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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.