Science Hon. 10 - Astronomy Test Notes PDF

Chapter 5 - Astronomy Test Notes 5.1 Solar System Characteristics A Tour through the neighbourhood. Solar System Contents: -​ Sun -​ 8 Planets -​ Dwarf planets -​ Over 67 natural satellites (moons) -​ Asteroids -​ Meteoroid...

Chapter 5 - Astronomy Test Notes 5.1 Solar System Characteristics A Tour through the neighbourhood. Solar System Contents: -​ Sun -​ 8 Planets -​ Dwarf planets -​ Over 67 natural satellites (moons) -​ Asteroids -​ Meteoroids -​ Comets The Structure of the Solar System: -​ The Sun is the star at the centre. -​ Planets revolve around the sun in elliptical orbits. -​ Planets can thus be distinguished from stars as they move relative to stars -​ Gravity, balanced by planetary motion, holds the planets in orbit. -​ Planets rotate about their axes → oblate spheroid shape. -​ The planets lie on the ecliptic plane Star or Planet? -​ Viewed from Earth, planets appear to move relative to the stars in the background. -​ Planets’ features can be distinguished with a telescope; stars only appear as brighter dots when viewed through a telescope. The Inner Planets: -​ Also called Terrestrial planets, meaning “earth-like” -​ Characteristics include rocky crusts, dense mantles, and denser cores -​ All inner planets are different in composition and structure 1.​ Mercury: -​ Slow rotation causes temperature extremes (400°C to -170°C). -​ Many impact craters. -​ Thin, almost non-existent atmosphere. -​ Smallest planet -​ So hot at day but so cold at night as there is no atmosphere, unable to retain heat, spins slowly 2.​ Venus: -​ Dense atmosphere (about 90 times the pressure of Earth’s atmosphere). -​ Atmosphere is mostly carbon dioxide. -​ High surface temperatures due to the “greenhouse effect”. -​ Atmosphere is dense, full of carbon dioxide, hot, and orange 3.​ Earth 4.​ Mars: -​ Thin atmosphere, mostly carbon dioxide. -​ Past volcanism. (The largest volcanoes in the solar systems are found here) -​ Frequent dust storms. -​ Rocky with canyons, volcano, dry lake beds, craters, red dust -​ Evidence of previous erosion by water, but no liquid water is present today. -​ Polar ice caps, made of solid CO2 (dry ice). The Outer Planets: -​ Also called Jovian, meaning “Jupiter-like” -​ All gas giants with rings and many moons -​ Note all Jovian plants have rings -​ Unique features common among Jovian planets that are not characteristic of any terrestrial planets include: -​ more than 1 moon, rings, made of gas 5.​ Jupiter: -​ Largest planet. -​ Mostly hydrogen and helium. -​ Strong magnetic field due to electric currents -​ Surface has alternating bands of swirling gases. -​ Great Red Spot is like a huge sustained hurricane. -​ Explanation of Jupiter's coloured bands and great red spot: -​ Ammonium hydrosulphide (salt), huge sustained hurricane (red spot), mystery -​ Has at least 16 moons and 4 rings. -​ Note what is meant by rings: -​ Refers to a series of narrow, faint bands of particles that orbit the planet. These rings are composed of small rocks, dust, and ice. Unlike the large, bright rings of Saturn, its rings are much darker, less dense, and harder to observe. 6.​ Saturn: -​ Composition similar to Jupiter, but very low density. -​ Has at least 22 moons. -​ Most complex system of rings in the solar system. -​ Lowest density in the solar system 7.​ Uranus: -​ Axis of rotation is almost horizontal relative to the plane of orbit. -​ Axis is titled on its side -​ Greenish colour indicates presence of methane. -​ Has at least 17 moons and 11 small rings. 8.​ Neptune: -​ Similar to Uranus in size, mass, and composition.  -​ Has at least 8 moons and 4 small rings. What is a planet: -​ In 2006, the International Astronomical Union (IAU) decided that, in order to be considered a planet, a body must: -​ orbit the sun. -​ have enough gravity to make it round. -​ have “cleared its neighbourhood of smaller objects”. -​ A dwarf planet is a celestial body that -orbits the sun, has enough mass to assume a nearly round shape, has not cleared the neighborhood around its orbit and is not a moon. -​ An exoplanet is a planet that orbits a star outside the solar system. What about pluto? -​ Now called a dwarf planet, no longer considered to be a planet. -​ Orbital plane is tilted 17° to the ecliptic. -​ Elongated orbit – sometimes cuts inside Neptune’s orbit. -​ At least 3 moons. One of its moons, Charon, is about ½ the size of Pluto. -​ Considered one of the bodies of the Kuiper Belt. -​ Pluto is simply too small -​ Reasons: -​ Pluto has not cleared its orbit of other objects and debris (Charon is not an example, it is a satellite) -​ According to the IAU, it meets the qualifications of a dwarf planet as it fulfills the first two requirements, but not the last one. -​ Pluto is relatively small and has insufficient mass to exert gravitational dominance over nearby celestial bodies. It is considered a body of the Kuiper belt -​ It is eccentric, a common characteristic of dwarf planets, and cuts into Neptune's orbit -​ Kuiper Belt: -​ A belt of objects outside of Neptune’s orbit. -​ Extends to 3 billion kilometres beyond Neptune’s orbit. -​ Pluto (2390 km across) and UB313 (bigger than Pluto) are among the largest objects discovered yet. -​ Over 70,000 other objects. Oort Cloud: -​ A spherical region surrounding the solar system. -​ Contains the most distant objects that orbit the sun. -​ Most comets originate here. Other Bodies in the Solar System: -​ Dwarf Planets -​ Round shape, like planets. -​ Has not cleared the neighbourhood around orbit -​ Not satellites. -​ A satellite, in the context of astronomy, refers to a natural or artificial object that orbits around a planet, dwarf planet, or other celestial body. -​ Usually eccentric (not central) and inclined orbits. -​ Most originate in the Kuiper Belt. -​ Asteroids -​ Killed the dinosaurs -​ Most located within a belt between the orbits of Mars and Jupiter, the asteroid belt. -​ Not enough gravity to form the almost spherical shape of planets.  -​ -​ Comets -​ Rock, frozen water, ammonia, methane, carbon dioxide. -​ Sometimes described as “dirty snowballs”. -​ When close to Sun, some of the ice at the nucleus evaporates and forms the coma. -​ Solarwinds blasts dust and rock away, forming the tail. -​ Originate in the Oort Cloud, which surrounds the solar system.  -​ Meteoroids -​ Small bits of rock and metal which move through the solar system. -​ Most are less than 1mm in diameter. -​ Meteoroids are space rocks that range in size from dust grains to small asteroids. When meteoroids enter Earth's atmosphere, or that of another planet, at high speed and burn up, they're called meteors. -​ Called a meteor while moving through the atmosphere, and a meteorite if it hits Earth’s surface. 5.2 Kepler’s Laws and Famous Planetary Satellites Johannes Kepler, a German astronomer, developed the Laws of Planetary Motion between 1609 and 1618. 1.​ First Law: Law of Ellipses -​ Each planet orbits in a path called an ellipse, not in a perfect circle  -​ The sun is located at one focus. -​ Perihelion = The point in a planet’s orbit when it is closest to the sun. -​ Aphelion = The point in a planet’s orbit when it is furthest from the sun. 2.​ Second Law: Law of Equal Mass -​ In a given time, a planet sweeps out the same area anywhere in its orbit. -​ A line connecting a planet to the Sun sweeps out equal areas in equal amounts of time. This means that when a planet is closer to the Sun, it moves faster in its orbit, and when it's farther away, it moves slower. The area swept by the line is always the same over equal time intervals. -​ The closer to the sun, the faster a planet moves. 3.