Ancient GreeksGolden Age of Astronomy

- in Greece- 600 BC to 150 BC

- said earth was round

- estimated earth’s circumference

- cataloged stars

Geocentric Model

Believed by Greeks…all Earth was center of universe

and everything revolved around it

Was logical and made sense Unchallenged for centuries

Retrograde Motion

As the planets passed by at night, it appeared they stopped, reversed direction, and then headed back on their original way!

Modern Astronomy

Almost nothing new for 1500 years!

age The of enlightenment begins a new day in astronomy

Nicolaus Copernicus was the 1st but other followed

Copernicus 1475 - 1550

Believed that Earth was just an ordinary planet…

Not the center of the universe… HELIOCENTRIC model Revolved around the sun in

perfect circles like the rest… This was a huge break in thinking!

Tyco Brahe 1550 - 1600

Had an observatory…woweee Made extremely precise

measurements Had an amazing assistant…

Johannes Kepler

Johannes Kepler 1575 - 1625 Used Brahe's measurements Close but no cigar… Orbits not circles, but ellipses! 3 laws of planetary motion

1 - orbits are ellipses around sun2 - planets sweep equal areas in equal

time…faster and slower3 - distance of a planet to the sun and time

to go around the sun are related

Galileo Galilei 1550 - 1650

Described moving objects Redesigned telescope Gave support to Copernicus Disc 4 moons of Jupiter Planets are real objects Phases of Venus Sunspots and rotation

Isaac Newton 1650 - 1725

The law of inertia The law of universal gravitation

Closer = more gravityBigger = more gravity

Earth - Moon - Sun

3 motions of earthRotation – once/dayRevolution – once/yearPrecession – once/26,000 yrs

2 types of daysSolar – noon to noon (24 hrs) Sidereal - 360º around (23h 56m 4s)

Rotation of Earth

Rotates in an ellipse Sun not at exact center Closest on Jan 3rd = perihelion Farthest on July 4th = aphelion Ecliptic = earth/sun rotation plane

Earth - Moon System

Moon has ellipse orbit also Perigee – closest Apogee – farthest

Has phases from reflecting sunlight Full – far side of earth/sun New – between sun and earth Waning – shrinking (getting less full) Waxing – growing (getting more full)

Lunar Orbit About 240,000 miles away ½ is always lit…

Crescent moon < ½ showing Gibbous moon > ½

Waning/waxing crescent/gibbous 1st quarter = ½ moon after new moon 2nd quarter = full 3rd quarter = ½ moon waxing 4th quarter = new moon

Lunar Orbit Synodic month = moon through all its

phases = 29½ days Sidereal month = 27⅓ days… same

reason for a sidereal day Orbit and rotation are the same (27⅓) Same side always faces earth Hot on lit side (260º F) Cold on dark side (-280º F)

Eclipses

Moon between sun/earth…casts shadow on earth and blocks out sun = solar eclipse

Moon on other side of earth/sun…casts shadow on moon only = lunar eclipse

Don’t occur every month

Eclipses…

Don’t occur every month! Moon’s orbit not in ecliptic…5º Moon’s shadow usually misses Earth Umbra = full shadow Penumbra = partial shadow Corona = bright outline of sun Total eclipse is rare…Aug, 21, 2017 in

USA

The Moon

Most of our info comes from the Apollo missions of 69 – 72 (Apollo 11 – 17)

Its density is like mantle rock. We think it has a small iron core. It has 1/6 the gravity of earth

Dark lowlands = maria Light highlands No atmosphere = no weathering…also

means constant bombing of small debris…rocks get rounded.

Its biggest features are craters from impacts

Some craters have rays = bright lines from impact.

Most of the lunar surfaceCover far side of the moon

Highlands

Dark and relatively smoothAre beds of basaltic lava from meteor

impactsMare = singular, maria = plural

Maria

Most of surface covered by a layer of debris

Is soil-like and called lunar regolithComposed of ig rx, glass beads, and

fine lunar dust from impactsApprox 3 meters thick!

Regolith

Lunar History

Most widely accepted model for formation is impact from a mars sized body early in earth’s history.

It dates to about 4.5 billion years old, about the same as earth.