Ast 1002 - Summary Descriptive Astronomy PDF

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test 1 of astronomy notes. received an A using my own notes. ...

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Astronomy 1002 Tuesdays & Thursdays

Chapter 1: astronomy and the universe There are different solar systems. Beyond our solar system: Gas Coles pillars: gas -> forming stars (where stars are born) The scientific method: 1. Observe a phenomenon 2. propose a hypothesis to explain 3. a prediction based on the hypotheses (use mathematics to describe things) 4. test the prediction a body of related hypotheses can be pieced together called theory. The oldest objects found on earth are meteorites: chemically distinct bits of interplanetary debris sometimes fall to our planets surface. -

Supernova: some stars that are bigger than the sun ends their lives. Pulars: some dead stars become pulars, which can spin rapidly at rates of tens or hundreds of rotations per second. Blackholes: some stars end their lives as almost inconceivably dense objects

1.4 by observing galaxies, astronomers learn the origin and fate of the universe: stars are not spread uniformly across the universe but are grouped together in huge assemblages called galaxies. Other sources of energy are found even deeper in space. Often located at distances so great that their light takes billions of years to reach earth -> quasars. Cosmic explosion: big bang! 1.5: astronomers use angels to denote the positions and apparent sizes of objects in the sky. Angels are measured in degrees ( ) There are 360 degrees in a complete circle and 90 in a right angle - The angular distance between two stars about is 5 degrees - Astronomers use angels to describe the apparent size of a celestial object -> how wide the object appears to be in the sky The small angle- formula:

Astronomy 1002 Tuesdays & Thursdays

1.7 astronomical distances are often measured in units: light years or parsecs - Astronomical unit: the average distance between earth and sun 1 AU = 1.496 x 108 km = 92.96 million miles average distance between sun and Jupiter is 5.2 AU - light year: the distance that light travels in one year 1 Ly: 9.46 x 1012 km = 63.240 AU parsec (PS): unit of length used by astronomers -> equal to 3.26 light years. 1 PS = 3.09 x 1013 km = 3.26 Ly

Chapter 2: knowing the heavens: 2.1 naked eye astronomy had an important place in civilizations of the past positional astronomy: study of positions of objects in the sky and how the positions change 2.2 88 constellation cover the entire sky -

grasping’s of stars -> constellations entire sky is divided into 88 regions each one is called constellations orion = brightest star - diurnal motion: daily motion of the sky - stars rise to us in the east and set in the west just like the sun and moon. Earth goes around the sun It is convenient to imagine that the stars are located on a celestial sphere - celestial sphere: stars to be bits of fire imbedded in the inner surface of an immense hollow sphere and earth its center. Projections: the projection of a point on earth is made by extending an imaginary line perpendicular to the surface of earth - if we project earths north and south poles into space, we obtain north celestial pole + south celestial pole. - Where earth axis of rotation intersects the celestial sphere-> celestial equator. Earth turns from west to east Circumpolar: stars that never rise nor set Sunlight strikes the ground at different angels

Astronomy 1002 Tuesdays & Thursdays

Your latitude and longitude describe where on earth surface you are located. - Latitude: of your location denotes how far north or south of the equator you are - Longitude: denotes how far east or west you are of an imaginary circle that runs from north pole through south pole. Astronomers use coordinates called declinations and right ascension to describe the position of a planet or stars. - Declination is analogous to latitude. Declination of an object is its angular distance north or south of the celestial equator, measured along a circle passing through both celestial poles. - Right ascension: is analogous to longitude. Angular distance from the vernal equinox eastward along the celestial equator to the circle used in measuring its declination (time units: hours, mins, seconds) How the sun moves on the celestial sphere: The plane of earth’s orbit around the sun is called -> ecliptic plane - Ecliptic: the circular path that the sun appears to trace out against the background of stars Because there are 365 ¼ days in a year and 360 degrees in a circle, the sun appears to move along the ecliptic at a rate of 1 degrees per day. Ecliptic and celestial equator intersect only two points, which are opposite on celestial sphere. -> equinox - Where the ecliptic passes the celestial equator at two points: vernal equinox and autumnal equinox March 21 -> sun passes northward across celestial equator -> vernal equinox Sepetember 22 -> sun moves southward across celestial equator -> at the autumnal equinox Winter solstice (sun located here shortest day of year) Summer solstice (sun located longest day of year) Time: - Sidereal year = 365.25 mean solar days The time it takes the earth to orbit the sun with respect to the fixed stars - Tropical year = 364.24 mean solar days Because of precession Time it takes the sun to return to the vernal equinox - Sidereal day = 23h, 56m, 4.01s 2.6 precession: the orientation of earth’s axis of rotation changes slowly called precession -

Precession is caused by the gravitational pull of the sun and moon on earths equatorial bulge Precession of earth’s axis causes the positions of the equinoxes and celestial poles to shift slowly. Because of the system of right ascension and declination is tied to the position of the vernal equinox It is also called precession of the equinoxes.