​ Third Law: Law of Periods -​ The farther a planet is from the sun, the longer one revolution takes. -​ Represented in the formula: P2 = D3 -​ P is the period of revolution (time it takes to rotate once around the sun), measured in Earth years. (In astronomy, the term period usually refers to how long an object takes to complete one cycle of revolution. In particular the orbital  period of a star or planet is the time it takes to return to the same place in the orbit.) -​ D is the average distance from the sun to the planet, measured in AU (Astronomical unit; 1 AU is the average distance from the earth to the sun.) The Galilean Satellites of Jupiter: -​ So named because Galileo first observed them with his primitive telescope in 1610. -​ These are the largest of Jupiter’s moons. -​ 1.​ Io: -​ Close to Jupiter. -​ Frequent volcanoes which erupted sulphur and sulphur compounds. -​ Internal heat due to tidal effects caused by Jupiter’s huge gravity. 2.​ Europa: -​ Smooth surface, probably frozen water. -​ May have deep oceans of water beneath ice → possibility of primitive life? 3.​ Ganymede: -​ Covered with thick layers of ice and rock. -​ Interior is probably solid silicate rock. -​ Largest moon in the solar system. 4.​ Callisto -​ Similar to Ganymede in structure and composition. -​ Many ancient impact craters. -​ Possible ancient crustal plate motion. -​ Tectonic plates, if they exist, are mostly ice. History of Earth's Moon:  -​ Moon formed during a collision between the Earth and another small planet, about the size of the planet Mars. The debris from this impact collected in an orbit around Earth to form the Moon. -​ Hot, liquid material cooled, forming a light-coloured crust. -​ Heavy bombardment by meteoroids created basins and craters. -​ Hot lava released into basins cooled and formed darker areas. Surface Features of Earth's Moon: -​ Highlands: -​ Light in colour. -​ Oldest rocks. -​ Maria: -​ Dark in colour. -​ Younger rocks. -​ Once thought to be oceans. -​ Craters: -​ Many impact craters, ranging in size from microscopic to 240 km across. -​ If you were walking on the moon, you would find no atmosphere, due to the low gravity. You would weigh only one-sixth as much as you weigh on Earth. Weathering and Erosion on Earth's Moon: -​ No atmosphere and no water → no chemical weathering. -​ Mechanical weathering and erosion occurs from meteoroid impacts.  5.3 Motion of Earth’s Moon The Moon's Orbit: -​ Elliptical orbit around Earth; Earth is located at one focus of the ellipse. -​ Period of one rotation = period of revolution around Earth -​ only one side is ever visible from Earth. -​ Plane of orbit is tilted 5° to the ecliptic Perigee vs Apogee: -​ Perigee: The point in its orbit when the moon (or an artificial satellite) is closest to Earth. (Compare with perihelion) -​ Apogee: The point in its orbit when the moon (or an artificial satellite) is farthest from Earth. (Compare with aphelion) -​ Barycentre: In astronomy, the barycenter or barycentre is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit Phases of the Moon: 1.​ New Moon: Only the far side is illuminated by sunlight. 2.​ Waxing Crescent -​ 3.​ First Quarter: Right half of the moon is illuminated -​ 4.​ Waxing Gibbous -​ 5.​ Full Moon: Entire near side of the moon is illuminated.  -​ 6.​ Waning Gibbous -​ 7.​ Third Quarter (Last Quarter): Left half of the moon is illuminated. Remember L for last and left so that all of the last phases have light on the left -​ 8.​ Waning Crescent: -​  -​ Note that the Moon's orbit is in sync with the earth's rotation, meaning that it keeps the same face toward Earth at all times. This is why, although it may seem like the right side of the moon is illuminated during the third quarter in the inner diagram, from the perspective of earth looking at the moon, the left side is illuminated. Lunar Eclipse: -​ Moon moves into Earth’s shadow. -​ Only happens during a full moon phase.  