forming stars and planets. Happened 14 billion years ago.
 * Nebular Theory: A massive cloud of gas and dust (nebula) was bombarded with high energy particles which caused the nebula to become unstable and caused matter to condense and formed protosun/protostars and protoplanets. Matter that escaped became asteroids, comets, and meteoroids. Happened 5 billion years ago.
 * Two groups of planets
 * **Terrestrial:** Earth-like planets. Small, Dense, and rocky planets with low escape velocities. Mercury, Venus, Earth, and Mars are Terrestrial planets. AKA: Inner Planets
 * **Jovian:** Jupiter-like planets. Large, low density, and gaseous planets with high escape velocities. Jupiter, Saturn, Neptune, and Uranus are Jovian planets. AKA: Outer Planets
 * [[image:TGA393t.jpg width="576" height="432"]]
 * Composition of Planets:
 * Substance that makes up the planets is divided into three compositional groups:
 * Gases: hydrogen and helium
 * Rocks: silicate minerals mainly and metallic iron
 * Ices: ammonia, methane, carbon dioxide, and water.
 * Terrestrial planets' composition is mainly rocky and metallic substances with little ices, making these planets very dense. Jovian planets' composition is mainly gases and ices making these planets not as dense as Terrestrial.
 * Atmosphere of planets is based upon their location from the sun and their size. Jovian planets are larger and further from the sun so their atmosphere is mainly water, ammonia, and methane ices. Terrestrial planets are closer to the sun so ices couldn't form. Mercury and the Moon have no atmosphere due to their mass; to small and weren't able to retain the atmosphere.
 * Click on handout for facts about planets based upon classwork activity [[file:GroupFactsOnPlaents.docx]]
 * Minor Members of the Solar System.
 * **Asteroids**: located between Mars and Jupiter (AKA the Asteroid Belt). Structures are irregular in shaped and are composed up of rock and metal. Thought to be fragments of a planet that exploded or the remains of a nebula. NEAR-Shoemaker spacecraft landed on the asteroid Eros in 2001 and was able to send images of the barren, rocky surface.
 * **Comets**:Mainly composed up of gas and dust (ices) with some rocky and metallic materials. thought to be left-over material from the formation of the solar system. Two categories of comets based upon their orbit: **Short-period** (less than 200 years for an orbit) and **Long-period.** As a comet approaches the Sun, solar particles melt some of the ices causing the head (or the Coma) of the comet to glow. Particles from the sun pull the material way from the coma forming the tail of the comet. The two solar forces used to form the tail are (1) Radiation pressure and (2) Solar Wind. The tail of a comet always faces away from the Sun in its orbit. Short period comets are said to come from the Kuiper Belt, which is a region beyond Neptune. These comets mainly move in circular orbits. Long-period comets come from a region known as the Oort Cloud. these comets are distributed in all directions
 * [[image:TGA400t.jpg width="512" height="384"]]
 * **Meteoroids:** Metal and rock composition that originated as interplanetary debris or lost material from the asteroid belt or solid remains of a comet. When they enter Earth's atmosphere, the Mesosphere (layer of atmosphere where the temperature is extremely cold so ice has formed here) creates friction on the falling Meteoroid and causes it to burn up. This is what is known as a meteor and can produce meteor showers. People normally call these objects "Shooting Stars or Falling Stars". If a Meteor doesn't burn up in the Mesosphere because either it is moving too fast or is too big, it strikes the earth's surface and is then referred to as a Meteorite. Meteorites can be classified based upon their composition as either (1) Iron, (2) Stony, (3) Stony-Irons, (4) Carbonaceous Chondrite (contains organic matter).
 * **Dwarf Planets:** In 2006, the International Astronomical Union determined that Pluto was not a 'real' planet. This category includes all celestial bodies that orbit the sun and are round due to their self-gravity. The NEW HORIZONS spacecraft was launched in 2006 and is scheduled to fly pass Pluto in 2015 and then explore the Kuiper belt.
 * Earth's Moon
 * Galileo used a telescope to view the surface of the moon and determined that moon had features and wasn't flat like originally thought.
 * Moon's size is unusually large compared to Earth which makes this satellite unique when compared to other planets and their moons.
