eclipses old dead guys part i - los angeles mission college

Astronomy 1 — Elementary Astronomy LA Mission College

Spring F2015

Eclipses Old Dead Guys Part I

Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015

Quotes & Cartoon of the Day

“I much prefer the sharpest criticism of a single intelligent man to the thoughtless approval of the masses. “

-- Johannes Kepler

http://www.brainyquote.com/quotes/quotes/j/johanneske143993.html


Announcements

• First HW will be graded Monday & key posted

• No late submissions accepted after key is posted.

• Practice HW on Lunar Phases posted with key

• Use this to study, no credit awarded

• Have you picked your observing project?

• First midterm Wednesday (10/1), through Night Sky material

• Eclipses from today, but not rest of today’s material

• Rest of schedule still needs tweaking

• Total Lunar eclipse Sunday night!


Last Class

• LT: Predicting Lunar Phases

• Eclipses (???)

• we just missed the questions, right?

• History Ancients-Galileo


This Class

• Eclipses (if not done Monday)

• History Ancients-Galileo

ECLIPSES


Eclipses

• Lunar eclipse — Earth precisely between Moon and Sun

• Earth’s shadow falls on Moon

• Moon goes dark (reddish actually)

• Solar eclipse — Moon precisely between Sun and Earth

• Moon’s shadow falls on Earth

• Sunlight blocked completely in some places (total solar eclipse)

• partly in some places (partial solar eclipse)

• and not at all in most places


Apparent Size of Sun and Moon

• The Sun and Moon appear to have the same size when viewed from Earth.

• Makes total solar eclipse possible


Eclipses

• So... once a month the Moon is between the Earth and the Sun....

• New Moon…

• Why don’t we have a solar eclipse every month?

• Or a lunar eclipse every month?


The Moon’s Orbit is tilted

• The Moon’s orbit tilted relative to the Earth’s orbit around the sun by about 5°

• (recall its apparent angular size is ~ 0.5°)

• Most of the time, the moon is above or below the direct line from Sun to Earth.


The Moon’s Orbit is tilted

• Periodically, the Moon crosses the line from Earth to Sun.

• If it does so at full moon, we have a Lunar Eclipse

• The Earth’s shadow falls on the Moon

• If it does so at new moon, we have a Solar Eclipse

• The Moon’s shadow Falls on the earth


Lunar Eclipse

Path for penumbral eclipse


Lunar Eclipse

Progression of Total Lunar Eclipse

<----------

Partial Lunar Eclipse ---------->


Lunar Eclipses 2010-2017


Solar Eclipses

Image: Sanhujinka.com


Solar Eclipse


A Total Solar Eclipse


Solar Eclipses

• Next good US TOTAL solar eclipse opportunity is in 2017

Let’s Practice


Suppose it is early in the month and you are going on a cruise to view a total solar eclipse later the same month. The moon is currently full. If it only takes a day or so to get to the viewing location, about when might your cruise depart?

A. tomorrow

B. next week

C. about two weeks from today

D. at the very end of the month


If you found yourself on a planet very similar to Earth with a moon very similar to our Moon, what would you conclude if you observed a total lunar eclipse every full moon?

A. That this planet’s moon orbits in the same plane as the planet orbits its star.

B. That this planet’s moon is much larger than our Moon.

C. That this planet’s star is much more distant than our Sun.

D. That this planet’s moon orbits over the poles of the planet rather than near its equator.


Spring F2015

Old Dead Guys

Greece to Kepler in 10 minutes

ARCHAEOASTRONOMY


Stonehenge

• Humans have been interested in the sky for a long time

• Built ~ 3000-2000 BC

• Many other sites built with astronomical alignments

ANCIENT GREECE


Contribution of the Ancient Greeks

• Many firsts

• First preserved written documents about ancient astronomy

• from ancient Greek philosophy

• Realized the Earth was round

• Estimated size of earth and distance to sun

• First star catalog


Limitations of Ancient Greek “Astronomy”

• Models were generally wrong because they were based on philosophical “first principles”, believed to be “obvious” and not questioned

• The Heavens are “perfect and unchangeable”

• Adhered to “perfect” shapes: spheres & circles

• The Earth is at the center of the universe and unmoving

• Geocentric


Limitations of Ancient Greek “Astronomy”

• Aristotle (384-322 BCE)

• 55 crystalline spheres

• Circles upon circles required to model motions of planets

• epicycles (Hipparchos)

• Ptolemy ~450 years after Aristotle, still Geocentric and “perfect”

• Lasted until 16th century AD

• 80 spheres

• Epicycle upon epicycle upon epicycle

NICOLAUS COPERNICUS THE RELUCTANT REVOLUTIONARY


Nicolaus Copernicus

http://www-history.mcs.st-andrews.ac.uk/PictDisplay/Copernicus.html

http://www-history.mcs.st-andrews.ac.uk/PictDisplay/Copernicus.html


The “Copernican Revolution”

• Heliocentric: The center of the universe near the Sun

• The Moon orbits Earth

• Earth & the planets orbit the Sun

• The daily rotation of the Earth on its axis is responsible for the apparent motion of the stars & the Sun.