The moon appears red during a lunar eclipse Partial Total Occurs when only a portion of the Moon Occurs when the entire Moon passes passes through the Earth's umbra (the through the Earth's umbra. The Moon is darkest part of its shadow). Part of the Moon completely darkened but typically appears remains in the penumbra (the lighter outer reddish due to sunlight being refracted and shadow), so not the entire Moon darkens. scattered by Earth's atmosphere. Solar Eclipse: -​ Types: -​ Total Solar Eclipse:  -​ The Moon completely covers the Sun, revealing the Sun’s outer atmosphere (the corona). -​ When an earth observer cannot see the sun at all as they are in the umbra -​ Partial Solar Eclipse: -​ When an observer is in the moon's penumbra -​ Annular Solar Eclipse: -​ The Moon appears smaller than the Sun and creates a "ring of fire" around the edges of the Sun. -​ An eclipse when the new moon is at apogee -​ -​ -​ Hybrid Solar Eclipse (Rare): -​ Description: A combination of a total and an annular solar eclipse. It may appear as a total eclipse in some locations and an annular eclipse in others. -​ Cause: Because Earth's surface is curved, sometimes an eclipse can shift between annular and total as the Moon's shadow moves across the globe. -​ -​ Moon casts a shadow on Earth. -​ Only happens during a new moon phase. -​ Eclipses can only happen when the sun, moon, and Earth are all aligned; the moon must cross the ecliptic during a new moon phase -​ This is why solar eclipses are uncommon, due to tilt Partial Total Tides: -​ Moon’s gravity pulls Earth’s oceans and causes “bulges”. -​ Largest tidal changes occur when moon, Earth, and sun are in line (full moon and new moon phases) → Spring tides. -​ Smallest tidal changes occur when moon, Earth, and sun describe right angles (first quarter and third quarter phases) → Neap tides. -​ Remember neap is weak -​ Tidal changes especially large during full and new moon phases as solar/lunar tidal effects adds up together  5.4 Structure of the Sun Characteristics (Memorization not needed): -​ 1,380,000 km in diameter (110 times the diameter of Earth). -​ Surface temperature = 5,500°C. -​ Interior temperature = 15,000,000°C. -​ 70% hydrogen, 28% helium, 2% heavier elements (like iron). Structure: -​ Core - at centre, site of nuclear fusion. -​ Radiative Zone - Moves energy through radiation. -​ Convective Zone- Moves energy by convection. -​ -​ Has rising and falling currents of plasma (charged gas particles) -​ Photosphere - Thin yellow surface layer, 400 km thick. -​ Chromosphere - Lower part of sun’s atmosphere, Red in colour due to glowing hydrogen and helium. -​ Corona - Outermost, least dense part of the sun’s atmosphere, only visible during a solar eclipse. Other features: -​ Sunspots: -​ Darker areas on the photosphere. -​ Allows us to see the sun's movement -​ Magnetic field 1000 times stronger than surrounding photosphere. -​ Show that the sun rotates faster at its equator than its poles. -​ Maximum occurrence on an 11 year cycle. -​ Solar Flares: -​ Sudden outbursts of energy that rise up in areas of sunspot activity. -​ Solar Prominences -​ Huge flame-like arches of material suspended above the sun’s surface by magnetic fields -​ Can extend thousands of kilometers into space before falling back to the sun's surface -​ Solar Wind: -​ Constant streams of charged particles (mostly protons and electrons) leaving the corona. -​ Interacts with Earth’s magnetic field, causing auroras (northern and southern lights). Sun's Energy: -​ From nuclear fusion of small atoms into larger ones.  -​ Four hydrogen nuclei fuse to form one helium nucleus. -​ During fusion, some mass is converted into energy according to E=mc2 -​ 4H → He + Energy (4.030 amu) (4.030 amu) ​ ​ ​ -​ About 4 million tonnes of matter is converted to energy every second. 5.5 Constellations Constellations: -​ A group of stars which appears to form a particular shape -​ Typically named from stories from mythology -​ They depict humans, animals, or fictional creatures -​ Examples: -​ Ursa Major (Great Bear) -​ Leo the Lion -​ Orion the Hunter Ursa Minor Story: -​ According to legend, Ursa Major was once the beautiful maiden Callisto, whom the god Zeus had an affair with. In order to protect her and their son, Arcas, from his jealous wife Hera, Zeus turned Callisto and Arcas into bears. He then picked up the bears by their short, stubby tails and threw them into the sky. While doing this the tails