 * General Characteristics of the Moon
 * contains no atmosphere
 * gravitational pull is 1/6th that of Earth's
 * diameter is about 1/4th that of Earth's
 * Density is 3.3 times that of water
 * Surface Features discovered by Galileo
 * Contains regolith: Igneous rock: Breccia, class beads and dust.
 * Maria: term that means "sea" are the lowlands/dark regions on the moon that are due to the flow of lava.
 * Highlands: originally called Terrae. These are the bright areas on the moon and are heavily cratered.
 * Craters: formed due to meteoroid impacts. Young craters will have rays and ejecta.
 * Rills: Cuts into the surface
 * [[image:TGA394t.jpg width="511" height="383"]]
 * Formation of the Moon
 * two theories for how the moon formed
 * Asteroid-Collision theory: as the Earth was still young, a massive asteroid hit its surface causing a chunk of the earth to reach escape velocity and become the moon.
 * Big Bang theory: formed when the rest of the solar system formed.

Signals from Space

 * Electromagnetic Spectrum (EMS) is a collection of electrical and magnetic wavelengths of energy. EMS is organized based upon whether wavelengths are long/short, high/low energy, and high/low frequencies. [[image:TGA311t.jpg]]
 * Visible light is the only portion of the EMS that we can see with the naked eye.
 * Wavelength is a measurement from the crest of one wave to the crest of the next consecutive wave (or from trough to next consecutive trough). Closer crest are together, the shorter the wavelength.
 * [[image:wavelength.jpg align="center"]]
 * Photons are particles of light that exert radiation pressure.
 * Spectroscopy is the study of the properties of light that depend on wavelength. By studying the spectra, scientist can determine the composition of starts and determine their velocity and direction.
 * Different types of spectrum produced are
 * Continuous spectrum- this is an uninterrupted band of color that can be caused when using an incandescent high pressure gas, liquid or solid.
 * Dark-line spectrum (aka: absorption spectrum) is a continuous spectrum with dark bands seen. This spectrum is caused when white light is passed through a cool gas at low pressure.
 * Bright-line spectrum (aka: emission spectrum) is a series of light bands on a dark background and its based upon light passing through hot gases at low pressure.
 * [[image:spectra.jpg]]
 * Doppler effect is the apparent shift in the wavelengths by motion based upon the source and the observer.
 * [[image:doppler1.jpg width="365" height="198"]]
 * As an object moves closer the the observer, wavelengths become closer together. As the object moves past the observer, wavelengths become further apart.
 * This is used to determine the direction and velocity of objects in our galaxy in regards to the Earth.
 * Scientist use this to determine if objects are moving towards or away from Earth. If an object is moving towards earth, the wavelengths would be closer together and a **BLUE shift** would appear on the spectrum (closer to the BIV end of the spectrum). If an object is moving away from Earth, the wavelengths would be further apart and a **RED shift** would appear on the spectrum (closer to the ROY end of the spectrum). Currently scientists have only noticed RED shifts in our galaxy and are using this evidence to support the **BIG BANG** theory. After the explosion, all matter in space was sent out in all directions and is moving further and further apart from each other.
 * [[image:doppler2.jpg]]
 * Those that believe in an **OPEN universe** state that eventually all matter in the universe will run out of energy and cease to exist. Those that believe in a **CLOSE universe** state that currently all matter is moving away from each other **(RED SHIFT)** and will eventually reach a finite point in space. Once matter gets to this region, the matter will start to move back towards the center of the universe and displace **BLUE SHIFTS**. Eventually all the matter will be centrally located again and another BIG BANG will happen causing matter to race again through space (like a rubber band).
 * Telescopes are instruments used by astronomers and scientists to learn more about our universe.
 * 2 Types of telescopes that can be used to view space: Optical and Non-optical.
 * Optical telescopes use visible light. There are two categories of optical telescopes: reflecting (uses series of mirrors to focus light) and refracting (uses series of concave mirrors to focus light). Reflecting telescopes cause color distortion while Refracting telescopes do not.
