Week 3 Lecture Notes
Week 3 Lecture Notes ASTR 1001
Popular in Stars, Planets, and Life in the Universe
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This 3 page Class Notes was uploaded by Joanna Seivard on Sunday September 20, 2015. The Class Notes belongs to ASTR 1001 at George Washington University taught by Dhuga, K in Fall 2015. Since its upload, it has received 37 views. For similar materials see Stars, Planets, and Life in the Universe in Astronomy at George Washington University.
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Date Created: 09/20/15
Measurement of Distance Triangulation uses geometry of right triangles For real astronomical objects the triangles are very long and skinny these are not easily measured with precision Parallax the position of the planet seems to change with respect to background stars as observer moves from point A to point B the apparent angular motion of the object under study 0 quotapparentquot because the observer is moving the object is not moving 0 Parallax 1distance 0 Larger distance smaller parallax angle 0 Parallax is measured in arcseconds Parsec and AU 0 AU the average distance between the earth and the sun 0 Astronomical unit 0 An object that subtends an angle of 1 degree at the baseline of 1 AU is 1 parsec away or has a parallax of 1quot Need larger baseline to measure smaller angles 0 Parsec 33 lightyears O Celestial Coordinates Coordinate System Systems of coordinates xed to celestial sphere Declination angular measure 0 How far an object is above or below the celestial equator 0 Equivalent of latitude 0 Units degrees 0 Full range 90 degrees NP to 90 degrees SP Rioht ascension angular measure 0 How far object is east to west 0 Measured around the equator Equivalent of longitude Units hr mins secs Full range 24 hours 1 rotation of earth Don39t confuse with units of time 0 Uses units of time due to earth39s rotation Corresponds with time but is only a measurement of angle OOOO Motions Earth rotates about its axis 1 day Revolves about the sun 365 days Axis precesses 26000 years 0 Precession continuous change in direction of rotation axis 0 Main cause gravitational pull of the sun and moon Evidence for rotation 0 Circular lines traced out by bright stars as earth rotates about its axis 0 Center of circles is the North Star or pole Motion of precession o Direction of axis of rotation slowly changes with time 0 One complete cycle in 26000 years Lunar Motions o Phases regular changes in appearance of moon 29day cycle 0 Eg new moon rst quarter third quarter full moon 0 Explanation relative motion of earth and moon Moon does not emit light of its own The sun illuminates one half of the moon As the moon orbits the earth we see varying amounts of the moon39s illuminated surface 0 We see the same half of th moon all the time moon is in synchronous motions o Eclipses o Occasionally the earth moon and sun align in such a way that the shadow of one falls on the other 0 Basically 2 types of eclipses occur a Lunar total partial Solar total partial annular o Lunar eclipse the moon falls into the earth39s shadow Moon completely covered by earth39s shadow 0 Solar eclipse moon39s shadow falls on the earth 0 The moon39s shadow does not cover the entire earth 0 One might expect two eclipses every month one solar and one lunar Difference in how big the shadow is and how far the shadow casts Inclined orbital planes 0 The Moon39s plane is inclined at an angle of 5 degrees 0 The planes intersect at the Line of Nodes Line of Nodes points toward the sun twice a year ie earth moon and sun in the same plane 0 Conditions the Line of Nodes has to be aligned with sun and earth 0 Phase of moon must be either full or new 0 Solar eclipses are not as frequent as lunar eclipses Measuring the Stars Stellar parallax apparent shift of a star relative to a distant background objet as the observer39s location changes 0 Angular measure 0 Unit is arcseconds 0 Very small Proxima Centauri 076 degrees 0 Full moon 30 arcminutes Sun 30 arcminutes o Stellar motion Stellar sizes 0 Luminosity amount of power being generated by the star in question 0 Stars39 temperature 0 Higher temperature higher energy content of the system 0 Thermal radiation nearly all large of dense objects emit thermal radiation including stars planets you 0 An object39s thermal radiation depends on only one property in temperature Continuous Spectrum 0 The spectrum of a common incandescent light bulb spans all visible wavelengths without interruption Red waves are larger lower temperature ess energetic Blue waves are smaller higher temperature more energetic
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