of the bears stretched out. Arcas can be seen in the night sky as the constellation of Ursa Minor. Circumpolar Stars: -​ Visible from Earth all year. -​ Located well above or below the ecliptic. -​ Can only be seen in certain hemispheres -​ For example, Polaris can only be seen in the Northern Hemisphere, meaning observers from the Southern Hemisphere will be unable to see it -​ Examples: -​ Polaris, the stars of the Big Dipper, the little dipper. -​ Note that the big dipper is a part of Ursa Major and that the little dipper is a part of Ursa Minor -​ It may seem that the stars trace a circular path around Polaris, which seems to stay still making the appearance of revolution around Polaris as it is near the Earth's axis points.  -​ Some stars travel a great distance over the course of the night. Polaris is different. Because it's so close to the celestial pole, it traces out a very small circle over 24 hours. So Polaris always stays in roughly the same place in the sky, and therefore it's a reliable way to find the direction of north Seasonal Constellations -​ Stars that are roughly in line with the ecliptic plane. -​ Can only be seen if Earth’s night sky points in their general direction, but can be seen by both hemispheres. -​ The signs of the zodiac are all seasonal constellations -​ Examples: -​ Lyra, Scorpius, Cygnus (summer) -​ Orion, Taurus (winter) Pointer Stars: -​ Readily recognizable stars/constellations that can help you find other important objects. -​ Helps explorer find directions in the olden days -​ Example: The two stars furthest from the handle of the big dipper describe a line that points towards Polaris. Polaris can be used to find North. -​ Polaris is also known as the North Star  5.6 Stars Stellar Distances: -​ Huge distances are measured relative to the speed of light (300,000 km/s). -​ One light year is the distance that light travels in one year. -​ The sun is the closest star, only 8 “light minutes” away from Earth. -​ The next closest star is Proxima Centauri, 4.21 light years away. -​ Polaris is 430 light years away. Composition of Stars: -​ Most are 98-99% hydrogen and helium, with 1-2% of mass made up of heavier elements, such as iron Star's Colour: -​ Depends on surface temperature: -​ Red star = 3,000°C -​ Yellow star = 5,000°C -​ White star = 10,000°C -​ Blue star > 30,000°C Magnitude/Brightness: -​ Apparent Magnitude: -​ The brightness as viewed from Earth. -​ Absolute Magnitude (Luminosity): -​ The actual brightness of the star. -​ How bright the star would appear if all stars were at 10 parsecs (32.6 light years) from Earth.  -​ Note: In astronomy, a lower magnitude corresponds to a brighter object. This is because the magnitude scale is a logarithmic scale where smaller numbers (or negative numbers) represent brighter objects. Stability of Stars: -​ Stable if explosive energy blowing star apart balances gravity pulling star together. Hertzsprung Diagram (Must know): -​ Shows the luminosity and temperature of stars -​ Sun: -​ Temp: 5770 °K -​ Luminosity: 1  -​ Note that the y-axis uses luminosity rather than magnitude, meaning that the higher up, the brighter the star. The life cycle of a star: 1.​ Stellar nebula: Clouds of gas and dust. Nebulae condense under the influence of gravity, and, if large enough, some areas, protostars, will begin to glow. 2.​ Protostar: Hot, Glowing area in the nebula a.​ IF the centre gets hot enough, nuclear fusion begins, giving birth to a star 3.​ Main Sequence Star: Fuses H into He in the core 4.​ Giant or Supergiant: When the hydrogen in the core is depleted, fusion slows down, and the core begins to contract under gravity. This causes the core temperature to rise, allowing helium to fuse into heavier elements like carbon and oxygen in the core. Hydrogen fusion occurs outside the core too, as the star expands into a giant or supergiant a.​ In about 5 billion years, our sun will become a red giant, ending its life as a white dwarf Giant: Typically stars with less than 8 Supergiant: Stars with greater than 8 times times the mass of the Sun the mass of the Sun.  5.