 * Non-Optical telescopes use other forms of energy from the EMS and not visible light. Radio telescopes pick up on Radio waves, Gamma telescopes pick up gamma radiation, Micro telescopes pick up micro waves, IR telescopes pick up signature heat series, UV telescopes detect ultraviolet radiation and X-rays telescopes pick up x-ray radiation. These telescopes have allowed scientists and astronomers to view deep space.
 * Artificial Satellites like the HUBBLE telescope, Chandra, CGRD, and SpritzersT have allowed for discover of far off distance stars, galaxies, planetary systems, because they have been able to pick up on EM radiation instead of just visible light.
 * [[image:hubble.jpg width="516" height="276"]]

SUN

 * The sun is the closest star to Earth. It is on average 93 million miles away from earth. It is categorized as a Main Sequence star (90% of all stars in the universe fall in this category). It is a medium-sized star and a yellow star (based upon its surface temperature). It contains 99.8% of all the solar system mass and is 110x the diameter of Earth.
 * Structure of the Sun is divided into the Interior, Photosphere and the Atmosphere.
 * Interior of the Sun is where nuclear fusion takes place. This the process of fusing Hydrogen ions into Helium ions. This reaction produces heat and light. Stars go from being a protostar (star not producing heat and light) to a Star once they start nuclear fusion. 74% of the sun's composition is Hydrogen, 24% is Helium and the remaining 2% is Oxygen, Iron, Neon, and Carbon. Because of nuclear fusion, the average temperature of the core is 15 million Kelvins.
 * Photosphere is the light sphere- the surface of the sun you see. The granules located here are caused by convection currents of plasma material. This is where the surface temperature of the ranges about 6,000 K (10,000F)
 * The Atmosphere of the sun is divided into two parts, the Chromosphere and the Corona. The chromosphere is a layer of thin, hot gas with spicules of rising material. The Corona is the layer of ionized gas spread via solar wind. This layer can only be seen during a total eclipse of the sun.
 * [[image:sunlayers.gif]]
 * Galileo discovered sunspots on the sun when he viewed the sun with his telescope. This eventually lead to Galileo going blind later on in life. Sunspots are solar features where there is cooler temperatures on the sun (4500K. These show up as dark spots on the sun. Galileo discovered that these sunspots go through a 11 year cycle.
 * Prominences are arcs of erupting gas coming form the photosphere and extending out to the corona. These arcs are massive and can engulf the earth if the earth was close enough.
 * Solar Flares are coronal mass projections of energized ions that leave the sun. These particles are sent through space (solar wind) and when these particles collide with gases in our atmosphere, they produce the Auroras. Solar Flares can damage communication satellites. A correlation between active sunspots and increased solar storms has been made.
 * [[image:auroras.jpg align="center"]]
 * The SOHO telescope (Solar & Heliospheric Observatory) was designed by NASA to observe the sun.
 * [[image:SOHO.jpg width="293" height="237" align="center"]]

Stars

 * Stellar Parallax was invented by Tycho Brahe. It's a way to determine the position of a star in the night sky based upon the location of the star 6 months apart. Due to the shift in the star based upon the planet's orbit, the exact location can be determined. This only works with stars that are close distances from earth.
 * Light years is the measurement used to measure distances in space. It's based upon objects moving the speed of light. 1 LY is 5.8 trillion miles. The next closest star to earth is Proximi Centuari which is 4.3 LY from earth. It takes light from this star system 4.3 years to reach earth.
 * Stellar Brightness is controlled by the size, temperature and distance of a star.
 * Apparent Magnitude is how bright a star appears from earth. The larger the apparent number on the diagram, the dimmer it appears.
 * Absolute magnitude is how bright a star actually is. Larger, positive numbers on the HR diagram, extremely bright.
 * Color and Temperature of a star are related. The color of a star is determined by its temperature.Hotter temperature stars are white or blue. Cooler temperature stars are red.
 * Red=3000K
 * Orange=4000K
 * Yellow=6000K
 * White=10000K
 * Blue=50000K
 * Hertzsprung-Russell Diagram shows the relationship between a star's absolute magnitude and its surface temperature. Majority of all stars fall in the Main Sequence. This is located on the upper left-hand corner to the lower right-hand corner on the HR diagram. Majority of Main Sequence stars are medium sized stars.
