Astro-7N Unit-1 Review Notes PDF

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Review notes for Exam 1...

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Astro 7N: the Artistic Universe Review Notes for Unit 1! In addition to these notes, refer to the game's companion "Encyclopedia," for Unit 1: http://www.psuastrogame.com/encyclopedia/unit1/

Information on the test itself

("Test 1" covers Units 1 & 2)

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50 multiple-choice questions (5 answer choices each)

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Half of the questions will relate to material from each of seven topics in Unit 1 — Gravity, Seasons, Moon Phases, Constellations, Light, Spectroscopy, and Telescopes. (the other half of the questions will relate to topics in Unit 2; see Unit 2's review notes)

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Some questions will be identical to those given in the game material — selected from "Copper’s" quiz questions and those in with the lessons' dialogue

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Some questions will be drawn directly from the "Sample Test-1 Questions" packet

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Additional questions similar in nature to questions you have seen before

BE CAREFUL —! Although we are not intentionally being tricky, some questions will be similar to ones you have seen, but you need to read carefully. For example: we might ask something about solar eclipses on the test similar to a question you may have seen about lunar eclipses, before. Again: be sure read each question, carefully. This document contains an overview of things that you should take away from Unit 1 to prepare for the first test (which also covers Unit 2). These are the major points, but of course the game material gives more detail and explanation. Remember that you can review material by starting the game, selecting the Pause Menu pressing either the [escape] or [P] key during the game, and selecting “Repeat a Lesson.” You can also retry Copper’s quiz questions by finding him in the lobby of the dorm building in the underground portion of the Mars colony; use the Pause Menu's "Maps" screen to travel there quickly — or between other key locations in the game (tapping the [M] key during the game also gives access to the fast-travel map).!

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1. Gravity Newton’s Laws 1. An object at rest, or in motion in a straight line at a constant speed, will remain in that state unless acted upon by a force. (example: If the Sun suddenly disappeared, the Earth would continue in the • direction that it was traveling in its orbit at that time.) 2. The acceleration of a body due to a force will be in the same direction as the force, with a magnitude directly proportional to its mass. Force = mass x acceleration • (A smaller mass will move faster, if the same force is applied to it.) • 3. For every action, there is an equal and opposite reaction. (The Sun exerts force on planets, and they orbit it — the planets exert equal • force on Sun, but it only moves slightly because of its very large mass relative to the planets.) Surface Gravity on a Planet ! •

The strength of gravity, g, on the surface of a planet is given by g = M / R2 where M is the mass of the planet and R is its radius. Note the radius is squared but the mass is not. !

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More mass = more gravity. If the mass of a planet were twice that of another, but they had the same radius, the gravity felt on the surface of the more-massive one would be twice as strong.

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Larger separation = less gravity. If the radius of a planet were twice that of another, the gravity is 1 / (2) 2 = 1/4 as strong. !

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Putting the effects of mass and radius together, you should be able to figure out the surface gravity of Mars, relative to the Earth. Mars has 1/10 the mass of the Earth and 1/2 the radius of Earth. So for Mars, g = (1/10) / (1/2) 2 = (1/10) / (1/4) = 4/10 Mars has a surface gravity 4/10 that of Earth. You will need to be able to do this type of estimate for the test, given the numbers for mass and radius.

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Newton’s Universal Law of Gravitation This law gives the force of gravity between any two objects in the Universe. The force of gravity is proportional to (mass of object 1) × (mass of object 2) divided by the distance between the two objects squared: F ∝ M1 x M2 / d 2 Again, more mass = stronger gravity. If the objects were moved 2 times closer (or, to half of their initial distance between), ... F ∝ M1 x M2 / (1/2) 2 = M1 x M2 / (1/4) = 4 (M1 x M2) ... so, the gravitational attraction would become 4 times as great.

2. The Seasons, Day & Night Q: A:

What causes day and night? Rotation of the Earth on its axis.

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How does the Sun appear to move in the sky in the course of a day?! East to West, because of Earth’s rotation. The stars and planets move in the same way from our point of view, also, because of Earth’s rotation.

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What happens to the Earth in one year? It orbits the Sun, once (also referred to as one complete revolution about the Sun).

