Published on February 11, 2009
The Celestial Sphere LACC: §3.2, 3.5, 3.7 • Coordinates--Declination Latitude, Right Ascension Longitude • North and South Celestial Poles, Celestial Equator, Ecliptic • Using the stars to navigate What is out there? Wednesday, February 10, 2010
Earth Coordinates http://www.passivesolarenergy.info/ Wednesday, February 10, 2010
Earth Coordinates • North and South • axial tilt = 23.5° poles • Arctic Circle, 66.5°N • equator • Antarctic Circle, 66.5° S • latitude • tropic of Cancer, 23.5° N • longitude • tropic of Capricorn, 23.5° S Wednesday, February 10, 2010
Celestial Coordinates http://visual.merriam-webster.com/astronomy/astronomical-observation/celestial-coordinate-system.php Wednesday, February 10, 2010
North Celestial Pole http://astro.unl.edu/classaction/images/coordsmotion/startrails.html Wednesday, February 10, 2010
Celestial Coordinates • North and South • spring and autumnal celestial poles equinox (20 Mar., 22 • zenith Sept.) • meridian • summer and winter solstice (21 June, 21 • celestial equator Dec.) • ecliptic plane • right ascension [RA] (Earth’s orbit, Sun’s Path) • declination [dec] http://astro.unl.edu/classaction/animations/coordsmotion/radecdemo.html Celestial-Equator (RA/Dec) Demonstrator http://astro.unl.edu/classaction/animations/coordsmotion/celhorcomp.html Rotating Sky Explorer Los Angeles: Latitude: 34° 05', North. Longitude: 118° 22', West Wednesday, February 10, 2010
Navigation If you know the declination of an object, and you measure it’s altitude when it’s on the meridian, then you can determine your latitude. Finding latitude with the Pole Star Imagine yourself standing at night at point P on Earth and observing the pole star (or better, the P position of the north celestial pole, near that star), at an elevation angle λ above the horizon. The angle between the direction of the pole and the zenith is then (90°–λ) degrees. If you continue the line from zenith downwards (see drawing) it reaches the center of the Earth, and the angle between it and the Earth's axis is also (90°–λ). Therefore (as the drawing shows) λ is also your latitude. http://www-istp.gsfc.nasa.gov/stargaze/Snavigat.htm Wednesday, February 10, 2010
Movement of the Celestial Sphere The celestial sphere isn’t what is moving. (Of course, a spherical shell of stars doesn’t even exist.) The earth rotates inside of it. Objects in space appear to “rise in the East and set in the West”. One can imagine why people thought the Earth was ﬁxed in space, and the celestial sphere rotated around it--we don’t feel the Earth rotating. Actually, the earth’s rotation makes it appear that objects in space move from east to west over the course of the day and/or night. Imagine a globe inside a celestial sphere. Wednesday, February 10, 2010
AstroTeam Classwork • Fill in this table with these four answer choices: latitude | longitude | right ascension | declination North/South East/West Location Location Earth’s Surface Celestial Sphere • You wake up with no memory of who or where you are, but it is night and you recognize the North Star (Polaris, the star in the tail of the Little Dipper). If the Polaris is at zenith, where are you? What if it is on the horizon? What if it is at an altitude of 23.5°? Wednesday, February 10, 2010
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 3, pp. 82-83: 1, 9. Due on the ﬁrst class of the following week, at the beginning of class. Wednesday, February 10, 2010
Celestial Mechanics LACC: §3.2, 3.5, 3.7 • Marking Time: day rotation, year revolution • Effects of the Sun: solar vs. sidereal, seasons • Changes in the Sky: Moon Phases, Eclipses What is going on out there? Wednesday, February 10, 2010
Time -- Time Zones Wednesday, February 10, 2010
Time -- Days Sidereal Day Solar Day 23h 56m 4.09s 24h The time The time between a between our star’s zeniths sun’s zeniths Wednesday, February 10, 2010
Time--Year and Seasons http://visual.merriam-webster.com/ earth/meteorology/seasons-year.php http://astro.unl.edu/classaction/animations/coordsmotion/transitmovie.html Time-Lapse Season Demonstrator http://astro.unl.edu/classaction/animations/coordsmotion/daylighthoursexplorer.html Daylight Hours Explorer http://astro.unl.edu/classaction/animations/coordsmotion/eclipticsimulator.html Seasons and Ecliptic Simulator Wednesday, February 10, 2010
The Earth-Moon System: Moon Phases http://www.astrosociety.org/education/ publications/tnl/12/12.html http://astro.unl.edu/classaction/animations/lunarcycles/lunarapplet.html Lunar Phase Simulator http://astro.unl.edu/classaction/animations/lunarcycles/moonphases.html Three Views Simulator Wednesday, February 10, 2010
The Earth-Moon System: Lunar Eclipses http://hyperphysics.phy-astr.gsu.edu/ hbase/solar/lunecl.html http://astro.unl.edu/classaction/animations/lunarcycles/eclipsetable.html Eclipse Table Wednesday, February 10, 2010
Wednesday, February 10, 2010
The Earth-Moon System: Lunar Eclipses http://astro.unl.edu/classaction/images/ lunarcycles/lunareclipse.html http://astro.unl.edu/classaction/images/ lunarcycles/lunareclipse2004.html Wednesday, February 10, 2010
The Earth-Moon System: Solar Eclipses http://astro.unl.edu/classaction/images/lunarcycles/ http://astro.unl.edu/classaction/images/ solareclipse.html lunarcycles/solareclipse1999.html http://astro.unl.edu/classaction/images/lunarcycles/ http://astro.unl.edu/classaction/images/ solareclipse2.html lunarcycles/solareclipse1994.html Wednesday, February 10, 2010
The Earth-Moon System: Solar Eclipse http://astro.unl.edu/classaction/images/lunarcycles/solareclipse1999mir.jpg Wednesday, February 10, 2010
AstroTeam Classwork • What are two ways the 23.5° tilt of the Earth’s axis causes summers in the United States to be warmer than the winters? (Voyages, Ch. 3, pp. 82-83: 5) Due presently. Wednesday, February 10, 2010
LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 3, pp. 82-83: 11, 16. • Ch 4: Tutorial Quizzes accessible from: www.brookscole.com/cgi-brookscole/course_products_bc.pl? http:// ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due on the ﬁrst class of the following week, at the beginning of class. Wednesday, February 10, 2010
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