Chapter 1 Notes
Chapter 1 Notes 41087 - AST 115 - A
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This 7 page Bundle was uploaded by Ashley Notetaker on Monday September 14, 2015. The Bundle belongs to 41087 - AST 115 - A at Missouri State University taught by Robert S Patterson in Fall 2015. Since its upload, it has received 84 views. For similar materials see Basic Astronomy in Physics 2 at Missouri State University.
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Better than the professor's notes. I could actually understand what the heck was going on. Will be back for help in this class.
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Date Created: 09/14/15
AST115 Chapter 1 Notes Preview Powers of Ten Scientific Notation abc 10quotd A a digit that runs from 19 BC Ranges from 0099 Round to 2 decimal places B Any integer AU The average distance between the Sun and the Earth Astronomical Unit Metric System Size Distance across an object Fundamental unit of distance or length is a meter Mass Fundamental unit of mass is a kilogram Naming of Stars Given name Greek letters Catalog 5 Stars to Know Only the 250 brightest stars have given names Polaris The North Star Located upward from the farthest two stars of the bowl from the big dipper handle Regulus Located downward from the closest two stars of the bowl from the handle of the big dipper Regulus is the dot of the backwards question mark Arcturus Arc from the handle of the big dipper to Arcturus Spica Spike to Spica from Arcturus UISA MINOI Little Dipper Bo TES Polaris Arcturus 0 North Star URSA MAJOR Big Dipper ZOI S WH FrecnIan and Company Many illusions of the night sky Asterism Pattern of bright stars Constellations An entire region of the sky and everything in that region Only close together in terms of angular separation not physical separation or distance 88 official constellations Celestial Sphere An illusion of a dome in the night sky used to interpret distances to points of light Celestial Equator Imaginary line on the celestial sphere directly above the Earth s equator North Celestial Pole Imaginary point directly above zenith Polaris is near the North Pole Earth s Rotation makes the Sun Moon Planets and stars appear to rise and set Earth rotates E making everything else appear to move W Depending on latitude some starsconstellations never disappear below the horizon Instead they trace complete circles in the sky over the course of each night Ex North Pole Circumpolar All the stars that never setrise at a given latitude IE All the stars between Polaris and the northern horizon Navigating the Night Sky Declination DEC Latitude of the sky horizontal line used to differentiate North and South Right Ascension RA Longitude of the sky vertical line used to differentiate East and West Altzazimuth System depends on your location and time of night The horizon right below Polaris is 00 in the altzazimuth system Altitude The angle straight up from the horizon toward your zenith Altitude runs from between 0 degrees at the horizon and 90 degrees at the zenith Azimuth The angle to the right of North along the horizon Ranges from 0360 degrees Ex Azimuth of E is 90 degrees and azimuth of S is 180 degrees RA and DEC are constant while altitude and azimuth are always changing Earth and the Sun Ecliptic The path of Earth on the Celestial Sphere as seen from the Sun is precisely the sam as the path of the Sun as seen from the Earth Earth s Axis Tilted by 235 degrees Angular Distance Astronomers measure the relative positions of two objects by the angle between them Therefore to locate stars in the sky we do not need to know their distance from Earth but the angle from one star to another in the sky Angular Measure Astronomers use angular measure to describe the apparent sizes of celestial objects Angular size does not tell you anything about the physical size Ex Angular size of the moon is 12 degree Vernal Equinox First day of Spring one of the only 2 days in the year with exactly 12 hours of sunlight and darkness Autumnal Equinox First day of fall one of the only 2 days in the year with exactly 12 hours of sunlight and darkness Summer Solstice When the Sun is as far North as possible in June Winter Solstice When the Sun is as far South as possible in December Autumnal Equinox gt Winter Solstice gt Vernal Equinox gt Summer Solstice Earth s Seasons The seasons are caused by Earth s tilt being maintained through Earth s orbit of the Sun Seasons have nothing to do with the distance from the Sun or the heat output of the Sun SpringSummer in the Northern Hemisphere The half of the year Earth is tilted towards the Sun FallWinter in the Northern Hemisphere The half of the year that the sun is tilted away from the Sun The Sun travels through the 1213 zodiacs through the Celestial Sphere through the year Spends about 1 month in each Clocks amp Calendars Sidereal day The length of time from when any star is one place in the sky until the next time it is in the same place Solar day The length of time between when the Sun is highest in the sky until it is in the same place the next day 24 hours LAT Local apparent solar time the sundial Hour angle of the sun 12 hours LMT Local mean solar