Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

2. The Discovery of the Solar System

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The celestial sphere isn’t real, but it’s a good concept for making maps of the sky.

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Map of some winter constellations

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Geographical coordinates LATITUDE (north – south) LONGITUDE (east-west)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

For example, Minneapolis: Latitude 45° N, longitude 93° W (approximately)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

On a celestial map (sky map)

“DECLINATION” replaces latitude (N-S)“RIGHT ASCENSION” replaces longitude (E-W)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

A puzzle ...

Geographical map:

NW E

S

NE W

SSky map:

(Why ??)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

CIRCUMPOLAR stars

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

CIRCUMPOLAR stars

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

CIRCUMPOLAR stars

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

CIRCUMPOLAR stars

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Next ...Something about TIME

(or rather time-keeping)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Our LOCAL MERIDIAN

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Think of our meridian as a fan or sheet, rotating with the Earth:

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

“Solar time” refers to the Sun; approximately the same as ordinary clock time.

“Sidereal time” refers to the stars; 1 sidereal day = 23h 56m solar time.

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

In fact, sidereal time = right ascension currently “on the meridian”.

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

( Remember to mention why sidereal time was formerly used to regulate clocks – genuine solar time was irregular. )

( Also mention time zones. )

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Next: The ecliptic and the planets.

(The Big Question: Who goes around whom??)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

THE ECLIPTIC(Sun’s annual path across the

constellations)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

THE ECLIPTIC(Sun’s annual path across the

constellations)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

THE ECLIPTIC: related to Earth’s 23.5-degree tilt

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The planets stay close to the ecliptic too.

In ancient times: -- Mercury -- Jupiter -- Venus -- Saturn -- Mars

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

A crucial trick that planets do: RETROGRADE MOTION

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Some Greek philosophers were the first to really try to figure out WHAT IS ACTUALLY HAPPENING. (beginning about 600 BCE)

The most influential, and almost the last, was CLAUDIUS PTOLEMY – a textbook writer about 1900 years ago.

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

GEOCENTRIC theory ...

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

... But RETROGRADE MOTION is hard to explain.

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

... Ptolemy’s solution (actually invented by someone else): EPICYLES

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

“DEFERENTS” and “EPICYCLES”

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

... and EQUANTS, and G.K.W.E.

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

... Fall of the Empire, interregnum, the East, medieval, then renaissance...

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Ptolemy’s theory worked fairly well. The Alphonsine tables...

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

COPERNICUS (?)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Copernicus’ contemporaries, c. 1520 ... Martin Luther Henry VIII of England Charles V of the H.R. Empire & Spain Suleiman the Magnificent Magellan Cortez Rabelais ...

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

HELIOCENTRIC !

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Why heliocentric? Retrograde motion...

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

WHICH WAS RIGHT?

Ptolemy, or Copernicus? Geocentric, or Heliocentric? Were there theological or political implications? For more than 70 years no one could think of a way to really answer the question. (Mention some of the arguments)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

MeanwhileThomas Diggesrealized somethingvery important.

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

1600—1620: GALILEO and KEPLER solved the problem in two different ways.

Contemporaries: -- Shakespeare -- Cardinal Mazarin -- James I of England -- Cervantes -- The Virginia and Massachusetts colonists

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

GALILEO

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

What Galileo did...

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The Moons of Jupiter

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The Moons of Jupiter

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The Moons of Jupiter

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The Phases of Venus

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The Phases of Venus

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

The Phases of Venus

Ast 1001 lecture 2 -- 2007 Sept 6 (kd)

Next topic: Kepler