001: Astro WEB CLASS Review Notes for Exam 2 Thursday June 3
I. Information on the Test Itself - The exam will be taken on Angel, between 12:00am and 11:55pm on Tuesday 25 May. - You may start it anytime you wish, as long as you are finished by 11:55pm. You will have 60 minutes to complete the exam once you start. Do not start after 10:55pm or you may run out of time. - Test will be taken under the honor system: no notes, course materials, books, electronic devices, other people, or outside websites to help you. Just you, your brain, a BLANK piece of scratch paper and a pen if you like (in case you would like to draw a diagram or do a calculation), and the test questions themselves on Angel. - 50 multiple choice questions (5 answer choices each) - 2-7 questions relating to material in each part (Intro and Parts 1-11), tending to be more for longer units Of the 50 questions: - 2 on constellations (covering only the four given in Interludes 1-4) - 14 questions (2 from each Part) identical to questions given in the Angel material - 7 questions drawn from 25 sample test questions given here - 27 additional questions similar in nature to questions you have seen several of the 27 will present pictures of planets or common moons that you will be asked to identify This document contains a concise list of things that you should know for the Unit 2 exam. These are the major points, but of course the Angel material gives more detail and explanation. One thing to note is that you are not expected to remember exact dates and numbers. Try for understanding rather than memorization so that you can possibly pick the number out from very different values. For example you might be asked if Jupiter is 10X less massive, roughly equal mass, 3x more massive, 300X more massive, or 3 billion times more massive than the Earth. The answer is 300X more massive. You are expected to know the names and be able to identify the 8 planets and several moons (as noted below), and their basic properties. I. Part 1: Earth Distance between Earth and Sun = 1 Astronomical Unit = 1AU Time for Earth to orbit the Sun = 365 days Kepler used Brahes data to determine laws: 1st law = The planets orbit the Sun in elliptical orbits with the Sun at one focus. Ellipses are nearly circular in our solar system. 2nd law = A line joining a planet and its star sweeps out equal areas during equal intervals of time. The speed is fastest when the planet is closest to the Sun (perihelion) and slowest when it is farthest away (aphelion) 3rd law = P =a where P is the period in years and a is the semimajor axis (average distance to Sun) in AU. Example of 3rd law = A hypothetical planet takes 3 years to orbit the Sun. How far from the Sun does it 2 2 3 3 3 orbit? 3 years is the period. (Why? Take P =3 =33=9. So a =9. Well, 2 =222=8, and 3 =333=27. So a must be much closer to 2 than to 3 - just greater than 2. You would be given choices that made it pretty obvious which answer is correct like 1AU, 2.08AU, 3.08AU, 9AU, and 9.7AU. No calculator needed! Properties of Earth thick atmosphere that extends to 200km above the surface; mostly composed of nitrogen and oxygen molecules; atmosphere causes sky to appear bright during the daytime; this is the scattered light of the Sun; otherwise sky would appear dark large magnetic field; magnetic axis tilted from spin axis by small angle; Van Allen belts of charged particles trapped in field; some solar wind particles hit atmospheric gas and lead to emission of different colors producing the aurora phenomenon. plate tectonics = plates on the surface of Earth float on denser fluid and move around = continental drift;
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mountains caused by collisions of plates; faults caused by plates sliding past one another causing fractures ozone (three oxygen atoms bonded together) layer (in stratosphere) protects Earth from UV radiation - can be destroyed by human-produced gases. Greenhouse Effect = Energy from Sun heats Earth. Earth tries to radiate this heat back to space by giving off infrared radiation. Particular gases (including water vapor and CO2) in the Earths atmosphere trap this heat, preventing it from escaping to space. This trapped heat is redistributed back on Earth. The naturally abundant greenhouse gases in the Earths atmosphere act like a thermal blanket keeping Earth warm. Without Greenhouse gases Earths surface would be 33 degrees Centigrade cooler. When humans produce Greenhouse gases it leads to extra heating, i.e. global warming. Formation of the Solar System (1) gas and dust cloud collapses due to gravity, (2) spinning cloud forms disk, (3) Sun forms at center, (4) lumps in disk become planets, (5) region around them clears out, (6) takes a few tens of millions of years to form, (7) solar system has existed for 4.5 billion years II. Part 2: Moon terra (Latin for land): light colored features, heavily cratered, peaks, geologically older, uplifted from impacts in early solar system maria (Latin for seas): dark colored, less cratered, valleys, geologically younger, filled by lava 3 billion years ago regolith = finely-grained soil that covers moon = broken apart by small meteorites hitting moon impact craters = due to explosions from asteroids or comets that