time Hour angle of mean sun 12 hours This is used for the different time zones Because the Earth rotates and revolves this changes the locations of the stars daily Stars appear to rise 4 minutes earlier each day The length of a year is approximately 365 days Because of this the Julian calendar added an extra day to the calendar every 4 years leap year This would have worked if Earth s rotation axis never changed direction To accommodate for this we use the Gregorian calendar which only allows for a leap year if the century years years that end in 00 are divisible by 400 Sidereal month The time it takes the moon to complete 1 full orbit of 360 degrees around the Earth This takes approximately 273 days Ex 1 location in the sky to the same location can vary by 7 hours due to gravitational pull changing the orbital speed throughout the year Sydonic month The time it takes to complete one cycle of moon phases Takes approximately 295 days Ex Full moon to full moon can vary by 12 hours due to gravitational pull changing the orbital speed throughout the year Sydonic month is longer because Earth is orbiting the Sun while the Moon goes through it s phases Earth s Axis of Rotation Earth s axis of rotation changes slightly with respect to the Celestial Sphere over time Precession Earth stays at the same tilt but the direction of which the axis or ration changes due to the gravitational forces from the Moon and Sun pulling on the slight bulge at the Earth s equator created by Earth s rotation Without the Moon Earth would not keep it s tilt it would change dramatically over millions of years The moon stabilizes the seasons as we know them This will eventually cause the North Celestial Pole to drift away from Polaris Precession of Equinoxes The slow Westward motion of equinoxes along the ecliptic due to Earrth s precession The Phases of the Moon The moon s rotation is synchronized to it s revolution Lunar phases As the moon orbits the Earth it moves from West to East on the Celestial Sphere changing position among the background of stars It s position relative to the Sun also changes as a result we see different lunar phases It takes 4 weeks for the Moon to complete one cycle this is what inspired the month The Moon s phases depends on how much of it s sunlight hemisphere is facing Earth Far side of the Moon The side always facing away from the Earth Dark side of the Moon The side of the moon the sun is not shining on The far side is not always the dark side Phases of the Moon Full Moon The moon is fully illuminated Quarter Moon Half of the moon is illuminated Crescent Moon Less than half the moon is illuminated Gibbous Moon More than half is illuminated rounded on both sides New Moon Not illuminated at all Waning Decreasing Waxing Increasing Planets have phases too Inferior Mercury Venus Closer to the Sun Superior Mars Jupiter Further from the Sun Terminator Line The line between the light and dark regions Meridian Imaginary circle on Earth that passes through North and South Pole Eclipses Lunar Eclipse Moon passes through Earth s shadow Ex Sun Earth Moon This only happens if the 3 are in a straight line during a full moon Solar Eclipse Moon s shadow moves across Earth s surface As seen from Earth the Moon moves in front of the sun Ex Sun Moon Earth The Moon orbit is tilted 5 degrees this is why the eclipse does not occur ever fullnew moon The Sun Earth and Moon must be exactly aligned The moon is usually above or below the plane of Earth s orbit Line ofNodes The line along which the plane of the Moon s orbit intersects the plane of the ecliptic Eclipse occurs when the Moon crosses the plane of the ecliptic while a fullnew moon Always at least two eclipses never more than seven Umbra Part of Earth s shadow where all direct sunlight is blocked by Earth Penumbra Part of Earth s shadow where Earth blocks only some of the sunlight 3 Types of Eclipses w Penumbra Moon passes through only Earth s penumbra Easy to miss moon still looks full just dimmer and slightly reddish Partial Only part of the Moon passes through umbra looks like a bite has been taken out of the moon Total Moon passes completely through umbra last a max of 1 hour 47 minutes Moon has an analogous umbra and penumbra Solar Partial When only the Moon s penumbra sweeps across Earth s surface Sun looks crescent shaped as seen from the Earth Annular The Moon is too distant to cover the Sun completely a ring of sunlight is seen around the moon Complete blockage of the Sun during a solar eclipse never lasts more than 7 12 minutes Astronomical Distances 5 cm along the arc 10x larger Going from the size of a proton to the size of an atom is roughly the same space on the arc as the distance between Earth and Sun to the distance of Earth and the nearby stars Asteroid Rocky objects larger than 10m in diameter not classified as a planet that orbits the Sun or Moon Meteoroid Piece of debris smaller than 10m in diameter composed mostly of rock or metal Comet Small body of ice and dust in orbit of the sun While near the sun vaporized ice gives rise to a coma tails and hydrogen envelope Clusters Groups of galaxies Super Clusters Clusters of galaxies
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