THE VIEW FROM EARTH

EARTH IN MOTION

1. Rotation: Period = 24 Hours

2. Revolution: Period = 365.2564 Days

3. Precession: Period 26, 000 years

4. Motion of Solar System relative to nearby stars

5. Solar System orbits center of Milky Way: Period 230 million years

6. Milky Way Moves within Local Group ‘Swarm’

7. Local Group partakes of Expansion of Universe

North Pole

Rotation

750 mi/hrat State College!

To Sun

Night Day

TwilightZone

Night & Day

One way to get rotation period . . .

Revolution

1 AU

View from aboveEarth’s north pole.

67,000 mi/hr!

Orientation of Earth in Space

Orbit Plane(‘Ecliptic Plane’)

EquatorialPlane

North

I

I = 23.5o

Gravity

TopPrecession

Gravity of sun & moon try to change directionof Earth’s rotation axis – Earth Precesses.

Rotation axis fixed in space – over short intervals.

p. 20

Motion relative to nearbystars

p. 22

Orbit about center of Milky Way

500,000 mi/hr

p. 23

M31

Milky Way

180,000 mi/hr

Motion within Local Group

3,000,000 ly

Collisionof MilkyWay & AndromedaSpiral (M31)

Expansionof theUniverse

p. 24

‘Raisin Cake’Model

BeforeBaking

After Baking

LATITUDE, LONGITUDE& ALL THAT

The Meaning of Latitude

Earth

N

L

L Latitude

66.5o N

23.5o N

90o N

0o N

Terminator

p. 33

Longitude

p. 33

Earth’s Grid

State College, PALatitude =Longitude =

p. 33

CELESTIAL SPHERE:A MODEL OF THE SKY

RISING & SETTING

Earth seen from abovenorth pole

4 hours later

Meridian

A locale in the northern hemisphere.

Rising or setting?(Lookingwest orlookingeast?)

Anglo-AustralianObservatory

South CelestialPole

Circumpolar Stars

35o N Lat

Circumpolar

p. 33

THE SKY & YOUR LATITUDE

Z

A

A = latitude of observer

At a Mid-Northern

Latitude

At the North Pole

At the Equator

Position of NCPrelative to stars

shifts due toprecession.

DIFFERENT STARS INDIFFERENT SEASONS

November

September

July

CONSTELLATIONS

“Traditional”: Person, animal, object depicted by pattern of stars.

e.g., Cygnus – SwanUrsa Major – Big BearScorpius – ScorpionBoötes – Herdsman

Greco-RomanTradition

Antlia – Air Pump 18th Century

p. 28

Orion - Hunter

“Modern” (from 1928): Well-defined region of celestial sphere. * 88 modern constellations.

Winter Triangle

Orion

Milky Way

p. 30