 * Super Giant stars-100-1000x the size of the sun are located at the top of the HR diagram.
 * Giant stars-10x the size of the sun are located below Super Giants
 * Medium stars-100x the size of earth are located within the Main Sequence region
 * Dwarf stars- 10x the size of the earth are located at the bottom of the HR Diagram
 * [[image:whs-earthscience/HR diagram.jpg width="392" height="365"]]
 * Binary Stars are two stars orbiting around each other. More than 50% of the stars in the night sky are binary stars. Usually the companion star is bigger and dimmer than the star it orbits.
 * [[image:whs-earthscience/binary.jpg width="309" height="232" align="center"]]
 * Variable Stars are stars that fluctuate their brightness (apparent).
 * Pulsating stars are stars that alter their brightness regularly. Polaris (North Star) is an example.
 * Eruptive stars are stars that suddenly alter their brightness. Novas are examples of eruptive stars.
 * Nebula is a large cloud of gas and dust from which stars are born.
 * Bright nebulas glow due to being close to a hot star. If they are an Emission nebula, then the nebula is emitting visible light. If they are a Reflection nebula, then the nebula is reflecting the star light. Examples of Bright nebulas are the Pillar Nebula, Eagle Nebula.
 * Dark nebulas are not close to a star therefore they are not glowing. Horse Head Nebula in the Eagle Nebula is an example of a dark nebula.
 * Stellar Evolution depends upon how much mass a star has when it forms. There are two opposing forces in a star: gravity (wants to collapse the star) and thermal nuclear energy (counteracts gravity). If thermal nuclear energy ceases, gravity will cause the core of the star to collapse.
 * Stages of Stellar Evolution begins with
 * 1) Birth -dust compresses in a nebula to form a protostar
 * 2) Protostar- nuclear fusion begins and energy is released causing the star to expand.
 * 3) Main -Sequence - majority of star's life. Age of the star will be based upon its beginning mass
 * 4) Red Giant- outer portion expands when thermal nuclear fusion stops and the core collapses.
 * 5) Burnout and Death...What a star becomes after a red giant is all based upon its beginning mass.
 * 6) Planetary Nebula is when a star explodes and the gases form a white dwarf stars, which will continue burning up material until it fades.
 * 7) Supernova can either morph into a neutron star (very dense star) or a black hole.
 * Low Mass Stars will become a white dwarf after the Red Giant Stage
 * Medium Mass Stars will become a Planetary Nebula then a White Dwarf after the Red Giant stage.
 * High Mass Stars will become a SuperNova then either a neutron or black hole after the Red Giant stage.
 * [[image:whs-earthscience/Stellar_Evolution_large.jpg width="540" height="400"]]
 * Galaxies are collections of stars found in space. There are millions of galaxies located within space. The Hubble Space telescope help to identify many deep space galaxies.
 * 4 Types of galaxies can be found.
 * Spiral galaxies are galaxies with arms extending from the nucleus. 30% of all galaxies in space are spiral galaxies. The Milky Way (our galaxy) is an example.
 * Barred spiral galaxies are where the stars are in a bar in the nucleus. Only 10% of galaxies are this type.
 * Elliptical galaxies are ellipsoidal in shape and 60% of galaxies are this type. These galaxy are the smallest sized galaxies.
 * Irregular galaxies have no shape or symmetry because they are young stars that have formed. 10% of galaxies are this type.
 * Galacitc clusters are groups of galaxies
 * There is a debate amongst astronomers regarding if the universe is an open or a closed universe. Some state that the universe is an open universe and that eventually all matter will expand until it dies out. Some state the universe is a closed universe and will eventually expand to a definite region in space and then switch movement and come back together in a large clump creating another Big Bang. Evidence used to support both theories is the Red Shift evidence seen by the Hubble Telescope. All objects in space are growing further and further away from Earth showing a red shift (long wavelengths) on spectrograms. Close Universe astronomers say that once all matter reaches a definite distance, matter will start moving closer to earth and Blue shifts (shorter wavelengths) will be seen on spectrograms.