Astronomy 1002 Tuesdays & Thursdays

Seasons and the tilte of earths axis: earth axis of rotation is tilted at an angle of about 23 ½ degrees from the perpendicular to the plane of earths orbit. Seasons are caused by the title of earths axis. Over the course of a year the sun appears to move around the celestial sphere along a path called the ecliptic. The ecliptic is inclined to the celestial equator about 23 ½ degrees. G, o Meridian: north-south circle on the celestial sphere that passes through the zenith and both celestial poles o Upper meridian: local noon, is the half of the meridian above the horizon o Lower meridian: at local midnight, the sun crosses the lower meridian, the half of the meridian below the horizon. o Meridian transit: the crossing by meridian by any object in the sky (highest point of the horizon) o Apparent solar day: interval between two successive upper meridian transit of the sun as observed from any fixed spot on earth. Chapter 3 eclipses and the motion of the moon 3.1 why we see the moon go through phases - sun and moon both move from west to east on celestial sphere - imaginary celestial sphere -> ecliptic -> where sun travels only the moon orbits earth, earth-moon system orbits sun.

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lunar phases: different appearances of the moon: New moon Waxing crescent moon (moonlight is increasing) First quarter moon -> 6 pm Waxing gibbous moon Full moon -> midnight Waning gibbous moon Third quarter moon -> 6 am Waning crescent moon

Moon takes about 4 weeks’ to complete one orbit around earth - On average the moon rises and set an hour later each night. 3.2 the moon always keeps the same hemisphere or face toward earth - because it is rotating in a special way. It takes exactly as long for the moon to rotate on its axis as it does to make one orbit around earth. -> synchronous rotation

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sidereal and synodic months Sidereal month: the time it takes the moon to complete one full orbit of earth as measured with respect to the stars (equal to 27.32 days)

Astronomy 1002 Tuesdays & Thursdays

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Synodic month or lunar month: the time it takes the moon to complete one cycle of phases (new to new or full to full), with respect to the sun, (equal to 29.53 days)

Lunar day is equal to synodic month, but they vary somewhat from one another. - Because the suns gravity sometimes causes the moon to speed up or slow down slightly in the orbits depending on position. 3.3eclipses occur only when the sun and moon are both on the line of nodes Eclipses: all in straight line, when this occurs the shadow of earth can fall on the moon or the shadow od the moon can fall on earth - Lunar eclipse: when the moon passes through earth’s shadow (happens when sun, earth and moon are in a straight line) - Solar eclipse: when earth passes through the moons shadow. Moon moves in front of sun (moon between earth and sun) In order for the sun and earth and moon to be lined up for an eclipse, the moon must lie in the same plane as earth orbits the sun. -> plane is called ecliptic plane -

Line of nodes: the planes of earth’s orbit and the moons orbit intersect along a line “line of nodes” It passes through earth and points in a particular direction in space, Eclipses can only occur when the line of nodes points toward the sun. 3.4 character of a solar eclipse depends on the alignment of the sun, earth and moon - umbra: (sun is covered by earth), no portion of the sun’s surface can be seen from the moon (darkest part of the shadow) - penumbra: portion of suns surface is visible. Penumbral eclipse: when the moon passes through only earth’s penumbra (only blocks part of the sun’s light) o A total lunar eclipse: if the moon travels completely into the umbra o Partial lunar eclipse: if only a part of the moon passes through the umbra. The moons speed through earth’s shadow is roughly 1 kilometer per second (3600 kilometers per hour, 2280 m/h) -

Totality: the period when the moon is completely within earth’s umbra -> last as long as 1 hour and 42 mins 3.5 solar eclipse also depend on the alignment of the sun, earth and moon -

Solar corona: the sun’s thin hot outer atmosphere, which is normally too dim to be seen, blazes forth in the darkened daytime sky. Eclipse path: earth rotates, the tip of the umbra traces on eclipse path across earth’s surface

Astronomy 1002 Tuesdays & Thursdays

Perigee: the eclipse path is widest if the moon happens to be at the perigee, the point in its orbit nearest earth Width of eclipse can be as great as 270 km - Apogee: farthest position from earth Moon appears too small to cover the moon completely. - Annular eclipse: (3th solar eclipse): thin ring of the sun is seen around the edge of the moon. Length of moons umbra us 5000km. Complete cycle of eclipse -> p = 6585.3 days -

