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Astronomy Notes 1.docx

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Department
Natural Science
Course
NATS 1740
Professor
Randy Hoffman
Semester
Winter

Description
Astronomy Notes 1-5 Chapter 1 Horizon: divides the celestial sphere into the half you can see and the half you can't Zenith: is the point directly above you on the celestial sphere Meridian: is the line from north to south that passes through your Zenith -Angels and angular distances on the sky smaller than degrees, we use Arcminutes and arcseconds 60 arcminutes = 1 degree 60 arcseconds = 1 arcminute - 1 arcminute is the smallest separation your eyes can see/notice Constellation: is a grouping of stars in a specific area of the sky Chapter 1.3, 2.1, 2.2 When Earth is rotating its orbiting the sun completing one orbit each year. - Average orbital distance is called Astronomical Unit - AU = 150 million kilometers Ecliptic plane: the plane of Earth's orbit around the sun Axis Tilt: The amount by which a planet's axis is tilted with respect to a line perpendicular to the ecliptic plane Local sky: the sky as seen from where you're standing Circumpolar: Stars near the north celestial pole that do NOT rise or set - Circumpolar stars remain above the horizon and make daily counter clockwise circles around the North Celestial pole. - Stars near the South Celestial pole never rise above the horizon Reasons for Seasons (2.2) -longer/warmer days in the summer -shorter/colder days in the winter (why?) -Because the tilt of Earth's axis causes sunlight to fall different on Earth at different times of the year. -The steeper the angle= more sunlight hitting the earth is more concentrated (vise versa) Summer (June 21) Solstice = Northern Hemisphere tilted mostly directly towards the sun Winter (December 21) Solstice = Northern Hem. tilted away from the sun Spring (March 21) Equinox = N. Hem. goes from being tilted away from the sun to slightly towards it Fall (September 22) Equinox = N. Hem. starts tilting away from the sun Moon Phases Waxing = Increasing Waning = Decreasing New crescent = Waxing crescent Old crescent = Waning crescent Lunar eclipse: When earth is between the sun and the moon (Earth's shadow falls on the moon) Solar eclipse: When the moon is between the earth and the sun (Moon's shadow falls on the Earth [sun is blocked]) Umbra: Where sunlight is completely blocked Penumbra: Where sunlight is partially blocked Ancient mystery of planets 2.4 Retrograde motion: (Backwards) composed to the norm Stellar parallax: the apparent shift in the position of a nearby star (relative to distant object) that occurs as we view the star from different positions in Earth's orbit of the sun each year. Chapter 3 The Science of Astronomy Sun - > Sunday Moon -> Monday Mars -> Tuesday Mercury -> Wednesday Jupiter - > Thursday Venus - > Friday Saturn - > Saturday In ancient times they would track the days of the week by what was visible by the naked eye in the sky. -Determining time of day -> path of the sun or moon -Determining seasons -> used manmade structures -Modern science emerged from the Mediterranean and the middle east especially Ancient Greece. Kepler's First Law -Kepler discovered that the planets orbit the sun in ellipses with the sun at one focus. - The distance between the planet and the sun is called orbital radius - The average orbital radius is equal to the semi major axis regardless of eccentricity -Eccentricity = e = c/a For a circle the eccentricity e=0 Since the foci coincide (c=0) Example: Neptune's orbit is nearly circular and its average orbital radius is 30 AU. Pluto's average orbital radius is 40 AU. what would be the minimum eccentricity of Pluto's orbit for Pluto to sometimes be closer to the sun than Neptune. a) 0.1 b) 0.25 40AU *0.25 = 10 AU c)0.5 d)0.7 e) 0.95 Kepler's Second Law -An object moves faster in its orbit when it is closer to the sun, so that the line connecting the object around the sun sweeps out equal areas in equal times Keplers Third Law -For objects orbiting the sun, the square of the objects orbital period (P), measured in years, equals the cube of its semi major axis (a), measured in astronomical units. p2=a3 Example: p2=a3 sqr = Square root, cubed =3 Jupiter AU= 5 a= 125 p= ? p = sqr5cubed = sqr125 = 11.1 years Chapter 4 Speed- Tells us how far it will go in a certain amount of time " 100 Kilometers per hour" Velocity- Tells us both speed and direction "100 kilometers due north" Acceleration- Velocity is changing in any way, direction, speed or both -Acceleration of gravity =g - On Earth g= 9.8, roughly 10 m/s Exmaple: -drop rocks from a tall building -moment its let go, the speed is 0 m/s -after 1 second the speed is 10 m/s - after another second passes the speed is 20 m/s Therefore, acceleration of gravity is about 10 m/s Momentum - The product of its mass and its velocity (Momentum= Mass x Velocity) - Only way to change momentum is to apply force Mass- is the amount of matter in your body Weight - depends on both your mass and on the forces acting on your mass (including gravity) Newton's Laws of Motion -Newton showed that the same physical laws operate on Earth also operate in the heavens, bringing them into one universe -Astrophysics - applies physical laws discovered on earth to phenomena throughout the cosmos Newton's First Law -States that in the absence of a new force, an object will move with constant velocity. Objects at rest (velocity=0) tend to remain at res, and objects in motion tend to remain in motion with no change in either their speed or direction. Newton's Second Law -Tells us what happens to an object when a new force is present. Newton's Second law states that the amount of the acceleration depends on the objects mass and the strength of the net force. We write this law as " Force = mass x acceleration" or F= ma -Explains why large planets such as Jupiter have a greater effect on asteroids and comets than small planets like earth. Jupiter is massive compared to Earth. Therefore, it exerts a strong gravitational force on passing asteroids; sending them scattering with greater accelerations. Newton's Third Law -For every force there is always an equal and opposite reaction force. This is important in astronomy because it tells us that objects always attract each other through gravity. Conservation Laws Newton's and Kepler's Laws reflect a fundamental truth that certain quantities are conserved in any group or system of objects isolated from outside forces. Quantities: - Momentum -Angular Momentum -Energy The total energy of a system is always conserved. But the total energy can change
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