Earth Motions and the Heavens Rotation Revolution Precession What are the basic Earth motions? Rotation Revolution Precession http://www.snyder7hills.org/units/ss/ch1/rotrev.html What are the apparent celestial motions associated with Earth’s rotation? http://en.wikipedia.org/wiki/File:AxialTiltObliquity.png http://3.bp.blogspot.com/-hlq7nqAtZlk/Tt5FHTu6WI/AAAAAAAADEE/ukVSOFugs2w/s1600/startrails.jpg What are Star Trails? http://zuserver2.star.ucl.ac.uk/~idh/apod/image/0609/gemstartrails_schulz_f.jpg What is the apparent hourly rate of motion of the stars? Stars appear to move 15°/hr because the Earth rotates at 15°/hr. Star trails over the 60 inch dome at Palomar Observatory 3 hour view of night at Palomar http://www.astro.caltech.edu/palomar/images/star.trails.jpg How do star trails change with direction? North- circumpolar East- rising South- arc from east to west West- setting http://www.astro.caltech.edu/palomar/images/haletrails.jpg Looking out the window… North South East West Star positions change throughout the night (except for Polaris) because the Earth rotates A view of the GEMINI North dome on Mona Kea soon after sunset showing star trails from a time-lapse exposure. Also seen are trails from vehicle headlights as they drive passed the GEMINI dome. http://gemini.physics.ox.ac.uk/photos/gemini-trails-mr.gif Lecture Tutorial: Position Position You observe a star rising due east. When this star reaches its highest position above the horizon, where will it be? a) high in the northern sky b) high in the eastern sky c) high in the southern sky d) high in the western sky e) directly overhead Imagine you are standing in the northern hemisphere. Looking directly north, you see a star just above the horizon. A little later you notice that it has shifted position slightly. Which way did it move? a) to the right, (east) b) to the left, (west) c) up, (rising) d) down, (setting) Lecture Tutorial: Motion Motion Motion How much of the celestial sphere can an Earth observer see at one time? a) less than half b) exactly half c) more than half Review Lecture Tutorial Celestial Sphere: Geocentric View How is Polaris different from other stars? Polaris doesn’t appear to move (much) because it aligns with the spin axis (within about 1 degree). Polaris’ position is North, stationary, and its altitude is equal to the observer’s latitude The stars positions change throughout the night (except for Polaris) because the Earth rotates and Polaris aligns with the spin axis. What is special about Circumpolar Stars? Circle counterclockwise around Polaris Never rise or set during the night Visible all year Orion Why does Orion look different in the Southern Hemisphere? http://www.dimijianimages.com/Africa-p10/star-trails-south-TX-gallery.jpg Orion in Southern Hemisphere Sirius is blue Betelgeuse is red http://www.starrynightphotos.com/star_trails/images/star_trails_orion.jpg What is the affect of latitude on star trails? Near the equator, stars in the eastern sky trail directly up and over your head. At higher latitude stars are tilted with respect to the rotating "sphere" of the sky. At either pole the stars would go around the horizon. http://ganymede.nmsu.edu/tharriso/ast110/class05.html http://images.google.com/imgres?imgurl=http://www.dimijianimages.com/Africa-p10/star-trails-southTX-gallery.jpg&imgrefurl=http://www.dimijianimages.com/Africa-p10/star-trails-southTX.htm&usg=__Ko6DW_HfnHz6RuO4benYIjBf914=&h=592&w=850&sz=167&hl=en&start=54&um=1&itbs =1&tbnid=x7KgdoC9kpKAM:&tbnh=101&tbnw=145&prev=/images%3Fq%3DSTAR%2BTRAILS%26start%3D40%26um%3D 1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:enus%26ndsp%3D20%26tbs%3Disch:1 View East at Equator South Pole This is another picture of the South Pole, but shorter. Two nearby galaxies are visible in this image. The large fuzzy one, just above the