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Why do we have seasons? The tilt of the Earth’s axis of rotation, with respect to the plane of its orbit around the Sun (and not because of changing distance from Sun). The Earth's tilt is about 23 degrees.

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How is the Earth’s axis tilted when we have summer in the Northern hemisphere?! With the North pole toward the Sun.

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What season is it in the Southern hemisphere when it is summer in the Northern hemisphere?! Winter.

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Winter begins on or about Dec. 21 = in the Northern hemisphere, the nights are longer than days Spring begins on or about March 21 = days and nights have equal length Summer begins on or about June 21 = days longer than nights in the North Fall begins on or about Sept. 21 = days and nights have equal length !

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Seasons would not happen if the Earth’s axis were not tilted. The distance between the Earth and the Sun does not change very much over the course of a year, so the temperature does not change much for that reason. Without the tilt of Earth’s axis there would be no seasons on Earth. Mars has a similar tilt to its rotation axis as Earth does.

3. Moon Phases and Eclipses! Some general summary questions & answers: Q: A:

What happens to the moon in 1 month? It moves once around the Earth.

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What causes the phases of the Moon? The Sun is lighting up different fractions of the part of the Moon we see from Earth.

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What is the order of the phases of the Moon? New – Waxing Crescent – First Quarter – Waxing Gibbous – Full – – Waning Gibbous – Third Quarter – Waning Crescent – New (and repeat...)

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When is the full moon visible? Only at night. It transits (is highest in the sky, or overhead) at midnight; the full moon rises 6 hours earlier (at sunset), and sets 6 hours later (at sunrise).

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When is the new moon visible? The new moon is visible during the day. It transits at noon; it rises 6 hours earlier (at sunrise), and sets 6 hours later (at sunset).

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How are the Sun, Earth, and Moon positioned when it is new Moon?! in a straight line: Sun — Moon — Earth

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How are the Sun, Earth, and Moon positioned when it is full Moon? Sun — Earth — Moon

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What is a solar eclipse? The Moon is blocking the Sun’s light, or a location on the Earth’s surface is passing under the Moon’s shadow.

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How are the Sun, Earth, and Moon positioned when it is a solar eclipse? Sun — Moon — Earth (as in a new Moon).

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What is a lunar eclipse? Earth’s shadow passes across the Moon.

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How are the Sun, Earth, and Moon positioned when it is a lunar eclipse, and what phase is the Moon in? Sun — Earth — Moon (as in a full Moon).

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Why do eclipses not occur every month on Earth? The Moon orbits the Earth in a slightly different plane than the Earth orbits the Sun.

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What about eclipses of the moons of Mars? Mars has two small moons, Phobos and Deimos. Relative to Earth’s Moon, they are tiny, and closer to their planet and orbiting faster — and closer to the orbital plane of Mars around the Sun. This leads to more frequent eclipses visible from Mars.

Familiarize yourself with, or practice drawing,!a diagram of Moon phases, like below:

NOTE: Diagram not to scale! The distances between Earth, the Moon, and the Sun is much greater compared to their sizes than is depicted here.

The Sun should be far off the top of page; it is drawn here to show the direction from which distant sunlight is coming,

The outer ring of Moons shows the orientation of the Sun-illuminated half its surface; the inner ring of Moons shows how the Moon appears in our sky at those times. The Moon phase directly away from a point on the Earth's surface can be said to be "overhead" at the time of day that corresponds to that direction (e.g., a full Moon at midnight, first quarter at sunset, a waning crescent at 9:00am, etc.) A Moon phase rises about 6 hours before it is overhead, and then sets about 6 hours later." 5

4. Constellations •

constellation = large defined areas of the sky (like states in a map of a country) anything visibly within that region is considered "in" that constellation • there are 88 of them, in all (dividing up the total celestial sphere)! •

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Stars in the same constellation are likely to be at very different distances from us. Not necessarily close to each other, though they appear close projected on our sky. !

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Different constellations are visible at different times of year; e.g., "Orion the Hunter" is prominent in the Winter — because as the Earth travels around the Sun, its nighttime side faces different regions of space. !

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ecliptic = the apparent path of the Sun over the course of a year, with respect to the distant stars — also refers to the plane in which the Earth orbits the Sun. !