hit the moon Moon rotates on its own axis with exactly the same period that it takes to travel once around the Earth; same side of Moon always faces Earth; due to tidal locking Moon lacks high density material such as iron - no large iron core 1/4 diameter of Earth Moon has no atmosphere; daytime sky is dark Gravity is 6 times stronger on Earth than on the Moon. F M/R where F is the force due to gravity, M is the mass, and R is the radius of the planet. Large mass planets that are compact have larger gravity. Formed later than Earth from giant impact of large object with Earth. III. Part 3: Mars in 19th century thought that channels/canals might relate to Martian life day and night similar in length to those on Earth half Earths diameter; 1/10th Earths mass >12 spacecraft have visited Mars; rovers explored surface No thick atmosphere, but does have thin one that causes orangish sky, mostly carbon dioxide, only modest Greenhouse effect because atmosphere is so thin Average surface temperature -20C Iron oxide gives Mars its red color Has many impact craters on surface Southern hemisphere has more craters than Northern; Southern hemisphere is higher and older geologically; Northern craters erased by lava flows. Olympus Mons (volcano on Mars; dont need to remember name) is 3 times higher than Earths highest mountain; Martian volcanoes appear dormant Valles Marineris (dont remember name) is deepest canyon in solar system = >300 times size of Grand Canyon Water once existed on the surface of Mars, but it isnt flowing there at present; Permafrosts = water ice locked beneath Martian soil Dust storms common; make it hard to see surface features. IV. Part 4: Venus Closest to Earth; visible in western sky in evenings near Sun, and in eastern sky just before sunrise; looks
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like bright star Day/night cycle on Venus is longer (234 days) than a year (225 Earth days). Rotation is retrograde, i.e. clockwise when viewed from above. Dense atmosphere - 90 times atmospheric pressure on Earth - mostly carbon dioxide - gases produced by volcanic outgassing, but not dissolved in ocean like on Earth Very hot >600K; would be hotter but atmosphere reflects 80% of sunlight; high temperature because of the presence of large amounts of greenhouse gas (mostly CO2). Spacecraft have visited; radar used to map surface because we cant see through atmosphere; probes went down to surface Active volcanoes, huge lava flows; some craters like on Earth and the Moon. V. Part 5: Mercury Can only see close to Sun, and hard to do with the naked eye. Mercury is much smaller than Earth and only a bit bigger than Earths Moon Many craters like Moon; the cliffs called scarps Rotates slowly; 58 Earth days to rotate; 88 Earth days to orbit the Sun Only a very thin atmosphere, sky appears black in daytime; temperature is extremely high on the day side and extremely low on the night side (due to lack of atmosphere; same effects for any planet/moon without atmosphere) Some fly-by missions have occurred; MESSENGER will reach Mercury in 2011. VI. Part 6: Jupiter 3rd brightest in Earths night sky (after Moon and Venus) Jupiter is 300 times the mass of the Earth, but is far less dense. Made mostly of hydrogen and helium gas. Gaseous molecules of ammonia, methane, and water vapor also present; these lead to different colors. Clouds of different colors are at different altitudes. Light colored bands = zones; dark colored bands = belts. Windspeed 360km/hr; Great Red Spot = giant storm larger than Earth = like anticyclone on Earth Interior temperatures and pressures very high Hydrogen in liquid metallic form. In very center, likely to have rocky/metallic core. Albedo determines fraction of sunlight that is reflected or absorbed. Planets are visible to the human eye because of reflected sunlight. Jupiter emits more than it absorbs; due to continuing contraction due to large gravity produces energy; this generates heat; Jupiter is not a star, but could be called a failed star. Magnetosphere 10 times stronger than Earth; aurora like on Earth Many fly-bys; Galileo sent an atmospheric probe At least 63 moons; four largest discovered by Galileo - look like stars, but found to orbit Jupiter (remember names) (1) Io: coppery-yellow with black dots which are volcanic plumes - very active, low crater density - yellow from sulfur (2) Europa - water ice surface - no craters/ice movement wiped them out - could have liquid water below dark brown and red streaks are due to sulfur - could have microbial life in oceans. (3) Ganymede - largest moon in solar system; larger than Mercury; icy crust, may have ocean beneath, has craters. (4) Callisto - very heavily cratered, many young craters. VII. Part 7: Saturn Galileo discovered rings (though he didnt really know what they were). Mass is 100 times Earth and 1/3 Jupiter. Made of Hydrogen and Helium, belts and zones, cooler than Jupiter. Rings incredibly thin; made of individual orbiting objects composed of water ice crystals and some rocks; rings are only hundreds of millions of years old - otherwise would be darkened by accumulating dust - could be made of comet that was ruptured
