Earth Motions and the Heavens

Earth Motions and the Heavens Rotation Revolution Precession

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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

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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

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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?

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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

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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

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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

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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?

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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

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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

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Slow: 0.5 degrees per century

Precession http://www.astro.virginia.edu/class/oconnell/astr1230/im/precess-NS.gif

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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.