• Predicted retrograde motion without need for epicycles

• Didn’t get the timing right

• The orbits, however, were still perfect circles


Ptolemaic vs Copernican


Ptolemaic Model vs. Heliocentric

TYCHO BRAHE, OBSERVER EXTRAORDINAIRE THE MAN WITHOUT A NOSE WHO DIED AN

IGNOBLE DEATH (MAYBE)


Tycho Brahe (1546 - 1601)

http://www.humanities.uci.edu/users/vfolkenflik/VRF%20Sources/tycho%20brahe%20large.jpg

http://www.humanities.uci.edu/users/vfolkenflik/VRF%20Sources/tycho%20brahe%20large.jpg


The Uraniborg

• King Frederik II of Denmark gave funds for Tycho to build an observatory on the Island of Hven.

• First built in 1576

• an international research center...

• 100 students and artisans worked here

• (But no telescopes!)

• ... and also his own court (jester and moose included)


Late Career, Kepler and Endgame

• left Hven in 1597

• Relocated to Prague in 1599,

• Imperial Mathemetician

• among his duties was casting horoscopes

• He hired others to assist him, notably Johannes Kepler

• died in 1601, 11 days after famously refusing to leave a court banquet to relieve himself

• Ruptered bladder? Kidney stones? Mercury poisoning?

JOHANNES KEPLER, THE WEEDY PRIG WHO GOT IT ALL RIGHT


Johannes Kepler

• 1571-1630

• German mathematician, astronomer and reluctant astrologer

• Discovered “Kepler’s Laws of Planetary motion”


Biographical Notes

• No proverbial silver spoon here!

• Born prematurely and reputedly sickly as a child, suffered complications from smallpox

• Could not see well

• Father was a mercenary soldier who left home when Johannes was 5

• Mother was an innkeeper’s daughter and an herbalist/healer who was tried for witchcraft

• Early interest in astronomy

• Observed great comet of 1577 at age 6 with mother

• Observed lunar eclipse at age 9


Early Career

• Initially interested in (Lutheran) theology,

• hired to teach mathematics and astronomy at the University of Graz

• Adopted heliocentrism for both scientific and philosophical and theological reasons

• In 1600 he “went where the data was” to Tycho Brahe in Prague

• Uneasy alliance

• Upon Tycho’s death in 1601, succeeded to his post as Imperial mathematician and astrologer


Spring F2015

Kepler’s Laws

explaining retrograde motion


Kepler’s Laws


Context

• Kepler’s Laws were empirical and described the motion of the (known) planets in our solar system

• Describe, rather than explain

• also describes comets


The 3 Laws Summarized

• First Law: Planetary orbits are ellipses with the Sun at one focus

• Second Law: Planets are traveling fastest along their orbit when closest to the Sun

• Third Law: Planets farther from the Sun take longer to complete an orbit.


Kepler’s Laws Can Be Generalized

• Kepler’s laws work for Earth satellites

• Work any time a relatively small (low mass) object orbits a relatively large (high mass) object

Let’s Practice


Kepler’s second law says “a line joining a planet and the Sun sweeps out equal areas in equal amounts of time.” Which of the following statements means nearly the same thing?

A. Planets move the same speed at all points during their orbit of the Sun.

B. Planets move fastest when they are moving toward the Sun.

C. Planets move faster the closer they are to the Sun.


During how many of the portions of the planet’s orbit (A, B, C, or D) would the planet experience an increase in speed for at least a moment?

