Week Three Notes
Week Three Notes AST 111
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This 3 page Class Notes was uploaded by Ashley Childers on Friday September 4, 2015. The Class Notes belongs to AST 111 at University of Southern Mississippi taught by Christopher Sirola in Summer 2015. Since its upload, it has received 52 views. For similar materials see General Astronomy in Physics 2 at University of Southern Mississippi.
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Date Created: 09/04/15
Astronomy Week 3 Book notes chapter 2 Cosmology the study of the workings of the universe on the largest scale Retrograde motion motion in the westward sense backwards loops Geocentric the earth at the center and the planetssunmoon revolve around it Epicycle a uniform circle orbit Deferent arger orbits which they themselves orbit the smaller epicycle Ptolemaic model one of the rst explanatory models of the universe requiring a series of no fewer than 80 distinct circles Heliocentric sun centered model of the universe Nicolaus Copernicus rediscovered the heliocentric model of the universe Copernican Revolution critical realization that Earth is not the center of the universe Galileo Galilie observational scientist which proved the heliocentric theory James Bradley rst to prove the Earth revolves around the sun discovered the aberration of starlight Aberration of Starlight a slight 20 shift in the observed direction of a star caused by the Earth s motion perpendicular to slanted tracks on the line of sight Friedrich Bessal proved the Earth s orbital motion with use of stellar parallax 1838 Johannes Kepler developed the laws of planetary motion Tycho Brahe observational astronomer who recorded great detail the motions of the planets Laws of planetary motion Kepler s reasoning for the motions of the planets Eipse simply a attened circle like an oval A Focusfoci the x within the oval I Semimajor axis half the length of the long axmcg Eccentricity of an ellipse is simply a measure of how attened it is zero means perfect circle Sidereal orbita Period the time needed for the planet to complete one circle around the sun Astronomical unit the semimajor axis of Earth s orbit around the sun Radar Radio Detection and ranging using radio waves to detect astronomical bodies Empirical science resulting from only the analysis of observational data and not from theory or mathematical model Isaac Newton developed a deeper understanding of the way all objects move and interact with each other Newtonian mechanics three basic laws of motion gravity explained the behavior of the universe Frist law a moving object will move forever unless acted upon by some external force push or pull which alters the speed or direction of the motion Weight the force which gravity pulls towards the earth lnertia tendency of an object to keep moving at the same speed and in the same direction unless acted upon by a force Mass total amount of matter the object contains Velocity constant motion in constant direction Acceleration change in speed or direction Gravity prevents objects from zooming into space Gravitational force force attractive between to objects with mass Center of mass average position of all the matter making up two bodies Escape speed speed at which gravity can be surpassed Unbound escaped objects which no longer orbit in an ellipse Units of Time 1 Day a The sun is at the local meridian and behind it are background stars local noon Earth has two distinct basic motions i Rotates on its axis ii Orbits the sun b Sidereal day 23hours 56mins and 392 seconds c Solar day 24 hours 2 Month a A new moon occurs when the moon is between the earth and the sun i Each phase of the moon last about 3 12 days ii Moons orbital period with respect to the stars sidereal period is about 27 12 days iii Moons orbital period with respect to the sun is called synodic period last about 29 12 days iv Phases New Waxing growing Crescent rst quarter Waxing Gibbous Full Waning shrinking Gibbous third quarter Waning Crescent New 3 The calendar a Ours hails from the Egyptians who noted 360 days and ve festival days slightly too short b When julius Ceasar took over he adapted the Egyptian calendar but made a correction i A quotleap dayquot was added every fourth year to keep the calendar in line with the seasons c Adding 14 of a day per year was too much and the calendar was out of wack again by the 1500 s d Pope Gregory Xlll s astronomers made one nal alteration subtract 3 days every fourth century The Seasons a Earth s rotational axis is tilted by 23 12 degrees relative to the plane of its orbit b Different seasons are caused by the tilt of the Earth towards the sun c Summer happens when that side ns tilts toward the sun d Winter is when that side tilts away i Earth is furthers from the sun on the 4th ofJuly Equinox equal nightday Solstice sun stands still ltNorthern Hemigt a Spring Equinox March 21 b Autumnal Equinox September 21 c Summer Solstice June 21 d Winter solstice December 21 Week a From Babylon b Names after norse mythological gures Echses a Moon cuts between the Earth and Sun once every month like wise the moon moves behind the Earth once per month However we don t get monthly eclipses because i The plane of the moons orbit is tilted by 5 degrees relative to Earths which is to say the moon is usually above or below the earth 1 Solar Eclipse sun is covered 2 Lunar Eclipse the moon is covered 3 Total all of object is covered 4 Annular ring most of object is covered 5 Partial some of object is covered ii For lunar eclipse moon must be in full moon phase can last for hours iii For solar eclipse moon must be in new phase max of 7 mins iv A total solar eclipse will next hit the US on Aug 21st 2017
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