Spin axis of Saturn is tilted about the same as Earths More than 30 moons; Largest is Titan (remember) - second largest moon in solar system; very thick atmosphere; surface has few craters (young), highlands, and volcanoes; slushy lakes and rivers made of hydrocarbons; resembles early Earth before emergence of life. Cassini mission currently studying Saturn and its moons VIII. Part 8: Uranus Barely visible with naked eye; third largest. Found later than others, in 1781 (dont need to remember precise date) Made of gas, mostly hydrogen and helium, but some methane that gives the blue color; does not have belts or zones or bright clouds (due to lack of atmospheric convection); has solid core Spin axis is nearly in plane of orbit around Sun; poles receive more heating, but for unknown reasons the equator is hotter anyway. Has faint, dark rings; made of carbon (soot) - thought to come from methane in Uranuss atmosphere. 27 moons (dont need to know exact number or names of these); Titania (40-50% water ice; the rest rock); Miranda (heavily cratered with weird valleys and cliffs) - appearance caused by upwelling of ices IX. Part 9: Neptune Discovered in 1846 (dont memorize exact date) based on orbit of Uranus not looking quite right Similar to Uranus but bluer; atmosphere of hydrogen, helium, and methane (causes blue color); solid core the size of earth; surrounded by mantle of ices and rocks Rapid winds and large storms/vortices; include Great Dark Spot, a big storm that has existed for several decades Ring structure, faint and dark; made of more microscopic dust particles, not larger chunks like the other planets. 13 moons; Triton (dont need to know name) is largest; orbit around Neptune unstable; thin atmosphere made of nitrogen and methane; very few craters; ice cap in southern hemisphere; ice volcanoes with liquid nitrogen, dust, or methane coming out of them; dark streaks come from eruptions X. Part 10: Comets and Asteroids some civilizations thought comets were bad omen; Halleys comet is famous short period comet that returns every 75 years short period comet = period <200 years; come from Kuiper belt (trans-Neptunian objects) formed at time of solar system formation as small objects in outer solar; occasionally thrown into inner solar system (by outer planet gravity) and enter into orbits long period comet = period >200 years; come from Oort cloud which is a sphere surrounding the solar system, much beyond the planets and the Kuiper belt The tail of a comet is a transient feature. Comets develop tails as they are vaporized near the Sun; have nucleus made of dust and water ice and carbon dioxide dry ice (dirty snowball); two types of tails for each comet, dust tail (more prominent - driven away from Sun by radiation pressure) and ion tail - bluish (swept out by solar magnetic field) Deep Impact had flyby encounter with comet Temple 1 and released an object that impacted with the comet so they could study its composition asteroids = rocks left over when the planets form; orbits of some intersect Earths orbit and lead to meteors; asteroid belt between Mars and Jupiter has many asteroids including some large ones meteors = shooting stars = pieces of solar system debris (asteroids and debris left behind comet) that burn as they fall through Earths atmosphere; made of iron, nickel, carbon, and silicates; formed with the Solar System fireball = very bright meteor due to large chunk of debris meteorite = pieces of meteor that survive and hit Earth asteroid collisions; 65 million years ago a collision with Earth caused extinction of dinosaurs (KT event); dust, smoke in atmosphere caused extinction, not the impact itself; ongoing searches for near Earth objects
XI. Part 11: Pluto Pluto is now considered a dwarf planet Discovered in 1930; 248 year period of orbit; orbit more highly elliptical than planets, and not in the same plane; intersects orbit of Neptune Very small - Earths Moon is 7 times more massive 3 moons; largest is Charon, over half diameter of Pluto Not planet anymore because 1) other similar objects were found farther from the Sun: Quaoar, Sedna, Eris; 2) not like other outer planets/small Now considered an ice dwarf planet, which are very abundant beyond the orbit of Neptune New Horizons spacecraft will reach Pluto by 2015 XII. Planet Comparison Terrestrial Planets/Inner Planets are: Mercury, Venus, Earth, Mars. They are small and rocky, and have high densities, solid surfaces, slow rotation, no rings, and few moons. Gas Giants/Outer Planets are: Jupiter, Saturn, Uranus, Neptune. They are large and have gaseous (hydrogen and helium) deep atmospheres with solid cores, rings, and many moons Here are some other questions you should be able to answer: Which planets have dense atmospheres, thin atmospheres, no atmospheres? Which planets have strong and weak surface gravities? Which planets have the greenhouse effect? What are the colors of the planets? XIII. Constellations The only specific constellations you are responsible to recognize for this unit are the four that were covered in the Interludes: (1) Gemini, the Twins (2) Leo, the Lion (3) Taurus, the Bull (4) Virgo, the Maiden You should remember their shapes so you can tell which is which. XIV. Answers to 25 Sample Questions 1a 2d 3d 4c 5d 6c 7d 8a 9e 10c 11c 12c 13d 14d 15e 16c 17b 18e 19e 20a 21b 22a 23a 24d 25b