roof of the Commons Building, is the Large Magellanic Cloud, and the smaller fuzzy patch near the top of the image is the Small Magellanic Cloud. These galaxies are 200,000 light years away, yet easily visible to the naked eye in dark skies! Lecture tutorial: Seasonal Stars Intro You go out tonight and see the brightest star in the constellation Orion just rising above your eastern horizon at 10 PM. One week later at 10 PM this same star will be a) slightly higher in the sky. b) at the same height as before. c) below your horizon. d) setting on your western horizon. Lecture tutorial: Seasonal Stars What is the affect of Earth’s Revolution on the sky? http://bigbendnow.com/wp-content/uploads/2012/06/Night-Sky-Changes-with-the-Seasons.jpg http://ganymede.nmsu.edu/tharriso/ast110/ch02f14.0_0.jpg What is the affect of Earth’s Revolution on the night sky? Earth motion is counterclockwise in this picture Night stars will appear to have shifted to the westMeaning they have risen earlier How far do stars shift from night to night? Earth revolves around Sun 360° in one year So in 12 months Earth moves 360°, so the stars appear to shift 30° to the west And in one day, Earth moves 1°, so the stars appear to shift 1° to the west How does Earth’s revolution affect the times of star rising and setting? Stars appear to rise earlier every night 24 hours x 60 minutes = 1440 minutes per day day hours 1440 minutes/day = 4 minutes 360°/day Stars rise 4 minutes earlier each day What is the ecliptic? http://www.eso.org/public/outreach/eduoff/vt-2004/Background/Infol2/vt2004-if11-fig2.jpg http://www.calendrier-lunaire.fr/en_US/eclipses-de-lune-et-de-soleil-comprendre-le-calendrier-lunaire.html http://www.calendrierlunaire.fr/uploads/images/Anglais/UNDERSTA NDING/eclipse.jpg http://star.wind.mystarband.net/bib/images/m oon_orbital_phases.gif http://lcogt.net/files/styles/fourcolimage/public/spacebook/Ecliptic%20repair.png Ecliptic is the plane of the solar systemwhere we find the planets and the Sun http://cse.ssl.berkeley.edu/img/eclip.gif http://physics.uoregon.edu/~jimbrau/BrauImN ew/Chap06/FG06_05.jpg What can we see on the Ecliptic? http://ganymede.nmsu.edu/tharriso/ast110/class05.h tml http://upload.wikimedia.org/wikip edia/commons/b/bd/Earths_orbit _and_ecliptic.PNG How is the Ecliptic related to the seasons? When the sun is crosses the celestial equator, we have the first day of spring or fall. http://i131.photobucket.com/albums/p301/gl actus/space%20album%20three/ecliptic310x2 72.jpg What is the affect of Earth’s Revolution on the constellations blocked by the Sun? Earth motion is counterclockwise in this picture Gives an apparent eastward “motion” of the Sun The set of constellations that align on the ecliptic What is the Zodiac? http://www.starchamber.com/paracelsus/images/seasons.gif Ophiuchus, 13th sign of Zodiac! http://ganymede.nmsu.edu/tharriso/ast110/ch02f14.0_0.jpg How does Earth’s Precession affect the night sky? http://www.astro.virginia.edu/class/oconnell/astr1230/4.1-precession.html Slow: 0.5 degrees per century Precession http://www.astro.virginia.edu/class/oconnell/astr1230/im/precess-NS.gif Precession http://www.epm.ethz.ch/research/experimental_studies/exp_prec/precession_earth.jpg?hires http://cache.eb.com/eb/thumb?id=94898 Precession of the Pole Star http://religion.lilithezine.co m/images/EarthPrecession.gif Precession of the Equinox Age The “Age” is the constellation that lines up with the sun on the first day of spring. Tropic of Cancer The sun rose in the constellation Cancer on June 21 (summer solstice) when they named the Tropic of Cancer. (23.5 degrees N) The sun is overhead on June 21 at 23.5 degrees N. Tropic of Capricorn On the Winter Solstice, Dec 21, the sun is directly overhead at 23.5 degrees S. 150 BC- The sun rose with the constellation Capricorn on at that date.