Earth Motions and the Heavens

RotationRevolutionPrecession

What are the basic Earth motions?

http://www.snyder7hills.org/units/ss/ch1/rotrev.html

Rotation

Revolution

Precession

Click icon to add picture

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/Tt5F-HTu6WI/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

http://www.astro.caltech.edu/palomar/images/star.trails.jpg

3 hour view of night at Palomar

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

WestSouth

East

Star positions change throughout the night (except for Polaris) because the Earth rotates

http://gemini.physics.ox.ac.uk/photos/gemini-trails-mr.gif

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.

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 skyb) high in the eastern skyc) high in the southern skyd) high in the western skye) 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 halfb) exactly halfc) 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

OrionWhy does Orion look different in the Southern Hemisphere?

http://www.dimijianimages.com/Africa-p10/star-trails-south-TX-gallery.jpg

Orion in Southern HemisphereSirius is blueBetelgeuse 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-south-TX-gallery.jpg&imgrefurl=http://www.dimijianimages.com/Africa-p10/star-trails-south-TX.htm&usg=__Ko6DW_HfnHz6RuO4benYIjBf914=&h=592&w=850&sz=167&hl=en&start=54&um=1&itbs=1&tbnid=x7Kg-doC9kpKAM:&tbnh=101&tbnw=145&prev=/images%3Fq%3DSTAR%2BTRAILS%26start%3D40%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN%26rls%3Dcom.microsoft:en-us%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 bea) 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 west- Meaning 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 minutes360°/day

Stars rise 4 minutes earlier each day

Click icon to add picture

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.calendrier-lunaire.fr/uploads/images/Anglais/UNDERSTANDING/eclipse.jpg

http://star.wind.mystarband.net/bib/images/moon_orbital_phases.gif

http://lcogt.net/files/styles/fourcol-image/public/spacebook/Ecliptic%20repair.png

http://cse.ssl.berkeley.edu/img/eclip.gif

Ecliptic is the plane of the solar system- where we find the planets and the Sun

http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap06/FG06_05.jpg

http://ganymede.nmsu.edu/tharriso/ast110/class05.html

What can we see on the Ecliptic?

http://upload.wikimedia.org/wikipedia/commons/b/bd/Earths_orbit_and_ecliptic.PNG

How is the Ecliptic related to the seasons?

http://i131.photobucket.com/albums/p301/glactus/space%20album%20three/ecliptic310x272.jpg

When the sun is crosses the celestial equator, we have the first day of spring or fall.

What is the affect of Earth’s Revolution on the constellations blocked by the Sun?

Gives an apparent eastward “motion” of the Sun

Earth motion is counterclockwise in this picture

Click icon to add picture

What is the Zodiac?

http://www.starchamber.com/paracelsus/images/seasons.gif

The set of constellations that align on the ecliptic

http://ganymede.nmsu.edu/tharriso/ast110/ch02f14.0_0.jpg

Ophiuchus, 13th sign of Zodiac!

How does Earth’s Precession affect the night sky?

http://www.astro.virginia.edu/class/oconnell/astr1230/4.1-precession.html

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

Slow: 0.5 degrees per century

Precession

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.com/images/Earth-Precession.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.