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Zodiac constellations = the 12 (or 13) constellations that lie along the ecliptic. !

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The Sun is inside a Zodiac constellation at all times = in each one for about a month, each year. During that time you cannot see that constellation since it is behind the Sun all day and not on the nighttime side of Earth. !

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The Sun was in the constellation of your Zodiac "sign" during the month you were born. (You cannot see it at night at that time of year; you must wait six months.) !

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Winter Zodiac constellations = ones opposite the Sun in the winter !

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Summer Zodiac constellations = ones opposite the Sun in the summer !

5. Electromagnetic Radiation / Light ! •

Light has some properties of a wave and other properties of a particle. A "particle of light" is called a photon. !

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Forms of light, from high-energy to low-energy:

gamma ray > X-ray > ultraviolet (UV) > visible > infrared (IR) > microwave > radio !

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high-energy light = high frequency = low / short wavelength = a bluer color low-energy light = low frequency = high / long wavelength = a redder color!

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All forms of radiation travel at the speed of light. !

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wavelengths of radio waves = meters and centimeters !

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wavelengths of visible light = ten-billionths of a meter (hundreds of nanometers)!

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wavelengths of X-rays = even smaller (nanometers down to picometers)!

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A prism splits light into different colors by bending different wavelengths by different angles. !

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Blackbody spectrum: higher temperature = more light in total, and a peak intensity at a shorter wavelength (or at a bluer color)!

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The Sun's surface temperature is about 5800 degrees Kelvin. Its spectrum peaks in the visible light region (peak around green —!a "green star"!). !

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Room temperature is about 300 degrees Kelvin; a "blackbody" at room temperature peaks in the infrared (IR) region of light.

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What kinds of radiation get through the Earth’s atmosphere?! visible and radio (so, to be able to see other kinds of light with a telescope —!e.g., infrared, x-ray —! you would need to place that telescope in space)!

6. Spectroscopy ! Types of Spectra and their Origins ! •

continuum spectrum: light at all wavelengths !

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absorption spectrum: shows absorption lines — dark lines in the spectrum at certain wavelengths, superimposed on a continuum spectrum ! —! produced by a (less-energetic) gas cloud in front of a light source !

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An absorption line is produced when the electrons in atoms absorb photons and remove light of specific energies from the spectrum. Then the electons move ! from a lower to a higher energy level. !

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emission spectrum: shows emission lines — bright lines at specific wavelengths, in an otherwise empty (dark) spectrum, due to emission of photons from atoms in gas that have electrons in elevated levels (i.e., an "excited" gas) !

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An emission line is produced when electrons jump from higher to lower energy levels, and emit photons of those specific energies. !

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Different chemical elements have different energy levels that their electrons can occupy, and thus give rise to different placements and patterns of lines in their spectra; in other words, each chemical element has its own spectral fingerprint.!

7. Telescopes •

Reflecting telescopes — use a mirror to collect and focus light!

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Refracting telescopes — use a lens to collect and focus light!

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Important qualities of telescopes: light-gathering power, angular resolution, and the quality of the instruments. The magnification is not so important. !

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light-gathering power: Telescopes collect light in proportion to the area of their mirrors: The area of circle is proportional to its diameter squared. • example: a 2m-diameter telescope collects 2 x 2 = 4 ! • times as much light as a 1m-diameter telescope (1 x 1 = 1) or, a a 2m-diameter telescope collects the same amount of light as • a 1m-diameter telescope in 1/4 the time!

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angular resolution: the ability to distinguish or separate two nearby light sources (with good angular resolution)

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Earth’s atmosphere limits angular resolution, or ”seeing,” for ground-based telescopes — makes stars twinkle !

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magnification: zooms in on a smaller portion of the sky, to see more detail (but also observes a smaller overall area of the sky)

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Telescopes above Earth’s atmosphere are better because: certain kinds of radiation cannot get through atmosphere all the way to the • surface (X-ray, gamma-ray, UV, IR) conditions give clearer images without atmospheric blurring; i.e., better • seeing

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Telescopes above Earth’s atmosphere are worse because: it is hard (and expensive) to get a very large light-collecting area launched • into space

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