Greek astronomers also developed a system to measure the brightness of stars: Hipparchus build an observatory on island of Rhodes and compiled a star catalog. Hipparchus – 160 b.c, -> star catalog - Records positions - Relative brightness Magnitude system - brightest star = 1st magnitude dimmest star = 6th maginitude chapter 4: gravitation and the waltz of the planets: 4.1 how ancient astronmers attemted to explain the motions of the pplanets - the universe can be described and understood logically geocentric model: earth is at the center of the universe both the sun and moon always move from west to east on the celestial sphere. Sun follows the oath called ecliptic. Direct motion: most of the time planets move slowly eastward relative to the stars, just as the moon and sun do. This eastward progress is called direct motion. However, the planets seem to stop and then back up for several weeks or months. This occasional westward movement is called retrograde motion. - Epicycle: each planet is assumed to move in a small circle - Deferent: whose center in turn moves in a larger circle it is centered on earth. They both rotate in the same direction -> counterclockwise 4.2 Nicolaus Copernicus divided the first comprehensive heliocentric model (suncentered): in which all planets including earth, revolve about the sun Copernicus realized that because Mercury and Venus are always observed fairly near the sun in the sky, their orbit must be smaller than earths planets in such orbits called inferior planets. He therefore concluded that the orbits of Mars, Jupiter and Saturn must be larger than the earth orbit -> superior planet.

Astronomy 1002 Tuesdays & Thursdays

Greatest Eastern elongation: when mercury or Venus is visible after sunset Elongation: the angle between the sun and a planet as viewed from earth Planet is as far east of the sun possible, so appears above western horizon after sunset called “evening star” Greatest western elongation: mercury or Venus is as far west of the sun as it possibly can be. Before the sun “morning star” in east. When Mercury or Venus is at inferior conjunction, it is between us and the sun, and it moves from evening to morning sky over weeks or month. Superior conjunction, planet on opposite side of the sun, moves back to evening sky. Opposition: a superior planet shon: Mars, whose orbit is larger than earth, seen best in night sky Conjunction: when located behind the sun, best to see at day time -

Period: between the time a plant takes to complete one orbit and the size of the orbit Synodic period: is the time that elapses between two successive configurations as seen from earth Sidereal period: is the rule orbital period of a planet, the time it takes the planet to complete one full orbit of the sun relative to the stars.

Parallax: apparent position of an object changes because of the motion of the observer. 4.3 johannes kepler proposed elliptical paths for the planets about the sun - ellipse: noncircular curves an ellipse has two focus points called foci longest diameter called major axis and other semimajor axis.

Kepler’s first law: The orbit of a planet about the sun is an ellipse with the sun at one focus -

Perihelion: a planet moves most rapidly when it is nearest the sun, at this point on its orbit called perihelion Aphelion: planet moves slowly when farthest from the sun Eccentricity = flatness of an ellipse.

Kepler’s second law: A line joining a planet and the sun sweeps out equal areas in equal intervals of time. -> law of equal areas.

Astronomy 1002 Tuesdays & Thursdays

Keplers third law: The square of the sidereal period of a planet is directly proportional to the cube of the semimajor axis of the orbit P2= a3 P = planets sidereal period, in years a = planets semimajor axis, in AU.

Newton’s first law of motion: An object remains at rest, or moves in a straight line at a constant speed, unless acted upon by a net outside force. - Force: any push or pull that acts on the object

Newton’s second law: Speed: measure of how fast an object is moving Velocity: speed and direction of motion together constitute of an object’s velocity Acceleration: is the rate at which the velocity changes Second law of motion: F = ma - F = net outside force on an object - m = mass of object - a = acceleration of object ‘ mass: a measure of the total amount of material in the object (kg) or (g) weight: is the force of gravity that acts on an object (in pounds)

Newton’s third law: Whenever one object exerts a force on a second object, the second object exerts an oppositely directed force equal strength on the first object. The force that keeps the planet in its orbits around the sun is a pull that always act toward the sun -> gravity or gravitational force. Newton’s law of universal gravitation: Two objects attract each other with a force that is directly proportional to the mass of each object and inversely proportional to the square of the distance between them F=G F = gravitational force between two objects M1= mass of first object M2 = mass of second object r = distance between objects

Astronomy 1002 Tuesdays & Thursdays

G = universal constant of gravitation G – 6.67 x 10-11 newton . m2 / kg2 Air drag: feather falls to the ground it loses gravitational potential energy without gaining kinetic energy. The greater the orbital energy, the greater the average orbital distance (or the greater the semimajor axis, a)

The escape speed: Vescape = Vescape = escape speed M = mass of planet R= radius of planet ‘ G= universal constant gravitation

Newton’s form of kepler’s third law:

Conicsection: any curve that you get by cutting a cone with a plane

Tidal forces: are caused by differences in the gravitation pull that one object extorts on different parts of a second object. - The tidal force of the moon and the sun produce tides in earths oceans - The tidal forces of earth have looked the moon into synchronous rotation....