​ Planetary nebula: Halo of glowing 5.​ Supernova: Star collapses, producing a gases surrounding a white dwarf shock wave that blasts the outer layers 6.​ White Dwarf: Hot carbon-oxygen into space core of previous star 7.​ Black Dwarf: A black dwarf is a If the massive star If the massive star theoretical stellar remnant is less than 15 is more than 15 representing the final stage in the times (8-15) the times the mass of evolution of a white dwarf, which mass of the sun: the sun: has cooled so much that it no Neutron Star - So Black Hole - Mass of longer emits significant heat or dense that each star crushed into a light. However, no black dwarfs atom’s electrons are core denser than a currently exist in the universe, as crushed into the neutron star. Gravity the process of cooling to this nucleus (Potentially is so great that light stage takes far longer than the greater mass than cannot escape. It is current age of the universe (~13.8 our sun, but less the most dense billion years). than 20km across) object in the universe. 5.7 Galaxies A Galaxy: -​ Is a large system containing many stars bound together by gravitational attraction. -​ Has typical diameter of 100,000 light-years. -​ Contains, on average, about 100 billion (100,000,000,000) stars  -​ They also have clouds of gas and dust called Nebulae (singular = nebula). Types of Nebulae: -​ Bright Nebula: Glows from hot gases within, or from reflected light from nearby stars. -​ Dark Nebula: Absorbs light, so visible as a dark area against a lighter background. -​ How are nebulae formed: -​ Star Formation Nebulae (Emission Nebulae): These are regions where new stars are being born. The energy from these stars causes the surrounding gas to glow, creating a colorful nebula. -​ Planetary Nebulae: These are formed when medium-sized stars (like our Sun) reach the end of their life cycle. As the star runs out of fuel, it sheds its outer layers, creating a shell of gas and dust. The core of the star, now a white dwarf, emits ultraviolet radiation, which ionizes the surrounding gas, making it glow. -​ Supernova Remnants (Supernova Nebulae): After a massive star explodes in a supernova, the shockwave of the explosion disperses the outer layers of the star, forming a nebula. -​ Answer by Mrs. Wong: random stars that are close together and draws in by gravity Types of Galaxies: -​ Spiral: -​ Most common type of galaxy. -​ Has a nucleus (centre) of bright stars and “arms” of stars that spiral around centre. -​ Barred Spiral Galaxy: -​ Has a bar of stars running through the center.  -​ Elliptical: -​ Shapes range from nearly spherical to the shape of a convex lens. -​ Brightest at the centre, because that’s where most of the stars are. -​ Shaped like a squashed sphere -​ No “arms”; very little gas and dust. -​ Irregular: -​ Least common type of galaxy. -​ Smaller and fainter than other types. -​ No particular shape; stars are distributed unevenly. -​ Why the irregular shape? -​ Gravity may be insufficient to organize stars into well-defined shapes. -​ May be the result of two galaxies colliding. The Milky Way Galaxy: -​ We see the Milky Way as a cloud-like band of stars that stretches across the night sky. When you look at this, you are looking along the disk/plane of the galaxy.  -​ Spiral galaxy; rotates around its nucleus. -​ 100,000 light-years in diameter. -​ 2000 light-years thick at the nucleus. -​ The Sun is 30,000 light-years from the centre, located on one of the arms of the galaxy. -​ Our solar system revolves around the galaxy’s nucleus at about 250 km/s; one revolution takes about 200 million years. -​ Our galaxy has made about 23 revolutions around its nucleus (4.6 billion (age of solar system)/200 million) 5.8 Measurement and the Big Bang Measurement of Distance: Parallax -​ Determining distance to a star based on the shift in apparent position of the star when viewed from different angles. -​ Only accurate for nearby stars (