A. Only during one of the portions shown.

B. During two of the portions shown.

C. During three of the portions shown.

D. During four of the portions shown.

E. None of the above.

Kepler’s Second Law – Instructor’s Guide 31

© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy

Third Edition

ADDITIONAL QUESTIONS The planet in the orbit shown in the drawing at right obeys Kepler’s Laws. Use this drawing to answer the next four questions. 1) According to Kepler’s Second Law, during

which one of the portion of the planet’s orbit (B, C, or D), would the planet take the same amount of time as it took for the portion of the orbit identified with letter “A”? If you think all the portions of the orbit take the same amount of time, answer “E”. [B is the correct answer]

2) During which part of the planet’s orbit (A, B, C, or D) would the planet move with the

greatest speed? [C is the correct answer] 3) During how many portions of the planet’s orbit (A, B, C and D) would the planet be speeding

up the entire time? a) Only during one of the portions shown. b) During two of the portions shown. c) During three of the portions shown. d) During four of the portions shown. e) None of the above.

4) During which of the portions of the planet’s orbit (A, B, C, or D) would the planet experience

an increase in speed for at least a moment? a) Only during one of the portions shown. b) During two of the portions shown. c) During three of the portions shown. d) During four of the portions shown. e) None of the above.


Jupiter takes longer to orbit the Sun than the Earth does. Which of Kepler’s 3 laws describes this?

A. Kepler’s first law (shapes)

B. Kepler’s second law (equal areas in equal times)

C. Kepler’s third law (period/distance relationship)


If the Earth were moved to twice its current distance from the Sun, how would the length of a year be affected?

A. It would be half as long

B. It would be the same

C. It would be more than twice as long


Which of the following best describes what would happen if Mercury and Jupiter were to switch places in their orbits about the Sun?

A. Jupiter, the larger planet, would have a shorter orbital period than before.

B. Mercury, the smaller planet, would have a shorter orbital period than before.

C. Neither of the two planets would have any change in their orbital periods

GALILEO GALILEI: FALLING ROCKS, OBSERVATIONS, THE TELESCOPE AND THE

INQUISITION


Galileo Galilei

• 1564-1642

• Tycho 1546-1601

• Kepler 1571-1630

• Greatly improved the newly telescope, (did NOT invent the telescope!)

• First to report telescope observations of the sky

• support the Copernican Model of the Universe

Portrait by Domenico Crespi


Biographical Notes

• Born in Pisa, son of a musician

• Roman Catholic, considered the priesthood

• Had 2 daughters and a son (out of wedlock) • “Galileo’s Daughter” by Dava Sobel

• Studied Medicine at Pisa but wound up a Mathematician

• Contemporary of Kepler, but dismissed his ideas about tides and elliptical orbits

• Got in trouble with the Inquisition over Heliocentrism • “It is surely harmful to souls to make it a heresy to believe

what is proved.” (Galileo Galilei via Brainyquote.com)

• Herin hangs a fascinating tale, for which we don’t have time...

• Ultimately recanted and spent the last 10 years of his life under house arrest


Galileo

• Galileo is also credited with

• Playing a major role in making science science rather than philosophy (aka the Scientific Revolution)

• "Philosophy is written in this grand book, the universe ... It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures;...." Galileo Galilei in The Assayer

• Demonstrating that two objects fall at the same rate regardless of their mass (if you can neglect air resistance)

• Actual experiment probably apocryphal

• But illustrative of his approach


Galileo

• http://www.biography.com/people/galileo-9305220

• http://www.history.com/topics/galileo-galilei

http://www.biography.com/people/galileo-9305220

http://www.history.com/topics/galileo-galilei


Galileo’s Observations

• Built telescope in 1609 • Published Sidereus Nuncius

(Sidereal Messenger) in 1610 • Moon has mountains & valleys.

• Heavens are not perfect

• Milky way is made up of individual stars.

• Stars must be far away…and not on a fixed sphere

• Four “planets” orbiting Jupiter. • The Earth is not the only “center of

revolution”

• Subsequent important observations • The sun had spots. g d


• Venus had phases. • Venus MUST orbit the Sun


Galileo’s Observations

• Built telescope in 1609 • Published Sidereus Nuncius

(Sidereal Messenger) in 1610 • Moon has mountains & valleys.


• Milky way is made up of individual stars.

• Stars must be far away…and not on a fixed sphere

• Four “planets” orbiting Jupiter. • The Earth is not the only “center of

revolution”

• Subsequent important observations • The sun had spots.


• Venus had phases. • Venus MUST orbit the Sun

WRAP-UP


Topic for Next Class

• History part II

• Newton

• Gravity

• Tides

• Intro to light


Reading Assignment

• Ch 3&4 in Astro

• Ch 3,4&10 in the Astropedia


Homework

• No new HW yet

eclipses old dead guys part i - los angeles mission college

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